title: Twitch responses dependent on external calcium ions in the mouse diaphragm in a potassium-free bathing solution.
abstract: We examined the effect of external Ca2+ on twitches of mouse diaphragm under the inhibition of Na(+)-K(+)-ATPase in vitro. The muscle was directly stimulated in presence of d-tubocurarine (dTc). K+ removal potentiated the amplitude of twitches with a transient prior reduction. This potentiation depended on external Ca2+. Membrane potentials decreased after removal of both external K+ and Ca2+ and were restored after an addition of Ca2+. The removal of both ions increased the content of Na+ in tissues and decreased K+. These changes were restored to the levels in the K(+)-free bathing solution by the addition of Ca2+. These results imply that Na+/Ca2+ exchange can support twitch contraction under the inhibition of Na(+)-K(+)-ATPase activity.
authors.affiliation: Department of Pharmacology, University of Obihiro School of Veterinary Medicine, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nishimura
authors.forename: T
authors.initials: T
authors.lastname: Hasegawa
authors.forename: K
authors.initials: K
authors.lastname: Ito
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D003964:Diaphragm / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D009119:Muscle Contraction / Q000502:physiology; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000502:physiology*; D012132:Respiratory Muscles / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D014403:Tubocurarine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D003473:Neuromuscular Nondepolarizing Agents; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium; D014403:Tubocurarine