Recombinant human zona pellucida glycoprotein 3 induces calcium influx and acrosome reaction in human spermatozoa

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Abstract
Recombinant human ZP3 (rhuZP3) generated by Chinese hamster ovary cells transfected with a plasmid containing human ZP3 cDNA was used to study the acrosome reaction (AR) and intracellular calcium fluxes in capacitated human spermatozoa. Conditioned medium containing rhuZP3 significantly induced the AR (P n = 5). Sperm motility was not affected and acrosomal exocytosis in response to rhuZP3 was also shown to be time-dependent. Basal concentrations of sperm intracellular calcium were measured (82 ± 7 nM; mean ± SEM, n = 9). A transient increase in intracellular calcium (typically up to 400–450 nM) occurred within 1 min of rhuZP3 addition and was followed by sustained lower values of calcium (200–400 nM). These responses were dependent on the amount of rhuZP3. This is the first report of zona protein-induced changes in intracellular calcium levels in human spermatozoa. The results support the premise that ZP3 is an aganist of the human sperm AR and that rhuZP3 generated in a eukaryotic cell is effective in this respect.

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