The calcium dependence of the biphasic inotropic response to ouabain in the isolated rat heart.

From the results of this study the following significant conclusions can be drawn. First, there are two separate inotropic responses to ouabain in the rat ventricle and the isolated rat heart resulting in a biphasic dose-response curve. Second, both the "low dose" and "high dose" inotropic responses of ouabain in the rat heart result from the inhibition of NKA, i.