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Adenosine A1 and A2A receptors regulate GTP binding to G proteins in adrenergic stimulated cardiac membranes
Author(s) -
Fenton Richard A.,
Tikh Eugene I.,
Dobson James G.
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a428-a
Subject(s) - ccpa , gtp' , agonist , cgs 21680 , g protein , chemistry , adenosine , adenosine a1 receptor , gtp binding protein regulators , adenosine receptor , biochemistry , receptor , enzyme
Adenosine protects the heart from adrenergic‐induced necrosis and apoptosis by reducing β 1 receptor (β1R) responses via an adenosine A 1 receptor (A1R)‐mediated antiadrenergic action. Adenosine A 2A receptors (A2AR) inhibit A1R, thereby releasing β1R from inhibition. It is not known if these receptor interactions are apparent at the level of G‐protein signal transduction. The interaction of A1R, A2AR and β1R on GTP binding was studied using crude homogenates of rat hearts. Membranes were incubated in buffer containing [γ‐ 35 S]GTP for 1 hr at 30°C. Membrane‐bound [γ‐ 35 S]GTP captured on glass filters reflects receptor stimulated G‐protein cycling activity. Chlorocyclopentyladenosine (1 μM, CCPA, A1R agonist), CGS‐21680 (1 μM, CGS, A2AR agonist) and isoproterenol (1 μM, ISO, β1R agonist) elicited increases in bound [γ‐ 35 S]GTP representing 222, 214 and 166 pmol/mg protein suggesting enhanced GTP binding to αs‐ and αi‐subunits by β1R/A2AR and A1R, respectively. CGS reduced by 26% the GTP binding‐induced by CCPA. CCPA reduced the ISO‐induced GTP binding by 24%. Similar results were obtained using immunoprecipitation of [γ‐ 35 S]GTP‐bound to Gs α‐subunits. Summary: A2AR inhibit A1R‐mediated GTP binding to the αi subunit; A1R inhibit β1R‐induced GTP binding to the G protein αs subunit. Thus, A1R and A2AR interact early in the signaling cascade to modulate adrenergic responses. (PHS Grants: HL‐66045 & AG‐11491)