title: Contribution of intracellular stored calcium to contractile activation in contractures of stomach circular muscle of Bufo vulgaris formosus.
abstract: Contractile responses of stomach circular muscle of Bufo to high-K, to acetylcholine (ACh) in normal Ringer or in high-K solution, and to calcium in Ca-free high-K solution showed a phasic contraction which relaxed completely in 30-45 sec. K-induced contracture was abolished in Ca-free solution containing 1 mM ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) within 20 sec, while ACh-induced contracture was not abolished and 10-25% of control tension was kept up to 40 sec. This response increased to 40-50% when all extracellular Na was replaced with tris(hydroxymethyl)-aminomethane (Tris). K-induced contracture was inhibited completely by 1 mM La. ACh-induced contracture in the muscle depolarized by high-K solution was dependent on the depolarization time, 0-10, 60-70, and nearly 100% of control after 1, 3, and 10 min depolarization, respectively. These ACh-induced contractures were not inhibited by 1 mM EGTA or La. All contractures mentioned above were markedly inhibited by 5 mM procaine. These results suggest that activation of both contractures induced by high-K and ACh were, at least partly, dependent on the Ca at the intracellular Ca storage sites. Ca-induced contracture was dependent on depolarization time as was ACh-induced contracture, when the muscle was depolarized by Ca-free high-K solution without pre-treatment with Ca-free Ringer solution. These results suggest that activation of Ca-contracture is also dependent on intracellular stored Ca.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002025:Bufonidae; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D004533:Egtazic Acid / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D011343:Procaine / Q000494:pharmacology; D013270:Stomach; D014700:Verapamil / Q000494:pharmacology
chemical_list: D011343:Procaine; D004533:Egtazic Acid; D007811:Lanthanum; D014700:Verapamil; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium