KINETICS AND MAGNITUDE OF THE TIME-DEPENDENT POTASSIUM CURRENT IN THE RABBIT SINOATRIAL NODE - EFFECT OF EXTERNAL POTASSIUM

The properties of the time-dependent potassium current in the sinoatrial node of the rabbit heart were investigated. The following results were obtained: 1. When the slow inward current had been blocked an outward current consisting of an early exponential component and a late slow component was observed during voltage-clamp pulses. 2. The early component, which we will call iK, was well described by a first order Hodgkin-Huxley process for ion channel behaviour. The time course of the current depended on the potential at which the current was recorded but not on the potential preceding the pulse indicating a power of one for the kinetic variable. 3. The activation variable changed from 0 at about -50 mV to 1 at +10 mV. 4. No significant effect of the extracellular K concentration on the activation curve was detected. 5. The fully activated current displayed anomalous rectification. In most of the experiments no negative slope was observed. A major effect of raising the extracellular potassium concentration was to shift the fully activated current voltage relation along the voltage axis in the positive direction without producing a crossing-over phenomenon. The present observations on the potassium current iK agree with those obtained for similar current systems in other cardiac tissues. An important new finding is that the kinetics and the maximum conductance of iK show a remarkable insensitivity to changes in the external K concentration. © 1979 Springer-Verlag.