PROPERTIES AND MODULATION OF A CALCIUM-ACTIVATED POTASSIUM CHANNEL INRAT OLFACTORY-BULB NEURONS

1. Single calcium-activated potassium channels (K(Ca) channels) were r ecorded from membrane patches of rat olfactory bulb neurons in culture . Only one kind of K(Ca) channel was seen, and it was present in appro ximately 50% of detached patches. 2. This channel, like maxi-K(Ca) cha nnels of other tissues, had a single-channel conductance of 270 pS, a reversal potential (E(rev)) of 0 mV in symmetrical K+, and was highly selective for K+ over Na+ and Cl-. 3. The K(Ca) channel was blocked by d-tubocurarine (d-TC) on the cytoplasmic side, and charybdotoxin (CTX ) on the extracellular side. This pharmacology is identical to that of one type of K(Ca) channel from rat brain, observed previously in arti ficial bilayers and called the type 1 K(Ca) channel. 4. The probabilit y that the channel was in the open state (P(o)) increased with membran e depolarization. The position of the P(o) versus transmembrane voltag e (V(m)) curve was shifted by changes in [Ca2+]i so that the channel w as open more often in higher [Ca2+]i. The gating kinetics resembled th ose of the type 1 K(Ca) channel observed in bilayers. 5. P(o) was incr eased after superfusion of the cytoplasmic membrane surface with the a ctive catalytic subunit of cyclic AMP-dependent protein kinase (PK-A), together with MgATP. Phosphorylation altered the distribution of chan nel closed times but had little effect on open times. The results sugg est that phosphorylation is an important molecular mechanism in modula ting the activity of this K(Ca) channel from mammalian brain.