Effect of dexamethasone on skeletal muscle Na+,K+ pump subunit specific expression and K+ homeostasis during exercise in humans

The effect of dexamethasone on Na+,K+ pump subunit expression and muscle exchange of K+ during exercise in humans was investigated. Nine healthy male subjects completed a randomized double blind placebo controlled protocol, with ingestion of dexamethasone (Dex: 2 x 2 mg per day) or placebo (Pla) for 5 days. Na+,K+ pump catalytic alpha 1 and alpha 2 subunit expression was similar to 17% higher (P < 0.05) and the structural beta 1 and beta 2 subunit expression was similar to 6-8% higher (P < 0.05) after Dex compared with Pla. During one-legged knee-extension for 10 min at low intensity (LI; 18.6 +/- 1.0 W), two moderate intensity (51.7 +/- 2.4 W) exercise bouts (MI1: 5 min; 2 min recovery; MI2: exhaustive) and two high-intensity (71.7 +/- 2.5 W) exercise bouts (HI1: 1 min 40 s; 2 min recovery; HI2: exhaustive), femoral venous K+ was lower (P < 0.05) in Dex compared with Pla. Thigh K+ release was lower (P < 0.05) in Dex compared with Pla in LI and MI, but not in HI. Time to exhaustion in MI2 tended to improve (393 +/- 50 s versus 294 +/- 41 s; P = 0.07) in Dex compared with Pla, whereas no difference was detected in HI2 (106 +/- 10 s versus 108 +/- 9 s). The results indicate that an increased Na+,K+ pump expression per se is of importance for thigh K+ reuptake at the onset of low and moderate intensity exercise, but less important during high intensity exercise.