Smooth muscle 5-HT2A receptors mediating contraction of porcine isolated proximal stomach strips.
1. The aim of this study was to characterize the 5-HT receptors involved in the 5-HT-induced contraction of longitudinal muscle (LM) strips of porcine proximal stomach. This was done in a classical organ bath set-up for isotonic measurement. 2. The concentration-contraction curve to 5-HT was not modified by 5-HT(3) and 5-HT(4) receptor antagonism. Methysergide, ketanserin and mesulergine antagonized the curve to 5-HT. Concomitantly, increasing concentrations of ketanserin and mesulergine progressively revealed a biphasic nature of the 5-HT curve. Ketanserin antagonized the low-affinity receptor while it did not modify the high-affinity receptor. 3. Tetrodotoxin did not influence the concentration-contraction curve to 5-HT neither in the absence nor presence of ketanserin, indicating that nerves are not involved. 4. Ketanserin competitively antagonized the monophasic concentration-response curve to alpha-Methyl-5-HT, yielding a Schild slope that was not significantly different from unity. After constraining the Schild slope to unity, a pK(B) estimate of 8.23+/-0.90 was obtained. This affinity estimate of ketanserin closely approximates previously reported affinities at 5-HT(2A) receptors. 5. In the presence of ketanserin (0.1 microM; exposing the high-affinity receptor), a wide range of 5-HT receptor antagonists covering all 5-HT receptors known, was tested. Only methysergide and ritanserin inhibited the response to 5-HT, thus expressing affinity for the high-affinity receptor. This did not reveal the identity of the receptor involved. 6 It can be concluded that 5-HT induces pig proximal stomach (LM) contraction via 5-HT(2A) receptors located on smooth muscle. A ketanserin-insensitive phase of contractions could not be characterized between the actually known classes of 5-HT receptors with the pharmacological tools that were used.
Janssen
P
P
Heymans Institute of Pharmacology, Ghent University, Ghent, Belgium.
Prins
N H
NH
Meulemans
A L
AL
Lefebvre
R A
RA
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013270:Stomach / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D013552:Swine
D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists