Role of extracellular Ca2+ in ischemia-reperfusion injury in the isolated perfused rat liver.

The influx of extracellular Ca2+ has been postulated to be one of the mediators of ischemia-reperfusion injury. A possible link between Ca2+ influx and oxygen radical generation has also been suggested. In the present study, using the isolated perfused rat liver, we evaluated the role of extracellular Ca2+ on oxygen radical generation, liver damage, and lipid peroxidation during 30 min ischemia and 60 min of reperfusion. Oxygen radical generation in the liver was continuously monitored by lucigenin-enhanced chemiluminescence. Liver damage and lipid peroxidation were evaluated by measuring lactate dehydrogenase (LDH) and thiobarbituric acid reactive substances (TBARS) release into the effusate, respectively. In the absence of extracellular Ca2+ (much less than 30 microM) oxygen radical generation from the liver increased gradually over 2 hr and there were concomitant increases in LDH and TBARS release. When livers were made ischemic and then reperfused, oxygen radical generation increased at the onset of reperfusion and then decreased over 30 min of reperfusion. After 30 min of reperfusion, livers reperfused with low Ca2+ buffer showed a linear increase in oxygen radical generation as well as progressive increases in LDH and TBARS release. On the other hand, livers reperfused with Ca2+ containing (1.25 mM) buffer showed no further increase in oxygen radical generation and no evidence of progressive liver damage and lipid peroxidation. These results suggest that Ca2+ overload is not a primary cause of liver ischemia-reperfusion injury and that the presence of extracellular Ca2+ during reperfusion is necessary to maintain normal liver function.