Identification of GABABR2 in rat testis and sperm

GABA is capable of mimicking and potentiating the action of progesterone in initiating the acrosome reaction (AR) of mammalian sperm. The GABA-initiated AR is mediated by GABA(A)R; whereas GABA(B)R1 protein found in rat testis and sperm tends to modify this process. Moreover, the occurrence of GABA(B)R2, a subunit essential for the formation of a functionally active GABA (B)R, in rat testis and sperm has not been established. In the present study, rat testis and sperm were analyzed for the presence of GABA(B)R2 transcript and protein by RT-PCR, Northern blot, Western blot and an indirect immunofluorescence technique. Northern blot shows that the transcript of testis GABA(B)R2 is shorter (~3.0 Kb) than that of the brain (~5.6 Kb). The full length testis GABA(B)R2 cDNA was prepared by RACE-PCR and found to be shorter by 2.2 Kb in the segment at the extreme terminus of 3'UTR of rat brain GABA(B)R2 but, the sequences corresponding to the open reading frame and 5'-UTR of rat testis GABA(B)R2 were found to be identical to those of rat brain. GABA(B)R2 protein isolated from rat epididymal sperm was slighter larger than those of rat testis and brain. It was principally localized in the acrosome region of the head of rat sperm by an indirect immunofluorescence technique. The present results establish that GABA(B)R2 protein is produced in rat testis and sperm and may play a role in GABA triggering of AR.