MODIFICATION OF CARDIAC BETA-ADRENOCEPTOR MECHANISMS BY H2O2

From the role of oxidative stress in cardiac dysfunction, we investiga ted the effect of H2O2 an activated species of oxygen, on beta-adrenoc eptors, G proteins, and adenylyl cyclase activities. Rat heart membran es were incubated with different concentrations of H2O2 before the bio chemical parameters were measured. Both the affinity and density of be ta(1)-adrenoceptors were decreased, whereas the density of tile beta(2 )-adrenoceptors was decreased and the affinity was increased by 1 mM H 2O2. Time- and concentration-dependent biphasic changes in adenylyl cy clase activities in the absence or presence of isoproterenol were obse rved when membranes were incubated with H2O2 however, activation of th e enzyme by isoproterenol was increased or unaltered. The adenylyl cyc lase activities in the absence or presence of forskolin, NaF, and Gpp( NH)p were depressed by H2O2. Catalase alone or in combination with man nitol was able to significantly decrease the magnitude of alterations due to H2O2 The cholera toxin-stimulated adenylyl cyclase activity and ADP ribose labeling of G(s) proteins were decreased by treatment with 1 mM H2O2, whereas G(s) protein activities, as reflected by pertussis toxin-stimulation of adenylyl cyclase and ADP ribosylation, were unal tered. The G(s) and G(i) protein immunoreactivities, estimated by labe ling with respective antibodies, indicate a decrease in binding to the 45-kDa band of G(s) protein. whereas no change in the binding of anti bodies to the 52-kDa band of G(s) protein of the 40-kDa subunit of G(i ) protein was evident when the membranes were treated with 1 mM H2O2. These results suggest that H2O2 in high concentrations may attenuate t he beta-adrenoceptor-linked signal transduction in the heart by changi ng the functions of G(s) proteins and the catalytic subunit of the ade nylyl cyclase enzyme.