INTERACTION BETWEEN CA2-ADENOSINE-MONOPHOSPHATE, THE SUPEROXIDE ANION, AND TYROSINE PHOSPHORYLATION PATHWAYS IN THE REGULATION OF HUMAN SPERM CAPACITATION(, CYCLIC 3',5')

In order to fertilize the egg, spermatozoa must go through the capacit ation process where they experience Ca2+ uptake, increases in cyclic 3 ',5' adenosine monophosphate (cAMP) concentrations, superoxide anion p roduction, and protein tyrosine phosphorylation. Although the importan ce of these processes has been described, the interactions between the m, as well as the temporal sequence of these events, remain to be demo nstrated. Previous studies from our laboratory have demonstrated that tyrosine phosphorylation of p105 and p81 (p105/81), the two major huma n sperm phosphotyrosine-containing proteins, was under cAMP and oxygen derivatives regulation. In the present study, we investigated the imp ortance of intra- and extracellular Ca2+, as well as the phosphodieste rase inhibitor 3-isobutyl-1-methylxanthine and the phosphatase inhibit ors calyculin A and okadaic acid, in the production of superoxide anio n and p105/81 tyrosine phosphorylation. An increase in p105/81 phospho tyrosine content was observed when spermatozoa were incubated in the a bsence of extracellular Ca2+ or with the calmodulin antagonist N-(6-am inohexyl)-1-naphthalenesulfonamide. However, the human sperm capacitat ion inducer FCSu (ultrafiltrate of fetal cord serum) requires the pres ence of the extracellular Ca2+ to induce capacitation, superoxide anio n production, and tyrosine phosphorylation of p105/81, whereas free in tracellular Ca2+ had no effect on these last two processes. The produc tion of superoxide anion by spermatozoa was stimulated by inhibitors o f phosphodiesterases and serine/threonine phosphoprotein phosphatases. The tyrosine phosphatase inhibitor vanadate decreased by 40% the FCSu -stimulated superoxide anion production, although it had no effect whe n used alone. These results suggest that, during sperm capacitation, C a2+ induces an elevation in cAMP levels; this cAMP, through undefined serine/threonine protein phosphorylation, stimulates the generation of superoxide anion, which, in turn, causes the increase in p105/81 phos photyrosine contents.