MITOCHONDRIAL FREE CALCIUM TRANSIENTS DURING EXCITATION-CONTRACTION COUPLING IN RABBIT CARDIAC MYOCYTES

Mitochondrial free Ca2+ may regulate mitochondrial ATP production duri ng cardiac exercise, Here, using laser scanning confocal microscopy of adult rabbit cardiac myocytes co-loaded with Fluo-3 to measure free C a2+ and tetramethylrhodamine methylester to identify mitochondria, we measured cytosolic and mitochondrial Ca2+ transients during the contra ctile cycle. In resting cells, cytosolic and mitochondrial Fluo-3 sign als were similar, During electrical pacing, transients of Fluo-3 fluor escence occurred in both the cytosolic and mitochondrial compartments, Both the mitochondrial and the cytosolic transients were potentiated by isoproterenol. These experiments show directly that mitochondrial f ree Ca2+ rises and falls during excitation-contraction coupling in car diac myocytes and that changes of mitochondrial Ca2+ are kinetically c ompetent to regulate mitochondrial metabolism on a beat-to-beat basis.