LAUSR

The discovery of a slow Ca 2+ inward current in the heart by Reuter in 19671 was a milestone in the understanding of cardiac electrical activity. This current was shown to be the missing link between cardiac excitation and contraction (excitation contraction-coupling). Before this discovery, many of the major ion currents producing the cardiac action potential had already been defined, and the underlying cause of propagation in cardiac muscle was attributed to the inward Na+ current, INa. 2 However, since both the Na+ and Ca2+ currents correspond to inward movement of electrical charge, and consequently, depolarize cells, the question of whether and how these currents might interact to contribute to the propagation of the cardiac impulse became a major topic in cardiac electrophysiology.