Cardiac Action Potential and Ion Channels

Abstract

The initiating event in cardiac E-C coupling is the action potential (AP). The AP is the membrane potential (E_m) waveform that is determined by a complex interplay of many ion channels and transporters, and the Ca transient itself. The AP is also the driving E_m waveform that influences ion channels and transporters, and results in the genesis of the Ca transient. The AP is also responsible for the propagation of excitation information from cell to cell in the heart and allows the heart to function as a syncytium (electrically and mechanically). The underlying ionic currents also contribute to initiating pacemaker activity as well as arrhythmogenic delayed- and early afterdepolarizations (DADs & EADs) and conditions for re-excitation and reentry. This chapter is only a basic overview of cardiac ion channels and the cardiac AP. A comprehensive treatment of this topic could readily fill another book of this type. For additional depth and references I recommend some excellent recent reviews by Weiss (1997), Roden & George (1997), Yellen (1998), Carmeliet (1999) and Nerbonne (2000, 2001). The main focus here will be on the ventricular myocyte AP and basic understanding of the ionic currents which contribute to its shape and modulation.