Is pump stimulation associated with positive inotropy of the heart?

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Science  16 Jun 1978:
Vol. 200, Issue 4347, pp. 1287-1289
DOI: 10.1126/science.149369


A purified sodium and potassium dependent adenosinetriphosphatase isolated from cat heart was not stimulated by any concentration of ouabain that produced positive inotropy of cat papilliary muscle. Only inhibition of enzyme activity was observed. Concentrations of ouabain used ranged from 3.3 x 10(-10) molar to 5 x 10(-7) molar and produced an increased force of contraction without any evidence of toxicity. The results are inconsistent with a concept that stimulation of sodium pump activity is associated with positive inotropy.