QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: jpet.107.122317v1 jpet.107.122317v2 323/1/248    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Shi, J. Articles by Muma, N. A. Search for Related Content PubMed PubMed Citation Articles by Shi, J. Articles by Muma, N. A. Pubmed/NCBI databases Compound via MeSH Substance via MeSH Hazardous Substances DB FLUOXETINE

NEUROPHARMACOLOGY

Agonist Induced-Phosphorylation of G₁₁ Protein Reduces Coupling to 5-HT_2A Receptors

Department of Pharmacology and Experimental Therapeutics, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois (J.S., K.J.D., G.A.C., F.G., A.J.G., M.L., N.R.S., G.B.); and Department of Pharmacology and Toxicology, School of Pharmacy, Malott Hall, University of Kansas, Lawrence, Kansas (R.K.S., N.A.M.)

We previously demonstrated that 24-h treatment with (–)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI) causes phosphorylation of G₁₁ protein at serine 154 and that this phosphorylation causes desensitization of serotonin (5-HT) 2A receptor signaling in A1A1v cells (Shi et al., 2007). We now report that treatment of A1A1v cells with DOI for 24 h produces a greater reduction in the B_max of [¹²⁵I](±)-DOI-labeled high-affinity binding sites (46%) than the reduction of [³H]ketanserin binding sites (25%). Although the K_D values are not altered, there is a smaller amount of GTPS [guanosine 5'-3-O-(thio)triphosphate]-sensitive [¹²⁵I](±)-DOI binding in DOI-treated cells. These results suggest that DOI treatment causes down-regulation of 5-HT_2A receptors and reductions in G protein-coupled 5-HT_2A receptors. In contrast, in cells transfected with the phosphorylation state mimic G₁₁S154D, GTPS-sensitive [¹²⁵I](±)-DOI binding was decreased by 48%; however, there was no significant difference in the K_D and B_max values of [¹²⁵I](±)-DOI-labeled receptors. The receptor binding experiments suggest that phosphorylation of G₁₁ on serine 154 reduces coupling of 5-HT_2A receptors, whereas DOI causes down-regulation of 5-HT_2A receptors in addition to the phosphorylation-induced uncoupling of G₁₁ to 5-HT_2A receptors. To determine whether DOI increases phosphorylation of G_q/11 protein in vivo, rats were treated with 1 mg/kg/day DOI or saline for 1 to 7 days. Seven days of DOI treatment significantly decreased phospholipase C activity stimulated by an E_max concentration of 5-HT by 40% and increased phosphorylation of G_q/11 proteins by 51% in the frontal cortex. These data suggest that DOI causes phosphorylation of G_q/11 in vivo and could thereby contribute to the desensitization of 5-HT_2A receptors.

Address correspondence to: Dr. Nancy A. Muma, Department of Pharmacology and Toxicology, University of Kansas, School of Pharmacy, Lawrence, KS 66045. E-mail: nmuma{at}ku.edu