Evidence of Two Populations of GABA_A Receptors in Cerebellar Granule Cells in Culture: Different Desensitization Kinetics, Pharmacology, Serine/ Threonine Kinase Sensitivity, and Localization

Abstract

GABA_A receptors of rat cerebellar granule cells in culture have been studied by the whole cell patch clamp technique. The biphasic desensitization kinetic observed could be due either to different desensitization mechanisms of a single receptor population or to different receptor populations. The overall data indicate that the latter hypothesis is most probably the correct one. In fact, the fast desensitizing component was selectively potentiated by a benzodiazepine agonist and preferentially down-regulated by activation of the protein serine/threonine kinases A and G, as a consequence of the latter characteristic that receptor population was preferentially down-regulated by previous activation of N-methyl-d-aspartate glutamate receptors, via production of nitric oxide and PKG activation, most probably in dendrites. The other population is benzodiazepine insensitive and not influenced by activation of PKA or PKG. This slowly desensitizing population may correspond to the extrasynaptic δ subunit containing GABA_A receptors described by other authors. Instead, the rapidly desensitizing population appears to represent dendritic synaptic GABA_A receptors.