Abstract

The purpose of this study was to characterize SERCA expression and function in extensor digitorum longus (EDL) and soleus (SOL) muscles from Zuckerfa/fa obese (321±5 g) and lean (233±10 g) control rats (n=6/group). The rate of Ca2+‐uptake in EDL and SOL homogenates was measured spectrofluorometrically using Indo‐1. Maximal Ca2+‐ATPase activity (Vmax) was determined using a 96‐well spectrophotometric assay. When comparing Zucker to control rats, there were no differences (p>0.05) in Vmax in either EDL (592±40 vs. 536±31 μmol/g/min) or SOL (120±12 vs. 120±13). However, Ca2+‐uptake rates were higher (p<0.05) in the SOL from Zuckerfa/fa rats (4.10±0.30 μmol/g/min) when compared to control animals (2.92±0.61 μmol/g/min). In addition, the rate of Ca2+ leak from Ca2+ loaded SR vesicles in the SOL homogenate was lower (p<0.05) in Zuckerfa/fa rats compared to controls. These observations were not mirrored in the EDL. Furthermore, the SERCA1a and SERCA2a contents were not different between genotypes in either tissue. These data suggest that the reduced rate of Ca2+ leak in slow‐twitch skeletal muscle from Zuckerfa/fa rats improves Ca2+‐pumping efficiency and may result in a lower energy cost of Ca2+cycling.Research supported by NSERC Canada

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