Hamster sperm glycine receptor: Evidence for its presence and involvement in the acrosome reaction

Recent reports have provided evidence for the presence of amino acid neurot ransmitter receptor/chloride channels in human and porcine spermatozoa and their involvement in the acrosome reaction (AR). In this work we investigat ed whether a glycine receptor (GlyR) was present in golden hamster sperm, a nd whether it had a role in the hamster AR. The neuronal GlyR agonist glyci ne, stimulated in a dose-dependent manner, the AR of hamster spermatozoa pr eviously capacitated for at least 3 hr. This stimulation was completely inh ibited by 50 muM (+)-bicuculline and by concentrations of strychnine as low as 10-50 nM; both agents are antagonists of neuronal GlyR when used at the concentrations reported in this study. beta -Alanine, another agonist of t he neuronal GlyR, also stimulated the AR. The AR-stimulatory effect of this compound was completely abolished by 50 nM strychnine. The inhibitory effe ct of strychnine on the glycine-induced hamster sperm AR was completely ove rcome by subsequent treatment with the calcium ionophore ionomycin, demonst rating that the strychnine effect was specific for GlyR. Additional binding studies with (3)[H]-strychnine, the typical radioligand used to detect Gly R in several cells, demonstrated for the first time the presence of specifi c binding sites for strychnine in the hamster spermatozoa. Interestingly, b inding increased during in vitro capacitation, particularly in those sperm suspensions showing high percentages of AR. Taken together these results st rongly suggest the presence of a GlyR in the hamster spermatozoa, with a ro le in the AR when activated. (C) 2001 Wiley-Liss, Inc.