Verapamil, a Ca2+ channel antagonist, accelerates the in vitro penetration of zona-free hamster eggs by human spermatozoa.

Human spermatozoa were preincubated for 3.5 h with various concentrations (0-100 mumol/l) of verapamil, a Ca2+ channel antagonist, before they were mixed with zona-free hamster eggs. Control spermatozoa penetrated only 3% of the eggs, whereas the highest penetration (40.3%) was reached after preincubation with 100 mumol/l verapamil. Thus, verapamil increases the ability of human spermatozoa to penetrate zona-free hamster eggs, possibly by an acceleration of the acrosome reaction. Although it has been established that the acrosome reaction requires the entry of extracellular Ca2+ into the spermatozoa, the Ca2+ ions do not seem to enter by means of Ca2+ channels.