AMINO-ACID NEUROTRANSMITTER RECEPTOR CHLORIDE CHANNELS OF MAMMALIAN SPERM AND THE ACROSOME REACTION/

Two different amino acid neurotransmitter receptor/Cl- channels, a gam ma-aminobutyric acid (GABA(A)) 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 exocytot ic event essential to mammalian fertilization. The identity of the rec eptor/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 t he sperm GABA(A) receptor-like/Cl- channel. Cl- efflux through the lat ter has been shown to occur during the progesterone-initiated AR. Acti vation 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+ in flux important to the AR.