Single potassium channels recorded from vascular smooth muscle cells

Single-channel activities were recorded from smooth muscle cells of vascular fragments isolated from rat pancreas. Three K-selective channel types were identified and characterized from cell-attached and inside-out membrane patches. Mean single-channel slope conductances of the three channel types, under conditions of symmetrical K (145 mM), were 43, 91, and 276 pS. The channel types exhibited differential sensitivity to tetraethylammonium (TEA) and intracellular Ca concentrations (Ca2+i). Intracellular TEA (10 mM) was effective in blocking the small conductance channel whereas the large conductance channel was found to be sensitive to Ca2+i. The properties of the large-conductance K channel are consistent with its identification as a calcium-activated maxi K channel described in a variety of tissues. Each of the channel types showed sensitivity to membrane potential, with increasing opening transitions at depolarizing membrane potentials. The small conductance channel type was observed to be active at resting membrane potentials. The generality of each of these channel types to other smooth muscle cell preparations and possible physiological implications are discussed.