CALPAIN-MU IS ACTIVATED IN HEPATOCYTE MITOCHONDRIA DURING ISCHEMIA-REPERFUSION INJURY

Mitochondrial permeability transition (MMPT), a rapid increase in the permeability of the inner mitochondrial membrane to low molecular weig ht solutes, plays a predominant role in ischemia-reperfusion injury of hepatocytes. Calpain, a Ca2+-dependent neutral proteinase (EC 3, 4, 2 2, 17) has been considered to be involved in the induction of MMPT, bu t its activation in mitochondria remains to be proven. By immunoelectr on microscopic study with antibodies that specifically recognize the p ro-enzyme and intermediate (activated) forms of calpain-mu, its activa tion at mitochondria was investigated in a 15-min ischemia model of ra t liver. Activated calpain-mu was not detected in hepatocytes before i schemia, but was observed primarily in mitochondria 15 min after reper fusion. In contrast, the pro-enzyme form of calpain-mu was detected eq ually throughout the cytoplasm before ischemia, and no significant cha nge was observed after reperfusion. This data provides the direct evid ence that calpain-mu was activated in mitochondria during the ischemia -reperfusion injury of the liver. (C) 1998 Elsevier Science Ireland Lt d. All rights reserved.