8-hydroxy-2-(di-n-propylamino)tetralin-responsive 5-hydroxytryptamine4-like receptor expressed in bovine pulmonary artery smooth muscle cells.
Bovine pulmonary artery smooth muscle (SM) cells express a novel 5-hydroxytryptamine (5-HT) (5-HT4-like) receptor coupled to cAMP accumulation. cAMP radioimmunoassay established the agonist and antagonist profiles of this receptor. 5-HT (EC50 = 91 +/- 33 nM) and 5-methoxytryptamine were equipotent at the SM cell 5-HT receptor and both were more potent than 5-carboxamidotryptamine. Other tryptamine derivatives were less potent but remained full agonists. These findings are consistent with previous reports regarding 5-HT4 and 5-HT4-like receptors in the central nervous system. The most potent antagonists were the antidepressant compounds nortriptyline (IC50 = 177 +/- 153 nM) and zimelidine (IC50 = 202 +/- 101 nM). The 5-HT3 and 5-HT4 antagonist 3-tropanyl-indole-3-carboxylate (ICS 205-930) was also a competitive antagonist at this 5-HT4-like receptor (pA2 = 6.3). Antagonist affinities differed slightly at the SM cell receptor, compared with other 5-HT4 and 5-HT4-like receptors in the central nervous system. Nonetheless, the SM cell 5-HT4-like receptor displayed the same differential antagonist potencies as reported for these other receptors (ICS 205-930 > MDL 72222 and mianserin > ketanserin). 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was the most potent agonist for this 5-HT4-like receptor (EC50 = 6.4 +/- 3.4 nM). 8-OH-DPAT-induced cAMP accumulation could be blocked by ICS 205-930 but not by the 5-HT1A antagonist 1-(2-methoxyphenyl)-4-[4-(2-pthalimido)butyl]piperazine hydrobromide, distinguishing the SM cell 5-HT receptor from 5-HT1A receptors. The mechanism of 5-HT-stimulated cAMP production was also investigated. First, GTP augmented basal and 5-HT-stimulated cAMP accumulation. Second, antisera to the carboxyl terminus of the alpha subunit of Gs, attenuated 5-HT-mediated adenylate cyclase activation. This established that 5-HT-stimulated cAMP accumulation in SM cells required GS. These findings suggest that SM cells express a novel 5-HT4-like receptor positively coupled to adenylate cyclase. An unexpected finding was that 8-OH-DPAT is a potent partial agonist. These studies suggest that there may be heterogeneity among 5-HT4-like receptors.
Becker
B N
BN
Medical Service (Nephrology), Department of Veterans Affairs Medical Center, Durham, North Carolina 27705.
Gettys
T W
TW
Middleton
J P
JP
Olsen
C L
CL
Albers
F J
FJ
Lee
S L
SL
Fanburg
B L
BL
Raymond
J R
JR
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation; D006868:Hydrolysis; D007211:Indoles / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D011651:Pulmonary Artery / Q000378:metabolism*; D011863:Radioimmunoassay; D011985:Receptors, Serotonin / Q000096:biosynthesis* / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology; D000077526:Tropisetron; D010738:Type C Phospholipases / Q000378:metabolism
D007211:Indoles; D010716:Phosphatidylinositols; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; D000077526:Tropisetron; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000242:Cyclic AMP; D010738:Type C Phospholipases; D000262:Adenylyl Cyclases