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Pharmacological Characterization of 5‐Hydroxytryptamine 3 Receptors in Murine Brain and Ileum Using the Novel Radioligand [ 3 H]RS‐42358–197: Evidence for Receptor Heterogeneity
Author(s) -
Bonhaus Douglas W.,
Wong Erik H. F.,
Stefanich Eric,
Kunysz Elizabeth A.,
Eglen Richard M.
Publication year - 1993
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1993.tb09835.x
Subject(s) - radioligand , receptor , neuroscience , biology , chemistry , biochemistry
Previous studies have demonstrated species‐specific differences in 5‐hydroxytryptamine 3 (5‐HT 3 ) receptors, but unequivocal evidence of 5‐HT 3 receptor subtypes, within a species, has not yet been obtained. The purpose of the current study was to test for heterogeneity in 5‐HT 3 receptors in murine tissues. 5‐HT 3 receptors in membranes derived from brain cerebral cortex of CD‐1, C57BI/6, and Swiss Webster mice and ileum of CD‐1 mice were labeled with the 5‐HT 3 receptor antagonist [ 3 H]RS‐42358–197. Structurally diverse competing ligands were then used to characterize the binding site. [ 3 H]RS‐42358‐197 bound with similar affinity in each of the cortical tissues (mean K D = 0.14 n M ; range, 0.06–0.32 n M ) but bound with lower affinity in ileal tissue (2.5 n M ). The density of sites labeled with [ 3 H]RS‐42358–197 ranged from 10.4 fmol/mg of protein in Swiss Webster mouse cortex to 44.2 fmol/mg of protein in Sprague‐Dawley rat cortex. Displacing ligands produced a pharmacologic profile of the [ 3 H]RS‐42358–197 binding site consistent with it being a 5‐HT 3 receptor: ( R )‐YM060 > (S)‐zacopride > (R)‐zaco‐pride > MDL 72222 > 2‐methyl‐5‐HT. However, 10‐fold differences in the affinity of certain ligands were found when comparing 5‐HT 3 binding sites in membranes from cerebral cortex of the different strains of mice and when comparing 5‐HT 3 binding sites in brain and ileal membranes prepared from the CD‐1 mouse strain. Ligands demonstrating selectivity included RS‐42358–197, ( R )‐za‐copride, 1‐( m ‐chlorophenyl) biguanide, ( R )‐YM060, and MDL 72222. These studies demonstrate tissue‐and strain‐dependent differences in murine 5‐HT 3 binding sites. This suggests that 5‐HT 3 receptors exist as multiple subtypes within species and that subtype‐selective 5‐HT 3 ligands may be identified.