Phase2:depolarization（plateau）Ca++ channel open, Ca2+enters the cell through Ca2+channel.the slow (polarizing) outward leak of K+OmV100ms-85mVNatNatOutsideMembranceintsidea2+K+,ClChannel currentsPumpExchanger
Phase 2: depolarization ( plateau ) Ca++ channel open, Ca2+ enters the cell through Ca2+ channel. the slow (polarizing) outward leak of K+
Phase3:repolarization (Rapid repolarization)1.K+ channels open, K+leaves the cell through K+ channel. leadingtomembranerepolarization2.Upstroke ends as Na+ channels are rapidly inactivatedOmV电100ms-85mVNatNatOutsideMembranceintsidea2+K+,ClChannelcurrentsPumpExchanger
Phase 3: repolarization (Rapid repolarization) 1. K+ channels open, K+ leaves the cell through K+ channel. leading to membrane repolarization 2. Upstroke ends as Na+ channels are rapidly inactivated
Phase 4: forward current (Slow depolarization ,diastole)1.K+ is pumped into and Na+ is pumped out of the cell by Na+-K+-ATPase.2.In pacemakercellCa2+ slowlyenters the cell through Ca2+ channelOmV100ms-85mVNatNatOutsideMembranceintside92+aK+,CI-ChannelcurrentsPumpExchanger
Phase 4: forward current (Slow depolarization ,diastole) 1. K+ is pumped into and Na+ is pumped out of the cell by Na+- K+- ATPase. 2. In pacemaker cell Ca2+ slowly enters the cell through Ca2+ channel
20SAnode3-400threshold44-80福2-30Ventricular0muscle3044-90快反应电位与慢反应电位
-30 0 -90 4 4 0 1 2 3 Ventricular muscle 快反应电位与慢反应电位 0 -40 -80 0 2 3 4 4 SA node threshold
Phase0SuperiorSA nodevenacava-AtriumAVnodeOvershoot20PhaseOmVPurkinjeTricuspidvalve-100RestingpotentialMitralvalveVentricleActionpotentialphasesQ:Upstroke1:Early-fastrepolarization2:Plateau3:Repolarization4:DiastoleECGiQsQTPR200ms