title: Variable participation of 5-HT1-like receptors and 5-HT2 receptors in serotonin-induced contraction of human isolated coronary arteries. 5-HT1-like receptors resemble cloned 5-HT1D beta receptors.
abstract: BACKGROUND
  Serotonin may contract human large coronary arteries through two 5-hydroxytryptamine (5-HT) receptors, 5-HT1-like and 5-HT2. These 5-HT1-like receptors resemble both cloned 5-HT1D receptor subtypes, 5-HT1D alpha and 5-HT 1D beta. Although these subtypes have similar pharmacology, 5-HT1D beta receptors appear to have lower affinity for ketanserin than 5-HT1D alpha receptors. We assessed the relative participation of 5-HT1-like and 5-HT2 receptors and attempted to identify whether vasoconstrictor 5-HT1-like receptors are 5-HT1D alpha or 5-HT1D beta.
  
  
  RESULTS
  Epicardial coronary arteries were dissected from the hearts of 29 patients (including 1 healthy (donor) undergoing heart transplant operation. Endothelium-denuded strips were set up to contract at 37 degrees C. To assess the relative contributions of 5-HT1-like and 5-HT2 receptors, we blocked the latter with ketanserin (0.1 to 1.0 mumol/L) and ketanserin-resistant receptors with methiothepin (0.1 mumol/L). Concentration-effect curves for 5-HT, in the absence and presence of ketanserin, were analyzed by using a model for two receptor subtypes. The fractional contributions of 5-HT1-like and 5-HT2 receptors to the maximum effect of 5-HT, f1 and f2, were estimated in arteries from 28 patients: f1 (0.71 +/- 0.20, mean +/- SD) was significantly larger than f2 (0.29 +/- 0.20) (P < .0001). Using [3H]-serotonin to label transfected and expressed receptors, we verified that ketanserin has lower affinity for 5-HT1D beta (pKi [-log Ki, mol/L] less than 5.0) than for 5-HT1D alpha (pKi = 7.1 +/- 0.1) receptors. A concentration of ketanserin (1 mumol/L) that would occupy more than 90% of 5-HT1D alpha receptors failed to block 5-HT-induced contractions (4 patients). The 5-HT1-like receptor stimulant sumatriptan evoked maximal contractions that matched f1 and was equipotent with 5-HT through 5-HT1-like receptors (8 patients). No systematic influence of disease, atheroma, or therapy on f1 and f2 was detected.
  
  
  CONCLUSIONS
  Coronary artery contractile 5-HT1-like receptors resemble cloned 5-HT1D beta receptors and predominate over 5-HT2 receptors in mediating serotonin-evoked contractions. Sumatriptan contracts coronary arteries as a full agonist through 5-HT1-like receptors.
authors.affiliation: Clinical Pharmacology Unit, Addenbrooke's Hospital, Cambridge University, England.
authors.forename: A J
authors.initials: AJ
authors.lastname: Kaumann
authors.forename: M
authors.initials: M
authors.lastname: Frenken
authors.forename: H
authors.initials: H
authors.lastname: Posival
authors.forename: A M
authors.initials: AM
authors.lastname: Brown
mesh_terms: D000328:Adult; D001161:Arteriosclerosis / Q000503:physiopathology; D001667:Binding, Competitive; D002311:Cardiomyopathy, Dilated / Q000503:physiopathology; D003001:Cloning, Molecular; D003327:Coronary Disease / Q000503:physiopathology; D003331:Coronary Vessels / Q000187:drug effects*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000503:physiopathology; D011985:Receptors, Serotonin / Q000145:classification / Q000378:metabolism / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D018170:Sumatriptan / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
chemical_list: D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; D018170:Sumatriptan; D007650:Ketanserin