G-protein regulation of the solubilized human zona pellucida-mediated acrosome reaction and zona pellucida binding

Purpose: The study aimed to evaluate the (i) regulatory role of G(i)-like protein during the acrosome reaction (AR) of normal sperm donors and (ii) the role of intact acrosomes during sperm-zona binding. Methods: The acrosomal exocytosis of spermatozoa incubated with solubilized zona pellucida (ZP) at a final concentration of I ZP/mu l was compared with 10 mu M calcium ionophore A23187 and 30% (v/v) pooled human follicular fluid (HFF). Spermatozoa were incubated with I, 10, and loo ng/ml pertussis toxin (PT) during capacitation to functionally inactivate the G(i)-like protein. The sperm-zona binding potential of 100 ng/ml PT-treated spermatozoa followed by exposure tol ZP/mu l, revealed significantly higher zona- bound spermatozoa compared to controls treated with I ZP/ mu l only. Results: PT treatment of spermatozoa did not affect sperm motility, however, inhibited the percentage AR induced by solubilized ZP. In contrast, the A23187- and HFF-induced ARs were not sensitive to PT treatment. PT inhibition of the ZP-induced AR occurred in a concentration-dependent manner; with maximal effects observes at 100;ng/ml PI: Conclusions: In conclusion, it seems that PT-sensitive G(i)- like protein in human spermatozoa plays an important regulatory role in the AR induced by the human ZP and this underlines the importance of intact acrosomes during sperm-zona binding.