DIFFERENTIAL INTRACELLULAR REGULATION OF CORTICAL GABA(A) AND SPINAL GLYCINE RECEPTORS IN CULTURED NEURONS

Using patch-clamp techniques we studied several aspects of intracellul ar GABA(A) and glycine Cl- current regulation in cortical and spinal c ord neurons, respectively. Activation of PKA with a permeable analog o f cyclic AMP (cAMP) produced a potentiation of the Cl- current activat ed with glycine, but not of the current induced with GABA. The inactiv e analog was without effect. Activation of PKC with 1 mu M PMA reduced the amplitude of the GABA(A) and glycine currents. Internal applicati on of 1 mM cGMP, on the other hand, had no effect on the amplitude of either current. The amplitude of these inhibitory currents changed sli ghtly during 20 min of patch-clamp recording. Internal perfusion of th e neurons with 1 mu M okadaic acid, a phospatase inhibitor, induced po tentiation in both currents. The amplitude of GABA(A) and glycine curr ents recorded with 1 mM internal CaCl2 and 10 mM EGTA (10 nM free Ca2) decayed by less than 30% of control. Increasing the CaCl2 concentrat ion to 10 mM (34 mu M free Ca2+) induced a transient potentiation of t he GABA(A) current. A strong depression of current amplitude was found with longer times of dialysis. The glycine current, on the contrary, was unchanged by increasing the intracellular Ca2+ concentration. Acti vation of G proteins with internal FAl4- induced an inhibition of the GABA(A) current, but potentiated the amplitude of the strychnine-sensi tive Cl- current. These results indicate that GABA(A) and glycine rece ptors are differentially regulated by activation of protein kinases, G proteins and Ca2+. This conclusion supports the existence of selectiv ity in the intracellular regulation of these two receptor types. (C) 1 997 Elsevier Science B.V.