Amino acid neurotransmitter receptor/chloride channels of mammalian sperm and the acrosome reaction.

Two different amino acid neurotransmitter receptor/Cl-channels, a gamma-aminobutyric acid (GABA) receptor-like/Cl- channel and a glycine receptor/Cl- channel, have recently been found in mammalian sperm and shown to be involved in the sperm acrosome reaction (AR), an exocytotic event essential to mammalian fertilization. The identity of the receptor/channel involved in the AR depends upon the stimulatory ligand. The AR initiated by the egg zona pellucida requires the participation of the sperm glycine receptor/Cl- channel, whereas the AR initiated by another putative physiological AR initiator, progesterone, involves the sperm GABA receptor-like/Cl- channel. Cl- efflux through the latter has been shown to occur during the progesterone-initiated AR. Activation of sperm amino acid neurotransmitter receptor/Cl- channels may result in plasma membrane depolarization and thereby exert at least a partial control over voltage-sensitive sperm Ca2+ channels and Ca2+ influx important to the AR.