5-Hydroxytryptamine2A (5-HT2A) receptor desensitization can occur without down-regulation.
The connection between agonist-induced desensitization and down-regulation of 5-hydroxytryptamine2A (5-HT2A) receptors was examined in a clonal cell line that stably expresses the 5-HT2A receptor. Brief (2-hr) and prolonged (24-hr) exposure to the agonist quipazine or the agonist 4-iodo-(2,5-dimethoxy)- phenylisopropylamine (DOI) diminished 5-HT2A receptor-mediated phosphoinositide hydrolysis; no change in 5-HT2A receptor number or affinity was measured after 24 hr of exposure to DOI or quipazine. Immunohistochemical studies demonstrated that a 24-hr exposure to DOI did not alter surface 5-HT2A receptor immunoreactivity. Western blot analysis with G alpha q- and G alpha 11-selective antibodies indicate that a 24-hr agonist exposure did not alter the levels of phospholipase C-dependent G proteins. These results suggest that desensitization after prolonged DOI exposure can occur via a process independent of the levels of phospholipase C-coupled G proteins. Studies with a mutant 5-HT2A receptor (F340L) indicated that binding per se is not sufficient for desensitization. Down-regulation of the protein kinase C isozymes alpha and epsilon by overnight exposure to phorbol-12,13-dibutyrate attenuated the intermediate phase (i.e., after 2-6 hr of agonist exposure) of DOI- and quipazine-induced desensitization. These results indicate that the intermediate phase of DOI-induced desensitization is mediated by the alpha- and/or epsilon-protein kinase C isozymes but that neither is involved in the later phase (i.e., after 24 hr of agonist exposure) of desensitization.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA.
B L
BL
Roth
E P
EP
Palvimaki
S
S
Berry
N
N
Khan
N
N
Sachs
A
A
Uluer
M S
MS
Choudhary
D016475:3T3 Cells; D000662:Amphetamines / Q000494:pharmacology; D000818:Animals; D015536:Down-Regulation; D007527:Isoenzymes / Q000378:metabolism; D008024:Ligands; D051379:Mice; D011493:Protein Kinase C / Q000378:metabolism; D011814:Quipazine / Q000494:pharmacology; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000378:metabolism; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D000662:Amphetamines; D007527:Isoenzymes; D008024:Ligands; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; D011814:Quipazine; D011493:Protein Kinase C; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine