Acrosome reaction induced by recombinant human zona pellucida 3 peptides rhuZP3a22∼176 and rhuZP3b177∼348 and their mechanism

To explore the biological characteristics of the recombinant zona pellucida 3 (ZP3) peptides of rhuZP3a(22 similar to 176) and rhuZP3b(177 similar to 348), we examined whether rhuZP3a(22 similar to 176) or rhuZP3b(177 similar to 348) trigger the acrosome reaction (AR) of human spermatozoa and we investigated the underlying mechanism. The assessment of AR was performed using chlortetracycline staining. The intracellular free calcium concentration ([Ca2+]i) in Fura-2/AM-loaded human sperm was monitored with a spectrofluorophotometer. We found that rhuZP3a(22 similar to 176) and rhuZP3b(177 similar to 348) were capable of eliciting AR at different concentrations. With the addition of either peptide, the [Ca2+]i level was raised to a peak with or without plateau. The AR could be inhibited by pertussis toxin (PTX), EGTA, and pimozide (a T-type calcium channel blocker), whereas verapamil was less effective in this regard. The results of the present study suggest that peptides rhuZP3a(22 similar to 176) and rhuZP3b(177 similar to 348) have a role similar to human ZP3, and that the mechanism of the response to the peptides involves influx of calcium, the G protein pathway, and a T-type calcium channel.