In guinea pig spermatozoa, the procaine-promoted synchronous acrosome reaction results in highly fertile cells exhibiting normal F-actin distribution

Abstract

In guinea pig spermatozoa, procaine induces Ca 2+ independent hyperactivated motility suggestive of sperm capacitation. Nonetheless, in the presence of high extracellular Ca 2+, procaine increases cytoplasmic Ca 2+. We analyze the procaine effect on the acrosome reaction (AR) processes in guinea pig spermatozoa. Results indicated that: (i) in spermatozoa pre-incubated 5–30 min in MCM-PLG medium, procaine produced synchronous AR, (ii) the acrosome-reacted sperm number increased with the capacitation period before procaine treatment and with procaine concentration, (iii) acrosome reaction was blocked when Ca 2+ was omitted, (iv) plasma membrane–outer acrosomal membrane fusion started within 2 min after procaine treatment, (v) in acrosome-reacted spermatozoa, actin polymerization occurred and F-actin was located in the equatorial and post-acrosomal regions and (vi) procaine treatment resulted in highly fertile acrosome-reacted spermatozoa. This is the first report indicating that procaine promotes synchronic AR in mammalian spermatozoa. If procaine promotes premature AR of spermatozoa in vivo, it might be a factor for infertility in patients exposed to this local anesthetic.