Evidence for gamma-aminobutyric acid specific binding sites on human spermatozoa

The possible presence of gamma-aminobutyric acid (GABA) specific binding sites on human spermatozoa was investigated. Swim-up preparations of human spermatozoa were incubated with radiolabelled GABA in the presence of unlabelled GABA, alternatively displacers of GABAA/B receptors and GABA transport proteins. The results indicate that GABA specific binding sites are present on the surface of human spermatozoa, and that these binding sites possibly indicate the presence of GABA transport proteins. Furthermore, GABA at different concentrations was added to swim-up preparations of human spermatozoa. Possible effects of GABA on sperm motility, hyperactivation and acrosome reaction were explored. No significant differences were observed between treated groups and controls concerning motility parameters and hyperactivation. Incubation with GABA did not cause any increase in spontaneous acrosome reaction. However, spermatozoa treated with the calcium ionophore A-23187 showed a small but significantly increased ability to undergo the acrosome reaction following preincubation in 10(-4) M GABA (P < 0.05).