Functional characterisation of the human cloned 5-HT7 receptor (long form); antagonist profile of SB-258719.
1. The functional profile of the long form of the human cloned 5-HT7 receptor (designated h5-HT7(a)) was investigated using a number of 5-HT receptor agonists and antagonists and compared with its binding profile. Receptor function was measured using adenylyl cyclase activity in washed membranes from HEK293 cells stably expressing the recombinant h5-HT7(a) receptor. 2. The receptor binding profile, determined by competition with [3H]-5-CT, was consistent with that previously reported for the h5-HT7(a) receptor. The selective 5-HT7 receptor antagonist SB-258719 ((R)-3,N-Dimethyl-N-[1-methyl-3-(4-methylpiperidin-1-yl)propyl]ben zene sulfonamide) displayed high affinity (pKi 7.5) for the receptor. 3. In the adenylyl cyclase functional assay, 5-CT and 8-OH-DPAT were both full agonists compared to 5-HT and the rank order of potency for agonists (5-CT > 5-HT > 8-OH-DPAT) was the same in functional and binding studies. 4. Risperidone, methiothepin, mesulergine, clozapine, olanzapine, ketanserin and SB-258719 antagonised surmountably 5-CT-stimulated adenylyl cyclase activity. Schild analysis of the antagonism by SB-258719 gave a pA2 of 7.2+/-0.2 and slope not significantly different from 1, consistent with competitive antagonism. 5. The same antagonists also inhibited basal adenylyl cyclase activity with a rank order of potency in agreement with those for antagonist potency and binding affinity. Both SB-258719 and mesulergine displayed apparent partial inverse agonist profiles compared to the other antagonists tested. These inhibitory effects of antagonists appear to be 5-HT7 receptor-mediated and to reflect inverse agonism. 6. It is concluded that in this expression system, the h5-HT7(a) receptor shows the expected binding and functional profile and displays constitutive activity, revealing inverse agonist activity for a range of antagonists.
Thomas
D R
DR
Department of Neuroscience Research, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Harlow, Essex.
Gittins
S A
SA
Collin
L L
LL
Middlemiss
D N
DN
Riley
G
G
Hagan
J
J
Gloger
I
I
Ellis
C E
CE
Forbes
I T
IT
Brown
A M
AM
D000262:Adenylyl Cyclases / Q000378:metabolism; D002460:Cell Line; D003001:Cloning, Molecular; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D010880:Piperidines / Q000494:pharmacology*; D011485:Protein Binding; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology*; D013449:Sulfonamides / Q000494:pharmacology*; D000096926:Benzenesulfonamides
D000262:Adenylyl Cyclases; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010880:Piperidines; D011985:Receptors, Serotonin; D011994:Recombinant Proteins; D012702:Serotonin Antagonists; D013449:Sulfonamides; C111309:3,N-dimethyl-N-(1-methyl-3-(4-methylpiperidin-1-yl)propyl)benzenesulfonamide; D000096926:Benzenesulfonamides; C104425:serotonin 7 receptor