We examined the properties of K⁺ channels in smooth muscle cells dissociated from human esophagus using patch-clamp recording in the cell-attached configuration. The predominant channel observed had a conductance of 224 ± 4 pS, and current reversal was dependent on K⁺ concentration. Channel activity was voltage dependent and increased with elevation of intracellular free Ca²⁺ concentration ([Ca²⁺]_i), consistent with this being the large-conductance Ca²⁺-dependent K⁺ (K_Ca) channel. ACh as well as caffeine caused transient increases in K_Ca channel activity, and the effects of ACh persisted in Ca²⁺-free solution, indicating that Ca²⁺ release from stores contributed to channel activation. Simultaneous patch clamp and fluorescence revealed that K_Ca channel activity was well correlated with elevation of [Ca²⁺]_i. The functional role of K_Ca channels in esophagus was studied by measuring ACh-induced contraction of strips of muscle. Tetraethylammonium and iberiotoxin, blockers of K_Ca channels, increased ACh-induced contraction, consistent with a role for K⁺ channels in limiting excitation and contraction. These studies are the first to characterize K_Ca channels and their regulation in human esophageal smooth muscle.

acetylcholine; caffeine; fura 2; patch clamp; contraction

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