Mitochondrial free calcium transients during excitation‐contraction coupling in rabbit cardiac myocytes

Abstract

Mitochondrial free Ca²⁺ may regulate mitochondrial ATP production during cardiac exercise. Here, using laser scanning confocal microscopy of adult rabbit cardiac myocytes co-loaded with Fluo-3 to measure free Ca²⁺ and tetramethylrhodamine methylester to identify mitochondria, we measured cytosolic and mitochondrial Ca²⁺ transients during the contractile cycle. In resting cells, cytosolic and mitochondrial Fluo-3 signals were similar. During electrical pacing, transients of Fluo-3 fluorescence 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 free Ca²⁺ rises and falls during excitation-contraction coupling in cardiac myocytes and that changes of mitochondrial Ca²⁺ are kinetically component to regulate mitochondrial metabolism on a beat-to-beat basis.