SNAP-25, a SNARE protein, inhibits two types of K+ channels in esophageal smooth muscle

The plasma membrane-associated soluble N-ethyl male! mide-sensitive factors attachment protein receptors (SNARES), synaptosome-associated protein of 25 kilodaltons (SNAP-25), and syntaxin 1A. have been found to physically interact with and functionally modify membrane-spanning ion channels. Studies were performed in cat esophageal body and lower esophageal sphincter (LES) smooth muscle to (1) show the presence of SNAP-25, and (2) determine whether SNAP-25 affects K+ channel activity. Single circular muscle cells from the esophageal body and sphincter were studied. Cellular localization of SNAP-25 and K+ channel activity were assessed. SNAP-25 was found in the plasma membrane of all regions examined. Outward K+ currents in body circular muscle were mainly composed of large conductance Ca2+-activated channel currents (KCa, 40.1%) and delayed rectifier K+ channel currents (Kv, 54.2%). Microinjection of SNAP-25 into muscle cells caused a dosedependent inhibition of both outward K+ currents, maximal 44% at 10−8 mol/L. Cleavage of endogenous SNAP-25 by dialyzing botulinum neurotoxin A into the cell interior resulted in a 35% increase in outward currents. SNAP-25 protein is present in esophageal smooth muscle cells, and inhibits both Kv and KCa currents in circular muscle cells. The findings suggest a role for SNAP-25 in regulation of esophageal muscle cell excitability and contractility, and point to potential new targets for treatment of esophageal motor disorders.