Different toxic effects of ouabain and 16-epi-gitoxin on Purkinje fibres and ventricular muscle fibres.

Action potentials of isolated Purkinje fibres and ventricular muscle fibres of canine hearts treated with ouabain and 16-epi-gitoxin were recorded by microelectrodes. Under the influence of both glycosides, Purkinje system fibres became inexcitable earlier than ventricular muscle fibres. Being exposed to 0.125 muM ouabain and 2.5 muM 16-epi-gitoxin, both Purkinje and ventricular muscle fibres became poisoned in the same time as ventricular muscle fibres exposed to 0.1 muM ouabain and 1.5 muM 16-epi-gitoxin. At the lower 16-epi-gitoxin concentration Purkinje fibres had 2.5 times the survival time of that exposed to the lower ouabain concentration. Compared to 16-epi-gitoxin the inexcitability of Purkinje fibres after ouabain remained irreversible. The semisynthetic glycoside 16-epi-gitoxin exerts a weaker effect on the specialized conducting system.