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Mechanism of the excitatory action of palytoxin and N-acetylpalytoxin in the isolated guinea-pig vas deferens

Y Ohizumi and S Shibata

Palytoxin (PTX), one of the most well known potent toxic substances among marine toxins, caused a slow phasic contraction of the isolated guinea-pig vas deferens (second component) followed by the first rapid phasic contraction (first component) at concentrations above 3 x 10(-9) M. N-acetylpalytoxin, one of its derivatives, also produced similar actions but its potency was about 1/100 of that of PTX. The second component of PTX-induced contraction, but not the first component, was markedly inhibited by treatments with phentolamine, reserpine and 6- hydroxydopamine, but remained unaffected by atropine and mecamylamine pretreatment. Tetrodotoxin partially inhibited the second component, whereas the second component was markedly inhibited by solutions low in Na+ (85.2 mM) or containing verapamil (10(-6) M). Both components were completely abolished by high Mg++ or Ca++-free medium. It is concluded that the first component was the result of a direct action of PTX on smooth muscle sites, whereas the second phase was the result of an indirect action mediated through the norephinephrine release from the adrenergic nerve terminals.

Volume 214, Issue 1, pp. 209-212, 07/01/1980
Copyright © 1980 by American Society for Pharmacology and Experimental Therapeutics






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Copyright © 1980 by the American Society for Pharmacology and Experimental Therapeutics.