EXCITATORY EFFECT OF THE MOST POTENT MARINE TOXIN, MAITOTOXIN, ON THE GUINEA-PIG VAS-DEFERENS

  • 1 January 1983
    • journal article
    • research article
    • Vol. 227  (1) , 199-204
Abstract
The most potent marine toxin, maitotoxin (MTX) (10-9-3 .times. 10-8 g/ml) caused a slower contraction of the isolated guinea pig vas deferens (2nd component) in a dose-dependent manner after the 1st rapid phasic contraction (1st component). The 2nd component of the MTX-induced contraction was markedly inhibited by phentolamine and reserpine; the 1st component remained unaffected. Both components were inhibited or abolished by verapamil or a Ca-free medium, but were not affected by atropine, chlorpheniramine or tetrodotoxin. The tissue Ca content of the vas deferens was increased by MTX (10-9-3 .times. 10-8 g/ml) in a dose-dependent manner. MTX (10-9-3 .times. 10-8 g/ml) caused a dose-dependent release of norepinephrine from the tissue, which was inhibited or abolished by verapamil or a Ca-free medium. In Na+-free medium, MTX still caused a profound increase in the tissue Ca content and marked release of norepinephrine from the vas deferens. The major part of the 1st component was the result of a direct action of MTX on smooth muscle membrane; the 2nd component was primarily the result of indirect action mediated through the norepinephrine release from the adrenergic nerve terminals. Both components were possibly due to an increase Ca2+ permeability of the voltage sensitive Ca2+ channels in smooth muscle and nerve membrane.