R 56865 prevents electrical and mechanical signs of ouabain intoxication in guinea-pig papillary muscle.

The effect of the new compound R 56865 on ouabain-induced intoxication (8 X 10(-7) mol/l) was studied in guinea-pig papillary muscle. The positive inotropism induced by ouabain was not impaired by R 56865. Mechanical signs of intoxication, e.g. extrasystoles and contracture, as well as the development of spike-like action potentials could be prevented by pretreatment with R 56865 (3 X 10(-10)-10(-6) mol/l). We speculate that this new compound prevents ouabain-induced Ca overload of cardiac muscle.