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Am J Physiol Cell Physiol (February 5, 2003). doi:10.1152/ajpcell.00484.2002
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Submitted on October 17, 2002
Accepted on January 29, 2003

Creatine uptake and creatine transporter expression among rat skeletal muscle fiber types

Jeffrey J Brault1* and Ronald L Terjung2

1 Department of Physiology, College of Medicine, University of Missouri, Columbia, MO, USA
2 Department of Physiology, College of Medicine, University of Missouri, Columbia, MO, USA; Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, MO, USA; Dalton Cardiovascular Center, University of Missouri, Columbia, MO, USA

* To whom correspondence should be addressed. E-mail: braultj{at}missouri.edu.

Total creatine (Crtotal = phosphocreatine + creatine) concentrations differ substantially among mammalian skeletal muscle. Since the primary means to add Crtotal to muscle is uptake of creatine through the sodium dependent creatine transporter (CrT), differences in creatine uptake and CrT expression could account for the variations in [Crtotal] among muscle fiber types. To test this hypothesis, hindlimbs of adult rats were perfused with 0.05-1 mM [14C]-creatine for up to 90 min. Creatine uptake rates at 1 mM creatine were greatest in the soleus (140 ± 8.8 nmol/h/g), less in the red gastrocnemius (117 ± 8.3) and least in the white gastrocnemius (97 ± 10.7). These rates were unaltered by time, insulin concentration, or increased perfusate sodium concentration. Conversely, creatine uptake rates were correspondingly decreased among fiber types by lower creatine and sodium concentrations. The CrT protein content by Western blot analysis was similarly greatest in the soleus, less in the red gastrocnemius, and least in the white gastrocnemius, while CrT mRNA was not different. Creatine uptake rates differ among skeletal muscle fiber sections in a manner reasonably assigned to the 58 kD band of the CrT. Further, creatine uptake rates scale inversely with creatine content, with the lowest uptake rate in the fiber type with the highest Crtotal and vice versa. This suggests that the creatine pool fractional turnover rate is not common across muscle phenotypes and, therefore, is differentially regulated.




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K. A. Abraham, J. J. Brault, and R. L. Terjung
Phosphate uptake and PiT-1 protein expression in rat skeletal muscle
Am J Physiol Cell Physiol, July 1, 2004; 287(1): C73 - C78.
[Abstract] [Full Text] [PDF]




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