2000 British Journal of PharmacologyPH与NO对尼可开放通道的影响(基础)
E ects of acidosis and NO on nicorandil-activated K ATP channels in guinea-pig ventricular myocytes
1,2Gustavo A.Moncada,1Yukio Kishi,1Fujio Numano,3Masayasu Hiraoka&*,2Tohru Sawanobori
1The Third Department of Internal Medicine±Cardiology Division,Graduate School of Medicine,Tokyo Medical and Dental University,Yushima,Bunkyo-ku,Tokyo,Japan;2Department of Clinical Pharmacology,Medical Research Institute,Tokyo Medical and Dental University,Kanda-Surugadai,Chiyoda-ku,Tokyo,Japan and3Department of Cardiovascular Diseases, Medical Research Institute,Tokyo Medical and Dental University,Yushima,Bunkyo-ku,Tokyo,Japan
1Nicorandil is a hybrid compound of K+channel opener and nitrate.We investigated a possible
interaction of acidosis and nitric oxide(NO)-donors on the nicorandil-activated ATP-sensitive K+
channel(K ATP)in guinea-pig ventricular myocytes using the patch-clamp technique.
2In whole-cell recordings,external application of300m M nicorandil activated K ATP in the
presence of2m M intracellular ATP concentration([ATP]i)at external pH(pH o)7.4,but the
activated current was decreased by reducing pH o to6.5±6.0.
3Single-channel recordings of inside-out patches revealed decreased open-state probability(P o)of
K ATP activated by nicorandil with reducing internal pH(pH i)from7.2to6.0,whilst the channel
activity increased at low pH i in the absence of nicorandil.
4Application of NO donors,1m M-sodium nitroprusside(SNP)or-NOR-3to the membrane
cytoplasmic side at pH i7.2increased the channel activity but decreased it at pH i6.5±6.0.Neither
removal of the drugs nor application of NO-scavengers reversed depression of channel activity
induced by NO-donors.
5We conclude that an increase in pH o and pH i depresses rather than stimulates the nicorandil-
activated K ATP.Since NO-donors at low pH i exhibited a similar trend,involvement of H+and NO
interaction can be considered as a mechanism of decreased K ATP activated by nicorandil.
British Journal of Pharmacology(2000)131,1097±1104
Keywords:Nicorandil;K+channel opener;nitrates;NO-donors;patch-clamp
Abbreviations:[ATP]i,intracellular ATP concentration;[H+]o,external proton-concentration;[H+]i,internal proton-concentra-tion;K ATP,ATP-sensitive K+channel;KCO;K+channel opener;pH o,external pH;pH i,internal pH;Po,
open-state probability
Introduction
Nicorandil is a potassium channel opener that targets the ATP-sensitive potassium channel(K ATP)(Hiraoka&Fan, 1989;Nakayama et al.,1991;Takano&Noma,1990).Based on its chemical structure nicorandil can be considered as a hybrid compound having nitrate and K+channel opening properties(Taira,1987).The drug is clinically available by virtue of its ability to dilate the coronary vessels and increase the coronaryˉow reserve in patients with chronic ischaemic heart disease(Frampton et al.,1992;Goldschimidt et al., 1996;Krumenacker&Roland,1992).Recently much attention has been paid to its e ects mimicking ischaemic preconditioning(Matsubara et al.,2000;Patel et al.,1999). Whilst the potency for nicorandil to activate K ATP is not strong compared to other agents,the drug has a unique action requiring the presence of MgADP for the channel activation(Shen et al.,1991),whilst other studies demon-strated the channel activation by nicorandil in the absence of ADP at the single channel level(Takano&Noma,1990).It has been further suggested that nicorandil could activate K ATP in the absence of ADP in external acidotic condition suggesting more e ective action at low pH o than at normal pH o(Jahangir et al.,1994).Other studies indicated that K ATP activated by another KCO,pinacidil,was suppressed at low pH o and increased at high pH o,suggesting an external site of interaction for the channel and H+(Kwok&Kass,1994). During myocardial ischaemia important changes in external and internal pH as well as changes in the ratio of intracellular ATP and ADP concentrations take place(Allen et al.,1985). The modulation of K ATP has been studied to demonstrate that moderate increase in H+concentrations,acidosis,itself has the ability to increase the activity of K ATP(Cuevas et al.,1991; Davies,1990;Fan&Makielski,1993;Koyano et al.,1993). Therefore,nicorandil may exert its K+channel opening potency more strongly during ischaemia or acidotic conditions than in normoxic state and normal pH.However,it is not known how the other aspect of nicorandil as nitrate interacts with the K ATP activation.The present study was undertaken to examine a possible interaction between low pH and NO on the nicorandil-activated K ATP activity.
Methods
The investigation was conducted in accordance to the guidelines for the care and use of laboratory animals at Tokyo Medical and Dental University.
Cell isolation
Single ventricular myocytes were isolated enzymatically from the ventricles of female guinea-pigs weighing250±350g.The
British Journal of Pharmacology(2000)131,1097±1104?2000Macmillan Publishers Ltd All rights reserved0007±1188/00$15.00
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*Author for correspondence at:Department of Clinical
Pharmacology,Medical Research Institute,Tokyo Medical and
Dental University,2-3-10,Kanda-Surugadai,Chiyoda-Ku,Tokyo
101-0062,Japan;E-mail:sawa.cph@mri.tmd.ac.jp
technique for cell isolation used in our laboratory has been described previously(Hirano&Hiraoka,1988).In brief, guinea-pigs were anaesthetized with Na-pentobarbital (30mg Kg71,IP)and right after injected intravenously with heparin(300units Kg71).The chest was opened under arti?cial respiration(Respirator Model141,NEMI Corp, Medwey,MA,U.S.A.)and the aorta was canulated to perfuse retrogradely with the Tyrode solution before the heart was dissected out.After6min of perfusion on the Langendor apparatus,the heart was perfused with a nominally Ca2+free Tyrode solution for an additional 6min.The perfusate was switched to Ca2+free Tyrode solution containing collagenase(5mg50ml71,Yakult, Tokyo,Japan).After5±6min perfusion,the heart was washed out with a high K+,low Cl7solution.The temperature of the perfusates was maintained at35±368C. The isolated cells were obtained through a mesh(size 200m M).Rod-shaped cells with clear margin and striation were used for the experiments.
Solutions
In the whole-cell con?guration the bath solution was Tyrode solution,and its composition was(m M):NaCl144,NaH2PO4 0.33,KCl 4.0,CaCl2 1.8,MgCl20.53,glucose 5.5,and HEPES5.0;the pH was adjusted to7.3±7.4by addition of NaOH.The Ca2+-free Tyrode solution was prepared by omitting CaCl2from the Tyrode solution.High K+low Cl7 solution contained(m M):KOH80,glutamic acid70,taurin 15,KH2PO410,HEPES5,MgCl20.5,glucose11,and K2-ethyleneglycol-O-O'-bis(B-aminoethyl)-N,N,N',N'-tetraacetic acid(EGTA)0.5(pH7.4-KOH).The composition of the pipette solution was(m M):KCl120,K2ATP(Sigma Chemical Co.,St.Louis,MO,U.S.A.)2.0,HEPES5.0and K4BAPTA(Dojin Co.,Kumamoto,Japan)5.0;the pH was adjusted to7.2with KOH.The?nal K+concentration was kept constant at150m M.
