Ion channel diversity in the feline smooth muscle esophagus

We have characterized ion-channel identity and density differences along the feline smooth muscle esophagus using patch-clamp recording. Current clamp recording revealed that the resting membrane potential (RMP) of esophageal smooth muscle cells (SMC) from the circular layer at 4 cm above the lower esophageal sphincter (EBC4; LES) were more depolarized than at 2 cm above LES. Higher distal Na(+) permeability (but not Cl(-) permeability) contributes to this RMP difference. K(+) channels but not large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels contribute to RMP at both levels, because nonspecific K(+)-channel blockers depolarize all SMC. Depolarization of SMC under voltage clamp revealed that the density of voltage-dependent K(+) channels (K(V)) was greatest at EBC4 due to increased BK(Ca.) Delayed rectifier K(+) channels (K(DR)), compatible with subtype K(V)1.2, were present at both levels. Differences in K(Ca)-to-K(DR) channel ratios were also manifest by predictable shifts in voltage-dependent inactivation at EBC4 when BK(Ca) channels were blocked. We provide the first evidence for regional electrophysiological differences along the esophageal body resulting from SMC ion channel diversity, which could allow for differential muscular responses to innervation and varied muscular contribution to peristaltic contractions along the esophagus.