[Effect of streptolysin O on the Purkinje fibers of the heart in dogs].

Streptolysin "O", an exotoxin of the beta-hemolytic streptococcus, has been shown to have very marked cardiotoxic effects. The data found in the literature suggest that ventricular conducting tissues are severely damaged by this toxin. The purpose of this paper is to study the effects that several concentration of the toxin have on the transmembrane potentials, input resistance and ultrastructure of canine isolate Purkinje fibers. When the preparations were exposed to the toxin, they showed important changes in most of the parameters of the transmembrane potentials. The most important were: a depolarization, a reduction of the amplitude of the action potentials and their upstroke velocities, and a marked shortening of their duration. Input resistance was also markedly decreased. These actions were progressive, until unexcitability was reached. All of the changes observed were irreversible. The ultrastructure of the cells also showed important alterations, mainly at the sarcolemma and mitochondriae. From the results described in this paper, both in terms of the electrophysiological and the morphological effects of streptolysin "O", we can conclude that the cardiotoxic effects of the toxin are due to an effect on the ventricular conducting tissues.