[Characterization of surface fluorescence signals of isolated perfused rat kidney]

The NAD(P)H- and flavoprotein fluorescence signals of the isolated perfused rat kidney were characterized by their electrochemical properties and by comparing them with those of isolated kidney cortex mitochondria. From titration experiments with lactate pyruvate under anoxic conditions it is concluded that about 25% of the NAD(P)H-fluorescence can be attributed to the cytosolic pyridine nucleotides. For this signal a midpoint potential of -268 mV was calculated. The major part of the NAD(P)H-fluorescence signal was of mitochondrial origin, showing a midpoint potential of -304 mV which was titrated with beta-hydroxybutyrate/acetoacetate. A comparable value (Em7.4 = -310 mV) was found for isolated kidney cortex mitochondria using the same redox couple. The flavoprotein fluorescence could be totally attributed to the mitochondrial compartment and was found to originate from the NAD-dependent alpha-lipoamide dehydrogenase and the electron transfer flavoprotein of beta-oxidation to approx. 60% and 40%, respectively. A midpoint potential of -285 mV was determined for the NAD-dependent part of the flavoprotein signal. On the basis of these results it can be concluded that the fluorescence changes which were caused by ouabain in the normoxically perfused rat kidney reflect an increase in reduction of the mitochondrial NAD-system.