Normal skeletal muscle Na+-K+ pump concentration in patients with chronic heart failure

Intrinsic changes in skeletal muscle are being increasingly suspected as part of the underlying cause of exercise intolerance in patients with chronic heart failure (CHF). The objective of the present study was to determine whether differences existed between CHF patients and age-matched healthy controls in the concentration of skeletal muscle Na(+)-K(+)-ATPase (adenosine triphosphatase), a cation pump that functions to restore Na(+)-K(+) gradients and protect membrane excitability. Moreover, given the potency for physical activity in altering long-term regulation of the pump, an additional objective was to examine the role of activity level in pump expression in CHF patients. Na(+)-K(+)-ATPase concentration (pmol/g wet wt) determined in the vastus lateralis muscle of 27 CHF males (ejection fraction, 23 +/- 1.6%), using the vanadate facilitated [(3)H] ouabain binding technique, was not different (264 +/- 10) from 10 sedentary controls (268 +/- 19,P > 0.05). Similarly, no differences (P > 0.05) could be found between female patients (228 +/- 16, n = 7) and controls (243 +/- 13, n = 9). Differences between untrained control (294 +/- 20, n = 7), chronically active (251 +/- 20, n = 9), and trained (252 +/- 16, n = 6) CHF groups in Na(+)-K(+) pump expression were also insignificant. This study indicates that long-term regulation of Na(+)-K(+)-ATPase concentration is not altered in moderate CHF patients, regardless of the history of regular activity. However, the positive correlations (P < 0.05) that were observed between peak aerobic power (VO(2) peak) and Na(+)-K(+)-ATPase (r = 0.422) and VO(2) peak and maximal citrate synthase activity (r = 0.404) suggests a role for the skeletal muscle in explaining exercise intolerance in CHF patients.