This study demonstrates for the first time, that membrane vesicles originated from the hamster sperm head after the occurrence of the acrosome reaction, possess specific strychnine binding sites. [H-3]Strychnine binding was saturable and reversible, being displaced by unlabeled strychnine (IC50 = 26.7 +/- 2.3 muM). Kinetic analysis revealed one binding site with K-d = 120 nM and B-max = 142 fmol/10(6) spermatozoa. Glycine receptor agonists beta-alanine and taurine inhibited strychnine binding by 20-30%. Surprisingly, glycine stimulated binding by about 40-50%. Results obtained in this study strongly suggest the presence of glycine receptors-with distinctive kinetic properties on the periacrosomal plasma membrane of hamster spermatozoa. Localization of this receptor fits well with its previously proposed role in acrosomal exocytosis during mammalian fertilization. (C) 2003 Elsevier Science (USA). All rights reserved.