We examined the kinetics of the acrosome reaction induced in human spermatozoa by progesterone (Ca(2+)-dependent) and adenosine 5'-triphosphate (ATP; Ca(2+)-independent). ATP and progesterone did not induce the acrosome reaction unless spermatozoa were incubated in a capacitation medium. ATP exhibited a constant induction of the acrosome reaction regardless of the incubation period, while progesterone began to induce the acrosome reaction after > or = 6 h of incubation. At 24 h of incubation, the percentages of spermatozoa in which the acrosome reaction had been induced by both progesterone and ATP were almost equal. To determine whether a limited population of human spermatozoa was reactive to both progesterone and ATP, we employed an MH61 bead binding method. When the acrosome-reacted spermatozoa were removed with MH61 beads, their percentage in the sperm suspension was decreased to < 3%. At 24 h of incubation, progesterone and ATP induced the acrosome reaction in 12.0 and 10.0% of spermatozoa, respectively. After MH61 bead binding was performed, the remaining spermatozoa did not react to the other activator (progesterone-->ATP, ATP-->progesterone). These findings indicate that only a limited population of human spermatozoa has the potential to undergo the acrosome reaction when stimulated by both progesterone and ATP.
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Tomiyama et al. (1995) studied this question.