Characterization of the adenosine receptor in cultured embryonic chick atrial myocytes: Coupling to modulation of contractility and adenylate cyclase activity and identification by direct radioligand binding
Adenosine receptors in a spontaneously contracting atrial myocyte culture from 14-day chick embryos were characterized by radioligand binding studies and by examining the involvement of G-protein in coupling these receptors to a high-affinity state and to the adenylate cyclase and the myocyte contractility. Binding of the antagonist radioligand (3H)-8-cyclopentyl-1,3-diproylxanthine ((3H)CPX) was rapid, reversible and saturable and was to a homogeneous population of sites with a Kd value of 2.1 +/- 0.2 nM and an apparent maximum binding of 26.2 +/- 3 fmol/mg of protein (n = 10, +/- S.E.). Guanyl-5-yl-(beta, gamma-imido)diphosphate had no effect on either the Kd or the maximum binding and CPX reversed the N6-R-phenyl-2-propyladenosine-induced inhibition of adenylate cyclase activity and contractility, indicating that (3H) CPX is an antagonist radioligand. Competition curves for (3H) CPX binding by a series of reference adenosine agonists were consistent with labeling of an A1 adenosine receptor and were better fit by a two-site model than by a one-site model. ADP-ribosylation of the G-protein by the endogenous NAD+ in the presence of pertussis toxin shifted the competition curves from bi to monophasic with Ki values similar to those of the KL observed in the absence of prior pertussis intoxication. The adenosine agonists were capable of inhibiting both the adenylate cyclase activity and myocyte contractility in either the absence or the presence of isoproterenol. The A1 adenosine receptor-selective antagonist CPX reversed these agonist effects. The order of ability of the reference adenosine receptor agonists in causing these inhibitory effects was similar to the order of potency of the same agonists in inhibiting the specific (3H)CPX binding (N6-R-phenyl-2-propyladenosine greater than N6-S-phenyl-2-propyladenosine or N-ethyladenosine-5'-uronic acid).
- Research Organization:
- Brigham and Women's Hospital, Boston, MA (USA)
- OSTI ID:
- 5722903
- Journal Information:
- J. Pharmacol. Exp. Ther.; (United States), Journal Name: J. Pharmacol. Exp. Ther.; (United States) Vol. 249:3; ISSN JPETA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ADENOSINE
ANIMAL CELLS
ANTIGENS
AROMATICS
AZAARENES
BIOCHEMICAL REACTION KINETICS
BODY
CARDIOVASCULAR SYSTEM
CELL CULTURES
CHEMICAL COMPOSITION
CONTRACTION
CYCLASES
ENZYME ACTIVITY
ENZYMES
HEART
HETEROCYCLIC COMPOUNDS
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
LYASES
MATERIALS
MATHEMATICAL MODELS
MEMBRANE PROTEINS
MUSCLES
MYOCARDIUM
NUCLEOSIDES
NUCLEOTIDES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANS
PROTEINS
PURINES
RADIOASSAY
REACTION KINETICS
RECEPTORS
RIBOSIDES
TOXIC MATERIALS
TOXINS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
XANTHINES