Agonist-induced functional desensitization of recombinant human 5-HT2 receptors expressed in CHO-K1 cells

The desensitization characteristics of recombinant human 5-HT2A, 5-HT2B, an d 5-HT2C receptors (VSV and INI isoforms) stably expressed in CHO-K1 (Chine se hamster ovary) cells was investigated by calcium fluorimetry. Comparativ e desensitization characteristics of the agonists 5-HT, m-chlorophenylpiper azine (mCPP), and 2,5-dimethoxy-4-iodoamphetamine hydrobromide (DOI) were p erformed. Human 5-HT2C(INI) receptors exhibited a greater degree of desensi tization to all agonists tested than edited 5-HT2C(VSV) receptors. A 2-hr e xposure to 5-HT resulted in a significantly larger reduction in response up on re-exposure to 5-HT at 5-MT2C(INI) receptors, as compared to 5-MT2C(VSV) receptors (72% and 47% respectively, P < 0.01). Both receptor isoforms wer e expressed at similar densities. Human 5-HT2B receptors exhibited the most dramatic degree of desensitization, with prior exposure to 5-HT reducing s ubsequent response to 5-HT by 80%, with an extremely rapid time-course (t1/ 2 < 5 min). The response at 5-HT2A receptors was reduced by 54%. The partia l agonists mCPP and DOI also elicited desensitization, generally in line wi th their relative efficacies at each receptor, but exhibited more rapid kin etic profiles than 5-HT. Heterologous desensitization of an endogenously ex pressed G(q/11)-coupled purinergic receptor was also examined following pre incubation of the cell lines with 10 muM 5-MT. Only stimulation of 5-HT2C(V SV), receptors resulted in a profound attenuation of subsequent ATP mediate d responses. These results demonstrate differing degrees of both homologous and heterologous desensitization of 5-HT2 receptors. Additionally, the dif ferent desensitization profiles of 5-HT2C(INI) and 5-HT2C(VSV) receptor may be due to signal transduction differences caused by RNA editing. (C) 2001 Elsevier Science Inc. All rights reserved.