Homologous down-regulation of histamine H3 receptors in rat striatal slices.
Preincubation of striatal slices with the selective histamine H3-receptor agonist immepip (100 nM) decreased the specific binding of N-alpha-[methyl-3H]-histamine ([3H]-NMHA) to membranes obtained from the treated slices. The binding decrease was significant after 5 min, remained at similar reduced levels between 5- and 30-min incubations with agonist, and only a partial recovery was observed after 90-min washout (34, 41, and 44% at 90, 120, and 150 min, respectively). Saturation analysis showed a significant decrease in both receptor density (-44% +/- 9%) and affinity (dissociation constant, Kd 1.15 +/- 0.23 nM from 0.59 +/- 0.17 nM). The effect of immepip was mimicked by histamine and the H3 agonists imetit and R-alpha-methylhistamine, and was blocked by the H3 antagonist thioperamide. The reduction in [3H]-NMHA binding was fully and partially prevented by incubation at 4 degrees C and in hypertonic medium, respectively, but not by the endocytosis inhibitor phenylarsine oxide (10 microM). None of the following protein kinase inhibitors, Ro-318220 and Gö-6976 (PKC), H-89 (PKA) and staurosporine (general inhibitor) prevented the effect of immepip. In [3H]-adenine-labeled slices the preincubation with immepip (100 nM, 15 min) prevented the inhibitory effect of H3 receptor activation on forskolin-induced [3H]-cAMP accumulation (99% +/- 9% vs. 76% +/- 4% of control values). Taken together our results indicate that agonist binding promotes the down-regulation of striatal H3 receptors resulting in a significant loss of function.
Garduño-Torres
Belén
B
Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados, Apdo. Postal 14-740, 07000 México, D.F., Mexico.
Arias-Montaño
José-Antonio
JA
D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006632:Histamine / Q000378:metabolism* / Q000494:pharmacology; D017442:Histamine Agonists / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D009924:Organ Culture Techniques; D010880:Piperidines / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D011940:Receptor Aggregation / Q000187:drug effects / Q000502:physiology; D018100:Receptors, Histamine H3 / Q000187:drug effects / Q000378:metabolism*
D001152:Arsenicals; D004791:Enzyme Inhibitors; D017442:Histamine Agonists; D007093:Imidazoles; D010880:Piperidines; D018100:Receptors, Histamine H3; C029341:oxophenylarsine; C085755:4-(1H-imidazol-4-ylmethyl)piperidine; D005576:Colforsin; D006632:Histamine; D000242:Cyclic AMP