Effect of trypsin on a Ca(2+)-activated K+ channel reconstituted into planar phospholipid bilayers.

Exposure of the cytoplasmic side of calcium-activated, high (maxi)-conductance potassium [BK(Ca)] channels in basolateral membrane vesicles from rabbit colonocytes incorporated into planar phospholipid bilayers to trypsin rapidly reduces, but does not abolish, the sensitivity of this channel to activation by calcium without affecting its conductance or high selectivity for K+ over Cl-. The results of these studies also indicate that this BK(Ca) channel does not have intrinsic voltage-gating properties but that its voltage sensitivity is related to its ability to interact with calcium. This conclusion is consistent with the model proposed by Moczydlowski and Lattore (J. Gen. Physiol. 82: 511-542, 1983) for the role of membrane voltage in modulating the interaction between calcium and the BK(Ca) channel in rat skeletal muscle.