Copyright o The McGraw-Hill Companies, Inc. Permission required for reproduction or display The action potential of an autorhythmic cardiac cell Threshold Phase 4 口 k decay 100 0 0.15 0.30 Inactivated when Time(s) repolarized to 60mV 10.0 Activated when depolarized 5 Pca to -50mV 10 Cas*n 0.1 0.15 0.30 Time(s)The action potential of an autorhythmic cardiac cell. Phase 4： Ik decay Inactivated when repolarized to -60mV ICa,T Activated when depolarized to -50mV I f 25