Identification of single transiently opening (“A-type”) K channels in guinea-pig colonic myocytes

Abstract

Two K⁺ channel populations were identified in depolarized cell-attached membrane patches of myocytes freshly dispersed from the circular smooth muscle of guinea-pig proximal colon. First, a large-conductance (150 pS) Ca²⁺-activated K⁺ channel which was non-inactivating and sensitive to blockade by tetraethylammonium (TEA, 0.5–5 mM); and second, a smaller conductance K⁺ channel which opened and closed within 100 ms, was insensitive to TEA (0.5–5 mM), but was blocked by 5 mM 4-aminopyridine (4-AP) or maintained depolarization, and which had a unitary conductance of 12–13 pS. The averaged time course of these smaller conductance K⁺ channels closely resembled the time course of the 4-AP-sensitive, Ca²⁺-insensitive transient outward K⁺ current recorded in the whole-cell recording mode.