The concentration of sodium,potassium pumps in chronic obstructive lung disease (COLD) patients: the impact of magnesium depletion and steroid treatment

Abstract

To evaluate the concentrations of magnesium (Mg), potassium (K) and sodium,potassium pumps (Na,K pumps) in skeletal muscle in patients with chronic obstructive lung disease (COLD) treated with or without diuretics. An open cross-sectional study. COLD patients admitted to the Medical Department of Vejle Hospital, Denmark. Thirty-six consecutive COLD patients and 23 age- and sex-matched controls. Biopsies of skeletal muscle were performed in patients and controls for measurements of Mg, K and Na,K pumps. In a parallel animal experiment the influence of medical treatment on the concentration of Na,K pumps in skeletal muscle was evaluated by infusing 10-week-old rats for 14 days with vehicle, terbutaline, or dexamethasone. In the patients, mean muscle Mg and K concentrations were reduced by 22 and 14% respectively (P < 0.001), but in those patients who received diuretics muscle Mg and K were further reduced (by 31 and 27%, respectively, of the control values). The concentration of Na,K pumps was increased by 31% (P < 0.001), with a maximum increase of 61% (P < -0.001) in 12 intensive care patients receiving high dosages of glucocorticoids. Linear regression analysis showed a positive correlation between daily glucocorticoid intake and the concentration of Na,K pumps in the biopsy specimens from each patient (r = 0.38, P = 0.02). In the experimental study, dexamethasone induced 27-34% increase in the concentration of Na,K pumps (P < 0.01) in three different muscles, whereas there was no significant change following terbutaline infusion. COLD patients show reduced concentrations of Mg and K in skeletal muscle, associated with an upregulation of the Na,K pump concentration. It is plausible that this upregulation may be caused by glucocorticoid treatment. The clinical benefits of glucocorticoids may in part be due to an increase in the activity and capacity of the Na,K pump and thereby in a possible enhancement of muscle force.