MEASUREMENT AND BLOCK OF POTASSIUM CHANNEL CURRENTS IN THE HEART - IMPORTANCE OF CHANNEL TYPE

In heart as in other excitable tissues, potassium channel currents play an important role in maintaining the normal cell resting potential and controlling the action potential duration. In this study both theoretical and experimental procedures were used to examine the properties of the cardiac delayed rectifier potassium current (IDR) and the inward rectifier potassium current (IIR) and to determine the role that each plays in the repolarization of the action potential. IIR, a relatively time‐independent current, conducts potassium ions more readily in the inward than outward direction with outward current observed solely over the voltage range of ‐70 through ‐30 mV. Because of this behavior, IIR contributes only to the final stages of action potential repolarization. In contrast, IDR, a time‐dependent current with slow kinetics, conducts potassium ions outward over a broad positive voltage range and thus plays a dominant role in initiating and sustaining repolarization. A number of approaches, including single channel analysis and pharmacological interventions, have been begun to further characterize these two important ion currents. Copyright © 1990 Wiley‐Liss, Inc.