Creatine uptake and creatine transporter expression among rat skeletal muscle fiber
types.
Brault, Jeffrey J., and Ronald L. Terjung.
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
APStracts 10:0058C, 2003.
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 to 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«minus»1•g«minus»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.
Received 17 October 2002; accepted in final form 29 January 2003
APS Manuscript Number C484-2.
Article publication pending Am J Physiol Cell Physiol
ISSN 1080-4757 Copyright 2003 The American Physiological Society.
Published in APStracts on 25 March 2003