title: Role of Ca2+ in genesis of lower esophageal sphincter tone and other active contractions.
abstract: The effects of absent or low Ca2+ (0.5 mM), verapamil, nifedipine, Na nitroprusside, theophylline, La2+, and ethanol on basal active tension (tone), "off" contractions, and carbachol contractions were studied in opossum lower esophageal sphincter strips. Incubation in Ca2+-free Ringer (0.1 mM EGTA) abolished tone and contractions. Low Ca2+, verapamil, nifedipine, and theophylline depressed tone more rapidly than "off" contractions. Only verapamil and nifedipine depressed carbachol contractions. Na nitroprusside rapidly depressed tone but left contractions unchanged. La3+ at 1 X 10(-3) M behaved like Ca2+-free incubation but produced sustained contractions with muscle stimulation. Ethanol depressed "off" contractions more than tone and did not affect carbachol-induced contractions. These results suggest that tone probably results from inward leak of Ca2+, whereas "off" contractions depend on release of Ca2+ sequestered in the cell by a mechanism not immediately dependent on increased Ca2+ influx. Carbachol may increase Ca2+ influx as well as utilize sequestered Ca2+. Nifedipine and verapamil may act to block both resting and stimulated Ca2+ influx. Na nitroprusside may act by increasing Ca2+ efflux. Ethanol may act by decreasing the availability of sequestered Ca2+ or by inhibiting the function of a mediator responsible for "off" contractions.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D004943:Esophagogastric Junction; D000431:Ethanol / Q000494:pharmacology; D005260:Female; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D009893:Opossums / Q000502:physiology*; D013806:Theophylline / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D009599:Nitroprusside; D000431:Ethanol; D007811:Lanthanum; D013806:Theophylline; D014700:Verapamil; D009543:Nifedipine; D002118:Calcium