In the case of single-channel recordings(inside-out patch con?guration),the bath solution(intracellular medium) contained(m M):KCl140,glucose5.5,EGTA2and HEPES (or PIPES)5;the pH was adjusted to7.3with KOH.When experiments were conducted in acidotic conditions,bath solutions having di erent pH values(7.2,6.5or6.0)were adjusted with HEPES or PIPES bu er systems,accordingly. Final pH adjustment was done with0.1N HCl.When nucleotides were present in the bath,MgCl20.6±0.8m M was added to the bath.The drugs were dissolved in the bath solution at the concentration indicated in the text.The pipette solution(extracellular medium)contained(m M):KCl 140,CaCl21.8,MgCl20.53,glucose5.5and HEPES5;the pH was adjusted to7.3by adding KOH. Electrophysiological measurements
Whole-cell current recordings Membrane currents were recorded using the patch-clamp technique of whole cell con?guration(Hamill et al.,1981),using a patch-clamp ampli?er(Axopatch ID,Axon Instrument,Foster City,CA, U.S.A.).Glass patch electrodes were made from borosilicate capillary tubes with an outer diameter of1.5mm(Clark Electromedical Instruments,Pangbourne,England)using a microelectrode puller(Model PP-830,Narishige Co.Tokyo, Japan)and were heat-polished by a microforge(Model MF-830,Narishige Co.,Tokyo,Japan).The electrode resistance was2±4M O when the pipettes were?lled with an internal solution.The recording technique and the data acquisition systems have been described in previous reports(Hirano& Hiraoka,1988).When the ramp voltage-clamp method was employed,an intelligent arbitrary function synthesizer(model 1731,NF Instruments,Yokohama,Japan)was used to supply the command pulse.
The temperature of the bath chamber was maintained at 34±358C with a heating system(DTC-100TA,Dia Medical System,Tokyo,Japan).Before establishing contact between the electrode and the cell membrane,the junction potential was adjusted to zero at the level of the bath solution.At the end of each experiment the junction potential was veri?ed again and,adjusted if a di erence of more than+2mV existed between the?rst and second measurements.A time-interval of2±3min for sequential recording at di erent pH was established.
Single-channel recordings Single-channel current recordings were carried-out at room temperature with conventional inside-out patch con?guration(Hamill et al.,1981)using the same patch-clamp ampli?er as in the whole-cell experiments. The current signals were recorded and stored simultaneously on a videocassette recorder(HR-S7700,Victor,Tokyo, Japan)and a thermal recorder(Omnicorder8M14-3,NEC-Sanei Instruments,Ltd.,Tokyo,Japan)through a PCM data recorder system(RP-882,NF Instruments,Yokohama, Japan)at a conversion rate of40kHz.Recorded signals were?ltered o -line through a programmable eight-pole Bessel low-pass?lter(48dB/octave,3625,NF Instruments, Yokohama,Japan)and digitized at a sampling frequency of 10kHz and stored into a MO disk of a computer(Physio PC-01;Physio-tech,Tokyo,Japan)using an analogue-to-digital converter(Digidata1200Interface,Axon Instruments, Foster City,CA,U.S.A.)for later analysis.pCLAMP software (version6.0.4,Axon Instruments)was used to generate voltage pulse protocols,data acquisition and analysis.
Single channel data analysis Single channel records were analysed by pCLAMP6.0software program on a computer (Physio PC-01;Physio-tech,Tokyo,Japan).The unitary current amplitude of K ATP was measured from the all point histograms through Gaussian?tting,or by selecting well-de?ned long opening and close transitions and measuring the magnitude of the corresponding current steps with horizontal cursors.
Mean patch current(I)was obtained over30s as a time averaged currents of K ATP,measured as the di erence between the baseline(a current level where all channels are in a close state)and the current level where the channels were in the open state with a half height criteria.Data points over the signals were delimited by cursors.The number of active channels in the patch(N),while initially perfusing nucleotide-free solution was regarded as the maximum open state of activity for later comparisons to assess the e ect of nucleotides and/or drugs upon the active channels in the membrane-patch.Since the unitary current(i)changes at di erent pH levels,the I/i quotient was used as a proportional indicator of channel activity.Since K ATP could be subject to run-down phenomen-on,during each experiment,maximum channel activity was always veri?ed regularly and measurements and calculations were corrected accordingly assuming a linear decrease in the number of active channels.
Drugs
All drugs were freshly prepared before every experiment and diluted into the test solution to obtain the?nal concentration
British Journal of Pharmacology vol131(6)
H+and NO interaction on K ATP G.A.Moncada et al
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as indicated in the text.Nicorandil(2-nicotinamidoethyl nitrate;a gift from Chugai Pharmaceutical Co.,Tokyo, Japan)was diluted into the test solution.Glibenclamide(a gift from Hoescht Japan,Tokyo)was dissolved in2% dimethyl sulphoxide(DMSO)and diluted into the test solution.The?nal concentration of DMSO contained in the test solution was less than0.01%.We used two NO-donors:Sodium nitroprusside(SNP,Sigma Chemical Co.St. Louis MO,U.S.A.)and(+)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide(NOR-3,a gift from Fujisawa Phar-maceutical Co.Ltd.Osaka,Japan).They were directly dissolved into the perfusing solution at the concentration indicated in the text.Exposure to light and oxygen was minimized.NO-scavengers:5±10m M oxyhaemoglobin (HbO2,Calzyme Laboratories,Inc.CA,U.S.A.)and2±3m M C14H16N2NaO4(Carboxy-PTIO;Dojindo Kumamoto, Japan)were both directly dissolved into the perfusate to a ?nal concentration as indicated in the text.
Statistical analysis
Data are expressed as mean+s.d.The signi?cance for pH-e ect as the only changing factor when comparing more than two groups was assessed by analysis of variances(ANOVA). Comparisons between two groups of data were evaluated by paired or unpaired student t-test,accordingly.A value of P50.05was considered signi?cant.
Results
Reduction of external pH affects nicorandil-activated
K ATP current
Application of300m M nicorandil activated outward current at potentials positive to*60mV elicited by a ramp voltage clamp at pH o7.4.The nicorandil-activated current was completely inhibited by1m M glibenclamide con?rming the
current as K ATP(n=4;not shown).When pH o was lowered from7.4to6.8±6.0in the presence of2m M[ATP]i,the nicorandil-activated K ATP current was somewhat decreased at pH o 6.8and further suppression was noted at pH o 6.0 (Figure1a).Figure1b presents a summary of the results obtained from10di erent myocytes.The current at0mV in the control was 1.22+0.6nA and it was increased to 3.96+1.97nA in the presence of300m M nicorandil at pH o 7.4(P50.01).The nicorandil-activated current was decreased to1.96+0.95nA at pH o6.8in the presence of the drug (P50.05versus nicorandil at pH o7.4)and further decrease of the current was noted at pH o6.0(1.06+0.68nA;P50.01 versus nicorandil at pH o7.4).As we could not detect any increase in the nicorandil-activated K ATP current by the whole-cell con?guration,we proceeded to examine the modulatory action of pH i on the single K ATP currents with inside-out patch con?guration.
Increased K ATP activity by internal acidosis
First,we tested the low pH i-induced modulation of the K ATP activity in the absence of nicorandil under our experimental conditions,since reducing pH i from*7.4to6.5±6.0was shown to increase the channel activity(Cuevas et al.,1991; Davies,1990;Fan&Makielski,1993;Koyano et al.,1993; Vivaudou&Forestier,1995).Figure2a presents the e ect of lowering pH i on K ATP current.When the internal face of the patch-membrane was exposed to the ATP-free solution at pH7.2many channels were kept in the open state,and the channels were quickly and largely inhibited by addition of 0.35m M ATP i.The open-state probability(P o)of the channels was89+10%in the ATP-free solution and it was 7+5%at0.35m M[ATP]i(P50.01).A signi?cant increase of channel activity became apparent by decreasing pH i from7.2 to 6.0(P o;7+5%versus32+13%,respectively,n=9; P50.01)in the presence of Mg2+as previously reported. Run-down was excluded by observing near complete recovery of the initial Po upon removal of ATP from the internal solution(Figure2b).As reported previously reduction of pH i slightly decreased the unit amplitude of single-channel current (i)(data not shown).
