Abstract

The effects of ouabain on tissue Ca, Ca exchange, contractile and resting tension in isolated guinea-pig atria have been measured. Ouabain in concentrations producing a positive inotropic effect under conditions of varying extracellular Ca concentration and time of exposure to the agent had little or no effect on tissue Ca, but caused an increment in the exchangeable Ca fraction of the order of 0.08 to 0.3 mEq/kg intracellular space. There was a correlation between contractile tension and exchangeable Ca fraction. When contractures occurred in the presence of ouabain, tissue Ca increased from 5.2 ± 0.15 to 6.5 ± 0.15 mEq/kg and the exchangeable fraction from 0.94 to 2.60 mEq/kg.