Interaction of singlet oxygen with 5′-nucleotidase in rat hearts

This study was aimed to determine whether singlet oxygen (¹O₂) attenuates 5′-nucleotidase activity in the ischemic myocardium. Isolated rat hearts were exposed to either exogenous ¹O₂ produced by irradiating rose bengal or 40-min ischemia and reperfusion. Ecto-5′-nucleotidase activity was inhibited by exogenous ¹O₂ (3.74 ± 0.38 μmol/min/g dry weight), when compared with normal control (7.52 ± 0.41 μmol/min/g dry weight; P < 0.05). The enzymatic activity was significantly preserved by histidine (25 mM) - a ¹O₂ scavenger (7.04 ± 0.61 μmol/min/g dry weight; P < 0.05 v rose bengal group). After ischemia, the activity of ecto-5′-nucleotidase was greatly reduced (2.51 ± 0.25 μmol/min/g dry weight), when compared with normal control. Histidine significantly enhanced ecto-5′-nucleotidase activity (6.55 ± 0.52 μmol/min/g dry weight, P < 0.05 v ischemic control). Adenosine release was consistent with ecto-5′-nucleotidase activity. The time course studies of effects of ¹O₂ on coronary flow, cardiac function, and LDH release revealed that the damage by ¹O₂ to ecto-5′-nucleotidase activity and adenosine release primarily accounted for impaired coronary now cardiac dysfunction, and impaired cardiac metabolism. Lipid peroxidation induced by exogenous ¹O₂ or ischemia was in parallel with ecto-5′-nucleotidase deactivation by ¹O₂. It is concluded that ¹O₂ causes inactivation of ecto-5′-nucleotidase and attenuation of adenosine release which could possibly be one of the important mechanisms of oxygen radical-mediated myocardial injury.