[Morphologic characteristics and ATPase activity in permeabilized epididymal bull sperm]

The treatment of bull spermatozoa from epididymal cauda with 5 micrograms digitonin per microliters cells led to the destruction of the plasma membrane which was shown by electron microscopy. Structural changes of mitochondria and of the axoneme were not found. The functional intactness was maintained. The plasma membranes of hypotonically treated spermatozoa were permeable for succinate and the mitochondria showed a diminished functional intactness. For the total ATPase activity of digitonin-treated cells, mainly representing the dynein ATPase, a maximal activity of 20.3 nmol ATP x min-1 x microliters cells-1 (mean +/- S.D.; n = 8) and an apparent half saturation constant of 0.29 mM ATP were determined. The portions of Na(+)-K(+)-ATPase and mitochondrial ATPase in the total ATP-splitting activity were found to be less than 15%. In comparison to the capacity of mitochondrial ATP production, the maximal activity of ATP consuming reactions amounted to about 70%. These results support findings that the ATP turnover of spermatozoa is more limited by the ATP consumption than by the ATP production.