Figure 2.

Functional expression of γ-aminobutyric acid B receptors. GABA_B receptors are responsible for presynaptic inhibition of neurotransmitter release in the mammalian brain, and function as heterodimers that consist of GABA_B1 and GABA_B2 subunits. (A) Whereas the GABA_B1 receptor is essential for responses elicited by the binding of GABA, the GABA_B2 receptor mediates G-protein activation (Galvez et al., 2001). (B) GABA_B1- and GABA_B2-receptor subunits probably assemble in transport vesicles. Trafficking of the heterodimer to the cell surface depends on the presence of the GABA_B2 receptor. G, G protein.