title: Phospholemman is not required for the acute stimulation of Na⁺-K⁺-ATPase α₂-activity during skeletal muscle fatigue.
abstract: The Na(+)-K(+)-ATPase α2-isoform in skeletal muscle is rapidly stimulated during muscle use and plays a critical role in fatigue resistance. The acute mechanisms that stimulate α2-activity are not completely known. This study examines whether phosphorylation of phospholemman (PLM/FXYD1), a regulatory subunit of Na(+)-K(+)-ATPase, plays a role in the acute stimulation of α2 in working muscles. Mice lacking PLM (PLM KO) have a normal content of the α2-subunit and show normal exercise capacity, in contrast to the greatly reduced exercise capacity of mice that lack α2 in the skeletal muscles. Nerve-evoked contractions in vivo did not induce a change in total PLM or PLM phosphorylated at Ser63 or Ser68, in either WT or PLM KO. Isolated muscles of PLM KO mice maintain contraction and resist fatigue as well as wild type (WT). Rb(+) transport by the α2-Na(+)-K(+)-ATPase is stimulated to the same extent in contracting WT and contracting PLM KO muscles. Phosphorylation of sarcolemmal membranes prepared from WT but not PLM KO skeletal muscles stimulates the activity of both α1 and α2 in a PLM-dependent manner. The stimulation occurs by an increase in Na(+) affinity without significant change in Vmax and is more effective for α1 than α2. These results demonstrate that phosphorylation of PLM is capable of stimulating the activity of both isozymes in skeletal muscle; however, contractile activity alone is not sufficient to induce PLM phosphorylation. Importantly, acute stimulation of α2, sufficient to support exercise and oppose fatigue, does not require PLM or its phosphorylation.
authors.affiliation: Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, Cincinnati, Ohio;
authors.forename: Palanikumar
authors.initials: P
authors.lastname: Manoharan
authors.affiliation: Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio; and.
authors.forename: Tatiana L
authors.initials: TL
authors.lastname: Radzyukevich
authors.affiliation: Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio; and.
authors.forename: Hesamedin
authors.initials: H
authors.lastname: Hakim Javadi
authors.affiliation: Department of Chemistry, University of Cincinnati, Cincinnati, Ohio.
authors.forename: Cory A
authors.initials: CA
authors.lastname: Stiner
authors.affiliation: Department of Chemistry, University of Cincinnati, Cincinnati, Ohio.
authors.forename: Julio A
authors.initials: JA
authors.lastname: Landero Figueroa
authors.affiliation: Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, Cincinnati, Ohio;
authors.forename: Jerry B
authors.initials: JB
authors.lastname: Lingrel
authors.affiliation: Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio; and heinyja@ucmail.uc.edu.
authors.forename: Judith A
authors.initials: JA
authors.lastname: Heiny
mesh_terms: D000818:Animals; D015153:Blotting, Western; D004558:Electric Stimulation; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010805:Physical Conditioning, Animal / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013054:Spectrophotometry, Atomic
chemical_list: D008565:Membrane Proteins; D010750:Phosphoproteins; C069141:phospholemman; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Na+-K+-ATPase α2; fatigue; mammalian skeletal muscle; phospholemman