The study provides evidence that adenosine receptors couple to Gs proteins in bovine coronary arteries, with NECA acting via a different site or mechanism.
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Indicates receptor-specific Gs coupling by adenosine agonists in bovine coronaries; hypothesis-generating with no immediate clinical implications.
The coupling of adenosine receptor(s) to G proteins was investigated in bovine coronary artery smooth muscle membranes. Western blotting of membrane proteins with specific antisera confirmed the presence of 45- and 52-kDa proteins as alpha-subunits of stimulatory (Gs) protein. Cholera toxin (CT) also ADP ribosylated 45- and 52-kDa proteins. Guanosine 5'-O-(3-thiotriphosphate) (10 nM to 10 microM) stimulated the CT-induced ribosylation, suggesting that the ribosylation can be modulated by the activation of G proteins. 2-Chloroadenosine and (R)-phenylisopropyladenosine produced a concentration (10(-7) to 10(-4) M)-dependent increase in CT-induced ribosylation. These responses were completely blocked by adenosine receptor antagonist 8-sulfophenyltheophylline (10 microM). 5'-(N-ethylcarboxamido)adenosine (NECA) alone or in the presence of 8-cyclopentyl-1,3-dipropylxanthine (50 nM) did not affect the ribosylation. Furthermore, NECA did not counter the effects of 2-chloroadenosine and isoproterenol on CT-induced ribosylation. The data provide evidence for the adenosine receptor(s) coupling to Gs proteins and further suggest a different site or mechanism for the action of NECA in bovine coronary artery.
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Hussain et al. (1992) studied this question.
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