title: Myogenic NOS in canine lower esophageal sphincter: enzyme activation, substrate recycling, and product actions.
abstract: Depolarization elicited outward K+ currents from canine lower esophageal sphincter (LES) muscle cells, primarily through iberiotoxin (IbTX)- and tetraethylammonium-sensitive Ca(2+)-dependent K+ channels. Current magnitudes varied with pipette Ca2+ concentration (EC50 = 108.5 nM). NG-nitro-L-arginine (L-NNA, 10(-4)M), IbTX (10(-8)M), or buffering intracellular Ca2+ to 8 nM decreased outward currents > 80%. Sodium nitroprusside (NaNP, 10(-4)M) restored L-NNA-inhibited or low intracellular Ca2+ concentration (not IbTX)-inhibited currents. L-NNA or IbTX application depolarized LES cells from -43 to -35 mV. NaNP restored the membrane potential to -46 mV after L-NNA but not after IbTX application. Nifedipine (30 microM) reduced outward currents and abolished or reduced L-NNA or NaNP effects, respectively. Immunocytochemistry revealed the presence of both argininosuccinate synthetase and argininosuccinate lyase in LES muscle cells. L-Citrulline, like L-arginine, reversed L-NNA inhibition of outward currents; only L-arginine reversed inhibition of outward currents by an antibody to argininosuccinate synthetase. Therefore, endogenous nitric oxide production, activated by Ca2+ entrance involving L-type Ca2+ channels, may continuously enhance outward currents to modulate LES muscle cell membrane potential and excitability.
authors.affiliation: Playfair Neuroscience Unit, Toronto Hospital (Western Division), Ontario, Canada.
authors.forename: A M
authors.initials: AM
authors.lastname: Salapatek
authors.forename: Y F
authors.initials: YF
authors.lastname: Wang
authors.forename: Y K
authors.initials: YK
authors.lastname: Mao
authors.forename: M
authors.initials: M
authors.lastname: Mori
authors.forename: E E
authors.initials: EE
authors.lastname: Daniel
mesh_terms: D000818:Animals; D001120:Arginine / Q000378:metabolism; D002956:Citrulline / Q000378:metabolism; D004285:Dogs; D004553:Electric Conductivity; D004789:Enzyme Activation / Q000502:physiology; D004943:Esophagogastric Junction / Q000201:enzymology* / Q000502:physiology; D005260:Female; D008297:Male; D009132:Muscles / Q000201:enzymology; D009569:Nitric Oxide / Q000494:pharmacology / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D002956:Citrulline; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase