Graduate Thesis Or Dissertation
 

Contractile function and calpain activity in mouse skeletal muscle during hypoxia

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  • Calcium activated proteases, or calpains, are activated in cardiac muscles under conditions of ischemia/reperfusion and hypoxia. Their activity in skeletal muscle under similar conditions is poorly understood. We tested the hypothesis that hypoxia elevates calpain-mediated proteolysis in isolated glycolytic (extensor digitorum longus, EDL) and oxidative (soleus, SOL) mouse muscles studied in vitro at 35°C. Muscles performed a series of work loops during which time the tissue bath was equilibrated with either 95% O2, 5% CO2, or 95% N2, 5% CO2. A sensitive substrate of calpains, α-fodrin, and its calpain-specific 145 and 150 kDa breakdown products were assessed by Western blot. To confirm calpain activity, similar experiments were performed in the presence of E-64d, a calpain inhibitor, or DMSO, the E-64d solvent. We observed that hypoxia increased the levels of α-fodrin-positive 145 and 150 kDa peptides in both EDL and SOL. E-64d treatment during hypoxia prevented this increase. However, inhibition of calpain activity had no effect on peak power output and isometric force of either muscle during exposure to hypoxia. Our results provide compelling evidence that calpain activity is elevated in actively contracting, hypoxic EDL and SOL muscles, while unlike findings in cardiac muscles, we found no conclusive evidence that inhibition of calpain-mediated proteolytic activity improved skeletal muscle function during hypoxia or recovery.
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