Control of superoxide and nitric oxide formation during human sperm capacitation

We studied the modulation of superoxide anion (O2·−) and nitric oxide (NO·) generation during human sperm capacitation (changes needed for the acquisition of fertility). The production of NO· (diaminofluorescein-2 fluorescence assay), but not that of O2·− (luminescence assay), related to sperm capacitation was blocked by inhibitors of protein kinase C, Akt, protein tyrosine kinase, etc., but not by those of protein kinase A. Extracellular calcium (Ca2+) controlled O2·− synthesis but extra- and intracellular Ca2+ regulated NO· formation. Zinc inhibited capacitation and formation of O2·− and NO·. Zinc chelators (TPEN and EDTA) and sulfhydryl-targeted compounds (diamide and N-ethylmaleimide) stimulated capacitation and formation of O2·− and NO·; superoxide dismutase (SOD) and nitric oxide synthase inhibitor (L-NMMA) prevented these events. Diphenyliodonium (flavoenzyme inhibitor) blocked capacitation and related O2·− synthesis but promoted NO· formation, an effect canceled by SOD and L-NMMA. NADPH induced capacitation and NO· (but not O2·−) synthesis and these events were blocked by L-NMMA and not by SOD. Integration of these data on O2·− and NO· production during capacitation reinforces the concept that a complex, but flexible, network of factors is involved and probably is associated with rescue mechanisms, so that spermatozoa can achieve successful fertilization.