Rat skeletal muscle in culture expresses the α1 but not the α2 protein subunit isoform of the Na+/K+ pump

Orna Sharabani-Yosef, Asia Bak, Leah Langzam, Zhi Lui, Uri Nir, Liora Braiman, Kathleen J. Sweadner, Sanford R. Sampson

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24 Scopus citations

Abstract

Studies from this laboratory have shown that the physiological expression of the Na+/K+ pump in primary cultures of rat skeletal muscle increases with development. The molecular mechanisms underlying these changes are not known. Therefore, we have examined the expression of α and β subunits of the Na+/K+ pump at both the protein and mRNA levels during myogenesis of primary skeletal muscle cell cultures obtained from newborn rats. Protein isoforms were identified by Western blotting techniques with specific monoclonal and polyclonal antibodies and subunit mRNA was studied with specific cDNA probes. Freshly isolated skeletal muscle from newborn rats expressed both α1 and α2 protein subunits. From day 1 after plating, primary cultures expressed only the α1 protein isoform. In contrast, both β1 and β2 isoforms were expressed in freshly isolated muscle and in primary cultures, with β1 expression being stronger in both preparations. Studies on RNA expression showed that mRNA for α1, α2, β1, and β2 isoforms was identified both in freshly isolated muscle and after plating of cells in culture. These findings indicate that the lack of α2 protein expression in primary muscle cell cultures reflects a form of posttranscriptional regulation. There did not appear to be a quantitative difference in isoform expression as a function of age or of fusion in spite of developmental increases in Na+/K+ pump activity and its dependence on cell fusion. The lack of expression of the α2 subunit isoform suggests that the developmental changes in physiological expression of the Na+/K+ pump in primary cultures of skeletal muscle may be attributable either to the changes in activity of the α1 subunit or to differential activities of αβ complexes involving either of the β subunits.

Original languageEnglish
Pages (from-to)236-244
Number of pages9
JournalJournal of Cellular Physiology
Volume180
Issue number2
DOIs
StatePublished - Aug 1999

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