Abstract
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 GABAAR; whereas GABABR1 protein found in rat testis and sperm tends to modify this process. Moreover, the occurrence of GABABR2, a subunit essential for the formation of a functionally active GABA BR, in rat testis and sperm has not been established. In the present study, rat testis and sperm were analyzed for the presence of GABABR2 transcript and protein by RT-PCR, Northern blot, Western blot and an indirect immunofluorescence technique. Northern blot shows that the transcript of testis GABABR2 is shorter (~3.0 Kb) than that of the brain (~5.6 Kb). The full length testis GABABR2 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 GABABR2 but, the sequences corresponding to the open reading frame and 5'-UTR of rat testis GABABR2 were found to be identical to those of rat brain. GABABR2 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 GABABR2 protein is produced in rat testis and sperm and may play a role in GABA triggering of AR.
