The analysis of extracellular calcium exchange in perfused myocardium using mathematical modeling

1. A mathematical model of diffusional Ca exchange in a continuously perfused heart has been formulated. Based on biochemical studies, sarcolemmal Ca binding on the extracellular surface of cardiomyocytes is taken into account. The changes in sarcolemmal Ca binding may affect the kinetics of Ca washout from the myocardium. The model is consistent with the real dynamics of 45Ca washout from rabbit heart septum reported by Philipson and Langer (F Mol Cell Cardiol 11, 857 (1979)). 2. The changes in the kinetics of Ca washout calculated according to the proposed model agree with the real changes in the kinetics of 45Ca washout from rabbit heart septum at two coronary flow rate values reported by Shine et al. (Am J Physiol 221, 1408 (1971)). 3. The calculated dynamics of the decrease in sarcolemmal Ca content is close to the real dynamics of the myocardial contractility decrease demonstrated by Philipson and Langer (1979). 4. The model offers an estimation of the contribution of different myocardial compartments to the kinetic components of Ca washout curves resolved by the method of Solomon (In: Mineral Metabolism 1A, p. 119, New York, Academic Press, (1960)). According to the results of the modeling, more than 80% of the fast exchanging pool 0 is composed of sarcolemmal Ca. 85 and 95% of the slowly exchanging pools 2 and 3 are composed of intracellular Ca; pool 1 is determined by both sarcolemmal and intracellular Ca.