Continuous read-out of cytochrome b, flavin and pyridine nucleotide oxido-reduction processes in the perfused frog heart and contracting skeletal muscle.

The time-sharing instrument for continuous read-out of the fluorescence levels of NAD(P)H and oxidized-flavoproteins, which also makes simultaneous dual beam differential absorption measurements of cytochrome b, has been applied to the study of the metabolic control of the frog heart, perfused in vitro with normal and variously modified Ringer solutions, and to the frog skeletal muscle in situ. In the ionically depolarized resting heart, the long term kinetic analysis of the redox processes during oxygen/anoxia transitions has proved to be an adequate method for identifying and following three fundamental intracellular redox compartments: (1) the respiratory system, (2) the microsomal system, and (3) the glycolytic system. The provision of substrates and/or suitable inhibitors has allowed the description of functional interrelationships within the mitochondrial and the cytoplasmic spaces. The ouabain major site of response has been located on the cytosolic pyridine nucleotides, with a very small response in the mitochondrial space. The switching on and off of substantial fractions of the NAD(P)+/NAD(P)H and Fpoxidized/Fpreduced pools has been observed, which helps to clarify the large phase shift between the overall pyridine nucleotide and flavin oxidation-reduction processes, during the cycle of the spontaneously beating heart and during skeletal muscle contraction and recovery, here originally prompted out.