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 adeny lyl cyclase, the detailed selectivity of functional interaction between GAB A(B) receptors and G(i) subfamily members is still ambiguous. (+/-)-Baclofe n-stimulated high-affinity GTPase activity, which was competitively antagon ized by 2-hydroxy-saclofen, was attenuated by pretreatment of the membranes with N-ethylmaleimide (NEM) in a concentration- and incubation period-depe ndent manner. The NEM-pretreated (50 muM, 15 min at 4 degreesC) membranes r estored the (+/-)-baclofen-sensitive high-affinity GTPase activity when rec onstituted with pertussis toxin-sensitive bovine brain G proteins. Among re combinant rat G(alpha) subunits, G(i alpha -2) appeared most effective as c ompared 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 benzalkoni um chloride. These results indicate that GABA(B) receptors in rat cerebral cortex couple to NEM-sensitive G proteins, in particular G(i2), which are s ensitive to suramin and benzalkonium chloride.