Expression of Mammalian γ-Aminobutyric Acid Receptors with Distinct Pharmacology in Xenopus Oocytes

γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in mammalian brain, is known to interact with two classes of GABA receptors denoted GABAAand GABAB. Using Xenopus oocytes, we compared the electrical and pharmacological properties of GABA receptors expressed by poly(A)+RNA isolated from mammalian brain and retina. RNA from cerebral cortex expressed GABA responses with features characteristic of currents mediated by GABAAreceptors. In contrast, RNA from retina expressed responses mediated by GABAAreceptors and, in addition, GABA responses that were insensitive to the GABAAantagonist bicuculline and the GABABagonist baclofen and showed no modulation by barbiturates or benzodiazepines. The bicuculline/baclofen-insensitive GABA response was a Cl-current that was blocked by picrotoxin but showed little desensitization or outward rectification. Our results suggest that mammalian retina contains RNAs encoding GABA receptors with distinct pharmacology.