Use of NAD(P)H and flavoprotein fluorescence signals to characterize the redox state of pyridine nucleotides in epididymal bull spermatozoa.

The redox behaviour of the NAD(P) system and flavoproteins was registered by simultaneous fluorescence measurements in epididymal bull spermatozoa. The flavoprotein fluorescence signal can nearly exclusively be attributed to an NAD-linked enzyme, alpha-lipoamide dehydrogenase (Em7.4 = -286 mV). A comparison of intact with digitonin-permeabilized spermatozoa revealed that about 50% of the total NAD(P)H fluorescence signal was of mitochondrial origin. Under equilibrium conditions, the midpoint potentials of the NAD(P)H fluorescence signal of both compartments were almost identical (-300 mV). When lactate was present as substrate, 1 mM caffeine increased respiration oxidizing the NAD(P)H system in both mitochondria and cytosol. This indicates a close relationship of the two NAD pools in spermatozoa.