CALPAIN IS IMPLICATED IN RAT MYOCARDIAL INJURY AFTER ISCHEMIA OR REPERFUSION

Calpain activity was measured in the various subfractions of rat myoca rdia after global ischemia for 60 min or after ischemia followed by 30 min of reperfusion after the chromatographic separation of mu- and m- calpains. The activity of m-calpain after ischemia and that of mu-calp ain after reperfusion were both higher than that in the control. The a ctivity of the endogenous calpain inhibitor calpastatin in 10,000Xg su pernatant was decreased after both ischemia and ischemia-reperfusion. The increase in m- and mu-calpain activities was suppressed by pre-isc hemic perfusion with a synthetic calpain inhibitor, transepoxysuccinyl -L-leucylamido (4-guanidino) butane (E64d, 100 mu g/ml). After reperfu sion, the calpain activity in the 10,000Xg pellet was also increased, which was inhibited by pre-ischemic perfusion with E64d or dimethylsul foxide (a solvent for E64d) or by reperfusion with 1 mmol/L ethylenegl ycol bis (beta-aminoethylether)-N, N, N', N'-tetraacetic acid. SDS-pol yacrylamide gel electrophoresis revealed the proteolysis of several pr oteins, including fodrin, in the 10,000Xg and 100,000Xg pellet fractio ns after ischemia and reperfusion, some of which were confirmed to be in vitro substrates of calpain. The creatine kinase release during the reperfusion was also partially inhibited by E64d or dimethylsulfoxide . Thus, calpain activity in the soluble or particulate fractions was a ltered during ischemia or reperfusion, and appeared to be implicated i n the proteolysis of the membrane proteins, which may contribute to my ocardial