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-zone binding. Methods: The acrosomal exocytosis of spermatozoa incubated with solubilized zone pellucida (ZP) at a final concentration of 1 ZP/μl was compared with 10 μM calcium ionophore A23187 and 30% (v/v) pooled human follicular fluid (HFF). Spermatozoa were incubated with 1, 10, and 100 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 to 1 ZP/μl, revealed significantly higher zona-bound spermatozoa compared to controls treated with 1 ZP/μl 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 observed at 100 ng/ml PT. 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.