Net calcium exchange in adult rat ventricular myocytes: an assessment of mitochondrial calcium accumulating capacity.

Net calcium exchange has been measured in a suspension of cardiac myocytes after treatment with digitonin. The exchange is believed to be across the mitochondrial membranes and can be stimulated or inhibited by agents augmenting or blocking mitochondrial electron transport. The uptake of calcium shows a strong dependence on suspension pCa but is not evident below 1 microM (pCa 6.0). It is suggested that the net calcium exchange is a balance of the two processes which are equivalent at pCa 6.0. The measurement of mitochondrial specific activity for calcium uptake allows a calculation of the rapidity with which the cardiac mitochondria would affect sarcoplasmic calcium after a sudden rise. It is suggested that the organelle could partly affect relaxation especially at the peak of contraction.