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 × 2 mg per day) or placebo (Pla) for 5 days. Na⁺,K⁺ pump catalytic α1 and α2 subunit expression was ∼17% higher ( P < 0.05) and the structural β1 and β2 subunit expression was ∼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.