Effect of acidosis on the nicorandil-activated
K ATP current
Application of1m M nicorandil to the internal solution in the presence of0.25m M ATP,0.1m M ADP and Mg2+at pH i 7.2,K ATP was activated as similar as the removal of ATP. The nicorandil-activated K ATP currents were decreased with reduction of pH i to6.5and6.0(Figure3a).Return of pH i to 7.2or removal of[ATP]i restored the channel activity.Figure 3b represents the amplitude histograms of the records shown in Figure3a.Reduction of pH i decreased the channel activity.Figure4demonstrates the summary data from10 similar experiments as shown in Figure3.P o of
nicorandil-Figure1Suppression of nicorandil-activated whole-cell current by lowering pH o.(a)Superimposed traces of background I-V curves obtained from a typical case in a single myocyte,at3min intervals. *:Control at pH o7.4.*:Addition of300m M nicorandil to the bath at pH o7.4(Nicorandil,pH o7.4).~:Reducing pH o to6.8in the presence of nicorandil(Nicorandil,pH o6.8).&:Further reduction of pH o to6.0in the presence of nicorandil(Nicorandil,pH o6.0).(b) Summarized data from10myocytes revealed a signi?cant decrease of the nicorandil-activated K+current by reducing pH o from7.2to6.8 and 6.0.Each symbol corresponds to the value obtained from individual preparations.
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G.A.Moncada et al1099
activated K ATP at pH i 7.2was 84+16%.Decreasing pH i from 7.2to 6.5and 6.0,resulted in a signi?cant reduction of K ATP activity (P o ;57+20%at pH i 6.5;P 50.01and 38+12%at pH i 6.0;P 50.01when compared to pH i 7.2,respectively).Upon return to pH i 7.2,an almost complete recovery to the initial level of channel activity was restored (P o =80+5%).
Effects of Nitric Oxide on K ATP
Since nicorandil is a hybrid compound including NO in its chemical structure,we investigated a possibility that the reduced activity of the nicorandil-activated K ATP at low pH i might be caused by an interaction between H +and NO.For this purpose,we examined e ects of NO donors on K ATP .We used two di erent NO-donors:SNP and NOR-3(see Methods).Figure 5a shows the e ect of 1m M SNP in the
presence of 0.25m M [ATP]i at pH i 7.2.K ATP activity increased signi?cantly in the presence of the NO-donor.Figure 5b summarizes data from 11patches.P o was 17+
11%
Figure 2Increased K ATP activity by lowering pH at the cytoplasmic side of the membrane (pH i ).(a)Single-channel record obtained with inside-out patch con?guration.The membrane potential was held at 740mV,while having a 140m M symmetrical K +concentrations at both sides of the membrane.Control K ATP current was recorded in the absence of nucleotides at pH 7.2in the bath (pH i ).The control current was of large amplitude and o -scaled.Addition of nucleotides,0.35m M [Mg.ATP]i +0.12m M [K.ADP]i whilst keeping the same pH i markedly suppressed the current.Mg 2+was also present at a 0.6±0.8m M concentration.Whilst lowering pH i to 6.5at this [ATP]i did not exhibit any change in channel activity,further reduction of pH i to 6.0increased signi?cantly the P o of the channels.Application of 4.0-m M glibenclamide suppressed the current.C represents the closed level of the channel.Downward deˉection indicates inward currents in this and the following ?gures except Figure 3b.(b)The bar graph showing summarized data obtained from nine di erent patches under the same experimental condition as in
(a).
Figure 3E ects of low pH i on nicorandil-activated K ATP current.(a)Single channel current record with holding potential at 740mV.The bath contained 0.25m M Mg.ATP,0.12m M K.ADP,0.8m M Mg 2+and 1.0m M nicorandil.Lowering pHi from 7.2to 6.5and 6.0in the presence of nicorandil reduced the nicorandil-activated K ATP current.These e ects were reversible upon return of pH i to 7.2.(b)Current histograms of 30s-analysed segments taken from (a).The letters in brackets indicate the corresponding segment in
(a).
Figure 4Summarized data for e ects of low pH i on nicorandil-activated K ATP current.The bar graphs summarize data from 10di erent patches.Reducing pH i to 6.5and 6.0signi?cantly decreased the channels-activity induced by 1.0m M nicorandil compared at pH i 7.2.Upon washout of nicorandil and returning to ATP-and ADP-free pH i 7.2solution,near complete recovery of the initial activity was achieved in all patches excluding the rundown of the channel.Experimental conditions same as those in Figure 3.
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G.A.Moncada et al 1100
in the absence versus 32+12%in the presence of SNP 5minutes (P 50.05).Upon removal of the NO-donor,an increase in K ATP current was kept ongoing to reach P o values up to 73+38%following 10min of washout (P 50.05).On the contrary,lowering pH i from 7.2to 6.0at constant ATP and SNP concentration caused a signi?cant reduction in K ATP activity (P o ;54+34%at pH i 7.2versus 27+19%at pH i 6.0;P 50.01;n =11)(Figure 6a,b).Using NOR-3,a di erent NO donor,we observed similar tendency as with SNP.In the presence of 0.25m M [ATP]i at pH i 6.0,the P o was 28+15%in the absence,whilst in the presence of 1m M NOR-3,P o decreased to 8+6%(P 50.05;n =5).Washout of the drug did not reverse the current depression,similarly as with the application of SNP.On the other hand,we also observed that a switch in pH i from 6.0±7.2increased the activity of the channel (P o ;20+16%at pH i 6.0versus 46+19%at pH i 7.2;P 50.05;n =4)(Figure 6a).Contrary to what we observed at pH i 7.2,removal of NO-donor at pH i 6.0did not get complete recovery of the channel activity to
the previous level.This was not due to run-down of channel activity since the nucleotide-free solution at pH i 7.2restored complete recovery of the channel activity to the initial level.
Effects of NO-donors and NO-scavengers on K ATP
In the presence of NO-donors at low pH i ,we attempted to reverse their depressing e ects on K ATP by adding NO scavengers,either HbO 2or carboxy-PTIO.However,5±10m M HbO 2enhanced rather than reversed the depressing e ects of NO donors (Figure 7).P o was 60+5%in the presence of 1m M NOR-3alone versus 20+2%in the presence of HbO 2(P 50.01;n =4).At low pH i neither washout of HbO 2nor removal of the NO donor altered the decreased P o of the channels,but an increase of the pH i to 7.2could increase P o .Run-down was excluded by observing complete recovery of channel activity upon removal of nucleotides at pH i 7.2.Either at normal or low pH i ,the compound itself at concentrations ranging 5±10m M showed a direct suppressing e ect on the channel activity.This e ect was more prominent at low pH i revealing an additive action to that of the NO-donor.In two additional patches we tested the e ect of HbO 2on the nicorandil-activated K ATP
at
Figure 5Increased K ATP activity at normal pH i induced by NO-donor.(a)Single channel current record obtained from a typical patch.Application of nucleotides and NO-donor,1.0m M SNP in the bath is indicated at the top,pH i was kept constant at 7.2throughout these experiments.In the absence of nucleotides a large current was observed and o -scaled in the record.Decreased channel activity upon addition of 0.25m M Mg.ATP and 0.12m M K.ADP was gradually increased by adding 1.0m M SNP into the bath and continued after the removal of the NO-donor.Increasing [Mg.ATP]i to 0.5m M caused a similar P o as the level observed at 0.25m M [Mg.ATP]i before the exposure to SNP,suggesting a reduction to the inhibitory e ect of ATP.(b)The bar graphs of data from 11patches.The channel activity expressed by P o increased signi?cantly by addition of SNP in the presence of nucleotides and washout of the drug increased P o
.
