Subcellular origin of the surface fluorescence of reduced nicotinamide nucleotides in the isolated perfused rat heart

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Abstract
Surface fluorometric measurements and indicator metabolite determinations in the isolated perfused rat heart showed that the NADH+NADPH fluorescence of the intact tissue originates largely from the mitochondria. The redox potential of the lactate dehydrogenase system calculated from the endogenous lactate/pyruvate ratios was closely similar to that of the glycerol-3-phosphate dehydrogenase system calculated from the concentrations of glycerol-3-phosphate and dihydroxyacetone phosphate in the tissue. Thus, in contrast to the liver, the cytosolic redox state of the NADH/NAD+ system in isolated perfused heart oxidizing external glucose or fatty acid is not amenable to optical monitoring, but can be assessed from the state of the lactate dehydrogenase or glycerol-3-phosphate, dehydrogenase systems.