title: Oxytocin-induced Ca-free contraction of rat uterine smooth muscle: effects of divalent cations and drugs.
abstract: When rat myometrium that had been depleted of Ca by incubation with 3 mM EGTA for 50 min was challenged with 10(-2) unit/ml oxytocin, it showed sustained contraction in a medium with no added Ca (Ca-free contraction). It also showed Ca-free contraction of similar magnitude in the presence of 1 mM EGTA. The effects on this contraction of divalent cations (Co2+, Ni2+ and Mn2+) singly and in combination with D-600 (3 X 10(-6) M) were investigated. Co2+ and Ni2+ potentiated Ca-free contraction concentration-dependently, and their effects were greater in the presence of D-600. In contrast, Mn2+ evoked a triphasic response; first transient potentiation, second relaxation, and third persistent increase in tension. D-600 did not block the first or second, but blocked the third, resulting in persistence of the second phase of relaxation. The relaxing action of papaverine on Ca-free contraction was not affected by D-600. Isoproterenol and dibutyryl cyclic AMP also relaxed the contraction.
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology; D005260:Female; D005711:Gallopamil / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D010121:Oxytocin / Q000494:pharmacology*; D010208:Papaverine / Q000494:pharmacology; D051381:Rats; D014590:Uterine Contraction / Q000187:drug effects*
chemical_list: D002413:Cations, Divalent; D005711:Gallopamil; D010121:Oxytocin; D003994:Bucladesine; D010208:Papaverine; D007545:Isoproterenol; D002118:Calcium