Figure 6E ects of SNP on K ATP at low pH i (a)Experimental conditions of pH i ,presence of nucleotides and SNP are indicated on the top.The channel activity at pH i 6.0in the presence of nucleotides was signi?cantly reduced by the presence of 1.0m M SNP and return of pH i to 7.2resulted in increase of channel P o .(b)The bar graphs of summarized data from 11patches.The pH i at 6.0and nucleotides concentrations were kept constant with 0.25m M [Mg.ATP]i ,and 0.12m M [K.ADP]i throughout the experimental conditions.In all patches run-down was excluded by observing nearly complete recovery of activity when perfusing nucleotide-free,pH 7.2solution after these treatments.
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H +and NO interaction on K ATP G.A.Moncada et al 1101
normal pH i and again we observed a clear reduction of activity,with its reversal upon washout of HbO 2.No signi?cant changes in channel activity were observed by using carboxy-PTIO with a ratio 2:1or 3:1respect to the NO donor.
Discussion
In the present study we examined two major issues:?rst,how an increase in external and internal H +concentrations modulates the activity of nicorandil-activated K ATP in guinea-pig ventricular myocytes.Second,the possibility that the modulation caused by acidosis in nicorandil-activated K ATP may be related to H +and NO interaction.
Effect of external pH on nicorandil-activated K ATP current
Previous study demonstrated that lowering pH o could enhance the ability for nicorandil to activate whole-cell K ATP current in guinea-pig ventricular myocytes (Jahangir et al .,1994).The authors considered that the enhanced action of nicorandil during acidosis was not related to a di erent ionization state of the drug nor a change in the ATP/ADP ratio,but a direct e ect of H +modulating the interaction between the channel and the drug.E ectiveness of another KCO,pinacidil decreased at low pH o and increased at high pH o (Kwok &Kass,1994).The ?ndings were interpreted as H +might modulate the binding site for pinacidil located at the extracellular side of the membrane.Thus,the interaction between H +and the di erent types of KCO might be di erent depending on their chemical structures.
We tested a slightly di erent view from that of Jahangir et al .(1994)as to the nicorandil action on K ATP .That is how the nicorandil-activated K ATP could be modi?ed by low pH o ,the condition prone to be associated with myocardial ischemia.It turned out that lowering pH o decreased rather than increased the nicorandil-activated K ATP in whole-cell currents.Since pH o might lead to change in pH i ,and pH i itself would have modifying action on K ATP ,we proceeded to explore the modulating mechanism by increased H +con-centrations with inside-out patches,where involvement of the second messenger system produced by the drug could be largely excluded.
Effect of internal pH on nicorandil-activated K ATP
In the presence of MgATP and ADP in the bath (cytoplasmic face),lowering pH i remarkably increased the P o of the channels,the results consistent with previous reports (Cuevas et al .,1991;Davies,1990;Fan &Makielski,1993;Koyano et al .,1993;Vivaudou &Forestier,1995).This action of low pH i can be interpreted that an intrinsic proton binding site regulates ATP sensitivity for the channel inhibition in K ATP (Fan &Makielski,1993).Evidence of the importance of Mg 2+as a cofactor necessary to keep the channel in operative state in the presence of either ATP or nucleotide diphos-phates has been provided as well as its contribution in the enhancement of KCO e ect (Findley,1988;Lederer &Nichols,1989;Shen et al .,1991;Terzic et al .,1994;Tung &Kurachi,1991;Vivaudou &Forestier,1995).We used MgATP combined with small doses of ADP in all our subsequent experiments in order to keep the channel in operative state and minimize run-down.At physiologic pH i 7.2nicorandil markedly increased the P o of K ATP ,but when lowering pH i ,the P o of nicorandil-activated K ATP was signi?cantly decreased.Therefore,it appears that variations in pH i directly a ect the interaction between nicorandil and K ATP rather than via producing the second messengers such as the production of cyclic GMP (Kojda &Kottenberg,1999;Kubo et al .,1994;Murphy &Brayden,1995).This suppressive action on K ATP seems to overcome stimulating e ect of low pH i .
Modulation of K ATP by nitric oxide
In the present study,we demonstrated at the single-channel level that NO donors of di erent chemical structures increased the P o of K ATP at pH i 7.2.Furthermore,removal of NO donors did not abolish the increased activity but the activity was kept increasing,and higher doses of ATP were needed to inhibit the channels than those before the drug treatment,suggesting a reduction of sensitivity to the nucleotide-inhibitory e ect.Although the activation of the channels by NO donors was not as large as with nicorandil,the increase in P o was clear and signi?cant.At low pH i ,however,the presence of NO donors decreased the P o of the channels and removal of the NO donors did not reverse the phenomenon.Also,with raising pH i from 6.0to 7.2in the presence of the NO donors,the increase of P o was evident.Therefore,the e ects of the NO donors at either pH i 7.2or pH i 6.0were very similar to those observed with nicorandil.Recently,NO was reported to enhance the KCO-activated K ATP current with unde?ned mechanism (Shinbo &Iijima,1997).They demonstrated the enhancing action of NO with whole-cell and cell-attached patch recordings in guinea-pig ventricular myocytes at normal pH o and pH i .In their experiments the cyclic GMP pathway and/or metabolic inhibition did not appear to be responsible for NO e ects.Their ?ndings were similar to the present results,except they failed to demonstrate the enhancing action of NOR-3on K ATP in inside-out patches.Here,we were able to show a clear activation of the channels by application of two di erent NO donors to inside-out patches.At present,we could not ?nd any proper reason to explain the discrepancy between the two studies,but a direct action of NO on the modulation of cardiac K ATP might be supported.In
cultured
Figure 7E ects of NO scavenger,HbO 2on K ATP activity in the presence of NO-donor,NOR-3.Single channel records show that lowering pHi from 7.2to 6.0in the presence of nucleotides and Mg 2+increased K ATP activity.Increased channel activity was somewhat depressed by addition of 1.0m M NOR-3and further decrease was noted in the presence of 5m M of HbO 2.Neither removal of HbO 2nor NOR-3reversed the depressed activity of the channel,but a change in pH i from 6.0±7.2increased the P o of K ATP .Upon removal of the nucleotides complete recovery of the initial activity took place ruling out the presence of run-down.
British Journal of Pharmacology vol 131(6)
H +and NO interaction on K ATP
G.A.Moncada et al 1102
vascular smooth muscle cells,isosorbide dinitrate and atrial natriuretic factor were proven to modulate the gating of K ATP and the cyclic GMP pathway was involved(Kubo et al.,1994).There are,however,several lines of evidence that direct e ects of NO on channel modulation;for example, expressed cardiac L-type Ca2+channels(Hu et al.,1997), calcium-regulated potassium channel in vascular smooth muscle cells(Bolotina et al.,1994)and potassium channels in colonic muscle cells(Koh et al.,1995).Therefore,it may be possible that NO could directly modulate K ATP and our ?ndings add new evidence for its role on the modulation of cardiac K ATP.
Because of these similarity of actions between the NO donors and nicorandil,the suppression of the nicorandil-activated K ATP at low pH i can be attributed to a direct interaction of NO with H+at ATP-binding inhibitory sites of the channels,where stimulating action of pH i is supposed to interact on this site.This action may be di erent from the enhancing action of NO and nicorandil on K ATP at normal pH i,or some other mechanism to exhibit both stimulating and suppressive actions depending on pH may be involved. This issue is to be explored further.Dual modulations of cardiac K ATP have been demonstrated in the actions of pinacidil(Fan et al.,1990),nucleotides diphosphates and Mg2+(Findley,1988;Lederer&Nichols,1989;Tung& Kurachi,1990;Terzic et al.,1994),and pH i(Cuevas et at., 1991;Fan&Makielski,1993;Koyano et al.,1993;Fan et al., 1993).The dualistic modulations by these factors develop in variable ways and di erent mechanisms seem to be involved. For examples,pinacidil exerts voltage-independent activation of the channels and voltage dependent inhibition from inside of the membrane.Nucleotide diphosphates cause channel inhibition without Mg2+and stimulate the channels in the operative state in the presence of Mg2+.Mg2+produces channel inactivation and run-down on the one hand,and on the other it promotes the channels into the operative states. Low pH i promotes increased channel open probability but induces decreased single channel current amplitude.
