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 ischemi c-reperfused heart, we investigated the effects of H2O2 on the beta-ad renoceptor, G-protein and adenylyl cyclase complex. Rat hearts were pe rfused with 1 mM H2O2 for 10 min before isolating membranes for measur ing the biochemical activities. The stimulation of adenylyl cyclase by different concentrations of isoproterenol was depressed upon perfusin g hearts with H2O2. Both the affinity and density of beta(1)-adrenocep tors as well as the density of the beta(2)-adrenoceptors were decrease d whereas the affinity of beta(2)-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 a lone or in combination with mannitol was able to significantly decreas e the magnitude of alterations due to H2O2. The positive inotropic eff ect of 1 mu M isoproterenol was markedly attenuated upon perfusing hea rts with 200-500 mu M H2O2 for 10 min. These results suggest that H2O2 may depress the beta(1)-adrenoceptor, G(s)-proteins and catalytic sub unit of the adenylyl cyclase enzyme and thus may play an important rol e in attenuating the beta-adrenoceptor linked signal transduction due to ischemia-reperfusion injury.