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  • Title: Dual effect of ouabain on the palytoxin-induced contraction and norepinephrine release in the guinea-pig vas deferens.
    Author: Ishida Y, Kajiwara A, Takagi K, Ohizumi Y, Shibata S.
    Journal: J Pharmacol Exp Ther; 1985 Feb; 232(2):551-6. PubMed ID: 2857198.
    Abstract:
    Palytoxin (PTX), C129H223N3O54, isolated from marine coelenterates of Palythoa tuberculosa, caused a first rapid contraction followed by the slow phasic contraction of guinea-pig vas deferens. In the presence of ouabain (10(-5) M), PTX (10(-8) M) failed to cause the first contraction; however, the second contraction was potentiated. In the presence of phentolamine (10(-6) M), the second contraction was inhibited selectively. When ouabain was applied to the muscle in the presence of phentolamine, both first and second contractile responses to PTX were abolished. When the muscle was exposed to the potassium-depleted solution, the first contractile response to PTX was rather potentiated. PTX caused the release of norepinephrine from the muscle. Exposure of the muscle to ouabain (10(-5) M) markedly increased the PTX-induced release. It is indicated that the first and second contractile responses to PTX have entirely different properties. The second response is due to a release of norepinephrine from nerves and was potentiated by ouabain through the increase in the norepinephrine release, whereas the first response was not due to the norepinephrine release but presumably to a direct action on smooth muscle cell and was inhibited by ouabain. The mechanism of the action of PTX was discussed in the relation with Na,K-ATPase.
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