The fact that NO-scavengers were not able to prevent or reverse the actions of NO-donors on the K ATP is unclear and needs to be further investigated.In the case of HbO2,the compound itself was shown to a ect directly the channel at either normal or lower pH i,and that explains the prominent enhancement of the depressive e ect of NO-donors on the channel.Does the K ATP have the ability to sense and respond to HbO2levels?As for carboxy-PTIO,the dose required to abolish the NO e ect is much higher than that for HbO2, (Donor:Scavenger ratio=3:1)and the release rate of NO is slower,perhaps that might explains why it did not a ect NO-H+interaction respect to K ATP.
Possible pathophysiological implications
The openings of K ATP play an pivotal role for action potential shortening and are partly responsible for extra-cellular K+accumulation during early phase of myocardial ischemia and infarction,which may contribute to the development of arrhythmias(Venkatesh et al.,1992;Wilde &Janse,1994).At the same time,pH i may go down quickly. On the other hand,the openings of K ATP may exert the protective action on the second severe ischemic insult after a brief period of ischemia(preconditioning)(Downey&Cohen, 1997;Gross,1995;Grover,1994).If the patients taking nicorandil as anti-anginal drug develop ischemic attack,a quick opening of K ATP can be anticipated during early ischemic episode and yet,the opening e ects are subsequently suppressed due to decreased pH i,which may give a self-limiting factor for the prevention of further shortening of action potential duration and extracellular K+accumulation. At the same time,K ATP as the end e ector of cardioprotec-tion is also modulated by NO production(Bolli et al.,1997; Imagawa et al.,1999;Yao and Gross,1993).Therefore,these interplay and?nal results in the presence of nicorandil must be evaluated with caution.Acidosis is known to be pro-arrhythmogenic by a ecting multiple ionic currents including K ATP(Orchard&Cingolani,1994).Therefore,it might be necessary to further examine the pharmacological pro?le of these drugs in acidotic conditions.
Conclusions
The present study provides information concerning the e ect of H+at either side of the membrane in nicorandil-activated K ATP.We present new evidence of a cyclic GMP-independent modulating e ect of NO on K ATP during acidosis.These ?ndings may be relevant to the therapeutic action of these drugs,especially during ischemic or hypoxic conditions.
We thank Miss K.Totsuka for secretarial services and Mrs K. Yamamoto for excellent technical assistant.We are also grateful for the generous supply of nicorandil by Chugai Pharmaceutical, Co.Ltd.(Tokyo,Japan).Thanks are due to Fujisawa Pharma-ceutical Co.Ltd.(Osaka,Japan)for the generous supply of FK409 (NOR3).
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(Received June28,2000
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步进电机及单片机英文文献及翻译
外文文献： Knowledge of the stepper motor What is a stepper motor： Stepper motor is a kind of electrical pulses into angular displacement of the implementing agency. Popular little lesson: When the driver receives a step pulse signal, it will drive a stepper motor to set the direction of rotation at a fixed angle (and the step angle). You can control the number of pulses to control the angular displacement, so as to achieve accurate positioning purposes; the same time you can control the pulse frequency to control the motor rotation speed and acceleration, to achieve speed control purposes. What kinds of stepper motor sub-： In three stepper motors: permanent magnet (PM), reactive (VR) and hybrid (HB) permanent magnet stepper usually two-phase, torque, and smaller, step angle of 7.5 degrees or the general 15 degrees; reaction step is generally three-phase, can achieve high torque output, step angle of 1.5 degrees is generally, but the noise and vibration are large. 80 countries in Europe and America have been eliminated; hybrid stepper is a mix of permanent magnet and reactive advantages. It consists of two phases and the five-phase: two-phase step angle of 1.8 degrees while the general five-phase step angle of 0.72 degrees generally. The most widely used Stepper Motor. What is to keep the torque (HOLDING TORQUE) How much precision stepper motor? Whether the cumulative： The general accuracy of the stepper motor step angle of 3-5%, and not cumulative.
