Temporal responses of oxidative vs. glycolytic skeletal muscles to K+ deprivation: Na+ pumps and cell cations

Skeletal muscle releases intracellular fluid K+ to buffer the drop in extracellular fluid (ECF) K+ when K+ output exceeds input. To elucidate on the mechanism and muscle specificity of the K+ shift, rats were fed K+-deficient food for 2-10 days and two muscles at phenotypic extremes were studied: slow-twitch oxidative soleus and fast-twitch glycolytic white gatrocnemius. Findings revealed that the patterns of regulation of Na+ pump isoforms in oxidative and glycolytic muscles during K+ deprivation mediated by posttranscriptional regulation of alpha2beta1 and alpha2beta are distinct and that reductions in alpha2-isoform pools can occur early enough in both muscles to explain the shift of K+ to the ECF.