[Inactivation of potassium outward current depending on the extracellular calcium ions].

Inactivation of the potassium outward current depending on the extracellular calcium ions was studied in voltage clamp experiments on nonidentified intracellularly perfused neurons of the snail Helix pomatia. The decay of this current can be approximated by two exponents with time constants of 50-70 ms and 220-300 ms, respectively. The steady-state inactivation depended on the intracellular concentration of K ions. With a decrease of the latter to 20 mmol/l the current was inactivated completely. The inactivation degree was independent of the level of depolarizing shifts of the membrane potential and reduced with a rise of the extracellular K ions concentration. Addition of 5-10 mmol/l K+ to K+-free extracellular solution induced a slow-down of the fast component of the decay (tau = 167 ms) and acceleration of deinactivation. The possible mechanism of inactivation of the investigated current is discussed.