Effects of the alkylating agent EEDQ on regulatory G proteins and recovery of agonist and antagonist alpha2-adrenoceptor binding sites in rat brain.
The aim of this study was to assess the effect of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ)-induced alpha2-adrenoceptor inactivation on regulatory G proteins and the recovery of agonist and antagonist binding sites. EEDQ induced a rapid increase in the abundance of rat brain cortical Galphai1/2 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 Galphai3 and Galphao proteins. By using the standard monoexponential model, the analysis of the recovery of alpha2-adrenoceptor density (6 h-30 days) with [3H]UK 14304 (bromoxidine) and [3H]RX 821002 (2-metoxy idazoxan) in the cerebral cortex did not reveal differences in receptor turnover parameters. However, the recovery of [3H]UK 14304 binding fitted best to a new biphasic recovery model, suggesting the existence of two distinct phases of recovery of agonist sites (r1 and r2 = 15.7 and 7.4 fmol mg protein(-1) day(-1); k1 and k2 = 0.51 and 0.25 day(-1); (t1/2)1 and (t1/2)2 = 1.4 and 2.7 days). In contrast, the recovery of [3H]RX 821002 antagonist sites did not fit to the biphasic model (r = 8.1, k = 0.14, t1/2 = 4.9). Because agonist binding requires coupling to G proteins, the present results suggest that the rapid over-expression of Galphai1/2 proteins induced by EEDQ is related to the biphasic recovery of [3H]UK 14304 binding. The possible implication of the faster recovery of alpha2-adrenoceptor function after EEDQ inactivation is discussed.
Associate Unit of the Institute of Neurobiology Ramón y Cajal/CSIC, Department of Biology, University of Balearic Islands, Palma de Mallorca, Balears, Spain.
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Ribas
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Miralles
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García-Sevilla
D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000477:Alkylating Agents / Q000494:pharmacology*; D000818:Animals; D000068438:Brimonidine Tartrate; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D019329:Idazoxan / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D011804:Quinolines / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000477:Alkylating Agents; D011804:Quinolines; D011810:Quinoxalines; D000068438:Brimonidine Tartrate; C000470:EEDQ; C058525:2-methoxyidazoxan; D019204:GTP-Binding Proteins; D019329:Idazoxan