The cardiac glycoside binding site on the Na,K-ATPase [alpha]2 isoform plays a role in the dynamic regulation of active transport in skeletal muscle

The physiological significance of the cardiac glycoside-binding site on the Na,K-ATPase remains incompletely understood. This study used a gene-targeted mouse (α...) which expresses a ouabain-insensitive α2 isoform of the Na,K-ATPase to investigate whether the cardiac glycoside-binding site plays any physiological role in active .../... transport in skeletal muscles or in exercise performance. Skeletal muscles express the Na,K-ATPase α2 isoform at high abundance and regulate its transport over a wide dynamic range under control of muscle activity. Na,K-ATPase active transport in the isolated extensor digitorum longus (EDL) muscle of α2... mice was lower at rest and significantly enhanced after muscle contraction, compared with WT. During the first 60 s after a 30-s contraction, the EDL of α2.../R mice transported 70.0 nmol/g*min more ... than WT. Acute sequestration of endogenous ligand(s) in WT mice infused with Digibind to sequester endogenous cardiac glycoside(s) produced similar effects on both resting and contraction-induced ... transport. Additionally, the α2... mice exhibit an enhanced ability to perform physical exercise, showing a 2.1- to 2.8-fold lower failure rate than WT within minutes of the onset of moderate-intensity treadmill running. Their enhanced exercise performance is consistent with their enhanced contraction-induced Na,K-ATPase transport in the skeletal muscles. These results demonstrate that the Na,K-ATPase α2 isozyme in skeletal muscle is regulated dynamically by a mechanism that utilizes the cardiac glycoside-binding site and an endogenous ligand(s) and that its cardiac glycoside-binding site can play a physiological role in the dynamic adaptations to exercise. (ProQuest: ... denotes formulae/symbols omitted.)