The effects on canine cardiac Purkinje fibers of Chrysaora quinquecirrha (sea nettle) toxin

Abstract

Excised canine cardiac Purkinje fibers (false tendons) and excised canine cardiac papillary muscles were exposed to the toxin of Chrysaora quinquecirrha (sea nettle). Purkinje fibers showed loss of resting potential, diminution of upstroke velocity, reduced conduction velocity, partial and complete block of conduction between cells within the same bundle, spontaneous activity, and eventual loss of excitability. Papillary muscles showed none of these changes, remaining electrically normal and contractile when exposed to levels of toxin that caused complete inexcitability in Purkinje fibers. The toxic effects could be prevented by elevating the level of Ca 2+ in the perfusate and enhanced by lowering the level of Ca 2+ in the perfusate. Spontaneous activity, slow conduction, conduction block and eventual inexcitability in fibers of the ventricular conducting system are sufficient to explain the cardiac death that arises from intravenous injection of sea nettle toxin in mice and rats. The effects of the level of Ca 2+ suggest that the toxin interferes with the actions of Ca 2+ at the membrane of the affected cells since low levels of Ca 2+ have effects very like that of the toxin on Purkinje fibers and, like the toxin, have no effect on papillary muscle fibers.