Inducing the human acrosome reaction with a calcium ionophore A23187 decreases sperm-zona pellucida binding with oocytes that failed to fertilize in vitro

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Abstract
The human acrosome reaction was induced with the calcium ionophore A23187 and the proportion of reacted spermatozoa was determined with fluorescein-labelled Pisum sativum agglutinin. Human oocytes that failed to fertilize in vitro were used to test binding of spermatozoa to the zona pellucida (ZP) and oolemma. Differential labelling of spermatozoa with fluorescein and rhodamine was used to control for variability in the oocytes. Spermatozoa labelled with one fluorochrome were treated with A23187 and mixed with equal numbers of motile untreated control spermatozoa labelled with the other fluorochrome. The mixture was incubated with zona-intact and zona-free oocytes for 4 h. The sperm-ZP binding ratio of test to control spermatozoa was significantly decreased with increasing proportions of acrosome spermatozoa. In contrast, the sperm-oolemma binding ratio was significantly increased with A23187 treatment. This suggests that acrosome-reacted spermatozoa do not bind to the human ZP.