Glucocorticoids increase sodium pump alpha(2)- and beta(1)-subunit abundance and mRNA in rat skeletal muscle

Fourteen-day adrenal steroid treatment increases [H-3]ouabain binding sites 22-48% in muscle biopsies from patients treated with adrenal steroids for chronic obstructive lung disease and in rats treated with dexamethasone (De x). Ouabain binding measures plasma membrane sodium pumps (Na+-K+-ATPase) w ith isoform-dependent affinity. In this study we have established the speci fic pattern of Dex regulation of sodium pump isoform protein and mRNA level s in muscle. Rats were infused with Dex (0.1 mg/kg per day) or vehicle for 14 days. Abundance of sodium pump catalytic alpha (1)- and alpha (2)-subuni ts and glycoprotein beta (1)- and beta (2)-subunits was determined by immun oblot in soleus, extensor digitorum longus, whole gastrocnemius, and diaphr agm and was normalized to the mean vehicle control value. Dex increased alp ha (2) and beta (1) protein in all muscle types by 53-78% and similar to 50 %, respectively. Dex increased alpha (1) protein only in diaphragm (65 +/- 7%). At the mRNA level in whole hindlimb muscle, Dex increased alpha (2) (6 .4 +/- 0.5-fold) and beta (1) (1.54 +/- 0.15-fold) and decreased beta (2) ( to 0.36 +/- 0.6 of control). In summary, alpha (2)beta (1) is the Dex-respo nsive pump in all skeletal muscles, and changes in alpha (2) and beta (1) m RNA levels can drive the 50% change in alpha (2)beta (1)-subunits, which ca n account for the reported increase in [H-3]ouabain binding.