Indirect cardiotoxic activity of the caecilian Siphonops paulensis (Gymnophiona, Amphibia) skin secretion

The skin secretion of the caecilian S. paulensis has an indirect cardiotoxi c effect. It induces a rapid blockage of electrical activity and subsequent diastolic arrest on in situ toad heart preparations. This action is not bl ocked by atropine and is therefore not mediated through a cholinergic mecha nism. In addition, S. paulensis skin secretion is ineffective in inducing a ny response in isolated perfused toad heart assay, in the spontaneously bea ting isolated toad atria or in the electrically driven toad ventricle strip . These results, and the observation that S. paulensis skin secretion exhib its an hemolytic activity ([Schwartz, E. F., Schwartz, C. A., Sebben, A., M endes E. G. (1997) Cardiotoxic and hemolytic activities on the caecilian Si phonops paulensis skin secretion. J. Venom. Anim. Toxins 3(1), 190]), sugge st that the skin secretion cardiotoxicity could be mediated through an endo genous agent. The cardiotoxic action of S. paulensis skin secretion was inv estigated in isolated toad cardiac tissues in the presence of toad red bloo d cells (TRBC). In both atria and ventricle it evoked the same responses ob served in the in situ heart. The potassium concentrations of the suspending media, as determined by atomic absorption spectroscopy were 9.5 and 11.7 t imes greater, respectively, in the presence of TRBC than in its absence. Gi ven that increased levels of potassium also showed a negative inotropic eff ect in the: isolated ventricle strip, the action of the skin secretion was attributed to the hemolytic activity, which causes an increase in K+ concen tration of the medium. (C) 1998 Elsevier Science Ltd. All rights reserved.