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)
Roth
B L
BL
Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA.
Palvimaki
E P
EP
Berry
S
S
Khan
N
N
Sachs
N
N
Uluer
A
A
Choudhary
M S
MS
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