Ouabain-induced potentiation of Ca2+-contraction in the depolarized vas deferens of guinea-pig.

The effect of ouabain (10(-5) M) on the Ca2+-evoked phasic contraction was examined in various depolarized vas deferens of the guinea-pig. Ouabain-induced potentiation of the contraction occurred in muscle depolarized with 40 mM K+, but not in muscle depolarized with 0 mM or 137 mM K+. Furthermore, this potentiating effect of ouabain was investigated in the presence of Mn2+ and Mg2+, each of which has an inhibitory effect on Ca2+-contraction. It was strongly inhibited by Mn2+, but unaffected by Mg2+. From these findings it is suggested that ouabain facilitates Ca2+-entry, which is accompanied by the spike generation.