OSMO-SENSITIVITY OF THE HUMAN SPERM ACROSOME REACTION

The osmo-sensitivity of the human sperm acrosome reaction was investig ated by determining the effect of hyper- and hypo-osmolal conditions o n the ionophore A23187- and dbcAMP-induced reaction of both capacitate d and non-capacitated spermatozoa. Hyper-osmolal conditions inhibited the agonist-induced reactions of both types of spermatozoa. Hypo-osmol al conditions caused a spontaneous loss of acrosomes from capacitated but not from non-capacitated spermatozoa. The loss of acrosomes under hypo-osmolal conditions was further enhanced by dbcAMP but not by iono phore A23187. Although significant decreases in sperm viability were o ccasionally observed at the high and low osmolalities, these decreases were not consistent and could not account for the observed loss of ac rosomes. It is concluded that the human sperm acrosome reaction is osm o-sensitive. The acrosome reaction stimulated by ionophore A23187 (rai ses intracellular Ca2+) and dbcAMP (activates protein kinase A which c auses protein phosphorylation) appears to involve water entry downstre am from the action of these agonists. Preincubation in albumin (capaci tation) causes human spermatozoa to lose their acrosomes under hypo-os molal conditions. Finally, capacitation is not an essential prerequisi te to the acrosome reaction as long as agonists are used that by-pass certain membrane-related events.