GABA-gated Cl- channels in the rat retina

gamma-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the mammalian retina, and its physiological action is well established. GABA receptors have been localized immunocytochemically in the retina of different mammalian species, and all major retinal cell types have been found to express GABA(A) receptor subunits. Recently, a new type of GABA receptor with pharmacological and electrophysiological properties different from the known GABA(A) and GABA(B) receptors, has been described. These GABA(C) receptors are found predominantly in the vertebrate retina. This review concentrates on the electrophysiological characterization of GABA receptors expressed by amacrine and bipolar cells of the rat retina. We recorded GABA-induced currents from cultured neonatal amacrine and bipolar cells as well as from isolated bipolar cells of adult animals. While amacrine cells contain a homogeneous population of GABA(A) receptors, bipolar cells exhibit both GABA(A) and GABA(C) responses. Although both receptors gate chloride-selective ion channels, their biophysical and pharmacological properties differ markedly. These functional differences and the cellular distribution of GABA(A) and GABA(C) receptors suggest that they have different inhibitory functions in the rat retina. (C) 1997 Elsevier Science Ltd.