Regulation of gaba a receptor in cerebellar granule cells in culture: Differential involvement of kinase activities

Abstract

GABA A receptor function was studied in rat cerebellar granule cells in culture, by the whole-cell patch-clamp approach. The data show that GABA activates Cl − currents in these neurons which reverse at the appropriate membrane potential and are blocked by picrotoxin. The GABA-activated currents desensitize with time of application of the neurotransmitter at concentrations ≥10 −6M. The dose-response curve for the peak Cl − current gives a K a value of 2.3 μM with a Hill coefficient of 1.2. The peak Cl − current elicited by GABA decreases with time of cell registration, with a time-constant of 7.3 min. Residual responsiveness though is maintained thereafter. This “run-down” phenomenon can be completely prevented by adding adenosine-5′-triphosphate + Mg 2+ in the pipette solution. Treatments which directly (8-bromoadenosine-3,5'-cyclicmonophosphate; adenosine-3', 5'-cyclicmonophosphate) or indirectly (forskolin, isobutylmethylxanthine) increase the adenosine-3',5'-cyclicmonophosphate intracellular content reduce the GABA-induced Cl − current. Conversely, treatment with the protein kinase A and C inhibitor 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine potentiates the effect of GABA. On the whole, the data indicate that different protein kinase activities modulate the functional state of the GABA A receptors on granule cells from the rat cerebellum.