O2delivery and redox state are determinants of compartment-specific reactive O2species in myocardial reperfusion

Abstract

Reperfusion of the ischemic myocardium leads to a burst of reactive O2species (ROS), which is a primary determinant of postischemic myocardial dysfunction. We tested the hypothesis that early O2delivery and the cellular redox state modulate the initial myocardial ROS production at reperfusion. Isolated buffer-perfused rat hearts were loaded with the fluorophores dihydrofluorescein or Amplex red to detect intracellular and extracellular ROS formation using surface fluorometry at the left ventricular wall. Hearts were made globally ischemic for 20 min and then reperfused with either 95% or 20% O2-saturated perfusate. The same protocol was repeated in hearts loaded with dihydrofluorescein and perfused with either 20 or 5 mM glucose-buffered solution to determine relative changes in NADH and FAD. Myocardial O2delivery during the first 5 min of reperfusion was 84.7 ± 4.2 ml O2/min with 20% O2-saturated buffer and 354.4 ± 22.8 ml O2/min with 95% O2( n = 8/group, P < 0.001). The fluorescein signal (intracellular ROS) was significantly increased in hearts reperfused with 95% O2compared with 20% O2. However, the resorufin signal (extracellular ROS) was significantly increased with 20% O2compared with 95% O2during reperfusion. Perfusion of hearts with 20 mM glucose reduced the·NADH during ischemia ( P < 0.001) and the·ROS at reperfusion ( P < 0.001) compared with 5.5 mM-perfused glucose hearts. In conclusion, initial O2delivery to the ischemic myocardium modulates a compartment-specific ROS response at reperfusion such that high O2delivery promotes intracellular ROS and low O2delivery promotes extracellular ROS. The redox state that develops during ischemia appears to be an important precursor for reperfusion ROS production.