Intracellular effectors and modulators of GABA-A and GABA-B receptors: a commentary

The inhibitory neurotransmitter GABA activates two receptor subtypes that can be distinguished by their pharmacology. The GABA-A site is competitively antagonized by bicuculline and exclusively coupled to a chloride channel. The GABA-B receptor, for which baclofen is the only specific agonist, is resistant to bicuculline inhibition and, depending upon its localization, will activate K currents and/or inhibit Ca currents. Both electrophysiological and biochemical approaches have been applied to the study of each receptor. The membrane and intracellular components that to date have been implicated in GABA-B activation are discussed: G proteins, adenylate cyclase and intracellular calcium levels. This latter factor is also discussed with respect to GABA-A receptor action.