Abstract
An assay was developed for [ 3H]zacopride binding to 5-HT 3 specific sites in membranes from rabbit ileum muscularis. The binding was rapid, saturable, reversible, salt-insensitive, unaffected by pH between 6.5 and 9.5, and of high affinity (apparent K D = 0.65 ± 0.15 nM). ICS 205–930, a potent 5-HT 3 antagonist that inhibited competitively, was utilized to define 5-HT 3 specific binding. Other 5-HT 3 antagonists and agonists, although exhibiting marked differences in potency, were also effective inhibitors; whereas, antagonists of other classes of serotonin receptors, guanyl nucleotides and numerous receptor-specific ligands, including peptide hormones, were inactive. Vagus nerve exhibited the greatest amount of 5-HT 3 specific binding amongst rabbit tissues and virtually all of the [ 3H]zacopride was bound to 5-HT 3 binding sites. In rabbit, rat and ferret a fairly uniform distribution of 5-HT 3 binding sites was observed along the muscularis of the small bowel. [ 3H]Zacopride is a high-affinity ligand for detecting 5-HT 3 binding sites and rabbit small bowel muscularis membranes are a sensitive system for evaluating the potency of 5-HT 3 antagonists or agonists.
Published Version
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