大学生毕业个人总结2000字
篇一：2000字毕业生个人总结 个人总结 时间过得真快，不经意间我即将和大学挥手告别。回首这一年半的校园生涯和社会实践生活，有太多的回忆。大学的第一个学期在憧憬与新奇中飞快的度过了，这是一个崭新的世界，是一座通向社会的桥梁，那时的我们刚刚迈上。大学是挑战自我，充实自我，为实现人生价值打下基础的平台。我们总能一次又一次更加深刻的了解自己，反省自己，找到更适合自己的道路。回忆起刚刚入学的情景，同学间初次见面的扭捏与欣喜似乎还在眼前；军训时，操场上的飒爽英姿和病榻前的关怀问候随处可见；大学城的日子里，每天清晨结伴从宿舍走到教学楼，中午结伴去食堂用餐，夜幕中结伴在校园漫步，处处都洋溢着青春的笑脸，就连浓雾中的晨练也成为一道不可多得的风景线，至今令人无法忘怀。进入大学，首先是一次思想的进步，我告诉自己，我已经是一个大学生，在心智上应该逐渐成熟起来，凡事要首先自己独立进行考虑，沉着冷静得出结论。我能做到积极要求进步，积极靠近党组织，并在第一学期就向党组织提交了入党申请书，坚决拥护中国共产党。关心国家大事，让自己的思想紧紧跟上时代的步伐，时刻听从党的召唤，始终拥护党的纲领。我一直在追求人格的升华，注重自己的品行。在大学生活中，我坚持着自我反省且努力的完善自己的人格。利用课余时间阅读《菜根谭》等书籍，这对自己有所帮助，越来越认识到品行对一个人来说是多么的重要，关系到是否能形成正确的人生观世界观。所以无论在什么情况下，我都以品德至上来要求自己。无论何时何地我都奉行严于律己的信条，尊崇诚实做人的宗旨，并切实的遵行它。 作为一名大学生，首先，最重要的任务一定是完成自己的此阶段的学业。大学是一个培养具有科学文化素质青年的殿堂，踏过高考的千军万马，走过人生第一座险隘的独木桥，成功的迈进大学的校门，无论是怀着怎样的心情，我想我没有理由不好好学习。但那不得不承认的是，大学的课程的确和以前大不相同，难度的加深、数量的增加、学习方法的巨大改变，带来了一些问题，例如有一段时间，听课听不懂，做也不会做，想请教被人却不知道从何做起，这样除了刻苦的学习之外，还要摸索适合自己的学习方法，一切都是全新的挑战，但是还好，我顺利的完成了第一学期的学习任务。 回顾自己走过的路，从中学到大学，是人生的重大转折，大学生活的重要特点表现在：生活上要自理，管理上要自治，思想上要自我教育，学习上要求高度自觉。尤其是学习的内容、方法和要求上，比起中学的学习发生了很大的变化。要想真正学到知识和本领，除了继续发扬勤奋刻苦的学习精神外，还要适应大学的教学规律，掌握大学的学习特点，选择适合自己的学习方法。大学的学习既要求掌握比较深厚的基础理论和专业知识，还要求重视各种能力的培养。大学教育具有明显的职业定向性，要求大学生除了扎扎实实掌握书本知识之外，还要培养研究和解决问题的能力。因此，要特别注意自学能力的培养，学会独立地支配学习时间，自觉地、主动地、生动活泼地学习。还要注意思维能力、创造能力、组织管理能力、表达能力的培养，为将来适应社会工作打下良好的基础。 大学与原来最大的不同就是远离了父母。在生活上，原来父母包管了一切，现在只能自己一切都靠自己，还好，我基本上都可以和同学们友好相处，和睦共处，互帮互爱，自己的事情自己做，形成独立自理自立的良好品德。宿舍是一个大集体，六个人生活在同一个空间里面，但是各自的生活习性都不相，这就需要大家互相理解和迁就，只有这样才能和好相处，为我们的学习创造一个良好的学习和休息环境。 还没进入大学之前，哥哥姐姐们就告诉我，大学，就是一个小社会，通过大学，不仅要学习课本上的知识，也要培养个人的能力与素质，参加多项活动，在学院的篮球赛、乒乓球赛、跳绳比赛、辩论赛等活动中担任计分员，自己也参加了跳绳比赛、知识竞赛、书画摄影竞赛等，在这些活动中锻炼了自己的能力与品质，丰富了课余生活，在学院举办的职业生涯规划大赛中取得了不错的成绩，对自己的职业以及人生也做了一次深入的思考，收获颇为丰富。
2020大学生自我鉴定2000字
2020大学生自我鉴定2000字 四年的大学生活似弹指一挥间，转眼大学生活就该结束了，大学生自我鉴定对你是有帮助的，下面是小编为大家整理的大学生自我鉴定20xx字范文，仅供参考，希望对你有所帮助。 大学生自我鉴定20xx字篇一 在毕业之即，我对自已在学校的三年期间做了如下的总结：首先，在思想品德上，这学年以来我对自身严格要求，始终把耐得平淡、舍得付出、默默无闻作为自己的准则，始终把作风建设的重点放在严谨、细致、扎实、求实、脚踏实地埋头苦干上;并且我本人遵纪守法，有良好的道德修养，爱护公共财产,团结同学,乐于助人。并以务实求真的精神热心参与学校的公益宣传和爱国主义活动，积极地向党组织靠拢。 在学习上，大学时代是学习现代科学知识的黄金时代，因此在平日的学习中我会抓住这个有利的时机，用知识来武装自己的头脑并勤奋地学习本专业的相关知识，同时不断去学习其他相关领域的知识，这样越是学习，就越能发现自己所学的知识是有限的，进而就会不断的鞭策自己，做到不懂就问，不清楚就去查资
料，尽可能的多去了解身边的新生事物并给予客观、公正的评价。不断学习别人的长处，虚心请教，同时去伪存真，拒绝一些不健康，思想不进步的报刊书籍。我在学习经验方面主要有如下体会：①学习体会式;经过三年的努力终于毕业了。回顾在校的这三年，我感受到了每一位学生从艰辛到成功的历程。在这所大学里，我懂得了在学习的过程中确定自己学习方法的重要性。首先是要培养对自己专业的感情;第二是培养自己的自学能力，并根据课程和时间适当地提前预习;第三是全面了解书中的基础知识，并在理解的基础上加以总结和巩固;第四是多做习题，以适应考试的形式。另外，有明确的学习目的，学习是为更多更好地掌握知识，在考试失败时要增强自信心，永远保持乐观、向上的精神。②学以致用式;随着社会的不断进步与发展，人类的整体素质也在不断地提高。为了工作的需要，也为了提高自己自身的修养。在学习的道路上我深深地体会到“书山有路勤为径，学海无涯苦作舟”这句古话。在学习的过程中，我对自己所学的专业知识除了有深刻的认识以外，课余时间我还阅读了许多名人传记，从伟人的经历中获取养分，更进一步地充实自己。同时我也阅读了大量的文学作品，提高了自己的鉴赏水平。并在这期间，学习到了为人处世伦理哲学，以提高自己的道德修养。虽然我没担任过学生干部职务，但我积极参加班级、院系组织各类公益活动和社会活动，并在活动中积极工作，使我积累了许多宝贵的办事经验，从而大大提高了自己的组织能力、协调能力、交际能力和处事应变能力;
大学生社会实践报告2000字
大学生社会实践报告2000字
社会实践报告 院（系）部名称 xxxxxxx 专业： xxxxx 年级班级： xxxx 级 姓名： xxxxxx 学号: 实践单位：
实践时间： 2017年7月15日至2017年08月15日共31天 一、实践目的 作为祖国未来的事业的继承人，我们这些大学生应该及早树立自己的历史责任感，提高自己的社会适应能力。假期的社会实践就是很好的锻炼自己的机会。许多学校也积极鼓励大学生多接触社会、了解社会，一方面可以把学到的理论知识应用到实践中去，提高各方面的能力；另一方面可以积累工作经验对日后的就业大有裨益。作为一名尚未毕业的大学生，由于本身具备的专业知识还十分的有限，所以我选择了打散工作为第一次社会实践的方式。目的在于熟悉社会。就职业本身而言，并无高低贵贱之分，存在即为合理。通过短短几天的打工经历可以让长期处于校园的我们对社会有一种更直观的认识。 二、实践内容 就在2017年的暑假我开始了我这个假期的社会实践走进百姓家园餐厅做一个传菜员。在餐厅里,别人一眼就能把我人出是一名正在读书的学生,我问他们为什么,他们总说从我的脸上就能看出来,也许没有经历过社会的人都有我这种不知名遭遇吧!我并没有因为我在他们面前没有经验而退后,我相信我也能做的像他们一样好.我的工作是在那做传菜生,每天9点钟-下午2点再从下午的4点-晚上8:30分上班,虽然时间长了点但,热情而年轻的我并没有丝毫的感到过累,我觉得这是一种激励,明白了人生,感悟了生活,接触了社会,了解了未来.在餐厅里虽然我是以传菜为主,但我不时还要做一些工作以外的事情，有时要做一些清洁的工作，在学校里也许有老师分配说今天做些什么，明天做些什么，但在这里，不一定有人会告诉你这些，你必须自觉地去做，而且要尽自已的努力做到最好，一件工作的效率就会得到别人不同的评价。 三、实践结果 虽然这次的实践只有短短的几天，而且从事的是比较简单的服务工作，但是通过与各种各样的人接触，还是让我学会了很多道理。
单片机外文翻译
杭州电子科技大学信息工程学院毕业设计（论文）外文文献翻译 毕业设计（论文）题目用单片机实现的数字时钟电路设计文献综述题目单片机控制系统系电子工程 专业电子信息科学与技术 姓名郭筱楠 班级08091911 学号08919115 指导教师王维平
