Large-Conductance Ca2+ -Activated K+ Channels in Freshly Dissociated Smooth Muscle Cells

Freshly dissociated cells from the stomach muscularis of the toad Bufo marinus have been employed to carry out a systematic set of electrophysiological studies on the membrane properties of smooth muscle. The existence of Ca²⁺-activated K⁺ channels became apparent during the first studies under current clamp. In subsequent studies under voltage clamp, a Ca²⁺-activated, TEA-sensitive outward current was evident, and it was more than an order of magnitude larger than any other current observed in the cells. The channel responsible, at least in part, for this large outward current has been identified on the basis of single-channel records, and some of its main characteristics have been studied. It is similar in many respects to the large-conductance, Ca²⁺-activated K⁺ channel seen in other preparations. This channel has now been found in a considerable diversity of smooth muscle types.