摘要(Abstract)：

<正> Introduction:Some studles have described the M cells in the deepsubeploardial to midmyooardial layers of the canine ventricle.Transient outward current of potasium(ito)initiate the repolarization ofaction potentials,and has an important effect on the configuration ofaction potential of epicardium and endocardium.So.it is necessary tostudy further about the contribution of ito in M cells.Methods:Standard glass microelectrode was used to observe actionpotential properties of M cell in canine ventricular tissue allce.The whotecell patch clamp was used to investigate the effect of M cell's ito oh itsaction potential.Results:(1)configuration of action potential:M cell and epicardialpossess prominent spike and dome configuration at early repolarization,but lucks of it in endocardium.(2)Characteristics of action potential:resting potential in M cell was more negtive than of apicardium andendocardium(respectively-88.,-66.5 and -85.9mv),but no statistic'ssignificance.Vmax in M cell possessed much greater than inendocardium and epicardium(299.0,197.6 and 160.4V/s).APD90 in Mcell was longer thin In eplcardium and endocardium(304,227 and211ms when BCL-1000ms);(3)M cell had more rate dependence ofaction potential duration than endocardium and endocardinm when BCLwas 500-5000ms;(4)ito in M cell and epicardium are aignifcantly greaterthan that in endocardium;(5)ito has obvious rate dependence,whenBCL lengthened,ito became strong.Conclutions:M cell possesses special characterlatics of actionpotential,such as obvious spike and dome configuration,much greaterVmax,longer action potential duration and more rate dependence,ito inM cell is one of the ionic busis of its having spike and dome morphologyand obvious rate dependence.vious rite dependence.

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