Relationship between alpha 1-adrenergic receptor occupancy and response in BC3H-1 muscle cells

Journal Article · Wed Jul 01 04:00:00 EDT 1987 · Mol. Pharmacol.; (United States)

OSTI ID:6216369

Brown, R D; Berger, K D; Taylor, P

The relationship between alpha 1-adrenergic receptor occupancy by agonists or antagonists and the regulation of intracellular Ca/sup 2 +/ was examined. Receptor occupancy was measured using the antagonist (/sup 3/H)prazosin and correlated with agonist-elicited /sup 45/Ca/sup 2 +/ fluxes. The agonists epinephrine (E), norepinephrine (NE), and phenylephrine (PE) coordinately activated Ca/sup 2 +/ efflux, reflecting a substantial mobilization of intracellular Ca/sup 2 +/, as well as a smaller /sup 45/Ca/sup 2 +/ influx. The agonist concentration dependences for influx and efflux were similar, with the order of potency expected for alpha 1 receptors (E greater than or equal to NE greater than PE). To determine the relationship between receptor occupancy and response, the slowly dissociating antagonist prazosin was used to inactivate specified fractions of the receptor population. A linear relationship was observed between the remaining activatable receptors and residual /sup 45/Ca/sup 2 +/ efflux elicited by E or NE, except at saturating agonist concentrations where some curvature was observed. Moreover, the concentration dependence for agonist-elicited /sup 45/Ca/sup 2 +/ efflux was shifted toward slightly higher concentrations of E or NE following prazosin inactivation. These results suggest the presence of a modest receptor reserve which is revealed by E or NE, but not by PE. Agonist occupation was measured over the same interval as receptor activation by competition with the initial rate of (/sup 3/H)prazosin association. All three agonists exhibited the major fraction of receptor occupation over the same concentration ranges required for the functional response. Exposure of receptors to specified agonist concentrations for 30 min had little effect on the number of receptors or their ligand affinities, whereas a 2.5-hr exposure to agonist decreased apparent agonist affinity as well as the number of receptors recognized by (/sup 3/H)prazosin.

• Research Organization: Univ. of California, San Diego, La Jolla
• OSTI ID: 6216369
• Journal Information: Mol. Pharmacol.; (United States), Journal Name: Mol. Pharmacol.; (United States) Vol. 32:1; ISSN MOPMA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AFFINITY
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CALCIUM 45
CALCIUM COMPOUNDS
CALCIUM ISOTOPES
CATIONS
CHARGED PARTICLES
DAYS LIVING RADIOISOTOPES
DRUGS
EVEN-ODD NUCLEI
INTERMEDIATE MASS NUCLEI
IONS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LIGANDS
MAMMALS
MEMBRANE PROTEINS
MEMBRANE TRANSPORT
MICE
MUSCLES
NUCLEI
ORGANIC COMPOUNDS
PROTEINS
RADIOISOTOPES
REACTION KINETICS
RECEPTORS
RODENTS
SYMPATHOLYTICS
SYMPATHOMIMETICS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VERTEBRATES