MECHANISM OF THE EXCITATORY ACTION OF PALYTOXIN AND N-ACETYLPALYTOXIN IN THE ISOLATED GUINEA-PIG VAS-DEFERENS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 214  (1) , 209-212
Abstract
Palytoxin [Palythoa sp.] (PTX), 1 of the most well-known potent toxic substances among marine toxins, caused a slow phasic contraction of the isolated guinea-pig vas deferens (2nd component) followed by the 1st rapid phasic contraction (1st component) at concentrations above 3 .times. 10-9 M. N-acetylpalytoxin, one of its derivatives, produced similar actions but its potency was .apprx. 1/100 of that of PTX. The 2nd component of PTX-induced contraction, but not the 1st component, was inhibited by treatments with phentolamine, reserpine and 6-hydroxydopamine, but remained unaffected by atropine and mecamylamine pretreatment. Tetrodotoxin partially inhibited the 2nd component, but the 2nd 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-Mg2+ or Ca2+-free medium. The 1st component was due to direct action of PTX on smooth muscle sites, but the 2nd phase was due to an indirect action mediated through the norephinephrine release from the adrenergic nerve terminals.