Pharmacological characterisation of a cell line expressing GABAB1b and GABAB2 receptor subunits

The gamma-aminobutyric acid (GABA(B)) receptor has been shown to be a heterodimer consisting of two receptor subunits, GABA(B1) and GABA(B2). We have stably co-expressed these two subunits in a CHO cell line, characterised its pharmacology and compared it to the native receptor in rat brain membranes. Radioligand binding using [H-3]CGP54626A demonstrated a similar rank order of potency between recombinant and native receptors: CGP62349 > CGP54626A > SCH 50911 > 3-aminopropylphosphinicacid (3-APPA) > GABA > baclofen > saclofen > phaclofen. However, differences were observed in the affinity of agonists, which were higher at the native receptor, suggesting that in the recombinant system a large number of the receptors were in the low agonist affinity state. In contrast, [S-35]GTPgammaS binding studies did not show any differences between recombinant and native receptors with the full agonists GABA and 3-APPA. Measurement of cAMP accumulation in the cells revealed a degree of endogenous coupling of the receptors to G-proteins. This is most likely to be due to the high expression levels of receptors (B-max = 22.5 +/- 2.5 pmol/mg protein) in this experimental system. There was no evidence of GABA(B2) receptors, when expressed alone, binding [H-3]CGP54626A, [H-3]GABA, [H-3]3-APPA nor of GABA having any effect on basal [S-35]GTPgammaS binding or cAMP levels. (C) 2003 Elsevier Science Inc. All rights reserved.