Functional coupling of GABA(B) receptors with G proteins that are sensitive to N-ethylmaleimide treatment, suramin, and benzalkonium chloride in rat cerebral cortical membranes

Although it is known that GABA(B) receptors are negatively coupled to adenylyl cyclase, the detailed selectivity of functional interaction between GABA(B) receptors and G(i) subfamily members is still ambiguous. (+/-)-Baclofen-stimulated high-affinity GTPase activity, which was competitively antagonized by 2-hydroxy-saclofen, was attenuated by pretreatment of the membranes with N-ethylmaleimide (NEM) in a concentration- and incubation period-dependent manner. The NEM-pretreated (50 muM, 15 min at 4 degreesC) membranes restored the (+/-)-baclofen-sensitive high-affinity GTPase activity when reconstituted with pertussis toxin-sensitive bovine brain G proteins. Among recombinant rat G(alpha) subunits, G(i alpha -2) appeared most effective as compared with other subunits (G(i alpha -2) > G(i alpha -3) > G(i alpha -1) = G(o alpha)). The GABA(B) receptor-mediated high-affinity GTPase activity was also completely eliminated by 100 muM suramin and by 100 muM benzalkonium chloride. These results indicate that GABA(B) receptors in rat cerebral cortex couple to NEM-sensitive G proteins, in particular G(i2), which are sensitive to suramin and benzalkonium chloride.