Ca-activated potassium current in vertebrate sympathetic neurons.

Ca-activated K-currents (IC) in sympathetic neurones have been triggered by intracellular Ca-injection or by activating ICa. IC is strongly voltage-dependent, with a peak slope of 11 mV/e-fold depolarization above -50 mV. Relaxation, fluctuation and single channel analysis suggests this to result from voltage-dependent opening and closing rates. Time-constants for channel opening and closing are about 15 msec near zero mV. Single channel conductance is about 100 pS. Currents can be blocked by TEA. IC is activated very rapidly (less than or equal to 5 msec) and sometimes transiently by a depolarizing voltage-step. It is suggested that IC contributes to both spike repolarization and spike after-hyperpolarization. Spontaneous miniature ICs have also been recorded, probably activated by the release of packets of intracellular Ca.