Characterization of vascular histamine H1-receptors: Multiple affinity states of aortic histamine H1-receptor
We have shown that [3H]mepyramine labels histamine H1-receptor-binding sites in bovine aortic membranes. Further characterization of H1-receptors in this tissue was done by the interaction of an unlabelled histamine receptor agonist or antagonist, with the radioantagonist [3H]mepyramine-binding sites. The competition-binding assays have uncovered differences in the characteristics of the agonist/receptor interaction not shared by antagonists. Agonists interact in the heterogeneous manner with the radioantagonist-labelled sites, showing shallow competition curves with thenH 0.50–0.72, whereas antagonists were devoid of this effect (steeper slopes of the inhibition curvesnH≈1). The results suggest the presence in this tissue of multiple affinity states of histamine H1-receptor, differentiated by high and low affinity for agonists and the same affinity for antagonists.
KeywordsHistamine Receptor Agonist Steep Slope Histamine Receptor Mepyramine
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