Abstract
Summary
The effects of calcium, strontium, EDTA, rhodochlorin and ouabain have been evaluated on the isolated spontaneously beating frog heart. Ouabain is capable of eliciting a positive inotropic response in Sr-Ringer's solution, but rhodochlorin is without effect when present in the same solution. Following perfusion with Ca-free Ringer's solution containing EDTA, contractility may be partially restored by perfusing the heart with Ca-Ringer's solution with or without ouabain, but contractility was not restored by supra-normal Sr-Ringer's solution with or without ouabain. Sub-effective concentration of calcium when added to Sr-Ringer's solution containing rhodochlorin also elicited a weak cardiotonic action on the heart. It is suggested that strontium has little or no cardiotonic action of itself but depends upon calcium for its positive inotropic action, and that factors in addition to the facilitation of transmembrane flux of calcium or strontium ions may be important for the cardiotonic action of ouabain.
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