Cation distributions in the hypertrophic myocardium (aortic constriction) of the rat.

Calcium, magnesium, sodium, potassium, and water distributions were determined in rat ventricular muscle during the development of myocardial hypertrophy. Hypertrophy was produced by constriction of the ascending aorta with a silver band. Sham-operated controls were treated similarly, except that the aorta was not constricted. Cation and water distributions were examined at intervals of 1 hour, 1 day, 1 week. Myocardial extracellular space was determined by distribution of [35S] sulphate. In separate experiments, extracellular space was determined in different regions of the normal rat ventricle using [3H] inulin as the extracellular marker. Although some changes were observed in tissue calcium content and the plasma concentrations of several cations, at no time were the cellular concentrations of any cation significantly altered. Myocardial water content and distribution remained nearly constant after constriction of the aorta. Results do not support hypotheses that the heart responds to increased afterload with an accumulation or loss of myocytic calcium sufficiently large to be detectable with standard quantitative methods.