Build-up of calcium content and contractile force in the rabbit heart.

Build-up of whole heart calcium content and contractile force was studied in the isolated, perfused rabbit heart during uptake of calcium ion. Calcium content increased in one exponential phase (rate constant 0.119 s−1) from a constant unexchangeable pre-build-up value. Contractile force increased in one exponential phase (rate constant 0.084 s−1) from its resting value. The rate constants for calcium content and contractile force build-up did not differ significantly. A difference in the above build-up rate constants from those of calcium and force decay observed in prior work in the same preparation was presumed due to dependence of capillary permeability on calcium concentration.