Ca2+ Is Required for Mouse Sperm Capacitation and Fertilization In Vitro

Abstract

The temporal involvement of Ca2+ during mouse sperm capacitation in vitro was examined by releasing sperm into Ca2+‐free medium and then introducing Ca2+ (1.80 mM, final concentration) at 30 minute intervals during a total preincubation of 120 minutes. Sperm were then assessed for acrosome loss, whiplash motility, and fertilizing ability, and were compared with samples preincubated for 120 minutes in the presence of Ca2+ No significant differences were detected when Ca2+ was present for 60, 90, or 120 minutes, but significant differences in all parameters were observed when Ca2+ was introduced for either the final 30 or 5 minutes. When suspensions were preincubated in Ca2+‐containing medium for 25 minutes and 15 μM ionophore A23187 was added for 5 min, sperm were morphologically and functionally similar to those preincubated for 120 minutes in Ca2+‐containing medium. From these results, it is concluded that mouse sperm require extracellular Ca2+ for at least part of capacitation, as well as for the acrosome reaction and whiplash motility needed to successfully fertilize eggs, and that a critical intracellular concentration of Ca2+ may be responsible for triggering these responses. 1982 American Society of Andrology