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Neuronal GABAB receptors regulate calcium and potassium currents via G-protein-coupled mechanisms and play a critical role in long-term inhibition of synaptic transmission in the CNS. Recent studies have demonstrated that assembly of GABAB receptor GABABR1 and GABABR2 subunits into functional heterodimers is required for coupling to potassium channels in heterologous systems. However whether heterodimerization is required for the coupling of GABAB receptors to effector systems in neurons remains to be established. To address this issue, we have studied the coupling of recombinant GABAB receptors to endogenous Ca2+ channels in superior cervical ganglion (SCG) neurons using nuclear microinjection to introduce both sense and antisense expression constructs. Patch-clamp recording from neurons injected with both GABABR1a/1b and GABABR2 cDNAs or with GABABR2 alone produced marked baclofen-mediated inhibition of Ca2+ channel currents via a pertussis toxin-sensitive mechanism. The actions of baclofen were blocked by CGP62349, a specific GABAB antagonist, and were voltage dependent. Interestingly, SCGs were found to express abundantly GABABR1 but not GABABR2 at the protein level. To determine whether heterodimerization of GABABR1 and GABABR2 subunits was required for Ca2+inhibition, the GABABR2 expression construct was microinjected with a GABABR1 antisense construct. This resulted in a dramatic decrease in the levels of the endogenous GABABR1 protein and a marked reduction in the inhibitory effects of baclofen on Ca2+ currents. Therefore our results suggest that in neurons heteromeric assemblies of GABABR1 and GABABR2 are essential to mediate GABAergic inhibition of Ca2+ channel currents.

Heteromeric Assembly of GABABR1 and GABABR2 Receptor Subunits Inhibits Ca2+Current in Sympathetic Neurons

Heteromeric Assembly of GABA_BR1 and GABA_BR2 Receptor Subunits Inhibits Ca²⁺Current in Sympathetic Neurons