Agonist-induced contraction of rat myometrium in Ca-free solution containing Mn.

In Ca-free solution containing Mn, oxytocin caused the same extent of contraction of rat myometrium as in normal solution, whereas acetylcholine caused little contraction. The contraction caused by acetylcholine in medium containing Ca was inhibited by Mn dose-dependently, whereas that caused by oxytocin was not affected by Mn. The contraction caused by oxytocin in Ca-free solution containing Mn was inhibited dose-dependently by D-600. Mn ion had little effect on contractile protein, but the tissue level of Ca had an effect on oxytocin-induced contraction in Ca-free medium containing Mn.