Calcium in isolated mitochondria from the left ventricular wall

The content of calcium per mg mitochondrial protein has been measured by conventional biochemical methods in myocardial tissue of some mammalian species. In addition, a method is presented for (1) the analysis of mitochondrial volumes in the same tissues and (2) calculating the amount of calcium in units of 10(6) mitochondria. It appears that a highly significant correlation exists between the calcium content and the number of mitochondria, with a positive correlation coefficient of 0.92. The mean mitochondrial volume in fractions of the rabbit myocardium was found to be 1.3386 micron3. Electron microscopic studies demonstrate pure mitochondrial fractions and only moderate structural alterations. The method described may represent a useful supplement for the estimation of calcium fluxes in mitochondria and of alterations in their volume, number and structure under conditions of myocardial ischemia.