Pharmacological characterization of the human 5-HT 4(d) receptor splice variant stably expressed in Chinese hamster ovary cells

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Mialet, Jeanne | Berque-Bestel, Isabelle | Sicsic, Sames | Langlois, Michel | Fischmeister, Rodolphe | Lezoualc'H, Frank

Edité par CCSD ; Wiley -

International audience. The recently identified C-terminal splice variant of the human 5-HT4 receptor, the h5-HT4(d) receptor, was stably expressed in a CHO cell line at 493±25 fmol mg−1 protein. We analysed its pharmacological properties by measuring binding affinities and 5-HT4 ligand-induced cyclic AMP production.The pharmacological binding profile determined in competition studies with the specific antagonist [3H]-GR113808 revealed a rank order of affinity of 5-HT4 ligands for the h5-HT4(d) receptor that was consistent with those previously reported for other 5-HT4 receptor isoforms.In adenylyl cyclase functional assays, the h5-HT4(d) receptor displayed equipotent coupling for all 5-HT4 agonists tested (EC50 in the range of 1–6 nM). EC50 values were lower than those previously obtained with the 5-HT4(e) receptor stably expressed in CHO cells indicating that the 5-HT4(d) receptor was more efficiently coupled to its effector than the 5-HT4(e) receptor isoform. Moreover, in terms of agonist efficacy (Emax), the benzamide derivative, renzapride displayed full agonist properties at the h5-HT4(d) receptor (same Emax as 5-HT) whereas it was previously shown to be a partial agonist at the h5-HT4(e) receptor.A constitutive activity of the h5-HT4(d) receptor was observed in CHO cells in the absence of any 5-HT4 ligand. Surprisingly, two 5-HT4 ligands, SB204070 and RS39604 which are described as highly potent antagonists in various biological models, revealed partial agonist properties at the h5-HT4(d) receptor.We conclude that C-terminal tails of 5-HT4 receptor isoforms may directly influence their functional properties.

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