EFFECTS OF ADENOSINE-ANALOGS ON ADP RIBOSYLATION OF GS PROTEIN IN CORONARY-ARTERY

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 (G(s)) protein. Cholera toxin (CT) also ADP ribosylated 45- and 52-kDa proteins. Guanosine 5'-O-(3-thiotriphosphate) (10 nM to 10-mu-M) sitmulated 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-mu-M). 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 G(s) proteins and further suggest a different site or mechanism for the action of NECA in bovine coronary artery.