Exercise increases the plasma membrane content of the na+/k+ pump
and its mrna in rat skeletal muscles.
Tsakiridis, Theodoros, Peggy P. C. Wong, Zhi Liu, Carol D. Rodgers,
Mladen Vranic, and Amira Klip.
Division of Cell Biology, The Hospital for Sick Children, Toronto,
Ont., M5G 1X8, Canada; Departments of Physiology and # Medicine,
University of Toronto, Toronto, Ont., M5S 1A8, Canada; and School of
Physical and Health Education, University of Toronto, Toronto, Ont.,
M5S 1A1, Canada
APStracts 2:0507A, 1995.
Muscle fibers adapt to ionic challenges of exercise by increasing the
plasma membrane Na+/K+ pump activity. Chronic exercise training has
been shown to increase the total amount of Na+/K+ pumps present in
skeletal muscle. However, the mechanism of adaptation of the Na+/K+
pump to an acute bout of exercise has not been determined and it is
not known whether it involves alterations in the content of plasma
membrane pump subunits. Here we examine the effect of 1 h treadmill
running (20 m/min, 10% grade) on the subcellular distribution and
expression of Na+/K+ pump subunits in rat skeletal muscles. Red type
I and IIa (red-I/IIa) and white type IIa and IIb (white-IIa/IIb) hind
limb muscles from resting and exercised female Sprague Dawley rats
were removed for subcellular fractionation. By homogenization and
gradient-centrifugation, crude membranes and purified plasma
membranes were isolated and subjected to gel electrophoresis and
immunoblotting using pump subunit specific antibodies. Further, mRNA
was isolated from specific red type I (red-I) and white type IIb
(white IIb) muscles and subjected to Northern blotting using subunit
specific probes. In both red-I/IIa and white-IIa/IIb muscles,
exercise significantly raised the plasma membrane content of the a1
subunit of the pump by 64+/-24% and 55+/-22%, respectively
(P<0.05), and elevated the a2 polypeptide by 43+/-22% and 94+/
-39%, respectively (P<0.05). No significant effect of exercise
could be detected on the amount of these subunits in an internal
membrane fraction or in total membranes. In addition, exercise
significantly increased the a1 subunit mRNA in red-I muscle (by 50+/
-7%, P<0.05) and the b2 subunit mRNA in white-IIb muscles (by
64+/-19%, P<0.01) but the a2 and b1 mRNA levels were unaffected
in this time period. We conclude that increased presence of a1 and a2
polypeptides at the plasma membrane and subsequent elevation of the
a1 and b2 subunit mRNAs may be mechanisms by which acute exercise
regulates the Na+/K+ pump of skeletal muscle.
Received 22 August 1995; accepted in final form 9 November 1995.
APS Manuscript Number A921-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95