Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The action potential of a myocardial pumping cell ■ Phase0 a Threshold potential (-70mV) a Opening of fast Nat channel 口 Regenerative cycle(再生性循环 10.0 Opening of Na channels in membrane Pcaa(L) Decreased membrane Increased membrane 方1.0 potential (depolarization) Na’ permeability Increased flow of e Na’ into cell◼ Phase 0  Threshold potential (-70mV)  Opening of fast Na+ channel  Regenerative cycle（再生性循环） The action potential of a myocardial pumping cell