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The relationship between cellular calcium (Ca) stores and isometric contractile force was investigated in isolatcd, gas-pcrfuscd cat hearts.

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The results of this study indicate that two min of Ca-free perfusion did not significantly alter the exchange kinetics of mannitol or Ca in isolated heart preparations. A numerical solution for series Ca exchange between a superficial Ca pool, Ca1, and an intracellular pool, Ca2, was developed in terms of the coefficients and constants determined from a parallel analysis. The series and parallel models for Ca efflux yielded a high correlation between contractile activity and the rate of exchange and Ca content of Ca1. The kinetics of Ca influx were best described by a series model of exchange and agreed closely with the Ca contents and exchange properties measured during Ca efflux. No differences were detected between normal and myopathic hamster hearts in the kinetics of Ca exchange or the role of Ca1 in the E-C coupling process.