Pharmacological characterisation of the agonist radioligand binding site of 5-HT2A, 5-HT2B and 5-HT2C receptors

Abstract

In the present study we compared the affinity of various drugs for the high affinity "agonist-preferring" binding site of human recombinant 5-HT(2A), 5-HT(2B) and 5-HT(2C) receptors stably expressed in monoclonal mammalian cell lines. To ensure that the "agonist-preferring" conformation of the receptor was preferentially labelled in competition binding experiments, saturation analysis was conducted using antagonist and agonist radiolabels at each receptor. Antagonist radiolabels ([3H]-ketanserin for 5-HT(2A) receptor and [3H]-mesulergine for 5-HT(2B) and 5-HT(2C) receptor) bound to a larger population of receptors in each preparation than the corresponding agonist radiolabel ([125I]-DOI for 5-HT(2A) receptor binding and [3H]-5-HT for 5-HT(2B) and 5-HT(2C) receptor binding). Competition experiments were subsequently conducted against appropriate concentrations of the agonist radiolabels bound to the "agonist-preferring" subset of receptors in each preparation. These studies confirmed that there are a number of highly selective antagonists available to investigate 5-HT2 receptor subtype function (for example, MDL 100907, RS-127445 and RS-102221 for 5-HT(2A), 5-HT(2B) and 5-HT(2C) receptors respectively). There remains, however, a lack of highly selective agonists. (-)DOI is potent and moderately selective for 5-HT(2A) receptors, BW723C86 has poor selectivity for human 5-HT(2B) receptors, while Org 37684 and VER-3323 display some selectivity for the 5-HT(2C) receptor. We report for the first time in a single study, the selectivity of numerous serotonergic drugs for 5-HT2 receptors from the same species, in mammalian cell lines and using, exclusively, agonist radiolabels. The results indicate the importance of defining the selectivity of pharmacological tools, which may have been over-estimated in the past, and highlights the need to find more selective agonists to investigate 5-HT2 receptor pharmacology.

Serotonin Receptor 5-HT2BMediates Serotonin-Induced Mechanical Hyperalgesia

“…In addition, a high concentration of SB206553 was required to block ␣-m5-HT action on 5-HT 2C -expressing cells, which suggests that 5-HT 2B is more sensitive to SB206553. The study by Knight et al (2004) had reported that 5-HT 2A antagonist, ketanserin, is also a potent blocker of the 5-HT 2C receptor. Ketanserin did not inhibit 5-HT-induced mechanical hyperalgesia.…”

Regulation of 5-HT2A/C receptors and DOI-induced behaviors by protein kinase Cγ

“…This concentration was chosen based on the membrane binding experiments where the signal to noise ratio was the strongest. Because the affinity of DOI for 5-HT 2C receptors is only about 10-fold greater than the affinity for the 2A site (Appel et al, 1990;Knight et al, 2004;McKenna et al, 1989a), we make the assumption that both 2A and 2C receptor density was being measured. Non-specific binding was defined in the presence of 10 uM ketanserin.…”

Possible Involvement of Endogenous 5-HT in Aggravation of Cerulein-Induced Acute Pancreatitis in Mice

“…6). Five cerulein injections in the control mice increased plasma amylase and lipase levels a These data were referred from two published reports (16,18). Fig.…”