Contraction and increase in tissue calcium content induced by maitotoxin, the most potent known marine toxin, in intestinal smooth muscle

Abstract

Maitotoxin (MTX), the most potent known marine toxin, isolated from toxic dinoflagellates and poisonous fish, caused a dose-dependent contraction of the guinea-pig isolated ileum and taenia caeci at concentrations of 100 pg to 30 ng/ml. These contractile responses to MTX (3 ng/ml) in both tissues were abolished by incubation in Ca²⁺-free solution and were markedly inhibited by treatment with methoxyverapamil (D600), but were not affected by tetrodotoxin and atropine. Furthermore, MTX markedly elevated tissue Ca²⁺ content of the taenia caeci. These results suggest that MTX activates Ca²⁺ channels in the smooth muscle membrane of both tissues to increase Ca²⁺ influx and thus induces contractions.