CALCIUM-MODULATED INWARD RECTIFICATION OF A CALCIUM-ACTIVATED POTASSIUM CHANNEL IN NEURONS

1. Inward rectification of a calcium-activated K+ channel in neurons c ultured from the hypothalamus and brain stem of 1-day-old rats was stu died by using patch-clamp techniques. A big conductance calcium-activa ted K+ channel with a slow gating rate was observed in inside-out patc hes. With symmetrical K+ across patches, inward conductance of this ca lcium-activated K+ channel was 216 +/- 14 (SE) pS (n=4 patches), which changed little as different [Ca2+] was included in the bath solution. Outward conductance of this calcium-activated K+ channel was regulate d by [Ca2+] in the bath solution and was 74 +/- 15 pS with 500 muM Ca2 +. The higher level of Ca2+ on the intracellular side of the membrane caused the larger degree of rectification. Mg2+ only had a minor effec t on rectification of this calcium-activated K+ channel.