Release of Acrosomal Hyaluronidase Follows Increased Membrane Permeability to Calcium in the Presumptive Capacitation Sequence for Spermatozoa of the Bovine and Other Mammalian Species1
Brief exposure to a medium of elevated ionic strength combined with subsequent incubation in dialyzed fluid collected from bovine ovarian follicles results in an enhanced uptake of Ca2+ by bovine ejaculated sperm. Uptake of Ca2+ by either epididymal or ejaculated sperm is induced by treatment with the divalent cation ionophore A23187 [calcimycin] and is followed by release of the acrosomal enzyme hyaluronidase. A similar release of enzyme from ejaculated sperm is produced by hypertonic treatment and follicular fluid, but not by either alone. Uptake of Ca2+ and release of hyaluronidase likewise follow ionophore treatment of epididymal sperm from the guinea pig, rabbit and hamster. In control experiments, hyaluronidase release is not induced by treatment with the protonophore, carbonylcyanide-m-chlorophenylhydrazone, by the respiratory inhibitor, rotenone, or by treatment with A23187 in a Ca2+-free medium. Two presumptive components of the capacitation sequence of bovine spermatozoa, enhanced influx of Ca2+ and subsequent release of acrosomal contents, apparently are produced either by ionophore treatment or by hypertonic extraction and exposure to follicular fluid, procedures that produce capacitation in vitro for the sperm of several other mammalian species.