Preferential dègradation of the KMnO4-oxidized or N-ethylmaleimide-modified form of sarcoplasmic reticulum ATPase by calpain from chick skeletal muscle

Calpain inhibitor-1 reduces infarct size and DNA fragmentation of myocardium in ischemic/reperfused rat heart

Myocardial ischemia/reperfusion activates a calcium-dependent protease, calpain, in the ischemic myocytes. It is not known whether calpain is involved in the mechanism of ischemia/reperfusion injury in hearts. Thus the purpose of this study was to clarify the effect of a selective calpain inhibitor (CAI) on infarct size and the extent of DNA damage in ischemic/reperfused rat hearts. Rats were divided in four groups (n = 7 each). In saline group, 0.3 ml of saline was administered (i.v.) 10 min before 30-min coronary occlusion followed by 6-h reperfusion. In vehicle group, 0.3 ml of 10% dimethyl sulfoxide (DMSO) was administered 10 min before the 30-min ischemia. CAI (0.5 mg/kg) was administered 10 min before the 30-min ischemia (CAI-A group) and 10 min before the 6-h reperfusion period (CAI-B group). Infarct size was detected with triphenyl tetrazolium chloride, and DNA fragmentation was detected by agarose gel electrophoresis and by in situ nick end labeling (ISEL). Infarct size was significantly smaller in the CAI-A group compared with the vehicle group (13+/-9% vs. 48+/-12%; p < 0.01), and the incidence of ISEL-positive myocyte nuclei in the subendocardial region was significantly reduced in the CAI-A group compared with the vehicle group (26+/-3% vs. 59+/-6%; p < 0.01). However, the effects of CAI in CAI-B group were not significant. Activation of calpain is involved in the mechanism of ischemia/reperfusion injury, and the preischemic administration of CAI was effective in reducing myocardial infarct size and the DNA damage of the myocytes in ischemic/reperfused rat heart.

Calcium-supported calpain degradation rates for cardiac myofibrils in diabetes. Sulfhydryl and hydrophobic interactions

OBJECTIVE

The purpose was to investigate the calcium required for calpain-mediated degradation of selected cardiac myofibril proteins modified by diabetes, sulfhydryl (SH) and hydrophobic reagents.

METHODS

After 20 weeks of streptozotocin-induced (55 mg.kg-1) diabetes, calcium sensitive calpain (1.5 U.ml-1) degradation rates of purified cardiac myofibrillar proteins (1 mg.ml-1) were measured, in vitro, and compared to degradation rates for N-ethylmaleimide (NEM) and 2-p-toluidinylnapthalene-6-sulfonate (TNS) treated samples.

RESULTS

Diabetes (blood glucose of 550 +/- 32 mg.dl-1) reduced the yield of purified myofibrillar protein with minimal change in fibril protein composition. Total SH group reactivities (nmol.mg-1.30min) were 220 +/- 21, 163 +/- 17 and 156 +/- 24 for control, diabetic and NEM-treated (0.5 mM) myofibrils (p < or = 0.05). Calpain degradation rates were faster for all diabetic and SH modified myofibrillar proteins (p < or = 0.05), with a 45 and 35% reduction in the pCa50 for a 37 kDa protein of diabetic and NEM-treated fibril complexes. For control myofibrils, both 100 and 200 uM TNS, reduced calpain degradation rates to a similar extent for all substrate proteins. In contrast, diabetic and NEM-treated samples showed a further reduction in calpain degradation rates with increasing TNS from 100 to 200 uM.

CONCLUSION

Our results support the hypothesis that in diabetes the calcium requirements for calpain degradation rates are reduced and dependent upon sulfhydryl group status and Ca(2+)-induced hydrophobic interactions, implicating a 37 kDa myofbillar-complexed protein.

Increase in the level of m-calpain correlates with the elevated cleavage of filamin during myogenic differentiation of embryonic muscle cells

The activity of Ca(2+)-activated proteinase requiring millimolar Ca2+ (m-calpain) was found to increase dramatically in cultured chick embryonic myoblasts during the early period of myogenic differentiation. Furthermore, the protein level of m-calpain also markedly increased in parallel with the rise in its activity, and both remained elevated thereafter. On the other hand, the activity level of calpastatin, an endogenous inhibitor of the proteinase, remained similar during the entire period of the culture. In addition, the activity of Ca(2+)-activated proteinase requiring micromolar Ca2+ (mu-calpain) was not detected in either proliferating or differentiated myoblasts. Thus, the overall capacity of Ca(2+)-dependent proteolysis is likely to increase in differentiating myoblasts and should be contributed by m-calpain. Filamin (250 kDa), that is known to facilitate actin microfilament assembly and interfere with actin-myosin filament formation, was found to be cleaved in cultured myoblasts to 240 kDa products. This filamin-cleavage occurred in a manner similar to the in vitro cleavage of the cytoskeletal protein by the purified m-calpain. Moreover, the filamin-cleavage was most evident at the period of the cell fusion. Thus, it seems likely that the in vivo cleavage of filamin is mediated by m-calpain. These results suggest that m-calpain may play an important role in cytoskeletal reorganization that is requisite for myoblast fusion.