PMID: 7932207Sep 1, 1994Paper

Multiple alpha 2 adrenergic receptor subtypes. I. Comparison of [3H]RX821002-labeled rat R alpha-2A adrenergic receptors in cerebral cortex to human H alpha2A adrenergic receptor and other populations of alpha-2 adrenergic subtypes

The Journal of Pharmacology and Experimental Therapeutics
A RenouardM J Millan

Abstract

In the present study, we examined the binding of the alpha-2 adrenergic receptor (AR) antagonist [3H]-(2-(2-methoxy-1,4-benzodioxan- 2yl)-2-imidazoline ([3H]RX821002) to alpha-2 AR in rat cerebral cortex (CC) and compared the properties of these sites to those of rat alpha-2A (R alpha-2A) AR in submaxillary gland (SMG), human alpha-2A (H alpha-2A) AR in human platelets and alpha-2B AR in neonatal rat lung. In the presence of guanidinium phosphate, [3H]RX821002 bound with high affinity to a large and homogeneous population of sites in CC (Kd = 0.30 +/- 0.03 nM and Bmax = 271 +/- 7 fmol/mg of protein), SMG (Kd = 0.7 and Bmax = 274), human platelets (Kd = 0.6 nM and Bmx = 189) and neonatal rat lung (kd = 0.9 and Bmax = 161). A total of 34 chemically diverse AR ligands monophasically inhibited the binding of [3H]RX821002 from each site with, for the CC, the most potent ligand being atipamezole (Ki = 0.2 nM). For all ligands, and at each site, Hill coefficients did not differ significantly from unity. Although the profiles of inhibition of [3H]RX821002 were virtually identical in rat CC and SMG, these populations revealed several marked differences to human platelets; the alkaloids, rauwolscine and yohimbine, as well as the benzodio...Continue Reading

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