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1 Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
* To whom correspondence should be addressed. E-mail: leessj{at}missouri.edu.
The purpose of this investigation was to determine if there is a link between sarcoplasmic reticulum (SR) glycogen status and SR Ca2+ handling. In this investigation, skeletal muscle SR was purified from female Sprague Dawley rats (200-250 g). Glycogen was extracted from the SR purified from one hind limb, while the SR purified from the contra-lateral limb served as control. Prior to removal of the tissue, the animals were anesthetized with an i.p. injection of ketamine (80 mg/kg) and xylazine (10 mg/kg). Both 
-amylase treatment (AM) and removal of EDTA from the homogenization and storage buffers reduced the amount of glycogen associated with the SR (p< 0.05). AM treatment reduced the glycogen phosphorylase content of SR (p< 0.05). In contrast, creatine kinase (CK) and pyruvate kinase (PK) contents were increased following both glycogen extraction protocols (p< 0.05). Under exogenous ATP conditions, both AM and EF treatments resulted in an increase in Ca2+-stimulated ATPase activity when normalized to sarco(endo)plasmic reticulum calcium ATPase (SERCA) content (p< 0.05). CK and PK-supported SR Ca2+ uptake was decreased (p< 0.05) in the AM group when normalized to SERCA and CK or SERCA and PK content, respectively. AM was more effective than the EF for extracting glycogen associated with purified SR. Glycogen extraction alters the yield of purified SR proteins and must be taken into account when investigating SR calcium handling. Removal of glycogen from purified SR causes a change in Ca2+ handing properties as measured by ATPase and uptake activities.
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