The mode of action of contractile effects induced by external calcium and its related bivalent cations in the KCl-depolarized rat uterus.
The cumulative log dose-response curve (DRC) isometrically produced by CaCl2 on depolarized uteri of rats in Ca2+-free KCl Ringer's solution (pH 7.8) showed a plateau-shaped type, when responses were plotted as a percent of the maximal tension of 50 micrometer acetylcholine, whereas those produced by BaCl2 or SrCl2 were a simple sigmoid type with the maximal response near the height of the plateau induced by Ca2+. The plateau phase of Ca2+ was inhibited competitively by Mg2+ (0.5--50 mM) and non-competitively by Mn2+ (30 micrometer--1 mM), whereas the maximal contraction of Ca2+ was not inhibited by either ion. Dantrolene (0.1 mM) inhibited both the plateau and the maximal contraction of Ca 2+ and retained the plateau-shaped type. EGTA (2mM) potentiated the plateau to the maximal response level and changed the DRC induced by Ca2+ to the simple sigmoid type. From these results, the plateau of DRC induced by Ca2+ seems to be mainly due to actions of external Ca2+ on the calcium binding of internal surface of cell membrane, suggesting that the internal surface is the site of the bivalent cations tested.
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology*; D003620:Dantrolene / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008345:Manganese / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology*; D051381:Rats; D013324:Strontium / Q000494:pharmacology; D014590:Uterine Contraction / Q000187:drug effects*
D002413:Cations, Divalent; D001464:Barium; D008345:Manganese; D004533:Egtazic Acid; D011189:Potassium Chloride; D004492:Edetic Acid; D004110:Diltiazem; D003620:Dantrolene; D002118:Calcium; D013324:Strontium