BRAIN GABA(A) RECEPTORS STUDIED WITH SUBUNIT-SPECIFIC ANTIBODIES

Brain GABA(A)/benzodiazepine receptors are highly heterogeneous. This heterogeneity is largely derived from the existence of many pentameric combinations of at least 16 different subunits that are differentiall y expressed in various brain regions and cell types. This molecular he terogeneity leads to binding differences for various ligands, such as GABA agonists and antagonists, benzodiazepine agonists, antagonists, a nd inverse agonists, steroids, barbiturates, ethanol, and Cl- channel blockers. Different subunit composition also leads to heterogeneity in the properties of the Cl- channel (such as conductance and open time) ; the allosteric interactions among subunits; and signal transduction efficacy between ligand binding and Cl- channel opening. The study of recombinant receptors expressed in heterologous systems has been very useful for understanding the functional roles of the different GABA(A) receptor subunits and the relationships between subunit composition, ligand binding, and Cl- channel properties. Nevertheless, little is kn own about the complete subunit composition of the native GABA(A) recep tors expressed in various brain regions and cell types. Several labora tories, including ours, are using subunit-specific antibodies for diss ecting the heterogeneity and subunit composition of native (not recons tituted) brain GABA(A) receptors and for revealing the cellular and su bcellular distribution of these subunits in the nervous system. These studies are also aimed at understanding the ligand-binding, transducti on mechanisms, and channel properties of the various brain GABA(A) rec eptors in relation to synaptic mechanisms and brain function. These st udies could be relevant for the discovery and design of new drugs that are selective for some GABA(A) receptors and that have fewer side eff ects.