Pharmacological characterization of the human 5-HT(4(d)) receptor splice variant stably expressed in Chinese hamster ovary cells.
The recently identified C-terminal splice variant of the human 5-HT(4) receptor, the h5-HT(4(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-HT(4) ligand-induced cyclic AMP production. The pharmacological binding profile determined in competition studies with the specific antagonist [(3)H]-GR113808 revealed a rank order of affinity of 5-HT(4) ligands for the h5-HT(4(d)) receptor that was consistent with those previously reported for other 5-HT(4) receptor isoforms. In adenylyl cyclase functional assays, the h5-HT(4(d)) receptor displayed equipotent coupling for all 5-HT(4) agonists tested (EC(50) in the range of 1 - 6 nM). EC(50) values were lower than those previously obtained with the 5-HT(4(e)) receptor stably expressed in CHO cells indicating that the 5-HT(4(d)) receptor was more efficiently coupled to its effector than the 5-HT(4(e)) receptor isoform. Moreover, in terms of agonist efficacy (E(max)), the benzamide derivative, renzapride displayed full agonist properties at the h5-HT(4(d)) receptor (same E(max) as 5-HT) whereas it was previously shown to be a partial agonist at the h5-HT(4(e)) receptor. A constitutive activity of the h5-HT(4(d)) receptor was observed in CHO cells in the absence of any 5-HT(4) ligand. Surprisingly, two 5-HT(4) ligands, SB204070 and RS39604 which are described as highly potent antagonists in various biological models, revealed partial agonist properties at the h5-HT(4(d)) receptor. We conclude that C-terminal tails of 5-HT(4) receptor isoforms may directly influence their functional properties.
Mialet
J
J
Laboratoire de Cardiologie Cellulaire et Moléculaire, INSERM U-446, Université de Paris-Sud, Faculté de Pharmacie, F-92296 Ch atenay-Malabry, France.
Berque-Bestel
I
I
Sicsic
S
S
Langlois
M
M
Fischmeister
R
R
Lezoualc'h
F
F
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D000242:Cyclic AMP / Q000096:biosynthesis; D006801:Humans; D007211:Indoles / Q000378:metabolism; D020033:Protein Isoforms; D011985:Receptors, Serotonin / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D044422:Receptors, Serotonin, 5-HT4; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000378:metabolism
D007211:Indoles; D020033:Protein Isoforms; D011985:Receptors, Serotonin; D013449:Sulfonamides; D044422:Receptors, Serotonin, 5-HT4; D000242:Cyclic AMP; C082871:GR 113808