REGULATION OF GABA-A RECEPTOR IN CEREBELLAR GRANULE CELLS IN CULTURE - DIFFERENTIAL INVOLVEMENT OF KINASE-ACTIVITIES

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 greater-than-or-equal-to 10(-6) M. The dose-response curve for the peak Cl- current gives a K(a) value of 2.3 muM 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 + Mg2+ 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.