Agonist-induced functional desensitization of recombinant human 5-HT2 receptors expressed in CHO-K1 cells.
The desensitization characteristics of recombinant human 5-HT(2A), 5-HT(2B), and 5-HT(2C) receptors (VSV and INI isoforms) stably expressed in CHO-K1 (Chinese hamster ovary) cells was investigated by calcium fluorimetry. Comparative desensitization characteristics of the agonists 5-HT, m-chlorophenylpiperazine (mCPP), and 2,5-dimethoxy-4-iodoamphetamine hydrobromide (DOI) were performed. Human 5-HT(2C (INI)) receptors exhibited a greater degree of desensitization to all agonists tested than edited 5-HT(2C (VSV)) receptors. A 2-hr exposure to 5-HT resulted in a significantly larger reduction in response upon re-exposure to 5-HT at 5-HT(2C (INI)) receptors, as compared to 5-HT(2C (VSV)) receptors (72% and 47% respectively, P < 0.01). Both receptor isoforms were expressed at similar densities. Human 5-HT(2B) receptors exhibited the most dramatic degree of desensitization, with prior exposure to 5-HT reducing subsequent response to 5-HT by 80%, with an extremely rapid time-course (t(1/2) < 5 min). The response at 5-HT(2A) receptors was reduced by 54%. The partial agonists mCPP and DOI also elicited desensitization, generally in line with their relative efficacies at each receptor, but exhibited more rapid kinetic profiles than 5-HT. Heterologous desensitization of an endogenously expressed G(q/11)-coupled purinergic receptor was also examined following preincubation of the cell lines with 10 microM 5-HT. Only stimulation of 5-HT(2C (VSV)) receptors resulted in a profound attenuation of subsequent ATP mediated responses. These results demonstrate differing degrees of both homologous and heterologous desensitization of 5-HT(2) receptors. Additionally, the different desensitization profiles of 5-HT(2C (INI)) and 5-HT(2C (VSV)) receptor may be due to signal transduction differences caused by RNA editing.
Porter
R H
RH
Vernalis Research Ltd, Oakdene Court, 613 Reading Road, Winnersh, Wokingham, RG41 5UA, United Kingdom. richard.porter@roche.com
Malcolm
C S
CS
Allen
N H
NH
Lamb
H
H
Revell
D F
DF
Sheardown
M J
MJ
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D006801:Humans; D010879:Piperazines / Q000494:pharmacology; D011983:Receptors, Purinergic / Q000378:metabolism; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000819:agonists / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D013997:Time Factors; D014162:Transfection
D010879:Piperazines; D011983:Receptors, Purinergic; D011985:Receptors, Serotonin; D011994:Recombinant Proteins; D017366:Serotonin Receptor Agonists; D012701:Serotonin; C015068:1-(3-chlorophenyl)piperazine