Characterization of IBE 2254 Binding to Alpha - Adrenergic Receptors on Intact DDT Smooth Muscle Cells: Comparison with Membrane¹ Binding and Correlation with Phosphoinositides Breakdown

Abstract

The binding of the antagonist IBE 2254 (IBE) to α -adrenergic receptors was characterized on intact DDT smooth muscle cells. IBE binding was rapid, reversible, stable and saturable: Bmax = 113000±13000 recetors/cell, K = 110±13 pM (n = 25). Saturation and competition experiments analysed by non linear curve fitting indicated a single population of binding sites with a pharmacological profile typical for α-adrenergic receptors. Antagonists competed for IBE binding sites in the following order: prazosin > phentolamine = phenoxybenzamine > yohimbine. The rank order for agonists was clonidine > epinephrine > norepinephrine > phenylephrine. There was a significant correlation between IBE binding to intact cells, DDT₁ membranes and rat cortex membranes. Neither agonists nor antagonists showed noticeable changes in their affinity for IBE binding on either system. There was also a good correlation between IBE binding and breakdown of phosphoinositides (PI) measured in intact cells.