Identification and expression of GABAC receptor in rat testis and spermatozoa

Our previous studies showed that gamma-aminobutyric acid (GABA)(A) and GABA(B) receptors are involved in rat sperm acrosome reaction induced by progesterone or GABA. Here, we report the presence of GABA(C) receptor in rat testis and spermatozoa. Full-length complementary DNA encoding the rho 1, rho 2 and rho 3 subunits of GABA(C) receptor were cloned from rat testis; their sequences are identical to those of rat GABA(C) receptor in retina. Reverse transcription-polymerase chain reaction analysis showed that during the development of rat testis, the transcript levels of the rho 1 and rho 2 subunits showed little change, while the expression of rho 3 was gradually up-regulated. Immunofluorescence analysis using an anti-rho l antibody revealed that GABA(C) receptor exists on the elongated spermatid and sperm. Using a chlortetracycline assay, we found that N(4)-chloroacetylcytosine arabinoside, a GABA(C) receptor agonist, triggered rat sperm acrosome reaction; whereas (1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid, a GABA(C) receptor antagonist, inhibited the ability of N(4)-chloroacetylcytosine arabinoside to induce acrosome reaction. These results suggested that GABA(C) receptors are also involved in rat sperm acrosome reaction.