Effects of Strontium Ions on Heart Muscle: I. Influences on Contractility

The influence of the substitution of extracellular Ca by Sr on contractility of papillary muscles of the cat and isolated hearts of the rat and the frog was studied. This substitution resulted in a positive inotropic effect on the frog heart and on the papillary muscle. From the changes observed in the duration of the contraction phenomena, in the rate of tension development and in the force-velocity relationship in the papillary muscle, this positive inotropic effect can be attributed to a prolongation of the active state which offsets a decreased degree of activation. In a Sr containing medium the interaction of frequency with contractility persists but the tension developed at infraoptimal frequencies is higher and the optimal frequency is lower than in a normal medium.