STRUCTURE OF GABA_B RECEPTORS IN RAT RETINA

ABSTRACT

In the search for yet unknown subtypes of GABA_B receptors, the subunit architecture of GABA_B receptors in the retina was analyzed using selective antisera. Immunopurification of the splice variants GABA_B1a and GABA_B1b demonstrated that both were associated with GABA_B2. Quantitative immunoprecipitation experiments indicated that practical the entire GABA_B receptor population in the retina consists of the receptor subtypes GABAB_1a/GABA_B2 and GABA_B1b/GABA_B2, although low levels of GABA_B1c/GABA_B2 cannot be excluded. The data rule out the existence of GABA_B receptors containing the splice variants GABA_B1d and GABA_B1e. Moreover, no evidence for homomeric GABA_B1 receptors was found. Among the splice variants, GABA_B1a is by far the predominant one in neonatal and adult retina, whereas GABA_B1b is expressed only late in postnatal development and in the adult retina. Since GABA_B1a is expressed at high levels before functional synapses are formed, this specific receptor subtype might be involved in the maturation of the retina. Finally, subcellular fractionation demonstrated that GABA_B1a, but not GABA_B1b, is present in postsynaptic densities, suggesting a differential pre- and postsynaptic localisation of both splice variants.

Key Words: :

• GABA_Breceptor
• Rat retina
• Immunopurification
• Antisera