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Na⁺-K⁺-ATPase properties in rat heart and skeletal muscle 3 mo after coronary artery ligation

Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada

Submitted 26 March 2004 ; accepted in final form 6 April 2005

This study was designed to determine whether chronic heart failure (CHF) results in changes in Na⁺-K⁺-ATPase properties in heart and skeletal muscles of different fiber-type composition. Adult rats were randomly assigned to a control (Con; n = 8) or CHF (n = 8) group. CHF was induced by ligation of the left main coronary artery. Examination of Na⁺-K⁺-ATPase activity (means ± SE) 12 wk after the ligation measured, using the 3-O-methylfluorescein phosphatase assay (3-O-MFPase), indicated higher (P < 0.05) levels in soleus (Sol) (250 ± 13 vs. 179 ± 18 nmol·mg protein^–1·h^–1) and lower (P < 0.05) levels in diaphragm (Dia) (200 ± 12 vs. 272 ± 27 nmol·mg protein^–1·h^–1) and left ventricle (LV) (760 ± 62 vs. 992 ± 16 nmol·mg protein^–1·h^–1) in CHF compared with Con, respectively. Na⁺-K⁺-ATPase protein content, measured by the [³H]ouabain binding technique, was higher (P < 0.05) in white gastrocnemius (WG) (166 ± 12 vs. 135 ± 7.6 pmol/g wet wt) and lower (P < 0.05) in Sol (193 ± 20 vs. 260 ± 8.6 pmol/g wet wt) and LV (159 ± 10 vs. 221 ± 10 pmol/g wet wt) in CHF compared with Con, respectively. Isoform content in CHF, measured by Western blot techniques, showed both increases (WG; P < 0.05) and decreases (Sol; P < 0.05) in ₁. For ₂, only increases [red gastrocnemius (RG), Sol, and Dia; P < 0.05] occurred. The ₂-isoform was decreased (LV, Sol, RG, and WG; P < 0.05) in CHF, whereas the ₁ was both increased (WG and Dia; P < 0.05) and decreased (Sol and LV; P < 0.05). For ₃, decreases (P < 0.05) in RG were observed in CHF, whereas no differences were found in Sol and WG between CHF and Con. It is concluded that CHF results in alterations in Na⁺-K⁺-ATPase that are muscle specific and property specific. Although decreases in Na⁺-K⁺-ATPase content would appear to explain the lower 3-O-MFPase in the LV, such does not appear to be the case in skeletal muscles where a dissociation between these properties was observed.

chronic heart failure; sodium-potassium-adenosinetriphosphatase content; activity; isoforms