单片机控制系统 广义地说，微型计算机控制系统（单片机控制系统）是用于处理信息的，这种被用于处理的信息可以是电话交谈，也可以是仪器的读数或者是一个企业的帐户，但是各种情况下都涉及到相同的主要操作：信息的处理、信息的存储和信息的传递。在常规的电子设计中，这些操作都是以功能平台方式组合起来的，例如计数器，无论是电子计数器还是机械计数器，都要存储当前的数值，并且按要求将该数值增加1。一个系统例如采用计数器的电子钟之类的任一系统要使其存储和处理能力遍布整个系统，因为每个计数器都能存储和处理一些数字。 现如今，以微处理器为基础的系统从常规的处理方法中分离了出来，它将信息的处理，信息的存储和信息的传输三个功能分离形成不同的系统单元。这种主要将系统分成三个主要单元的分离方法是冯-诺依曼在20世纪40年代所设想出来的，并且是针对微计算机的设想。从此以后基本上所有制成的计算机都是用这种结构设计的，尽管他们包含着宽广的物理形式与物理结构，但从根本上来说他们均是具有相同基本设计的计算机。 在以微处理器为基础的系统中，处理是由以微处理器为基础的系统自身完成的。存储是利用存储器电路，而从系统中输入和输出的信息传输则是利用特定的输入/输出（I/O）电路。要在一个以微处理器为基础的时钟中找出执行具有计数功能的一个特殊的硬件组成部分是不可能的，因为时间存储在存储器中，而在固定的时间间隔下由微处理器控制增值。但是，规定系统运转过程的软件却规定了包含实现计数器计数功能的单元部分。由于系统几乎完全由软件所定义，所以对微处理器结构和其辅助电路这种看起来非常抽象的处理方法使其在应用时非常灵活。这种设计过程主要是软件工程，而且在生产软件时，就会遇到产生于常规工程中相似的构造和维护问题。 图1.1 微型计算机的三个组成部分 图1.1显示出了微型计算机中这三个单元在一个微处理器控制系统中是如何按照机器中的信息通信方式而联接起来的。该系统由微处理器控制，微处理器能够对其自身的存储器和输入/输出单元的信息传输进行管理。外部的连接部分与
辉煌中国纪录片观后感1000字
辉煌中国纪录片观后感1000字 《辉煌中国》是由中国共产党宣传部、中央电视台联合制作的6集电视纪录片。这里给大家分享一些辉煌中国纪录片观后感，希望对大家有所帮助。 辉煌中国纪录片观后感1 六集电视纪录片《辉煌中国》于近日在央视晚黄金时间播出，本片以创新、协调、绿色、开放、共享的新发展理念为脉络，全面反映党的十八大以来中国经济社会发展取得的巨大成就。 看了视频，我对祖国的未来充满信心，我相信，我们的国家在创新战略驱动下还会创造更多的人间奇迹。作为普通公民，我们立足本职岗位，尽心尽力，做好本职工作，同时借助科技发展的成果，努力充实自己，提升服务水平，提升生命质量，这也是我们在这辉煌的时代应有之举。 曾经，一些国人信奉“外国的月亮比中国的圆”。如今，走出国门的中国人，却处处觉得外国没有自己国家好。城市没有国内建得漂亮，交通没有国内便捷，安全没有国内有保障……许多的“不如”，累积着中国人的自信心和民族自豪感。
通过这次纪录片的观看，让我们了解到，科技创新的发展成果给中国带来翻天覆地的变化，交通变得如此发达，人们出门旅游十分方便，走南闯北带来诸多便利，也给诸多行业带来福利，旅游业、快递服务业、交通运输业的业绩水平都有明显的提高，交通条件发达带动中国经济收增长入。 我相信，努力，是黑夜里的一盏明灯，他指引着我前进的方向;汗水，是通向成功之路的阶梯，他引导这我努力攀登;毅力，是人生道路中前进的动力，有了他，我们才能真正成为生活的强者。愿我们不要害怕失败，带着毅力勇敢地走下去，因为努力铸就生活真强者! 辉煌中国纪录片观后感2 “民亦劳止，汔可小康。”——题记 中国，一个古老的国家，却也是一股新生的力量。 自1842年清鸦片战争战败，第一个不平等条约《南京条约》的签订起，中国人民曾经历了一个多世纪的荆棘之路、苦难之路。 1945年新中国成立，中国人民的思想得到了解放，中国的劳动人民不再遭受非人道的压迫、剥削。但四万万人民，四万万张嘴，数以万计的中国人民，还不能填饱自己的肚子。这个占了世界总人口五分之一的国家，该如何解决人民吃饭问题，成了党和国家和人民所必须面对的难题。
大学生毕业实习总结2000字
大学生毕业实习总结2000字实习是大学毕业参加工作之前将理论与实际结合的的锻炼机会，也是一个非常好的从大学生到就业者的过渡阶段，更是大学生培养自身能力的好的练刀石。作为一名刚毕业的应届大学生，能否在实习的过程中把握好实习内容，培养好工作能力，显的尤为重要。半年来，我严格遵照人事部发下的实习纲要，认真研读，逐一学习，在思想行动上，努力做到“想实习，会实习，实好习”，把培养工作能力，提高自身的素质当做自己的任务，很好的完成了这个阶段的实习任务。 一是加强思想理论的学习，主动找领导沟通，努力提高思想水平。 思想是人的灵魂，是人的内在力量，想要圆满完成实习任务，首先要调整好思想。领导们非常关心大学生的成长，为此特地为我们制定了“双导师实习制度”。双导师，顾名思义，就是两位导师，技术导师是教授工作技术的，而领导导
师是在思想上引领大学生，为其排忧解难，指引方向的。在此优势下，我主动与领导进行了沟通，在领导的谆谆教导下，我对实习有了更深层次的理解，更明确了我的工作目标，在思想上我对未来的工作有了新的认识，在行动上使我对未来人生有了新的规划。 二是注重理论联系实际，理论与实践相结合，努力提高实习质量。 一切认识都来源于实践。实践是认识的来源说明了亲身实践的必要性和重要性，但是并不排斥学习间接经验的必要性。实践的发展不断促进人类认识能力的发展。实践的不断发展，不断提出新的问题，促使人们去解决这些问题。而随着这些问题的不断解决，与此同时，人的认识能力也就不断地改善和提高!马克思主义哲学强调实践对认识的决定作用，认识对实践具有巨大的反作用。认识对实践的反作用主要表现在认识和理论对实践具有指导作用。认识在实践的基础上产生，但是认识一经产生就具有相对独立性，可以对实践进行指导。实践，就是把我们在学校所学的理论知识，运用到
大学生暑期社会实践报告2000字
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2000字A级信用单位”等荣誉称号。 三、实习内容 我在惠宝电脑科技公司做电脑组装及销售工作，通过培训及亲身实践学习熟悉业务。公司首先对我们进行基本的电脑销售培训，同时也教我们去组装电脑。负责培训的工作人员首先给我们讲解大概的电脑安装顺序，电脑安装主要是主机的安装，各个部件的安装也是要求顺序，这样电脑组装起来才不会有所损坏，而且组装起来更加迅速。经过几次真正实践，我熟悉了硬件组装过程装好电脑，接好线后，就是要装电脑操作系统，这个虽然简单，但也有细节要注意的，尤其是电脑显示器的屏幕测试，一定要够细心才可以。经过几次动手，终于掌握了基本的电脑组装。接下来要学的，就是要记住一些部件的型号、功能、价格等方面的信息。现代科学发展进步飞快，软硬件更新速度日新月异，面对一大堆电脑部件的信息，要想很快记住还是有一定难度的。整个培训虽然简单，但整个流程下来还是很费心的，我也深深体会到工作和上学的不同。 培训之后，正式开始接触销售了。通过不断地向顾客介绍推销过程中，让我懂得销售员是需要高度的激情和恒心的，这些天的销售工作提高我的交际能力，能锻炼我们的口才。在这一个多月的实习当中我接待了很多
单片机外文翻译--STC89C52处理芯片
外文资料翻译 STC89C52 processi ng chip Prime features: With MCS - 51 SCM product compatibility, 8K bytes in the system programmable Flash memory, 1000 times CaXie cycle, the static operation: 0Hz ~ 33Hz, triple encryption program memory, 32 programmed I/O port, three 16 timer/counter, the eight uninterrupted dual-career UART serial passage, low power consumption, leisure and fall after fall electric power mode can be awakened and continuous watchdog timer and double-number poin ter, power ide ntifier. Efficacy: characteristics STC89C52 is one kind of low power consumption, high CMOS8 bit micro-co ntroller, 8K in system programmable Flash memory. Use high-de nsity nonv olatile storage tech no logy, and in dustrial 80C51 product in structi on and pin fully compatible. The Flash memory chips allows programs in the system, also suitable for programmable conventional programming. In a single chip, have clever 