Cytological and electrophysiological basis of cardiac junctional escape rhythm

Objective To explore the cytological and electrophysiological basis of junctional rhythm.Methods Histological sections were stained by Masson method to observe the arrangement of cardiac cells in junctional area of rabbit heart;single viable cells were isolated enzymatically for morphological research;whole-cell patch clamp was employed to study the action potential properties of specialized cardiac cells.Results Histologically,the cellular components in compact AV node and PNE were heterogeneous;the cells were organized regularly.Cytologically,the specialized cells PC,TCα and β were presented with the former two types automatically contracted.Electrophysiologically,the action potential configuration,maximum depolarization potential,action potential duration to 90% repolarization,velocity of depolarization in phase 0,velocity of phase 4 depolarization,overshoot and amplitude of action potential between PC and TCα were not significantly different except for action potential duration to 90% repolarization and velocity of phase 4 depolarization(all P0.05);conversely,the above parameters between TCβ and PC,TCα respectively were significantly different(all P0.05).Conclusion The specialized PC and TCα which demonstrated automaticity might construct the leading pacemaking focus in junctional escape rhythm.