Evidence for regulated coupling of A1 adenosine receptors by phosphorylation in Zucker rats

Studies were designed to find the molecular basis for previous observations that lipolysis is less active and A1 adenosine receptor signaling is more active in adipocytes from obese than from lean Zucker rats. With quantitative immunoblot procedures for detection, Gi alpha 1 and Gs alpha 45 levels were found anomalously low in obese compared with lean membranes (50 and 30%, respectively), but other G alpha subunit levels were normal. However, the sensitivity of the receptor-Gi protein to GTP was about 5- to 10-fold higher in obese compared with lean membranes when assessed from 1) the ability of GTP to inhibit forskolin-stimulated adenylyl cyclase in the presence of an adenosine receptor agonist and 2) the ability of a nonhydrolyzable guanine nucleotide analogue to alter A1 adenosine receptor agonist binding. Alkaline phosphatase treatment of isolated adipocyte membranes from obese but not lean animals decreased guanine nucleotide sensitivity of agonist binding. Surprisingly, solubilized adipocyte A1 adenosine receptors from all animals exhibited the same high sensitivity to guanine nucleotides as that of intact obese membranes, and this high sensitivity could be decreased 20-fold by treatment with alkaline phosphatase. These data suggest that protein phosphorylation may regulate coupling of the A1 adenosine receptor in rat adipocyte membranes.

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Adenosine stimulates glycolytic flux in isolated perfused rat hearts by A1-adenosine receptors

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1989.257.6.h1952 ◽

1989 ◽

Vol 257 (6) ◽

pp. H1952-H1957 ◽

Cited By ~ 9

Author(s):

D. A. Wyatt ◽

M. C. Edmunds ◽

R. Rubio ◽

R. M. Berne ◽

R. D. Lasley ◽

...

Keyword(s):

Adenosine Receptor ◽

Adenosine Receptors ◽

Receptor Agonist ◽

Glycolytic Flux ◽

Adenosine Receptor Antagonist ◽

Exogenous Glucose ◽

Rat Hearts ◽

Adenosine Receptor Agonist ◽

Perfused Rat Hearts ◽

A1 Adenosine Receptors

This study was designed to assess the role of adenosine in the regulation of exogenous glucose utilization by myocardium. Perfusion of isolated rat hearts with buffer containing D-[3-3H]glucose and analysis of the coronary effluent for 3H2O production was used as an indicator of glycolytic flux. Initially, glycolytic flux was determined during five different conditions: 1) normoxia; 2) normoxia plus 100 microM adenosine; 3) normoxia plus 100 microM adenosine and 10 microM 8-(sulfophenyl)-theophylline (SPT), an adenosine receptor antagonist; 4) hypoxia; and 5) hypoxia plus 10 microM SPT. Both adenosine and hypoxia produced an approximate threefold increase in glycolytic flux that was attenuated by adenosine receptor blockade with SPT. Next, hearts were perfused during normoxic conditions with various concentrations of either R-phenylisopropyladenosine (PIA), an A1-adenosine receptor agonist, or 5'-N-ethylcarboxamidoadenosine (NECA), an A2-adenosine receptor agonist. Significant increases in glycolytic flux occurred with PIA, whereas NECA treatment resulted in only a marginal stimulation of glycolytic flux. These data provide evidence that: 1) exogenous adenosine stimulated glycolytic flux in the normoxic myocardium; 2) endogenous adenosine stimulated glycolytic flux during hypoxia; and 3) the effect of adenosine on glycolytic flux was mediated by interaction with A1-adenosine receptors.

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INO-8875, a Highly-Selective A1 Adenosine Receptor Agonist: Evaluation of Chronotropic, Dromotropic and Hemodynamic Effects in Rats

Journal of Pharmacology and Experimental Therapeutics ◽

10.1124/jpet.110.169383 ◽

2010 ◽

Cited By ~ 1

Author(s):

M. Mor ◽

A. Shalev ◽

S. Dror ◽

O. Pikovsky ◽

O. Beharier ◽

...

Keyword(s):

Adenosine Receptor ◽

Receptor Agonist ◽

Hemodynamic Effects ◽

A1 Adenosine Receptor ◽

Adenosine Receptor Agonist

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Interactions of purified bovine brain A1-adenosine receptors with G-proteins. Reciprocal modulation of agonist and antagonist binding

Biochemical Journal ◽

10.1042/bj2750651 ◽

1991 ◽

Vol 275 (3) ◽

pp. 651-656 ◽

Cited By ~ 55

Author(s):

M Freissmuth ◽

E Selzer ◽

W Schütz

Keyword(s):

G Proteins ◽

Adenosine Receptor ◽

Adenosine Receptors ◽

Bovine Brain ◽

Detergent Solution ◽

Maximal Effect ◽

A1 Adenosine Receptor ◽

Molar Excess ◽

A1 Adenosine Receptors ◽

Antagonist Binding

The bovine brain A1-adenosine receptor was purified 8000-fold by affinity chromatography on xanthine-amine-congener (XAC)-Sepharose. Addition of a 120-fold molar excess of a purified bovine brain G-protein preparation (Go,i a mixture of Go and Gi, containing predominantly Go) decreases the Bmax of the binding of the antagonist radioligand [3H]XAC to the receptor. This decrease is observed not only after insertion into phospholipid vesicles but also in detergent solution, and is reversed by GTP analogues. In the presence of Go,i, about 20 and 40% of the receptors display guanine-nucleotide-sensitive high-affinity binding of the agonist radioligand (-)-N6-3-([125I]iodo-4-hydroxyphenylisopropyl)adenosine after reconstitution into lipid vesicles and in detergent solution, respectively. The ability of Go,i to enhance agonist binding and decrease antagonist binding is concentration-dependent, with a half-maximal effect occurring at approximately 10-fold molar excess of G-proteins over A1-adenosine receptors. In the presence of the receptor, the rate of guanosine 5′-[gamma-[35S]thio]triphosphate (GTP[35S]) binding to Go,i is accelerated. This rate is further enhanced if the receptor is activated by the agonist (-)(R)-N6-phenylisopropyladenosine, whereas the antagonist XAC decreases the association rate of GTP[35S] to levels observed in the absence of receptor. These results show (1) that detergent removal is not a prerequisite for the observation of coupling between the A1-adenosine receptor and Go,i, and (2) that the regulatory effect of G-proteins on antagonist binding to the A1-adenosine receptor can be reconstituted by using purified components.

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