T20Phase 1020期Nat channels10inactivatedei60+80Ito channelsactivated1503001Time(ms)+inrapidefluxofpotassiumK+ outflowRapid repolarization120BO十十Na20Nat1Natin40Ito channels: Transient outward current, Ito60K+80K+ current. permeability for K+ . activated at --20 mV; opening for 5~10 ms30035020025050100150Na*Blocker: 4-aminopyridine
1期 Na+ K+ 按任意键显示动画2 Na+ channels inactivated + Ito channels activated ↓ K+ outflow ↓ Rapid repolarization Ito channels：Transient outward current, Ito K+ current. permeability for K+ . activated at – 20 mV; opening for 5~10 ms Blocker: 4-aminopyridine Phase 1
20仙Phase 2nL-type Ca2+ channels20activate60十80Ikchannels activate150300Time(ms)Ca2+ influxK+ outflowreach a balance1Repolarization十(plateau)20OCa2+channels:Long-lastingL-type20channels.Itsactivation and inactivationNa+4Care slow.60K+80Blockers: verapamil100300350100200250Na+Ca2+
L-type Ca2+ channels activate + IK channels activate ↓ Ca2+ influx K+ outflow reach a balance ↓ Repolarization （plateau） L-type Ca2+ channels: Long-lasting channels. Its activation and inactivation are slow. Blockers: verapamil. Na+ K+ Ca2+ K+ 按任意键显示动画2 Phase 2
atL-type Ca2+ channelfast Nat channel
L-type Ca2+ channel fast Na+ channel
Phase 3首L-type Ca2+channels3期1inactivate+泵Permeability for Ik FR50300K+ outflowpositivefeedbackfasionRapid repolarizationReachRPNatNat+209Phase 4: Ions (Nat, Ca?+, K+) return20Natin40to their original state.-6080Ion pumps: Na+-K+ pump, Na+-Ca2+2100exchanger, Ca2+ pump.101350泵Ca2+Na+Ca2+
L-type Ca2+channels inactivate + Permeability for IK ↑ ↓ K+ outflow positive feedback fasion ↓ Rapid repolarization Reach RP Phase 4: Ions (Na+ , Ca2+ , K+ ) return to their original state. Ion pumps: Na+ -K+ pump, Na+ -Ca2+ exchanger, Ca2+ pump. 3期 Na+ ○ K+ Ca2+ Na+ K+ 泵 按任意键显示动画2 ○泵 3期 Phase 3 Ca2+
SummaryFast Na+ channels open中+20Fast Na+ channels inactivated0oiieIto K+ channels open-20040Slow Ca2+ channels open-60Ik channels open-80Slow Ca2+ channels close3100Ik channels open300C100200Time(msec)Resting potential, pumps work
Summary Fast Na+ channels open Fast Na+ channels inactivated Ito K+ channels open Slow Ca2+ channels open IK channels open Slow Ca2+ channels close IK channels open Resting potential, pumps work