SNAP-25, a SNARE protein, inhibits two types of K channels in esophageal smooth muscle.
OBJECTIVE
The plasma membrane-associated soluble N-ethylmaleimide-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.


METHODS
Single circular muscle cells from the esophageal body and sphincter were studied. Cellular localization of SNAP-25 and K+ channel activity were assessed.


RESULTS
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 (K(Ca), 40.1%) and delayed rectifier K+ channel currents (K(V), 54.2%). Microinjection of SNAP-25 into muscle cells caused a dose-dependent 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.


CONCLUSIONS
SNAP-25 protein is present in esophageal smooth muscle cells, and inhibits both K(V) and K(Ca) 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.
Ji
Junzhi
J
Department of Medicine, University of Toronto, Ontario, Canada.
Salapatek
Anne Marie F
AM
Lau
Helena
H
Wang
Guotang
G
Gaisano
Herbert Y
HY
Diamant
Nicholas E
NE
D000818:Animals; D019274:Botulinum Toxins, Type A / Q000494:pharmacology; D002415:Cats; D002462:Cell Membrane / Q000737:chemistry; D051668:Delayed Rectifier Potassium Channels; D004305:Dose-Response Relationship, Drug; D004947:Esophagus / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D009465:Neuromuscular Agents / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D050600:SNARE Proteins; D050825:Synaptosomal-Associated Protein 25; D019789:Tetraethylammonium / Q000494:pharmacology; D033921:Vesicular Transport Proteins
D051668:Delayed Rectifier Potassium Channels; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D009465:Neuromuscular Agents; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D024642:Potassium Channels, Voltage-Gated; D050600:SNARE Proteins; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins; D019789:Tetraethylammonium; D019274:Botulinum Toxins, Type A