Existence of a calcium-dependent potassium channel in the membrane of cow cardiac Purkinje cells.

Single-channel currents were recorded in the membrane of cow cardiac Purkinje cells using the patch-clamp technique. Recordings from cell-attached and cell-free patches demonstrated large outward single-channel currents associated with depolarizing voltage-clamp pulses. The time course of the reconstructed mean current showed a rapid activation phase followed by a slower inactivation following a single exponential time course with a time-constant in the range 30 ms to 100 ms. The current-voltage relation of the channel was linear in the voltage range between +10 mV and +110 mV with a slope conductance of 120 pS in 10.8 mM external K. The results indicated that the channel is selective for K ions. In inside-out patches, when the internal Ca activity was raised from 0.01 microM to 1 microM, the frequency of opening of the K channel during a depolarizing pulse was markedly increased, indicating Ca-dependence of these channels. The relation between this ion channel and the previously described transient outward current in cow Purkinje fibres is discussed. In sheep Purkinje cells a channel, carrying a transient outward current, with different properties was found.