Role of H2O2 in changing beta-adrenoceptor and adenylyl cyclase in ischemia-reperfused hearts.

In view of the accumulation of H2O2 in the myocardium due to ischemia-reperfusion and changes in beta-adrenoceptor mechanisms in the ischemic-reperfused heart, we investigated the effects of H2O2 on the beta-adrenoceptor, G-protein and adenylyl cyclase complex. Rat hearts were perfused with 1 mM H2O2 for 10 min before isolating membranes for measuring the biochemical activities. The stimulation of adenylyl cyclase by different concentrations of isoproterenol was depressed upon perfusing hearts with H2O2. Both the affinity and density of beta1-adrenoceptors as well as the density of the beta2-adrenoceptors were decreased whereas the affinity of beta2-adrenoceptors was increased by H2O2 perfusion. Competition curves did not reveal any effect of H2O2 on the proportion of coupled receptors in the high affinity state. The basal as well as forskolin-, NaF- and Gpp(NH)p-stimulated adenylyl cyclase activities were depressed by perfusing the heart with H2O2. Catalase alone or in combination with mannitol was able to significantly decrease the magnitude of alterations due to H2O2. The positive inotropic effect of 1 microM isoproterenol was markedly attenuated upon perfusing hearts with 200-500 microM H2O2 for 10 min. These results suggest that H2O2 may depress the beta1-adrenoceptor, Gs-proteins and catalytic subunit of the adenylyl cyclase enzyme and thus may play an important role in attenuating the beta-adrenoceptor linked signal transduction due to ischemia-reperfusion injury.