Different affinity states of alpha-1 adrenergic receptors defined by agonists and antagonists in bovine aorta plasma membranes

Journal Article · Sun Nov 01 00:00:00 EST 1987 · J. Pharmacol. Exp. Ther.; (United States)

OSTI ID:5607744

Jagadeesh, G; Deth, R C

Evidence for a nonlinear relationship between alpha-1 adrenergic receptor occupancy and tissue responses, together with the finding of different affinity states for agonist binding, has raised the possibility of functional heterogeneity of alpha-1 adrenergic receptors. We have conducted studies to examine: 1) binding characteristics of (/sup 3/H)prazosin, 2) competition of antagonists at these sites and 3) different affinity states of the receptor for agonists and modulation of these states by 5'-guanylylimidodiphosphate (Gpp(NH)p). A plasma membrane-enriched vesicular fraction (F2; 15%/33% sucrose interphase) was prepared from the muscular medial layer of bovine thoracic aorta. (/sup 3/H)Prazosin binding was characterized by a monophasic saturation isotherm (KD = 0.116 nM, Bmax = 112 fmol/mg of protein). Antagonist displacement studies yielded a relative potency order of prazosin greater than or equal to WB4104 much greater than phentolamine greater than corynanthine greater than yohimbine greater than or equal to idazoxan greater than rauwolscine. Competition curves for unlabeled prazosin, WB4101 (2-(2,6-dimethoxyphenoxyethyl)-aminomethyl-1,4 benzodioxane) and phentolamine were shallow and were best modeled to two binding sites with picomolar and nanomolar KD values. Gpp(NH)p was without effect on antagonist affinity. Agonist (epinephrine, norepinephrine and phenylephrine) competition with (/sup 3/H)prazosin binding was biphasic with pseudo-Hill slopes less than 1.0. Binding was best described by a two-site model in which the average contribution of high affinity sites was 23% of total binding. KD values for the high affinity site ranged from 2.9 to 18 nM, and 3.9 to 5.0 microM for the low affinity site.

• Research Organization: Northeastern Univ., Boston, MA
• OSTI ID: 5607744
• Journal Information: J. Pharmacol. Exp. Ther.; (United States), Vol. 243:2
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
SYMPATHOMIMETICS
BIOCHEMICAL REACTION KINETICS
RECEPTORS
AFFINITY
AORTA
CALCIUM
CATTLE
CELL MEMBRANES
IN VITRO
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ALKALINE EARTH METALS
ANIMALS
ARTERIES
AUTONOMIC NERVOUS SYSTEM AGENTS
BLOOD VESSELS
BODY
CARDIOVASCULAR SYSTEM
CELL CONSTITUENTS
DOMESTIC ANIMALS
DRUGS
ELEMENTS
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
MAMMALS
MEMBRANE PROTEINS
MEMBRANES
METALS
ORGANIC COMPOUNDS
ORGANS
PROTEINS
REACTION KINETICS
RUMINANTS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques