Patch-clamp study of gamma-aminobutyric acid receptor Cl- channels in cultured astrocytes.
The membrane channels operated by gamma-aminobutyric acid (GABA) were studied in cultured astrocytes from rat cerebral hemispheres by using patch-clamp techniques. The channel properties appeared to be very similar, in many respects, to those present in neuronal cell membranes. The Cl- -selective channels were activated after the sequential binding of two GABA molecules to the receptor, as deduced from the slope of the dose-response curve. Single-channel currents displayed multiple conductance states of 12 pS, 21 pS, 29 pS, and 43 pS, with the main-state conductance being 29 pS. The gating properties could be described by a sequential reaction scheme for agonist-activated channels. GABA-induced whole-cell currents were potentiated by the benzodiazepine receptor agonist diazepam and also, to a lesser extent, by methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate an inverse agonist. In neurons and chromaffin cells, methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate reduces the sensitivity of the GABA receptor, indicating that neuronal and glial GABA/benzodiazepine receptor--Cl- channel complexes are different. Glial GABA receptor channels could be of functional importance in buffering extracellular Cl- in the cleft of the GABAergic synapse.
Bormann
J
J
Max-Planck-Institut für biophysikalische Chemie, Göttingen, Federal Republic of Germany.
Kettenmann
H
H
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology*; D001921:Brain / Q000502:physiology; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D004553:Electric Conductivity; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D011963:Receptors, GABA-A / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D002712:Chlorides; D007473:Ion Channels; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid