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Department of Physiology, College of Medicine, Department of Biomedical Sciences, College of Veterinary Medicine, and Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri 65211
Total creatine (Crtotal = phosphocreatine + creatine) concentrations differ substantially
among mammalian skeletal muscle. Because 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
1 · g
1),
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, whereas CrT mRNA was not different. Creatine uptake
rates differ among skeletal muscle fiber sections in a manner
reasonably assigned to the 58-kDa band of the CrT. Furthermore,
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.
phosphocreatine; insulin; creatine turnover
This article has been cited by other articles:
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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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