CALCIUM-DEPENDENT POTENTIATION OF M-CURRENT IN BULLFROG SYMPATHETIC NEURONS

Whole-cell voltage-clamp recordings were made from cultured bullfrog s ympathetic neurons to measure the steady-state activation curve of M-t ype potassium current. When measured with a calcium-deficient (10 nM) pipette solution M-conductance was 4.8 nS at -35 mV having the 50%-act ivation voltage at -20 mV. Respective values were 17.2 nS at -35 mV wi th the 50%-activation voltage at -42 mV when measured with a calcium-r ich (1 mu M) solution, indicating the hyperpolarizing displacement of the activation curve with high internal calcium. It is suggested that intracellular calcium ions can modulate kinetics of M-current which th ereby regulate the number of M-channels being open at given membrane p otentials.