Structure and function of GABA(c) receptors: a comparison of native versusrecombinant receptors

In less than a decade our knowledge of the GABA(c) receptor, a new type of Cl--permeable ionotropic GABA receptor, has greatly increased based on stud ies of both native and recombinant receptors. Careful comparison of propert ies of native and recombinant receptors has provided compelling evidence th at GABA receptor rho -subunits are the major molecular components of GABA(c ) receptors. Th me distinct rho -subunits from various species have been cl oned a nd the pattern of their expression in the retina, as well as in vari ous brain regions, has been established. The pharmacological profile of GAB A(c) receptors has been refined and more specific drugs have been developed . Molecular determinants that underlie functional properties of the recepto rs have bean assigned to specific amino acid residues in rho -subunits. Thi s information has helped determine the subunit composition of native recept ors, as well as the molecular basis underlying subtle variations among GABA (c) receptors in different species. Finally GABA(c) receptors play a unique functional role in retinal signal processing via three mechanisms: (1) slo w activation; (2) segregation from other inhibitory receptors; and (3) cont ribution to multi-neuronal pathways.