Our previous studies showed that gamma-aminobutyric acid (GABA)A and GABAB receptors are involved in rat sperm acrosome reaction induced by progesterone or GABA. Here, we report the presence of GABAC receptor in rat testis and spermatozoa. Full-length complementary DNA encoding the rho1, rho2 and rho3 subunits of GABAC receptor were cloned from rat testis; their sequences are identical to those of rat GABAC receptor in retina. Reverse transcription-polymerase chain reaction analysis showed that during the development of rat testis, the transcript levels of the rho1 and rho2 subunits showed little change, while the expression of rho3 was gradually up-regulated. Immunofluorescence analysis using an anti-rho1 antibody revealed that GABAC receptor exists on the elongated spermatid and sperm. Using a chlortetracycline assay, we found that N(4)-chloroacetylcytosine arabinoside, a GABAC receptor agonist, triggered rat sperm acrosome reaction; whereas (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid, a GABAC receptor antagonist, inhibited the ability of N(4)-chloroacetylcytosine arabinoside to induce acrosome reaction. These results suggested that GABAC receptors are also involved in rat sperm acrosome reaction.