title: The cardiac glycoside binding site on the Na,K-ATPase alpha2 isoform plays a role in the dynamic regulation of active transport in skeletal muscle.
abstract: The physiological significance of the cardiac glycoside-binding site on the Na,K-ATPase remains incompletely understood. This study used a gene-targeted mouse (alpha2(R/R)) which expresses a ouabain-insensitive alpha2 isoform of the Na,K-ATPase to investigate whether the cardiac glycoside-binding site plays any physiological role in active Na(+)/K(+) transport in skeletal muscles or in exercise performance. Skeletal muscles express the Na,K-ATPase alpha2 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 alpha2(R/R) 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 alpha2(R/R) mice transported 70.0 nmol/g.min more (86)Rb 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 (86)Rb transport. Additionally, the alpha2(R/R) 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 alpha2 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.
authors.affiliation: Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0576, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Radzyukevich
authors.forename: J B
authors.initials: JB
authors.lastname: Lingrel
authors.forename: J A
authors.initials: JA
authors.lastname: Heiny
mesh_terms: D000818:Animals; D001665:Binding Sites; D001693:Biological Transport, Active; D002301:Cardiac Glycosides / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D051379:Mice; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D002301:Cardiac Glycosides; D007527:Isoenzymes; D000254:Sodium-Potassium-Exchanging ATPase