EFFECTS OF THE ALKYLATING AGENT EEDQ ON REGULATORY G-PROTEINS AND RECOVERY OF AGONIST AND ANTAGONIST ALPHA(2)-ADRENOCEPTOR BINDING-SITES INRAT-BRAIN

The aim of this study was to assess the effect of N-ethoxycarbonyl-2-e thoxy-1,2-dihydroquinoline (EEDQ)-induced alpha(2)-adrenoceptor inacti vation on regulatory G proteins and the recovery of agonist and antago nist binding sites. EEDQ induced a rapid increase in the abundance of rat brain cortical G alpha(i1/2) proteins (30% at 6 h) which reached a maximum at 4 days (45%) and which then slowly returned (7-30 days) to control values. EEDQ did not alter significantly the levels of G alph a(i3) and G alpha(o) proteins. By using the standard monoexponential m odel, the analysis of the recovery of alpha(2)-adrenoceptor density (6 h-30 days) with [H-3]UK 14304 (bromoxidine) and [H-3]RX 821002 (2-met oxy idazoxan) in the cerebral cortex did not reveal differences in rec eptor turnover parameters. However, the recovery of [H-3]UK 14304 bind ing fitted best to a new biphasic recovery model, suggesting the exist ence of two distinct phases of recovery of agonist sites (r(1) and r(2 ) = 15.7 and 7.4 fmol mg protein(-1) day(-1); k(1) and k(2) = 0.51 and 0.25 day(-1); (t(1/2))(1) and (t(1/2))(2) = 1.4 and 2.7 days). In con trast, the recovery of [H-3]RX 821002 antagonist sites did not fit to the biphasic model (r = 8.1, k = 0.14, t(1/2) = 4.9). Because agonist binding requires coupling to G proteins, the present results suggest t hat the rapid over-expression of G alpha(i1/2) proteins induced by EED Q is related to the biphasic recovery of [H-3]UK 14304 binding. The po ssible implication of the faster recovery of alpha(2)-adrenoceptor fun ction after EEDQ inactivation is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.