Pharmacological characterization of a serotonin receptor (5-HT7) stimulating cAMP production in human corneal epithelial cells.
OBJECTIVE
To study the mRNA and pharmacology of a serotonin (5-HT) receptor positively coupled to adenylyl cyclase in normal, primary (P-CEPI), and immortalized human corneal epithelial cells (CEPI-17-CL4), by using numerous 5-HT agonists and antagonists. To determine and compare cloned human 5-HT7 receptor binding affinities of compounds with their functional potency data.


METHODS
RT-PCR was used to detect the presence of an mRNA for the human 5-HT7 receptor in CEPI-17-CL4 cells. Receptor-mediated production of cAMP in cultured cells was measured using an enzyme immunoassay. Compound binding affinities were determined using [3H]-lysergic acid diethylamide ([3H]-LSD) binding to cell membranes of human embryonic kidney (HEK-293) cells expressing the cloned human 5-HT7 receptor.


RESULTS
RT-PCR revealed the presence of a 5-HT7 receptor mRNA in CEPI-17-CL4 cells. Normal P-CEPI cells generated cAMP in response to 5-HT (-log EC50; pEC50=7.6), 5-carboxamidotryptamine (5-CT; pEC50=7.8), 5-methoxy-tryptamine (pEC50=7.0) and 5-methoxy-dimethyl-tryptamine (pEC50=5.7). In CEPI-17-CL4 cells, serotonergic agonists also stimulated cAMP production with different potencies (pEC50): 5-CT (7.4)>5-HT (6.5)> or =5-methoxy-tryptamine (6.1)>5-methoxy-dimethyl-tryptamine (5.4)> or =8-OH-DPAT (<5.0)=alpha-methyl-5-HT (<5.0). Various 5-HT receptor antagonists inhibited cAMP production induced by 5-CT in CEPI-17-CL4 cells with different potencies (pKi): methiothepin (8.5)>mesulergine (8.1)=metergoline (8.0)>spiperone (7.4)> or =clozapine (7.2)=SB-258719 (7.2)>mianserin (6.9)>ketanserin (6.3). Antagonist pKi values in P-CEPI cells were methiothepin (8.7), spiperone (7.4) and SB-258719 (6.6). The rank order of affinity for displacement of [3H]-LSD from the cloned human 5-HT7 receptor was: methiothepin>ritanserin>mesulergine=clozapine> or =metergoline=5-HT>SB-258719> or =spiperone>mianserin> or =ketanserin. The functional agonist and antagonist potency data obtained from CEPI-17-CL4 cells correlated well with cloned human 5-HT7 receptor binding affinity data (r=0.69), with P-CEPI cell functional data (r=0.85), and with functional potency data in the literature for the cloned human 5-HT7 receptor (r=0.88).


CONCLUSIONS
These collective data support the presence of a pharmacologically defined, adenylyl cyclase-coupled 5-HT7 receptor in the CEPI-17-CL4 cells that may have relevance to physiological and/or pathologic functions of 5-HT7 receptors in the human cornea.
Molecular Pharmacology Unit, Alcon Research, Ltd, Fort Worth, Texas 76134-2099, USA.
Julie Y
JY
Crider
Gary W
GW
Williams
Colene D
CD
Drace
Parvaneh
P
Katoli
Michelle
M
Senchyna
Najam A
NA
Sharif
D000262:Adenylyl Cyclases / Q000378:metabolism; D000328:Adult; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000096:biosynthesis*; D019573:Epithelium, Corneal / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000196:embryology; D008238:Lysergic Acid Diethylamide / Q000378:metabolism; D008875:Middle Aged; D012333:RNA, Messenger / Q000378:metabolism; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*
D012333:RNA, Messenger; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; C104425:serotonin 7 receptor; D008238:Lysergic Acid Diethylamide; D000242:Cyclic AMP; D000262:Adenylyl Cyclases