Subcellular distribution and immunocytochemical localization of Na,K-ATPase subunit isoforms in human skeletal muscle.
The expression of Na,K-ATPase isoforms was investigated in human skeletal muscle membranes isolated by subcellular fractionation. The alpha 1, alpha 2, alpha 3 and beta 1 subunits were detectable in membranes prepared from the human soleus muscle. The alpha 1 subunit was largely detected in a fraction enriched with plasma membranes (PM), its abundance in an intracellular membrane fraction (IM) accounted for only 4% of that in the PM fraction. No alpha 1 subunits were detected in membranes of sarcoplasmic reticulum (SR) origin. The PM and IM fractions were enriched with alpha 2 subunits which were less abundant in the SR-enriched fraction. The abundance of alpha 2 molecules within the IM fraction was about 75% of that in the PM fraction when the total protein content for the two fractions was taken into account. Immunocytochemical studies confirmed the localization of the alpha 1 subunit to the muscle cell surface. The alpha 2 subunit was also found to be present in the cell surface but the observation that alpha 2 immunofluorescence was diffusely dispersed throughout the muscle fibre indicated that it was also present intracellularly, consistent with its biochemical localization in the PM and IM membrane fractions. The alpha 3 subunit was detected largely in the PM fraction but the lack of good antibodies to this isoform precluded an analysis of its immunocytochemical localization. The beta 1 subunit was enriched in the PM fraction but was also detected to a modest extent in the IM.(ABSTRACT TRUNCATED AT 250 WORDS)
Hundal
H S
HS
Department of Anatomy and Physiology, University of Dundee, UK.
Maxwell
D L
DL
Ahmed
A
A
Darakhshan
F
F
Mitsumoto
Y
Y
Klip
A
A
D000906:Antibodies; D000918:Antibody Specificity; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000032:analysis* / Q000276:immunology; D046911:Macromolecular Substances; D008566:Membranes / Q000737:chemistry / Q000201:enzymology; D018482:Muscle, Skeletal / Q000737:chemistry / Q000201:enzymology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis* / Q000276:immunology; D013347:Subcellular Fractions / Q000737:chemistry / Q000201:enzymology
D000906:Antibodies; D007527:Isoenzymes; D046911:Macromolecular Substances; D000254:Sodium-Potassium-Exchanging ATPase