INTERACTION OF BETA-ADRENOCEPTOR AND ADENOSINE RECEPTOR AGONISTS ON PHOSPHORYLATION - IDENTIFICATION OF TARGET PROTEINS IN MAMMALIAN VENTRICLES

The influence of the adenosine derivatives (-)-N-6-phenylisopropyladen osine (R-PIA, 1 mu M) and 5'-N-ethylcarbox-amidoadenosine (NECA, 1 mu M) on beta-adrenergic stimulated (isoproterenol, 10 nM) phosphorylatio n of sarcolemmal (15 kDa protein), sarcoplasmic reticular (phospholamb an) and myofibrillar proteins (troponin I, C-protein) was studied in i solated P-32-labeled guinea-pig ventricles. The identification of the 15 kDa protein, phospholamban, troponin I and C-protein was based on t heir reaction with specific antibodies. Isoproterenol increased contra ctile parameters (developed tension, rate of tension development, rate of relaxation) and stimulated the phosphorylation state of a 15 kDa p rotein (now named phospholemman), of phospholamban, troponin I and C-p rotein (regarded as regulatory proteins), Isoproterenol concomitantly increased myocardial cyclic AMP levels. R-PIA and NECA attenuated the effects of isoproterenol on contractile parameters as well as on the p hosphorylation of the regulatory proteins without affecting cyclic AMP levels. The effects of I mu M R-PIA and 1 mu M NECA on the isoprotere nol-stimulated phosporylation of regulatory proteins were blocked by t he adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (D PCPX, 1 mu M). Therefore, it is concluded that adenosine derivatives a cting via adenosine receptors can reduce the isoproterenol-stimulated phosphorylation state of the following regulatory proteins: phospholem man, phospholamban, troponin I and C-protein. (C) 1995 Academic Press Limited