Effect of an unknown toxin isolated from dinophysis sp.‐contaminated French mussels, on the electrical and mechanical activity of frog heart

Abstract

The effects of an unknown toxin, isolated along with okadaic acid from the hepatopancreas of French mussels contaminated by Dinophysis sp., producing ataxia, neurologic symptoms, bradycardia, arrhythmias, electrocardiographic changes, and cardiac arrest, have been studied in terms of the electrical and mechanical activity of frog atrial heart muscle. The toxin, in a dose-dependent manner, decreased the amplitude of the stimulated peak tension of isolated fibers. The toxin (1-36 micrograms/ml) did not modify the membrane resting potential but decreased the amplitude of the plateau and shortened the duration of the action potential. The toxin inhibited the Cd-sensitive L-type Ca current and increased a 4-aminopyridine-sensitive outward current in voltage-clamped cardiac myocytes. The data show that the cardiac effect of the toxin is markedly different from that of okadaic acid.