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Departments of 1 Anatomy and Physiology and 2 Kinesiology, Kansas State University, Manhattan, Kansas 66506-5802
The mechanisms
responsible for the decrements in exercise performance in chronic heart
failure (CHF) remain poorly understood, but it has been suggested that
sarcolemmal alterations could contribute to the early onset of muscular
fatigue. Previously, our laboratory demonstrated that the maximal
number of ouabain binding sites (Bmax) is reduced in the
skeletal muscle of rats with CHF (Musch TI, Wolfram S, Hageman KS, and
Pickar JG. J Appl Physiol 92: 2326-2334, 2002). These reductions may coincide with changes in the
Na+-K+-ATPase isoform (
and
) expression.
In the present study, we tested the hypothesis that reductions in
Bmax would coincide with alterations in the
- and
-subunit expression of the sarcolemmal Na+-K+-ATPase of rats with CHF. Moreover, we
tested the hypothesis that exercise training would increase
Bmax along with producing significant changes in
- and
-subunit expression. Rats underwent a sham operation (sham;
n = 10) or a surgically induced myocardial infarction followed by random assignment to either a control (MI;
n = 16) or exercise training group (MI-T;
n = 16). The MI-T rats performed exercise training (ET)
for 6-8 wk. Hemodynamic indexes demonstrated that MI and MI-T rats
suffered from severe left ventricular dysfunction and congestive CHF.
Maximal oxygen uptake (
O2 max) and endurance capacity (run time to fatigue) were reduced in MI rats compared with sham. Bmax in the soleus and plantaris
muscles and the expression of the
2-isoform of the
Na+-K+-ATPase in the red portion of the
gastrocnemius (gastrocnemiusred) muscle were reduced in MI
rats. After ET,
O2 max and run time
to fatigue were increased in the MI-T group of rats. This coincided
with increases in soleus and plantaris Bmax and the
expression of the
2-isoform in the
gastrocnemiusred muscle. In addition, the expression of the
2-isoform of the gastrocnemiusred muscle was
increased in the MI-T rats compared with their sedentary counterparts.
This study demonstrates that CHF-induced alterations in skeletal muscle
Na+-K+-ATPase, including Bmax and
isoform expression, can be partially reversed by ET.
ouabain; exercise; performance; oxygen uptake; congestive heart failure
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