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Characterisation of a 5-HT(7) binding site in mouse ileum
M Hemedah1, I M Coupar, F J Mitchelson
1Department of Pharmaceutical Biology and Pharmacology, Victorian College of Pharmacy, Monash University (Parkville Campus), 381 Royal Parade, Parkville, Victoria 3052, Australia.
Abstract:
The aim of the present study was to identify 5-hydroxytryptamine(7) (5-HT(7)) binding sites in the mouse ileum, where the presence of mRNA for the receptor has been reported. Studies were performed using [3H]mesulergine, an antagonist with high affinity at 5-HT(7) receptors. In the presence of a combination of masking drugs to inhibit the binding of the radioligand to other receptors at which it has affinity, such as 5-HT(2A), 5-HT(2C) and dopamine D(2) receptors as well as alpha(1)/alpha(2)-adrenoceptors, [3H]mesulergine labelled two sites with pK(D) values of 9.7+/-0.7 and 7.4+/-0.4 and B(max) values of 37.2+/-21.4 and 247.8+/-62.1 fmol mg protein(-1), respectively. Displacement studies also indicated the presence of non-homogenous binding sites, which showed a significant correlation (Pearson correlation factors of 0.91 and 0. 85) with the 5-HT(2C) and 5-HT(7) receptors, respectively. Total binding to the 5-HT(2C) receptor was minimal; <30% of the total specific receptor binding. The antagonist order of affinity at the greater proportion of receptors was: risperidone (pK(i)pindolol (5. 6). This receptor also showed a high affinity for 5-carboxamidotryptamine (5-CT; 10.6) and moderate affinity for (+/-)-2-dipropyl-amino-8-hydroxy-1,2,3,4,-tetrahydronaphthalene (8-OH-DPAT; 7.2), which is typical of the 5-HT(7) receptor profile.
Insights
This study identified 5-hydroxytryptamine(7) (5-HT(7)) binding sites in mouse ileum using [3H]mesulergine. Researchers confirmed the presence of 5-HT(7) receptors and characterized their binding properties.
Area of Science:
- Pharmacology
- Neuroscience
- Gastroenterology
Background:
- The 5-hydroxytryptamine(7) (5-HT(7)) receptor mRNA has been reported in the mouse ileum.
- Understanding receptor binding is crucial for drug development targeting gastrointestinal function.
Purpose of the Study:
- To identify and characterize 5-hydroxytryptamine(7) (5-HT(7)) binding sites in the mouse ileum.
- To investigate the binding affinity and density of these receptors.
Main Methods:
- Radioligand binding assays using [3H]mesulergine, a selective 5-HT(7) receptor antagonist.
- Inhibition of non-specific binding using masking drugs targeting 5-HT(2A), 5-HT(2C), dopamine D(2), and alpha-adrenoceptors.
- Displacement studies to determine receptor affinity and identify binding site characteristics.
Main Results:
- Two distinct binding sites for [3H]mesulergine were identified, with pK(D) values of 9.7 and 7.4.
- Binding site characteristics showed significant correlation with 5-HT(2C) and 5-HT(7) receptors.
- The predominant receptor population exhibited characteristics consistent with the 5-HT(7) receptor profile, including high affinity for 5-carboxamidotryptamine (5-CT).
Conclusions:
- The study successfully identified and characterized 5-HT(7) binding sites in the mouse ileum.
- These findings provide valuable insights into the role of 5-HT(7) receptors in ileum function.
- The characterized binding sites offer potential targets for therapeutic interventions in gastrointestinal disorders.