title: Mechanism of the excitatory action of palytoxin and N-acetylpalytoxin in the isolated guinea-pig vas deferens.
abstract: 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.
mesh_terms: D000178:Acrylamides; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003064:Cnidarian Venoms / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008387:Marine Toxins / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009638:Norepinephrine / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D014649:Vas Deferens / Q000187:drug effects / Q000502:physiology; D000095702:Polyether Toxins
chemical_list: D000178:Acrylamides; D002118:Calcium; D003064:Cnidarian Venoms; D008274:Magnesium; D008387:Marine Toxins; D009638:Norepinephrine; D011942:Receptors, Adrenergic, alpha; C026014:N-acetylpalytoxin; D000095702:Polyether Toxins; C010272:palytoxin