Cell specific differences in the protein abundances of GAPDH and Na+,K+-ATPase in skeletal muscle from aged individuals

Abstract Na + , K + -ATPase (NKA) isoforms (α 1 ,α 2 ,α 3 ,β 1 ,β 2 ,β 3 ) are involved in the maintenance of membrane potential and hence are important regulators of cellular homeostasis. Given the age-related decline in skeletal muscle function, we investigated whether the natural physiological process of aging is associated with altered abundance of NKA isoforms (α 1 ,α 2 ,α 3 ,β 1 ,β 2 ,β 3 ) or of the commonly used control protein, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Importantly, measurements were made in both whole muscle or specific fiber types obtained from skeletal muscle biopsies. Seventeen healthy older (AGED, 69.4 ± 3.5 years, mean ± SD) and 14 younger (YOUNG, 25.5 ± 2.8 years) adults underwent a muscle biopsy for biochemical analyses. Comparing homogenates from AGED and YOUNG individuals revealed higher β 3 isoform (p  3 and β 2 isoforms, and more GAPDH in Type II compared with Type I fibers (p   0.05). Compared with the same fiber type in YOUNG, α 1 was greater (Type I) and α 3 lower (Type II), while in both fiber types, β 2 was lower, β 3 greater and GAPDH lower, in muscle from AGED individuals (all p