Regulation of Na,K-adenosine triphosphatase gene expression by sodium ions in cultured neonatal rat cardiocytes

• Published in: The Journal of clinical investigation 1993-10, Vol.92 (4), p.1889-1895
• Main Authors: YAMAMOTO, K, IKEDA, U, SHIMADA, K, SEINO, Y, TSURUYA, Y, OGUCHI, A, OKADA, K, ISHIKAWA, S.-E, SAITO, T, KAWAKAMI, K, HARA, Y
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Biological and medical sciences; Calcium - metabolism; Calcium - pharmacology; Cells, Cultured; Egtazic Acid - pharmacology; Enzyme Induction; Enzymes. Coenzymes. Vitamins. Pigments; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Enzymologic - drug effects; Heart - drug effects; Isoenzymes - biosynthesis; Luciferases - biosynthesis; Macromolecular Substances; Metabolisms and neurohumoral controls; Myocardium - enzymology; Myocardium - metabolism; Ouabain - pharmacology; Rats; Rats, Sprague-Dawley; Recombinant Fusion Proteins - biosynthesis; RNA, Messenger - biosynthesis; Sodium - metabolism; Sodium - physiology; Sodium-Potassium-Exchanging ATPase - biosynthesis; Sodium-Potassium-Exchanging ATPase - genetics; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0021-9738; 1558-8238
• DOI: 10.1172/JCI116781

Na,K-ATPase (Na,K-pump) plays an important role in the regulation of intracellular ion composition. The purpose of this study is to determine whether Na+ regulates the levels of mRNA coding for Na,K-ATPase alpha and beta subunits in cultured neonatal rat cardiocytes. We measured intracellular Na+ levels ([Na+]i) in cardiocytes using a Na(+)-sensitive fluorescence dye (SBFI). 1 mM ouabain caused a significant increase in [Na+]i in cardiocytes; from 12.8 +/- 0.3 to 28.8 +/- 1.8 mM. Exposure of cardiocytes to 1 mM ouabain resulted in a three- to fourfold increase in alpha 1, alpha 2, and alpha 3 mRNA accumulation, and an approximate two-fold increase in beta 1 mRNA accumulation. A maximum elevation was reached at 60 min in both cases. The ouabain-induced alpha 1 mRNA accumulation was still observed in the Ca(2+)-free culture medium. Exposure of cardiocytes to 10 microM monensin in the absence of extracellular Ca2+ also resulted in a threefold increase in alpha 1 mRNA accumulation. The increased alpha 1 mRNA expression by 1 mM ouabain was associated with a fourfold increase in alpha 1 subunit protein accumulation. Transfection experiments with chimeric plasmids containing 5'-flanking sequences of alpha 1, alpha 2, and alpha 3 isoform genes and a luciferase reporter gene revealed that 1 mM ouabain caused a twofold increase in luciferase activity in each alpha system. These results suggest that Na+ directly regulates Na,K-ATPase gene expression in cardiocytes. The transfection study further supports the premise that Na(+)-responsive elements are located within the 5'-flanking sequences of each alpha isoform gene.