8 bits CPU and on li ne system programmable Flash, in crease STC89C52 for many embedded control system to provide high vigorous application and useful solutions. STC89C52 has following standard efficacy: 8k byte Flash RAM, 256 bytes, 32 I/O port, the watchdog timer, two, three pointer numerical 16 timer/counter, a 6 vector level 2 continuous structure, the serial port, working within crystals and horological circuit. In addition, 0Hz AT89S52 can drop to the static logic operation, support two software can choose power saving mode. Idle mode, the CPU to stop working, and allows the RAM, timer/c oun ters, serial, continu ous to work. Protectio n asa na patter n, RAM content is survival, vibrators frozen, SCM, until all the work under a continuous or hardware reset. 8-bit microcontrollers 8K bytes in the system programmable Flash AT89S52 devices. Mouth: P0 P0 mouth is a two-way ope n drain I/O. As export, each can drive eight TTL logic level. For P0 port to write "1", foot as the high impeda nee in put. When access to exter nal programs and nu merical memory, also known as
毕业生个人实习总结2000字范文
毕业生个人实习总结2000字范文 毕业生个人实习总结2000字一 作为一名即将毕业踏入社会的大学生，这次实习就像是上台前的最后一次彩排，当我走进公司时那种激动而又紧张的心情不言而喻。生怕会在工作中出现差错，然而现在看来所有在实习中出现的困难，都是一笔珍贵的财富，警示着我在今后的工作中做得更好。 一、实习过程 开始实习之前，我多少有些心虚。因为我的许多朋友都有过假期打工的经历。而作为一名英语专业的学生，这次的实习却是我的第一次工作经历。从工作那天开始，我过着与以往完全不一样的生活，每天在规定的时间上下班，上班期间要认真准时地完成自己的工作任务，不能草率敷衍了事，我们肩上扛着的责任，不再只是对自己了，而是对一个公司，所以凡是都要小心谨慎。 学校换成了公司，同学换成了同事，不再有自由支配的时间，一切来得那么无情，但是去必须适应。其实我的工作就是、做些翻译、收发信函、报价、传真和邮件、绘制表格等。每天重复着这些烦琐的工作，时间久了容易厌倦，但是工作烦琐也不能马虎，一个小小的错误不但会给自己带来麻烦，更会给公司带来巨大的损失，而像公司的业务员每天都得到处奔波，他们必须具
备坚韧不拔的个性，遭遇挫折时绝不能就此放弃，犯错时遭到领导责骂还不能赌气就此辞职，每次看到他们我就会充满干劲。 踏上了社会我们开始与形形色色的人打交道，由于存在着利益关系，很多时刻同事不会像同学一样嘘寒问暖，有时候我会很矫情的想起安妮宝贝说过的，纯粹的东西总是死的很快，而现在所能做的，只有在怀念中适应变化的一切。 二、实习感悟 “在大学里学的不是知识而是一种叫自学的能力。”当我真正走上工作岗位时才深刻的体会到这句话的含义，除了英语和计算机操作外，课本上学的理论用的很少，我担任的助理一职平时做些接待客户、处理文件，有时觉得没有太多挑战性，而同公司的网站开发人员就大部一样了，计算机知识日新月异，他们不得不以自学尽快掌握新知识，迎接一个一个新的挑战，如果他们之靠在学校中学到的知识肯定是不行的。我们必须工作中勤于动手，不断学习新知识积累经验，没有自学能力的人迟早会被企业和社会淘汰。 我的感悟就是真诚所至，金石为开。不管多难做，做好自己的那一份，总有一天会有收获，只是时间的问题。但如果你不去做，这一天永远不会像天上掉馅饼那样到来。 另外，人际关系的处理也很关键，虽说在工作中能力必须有，但如果没有同事的合作与包容，你可能什么都做不了。
大学生四年年度自我总结2000字
大学生四年年度自我总结2000字 珍贵的四年大学生活已接近尾声，感觉非常有必要总结一下大学 四年的得失，从中继承做得好的方面改进不足的地方，使自己回顾走 过的路，也更是为了看清将来要走的路。 学习成绩不是非常好，但我却在学习的过程中收获了很多。首先 是我端正了学习态度。在我考进大学时，脑子里想的是好好放松从重 压下解放出来的自己，不过很快我就明白了，大学仍需努力认真的学习。看到周围的同学们拼命的学习，我也打消了初衷，开始大学的学 习旅程。其次是极大水准的提升了自己的自学水平。因为大学的授课 已不再像高中时填鸭式那样，而是一节课讲述很多知识，只靠课堂上 听讲是完全不够的。这就要求在课下练习巩固课堂上所学的知识，须 自己钻研并时常去图书馆查一些相关资料。日积月累，自学水平得到 了提升。再有就是懂得了使用学习方法同时注重独立思考。要想学好 只埋头苦学是不行的，要学会“方法”，做事情的方法。古话说的好，授人以鱼不如授人以渔，我来这里的目的就是要学会“渔”，但说起 来容易做起来难，我换了好多种方法，做什么都勤于思考，遇有不懂 的地方能勤于请教。在学习时，以“独立思考”作为自己的座右铭， 时刻不忘警戒。随着学习的进步，我不止是学到了公共基础学科知识 和很多专业知识，我的心智也有了一个质的飞跃，能较快速的掌握一 种新的技术知识，我认为这对于将来很重要。在学习知识这段时间里，我更与老师建立了浓厚的师生情谊。老师们的谆谆教导，使我体会了 学习的乐趣。我与身边很多同学，也建立了良好的学习关系，互帮互助，克服难关。现在我已经大四，正在做毕业设计，更锻炼了自我的 动手和分析问题水平，受益匪浅。 一直在追求人格的升华，注重自己的品行。我崇拜有巨大人格魅 力的人，并一直希望自己也能做到。在大学生活中，我坚持着自我反 省且努力的完善自己的人格。四年中，我读了一些名著和几本完善人 格的书，对自己有所协助，越来越理解到品行对一个人来说是多么的 重要，关系到是否能形成准确的人生观世界观。所以无论在什么情况
大学生社会实践报告2000字
大学生社会实践报告2000字作为祖国未来的事业的继承人，新一代大学生应该及早树立自己的历史责任感，提高自己的社会适应能力。假期的社会实践就是很好的锻炼自己的机会。那么，实践报告该怎么写，你知道吗 社会实践报告(一) 作为祖国未来的事业的继承人，新一代大学生就应及早树立自我的历史职责感，提高自我的社会适应潜力。假期的社会实践就是很好的锻炼自我的机会。当下，挣钱早已不是打工的唯一目的，更多的人将其视为参加社会实践、提高自身潜力的机会。许多学校也用心鼓励大学生多接触社会、了解社会，一方面能够把学到的理论知识应用到实践中去，提高各方面的潜力;另一方面能够积累工作经验对日后的就业大有裨益。进行社会实践，最理想的就是找到与本专业对口单位进行实习，从而提高自我的实战水平，同时能够将课本知识在实践中得到运用，从而更好的指导自我今后的学习。但是作为一名尚未毕业的大学生，由于本身具备的专业知识还十分的有限，所以我选取了打散工作为第一次社会实践的方式。目的在于熟悉社会。就职业本身而言，并无高低贵贱之分，存在即为合理。透过短短几天的打工经历能够让长期处于校园的我们对社会有一种更直观的认识。 实践过程：自从走进了大学，就业问题就似乎总是围绕
在我们的身边，成了说不完的话题。在现今社会，招聘会上的大字报都总写着“有经验者优先”，可还在校园里面的我们这班学子社会经验又会拥有多少呢为了拓展自身的知识面，扩大与社会的接触面，增加个人在社会竞争中的经验，锻炼和提高自我的潜力，以便在以后毕业后能真正真正走入社会，能够适应国内外的经济形势的变化，并且能够在生活和工作中很好地处理各方面的问题，我开始了我这个假期的社会实践走进赣州市金源休闲餐厅。 实践，就是把我们在学校所学的理论知识，运用到客观实际中去，使自我所学的理论知识有用武之地。只学不实践，那么所学的就等于零。理论就应与实践相结合。另一方面，实践可为以后找工作打基础。透过这段时光的实习，学到一些在学校里学不到的东西。因为环境的不一样，接触的人与事不一样，从中所学的东西自然就不一样了。要学会从实践中学习，从学习中实践。而且在的经济飞速发展，又加入了世贸，国内外经济日趋变化，每一天都不断有新的东西涌现，在拥有了越来越多的机会的同时，也有了更多的挑战，前天才刚学到的知识可能在这天就已经被淘汰掉了，的经济越和外面接轨，对于人才的要求就会越来越高，我们不只要学好学校里所学到的知识，还要不断从生活中，实践中学其他知识，不断地从各方面武装自已，才能在竞争中突出自已，表现自已。