Na+,K+-ATPase Na+ Affinity in Rat Skeletal Muscle Fiber Types

Na+,K+-ATPase Na+ Affinity in Rat Skeletal Muscle Fiber Types Previous studies in expression systems have found different ion activation of the Na+/K+-ATPase isozymes, which suggest that different muscles have different ion affinities. The rate of ATP hydrolysis was used to quantify Na+,K+-ATPase activity, and the Na+ affinity of Na+,K+-ATPase was studied in total membranes from rat muscle and purified membranes from muscle with different fiber types. The Na+ affinity was higher (K m lower) in oxidative muscle compared with glycolytic muscle and in purified membranes from oxidative muscle compared with glycolytic muscle. Na+,K+-ATPase isoform analysis implied that heterodimers containing the β1 isoform have a higher Na+ affinity than heterodimers containing the β2 isoform. Immunoprecipitation experiments demonstrated that dimers with α1 are responsible for approximately 36% of the total Na,K-ATPase activity. Selective inhibition of the α2 isoform with ouabain suggested that heterodimers containing the α1 isoform have a higher Na+ affinity than heterodimers containing the α2 isoform. The estimated K m values for Na+ are 4.0, 5.5, 7.5 and 13 mM for α1β1, α2β1, α1β2 and α2β2, respectively. The affinity differences and isoform distributions imply that the degree of activation of Na+,K+-ATPase at physiological Na+ concentrations differs between muscles (oxidative and glycolytic) and between subcellular membrane domains with different isoform compositions. These differences may have consequences for ion balance across the muscle membrane. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Na+,K+-ATPase Na+ Affinity in Rat Skeletal Muscle Fiber Types

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Publisher
Springer-Verlag
Copyright
Copyright © 2010 by Springer Science+Business Media, LLC
Subject
Life Sciences; Human Physiology ; Biochemistry, general
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-010-9237-6
Publisher site
See Article on Publisher Site

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