REGULATION OF NA,K-ADENOSINE TRIPHOSPHATASE GENE-EXPRESSION BY SODIUM-IONS IN CULTURED NEONATAL RAT CARDIOCYTES

Citation
K. Yamamoto et al., REGULATION OF NA,K-ADENOSINE TRIPHOSPHATASE GENE-EXPRESSION BY SODIUM-IONS IN CULTURED NEONATAL RAT CARDIOCYTES, The Journal of clinical investigation, 92(4), 1993, pp. 1889-1895
Citations number
48
Categorie Soggetti
Medicine, Research & Experimental
ISSN journal
00219738
Volume
92
Issue
4
Year of publication
1993
Pages
1889 - 1895
Database
ISI
SICI code
0021-9738(1993)92:4<1889:RONTGB>2.0.ZU;2-Z
Abstract
Na,K-ATPase (Na,K-pump) plays an important role in the regulation of i ntracellular ion composition. The purpose of this study is to determin e whether Na+ regulates the levels of mRNA coding for Na,K-ATPase alph a 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 i n [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 alpha1, alpha2, and alpha3 mRNA accumulation, and an approximate t wo-fold increase in beta1 mRNA accumulation. A maximum elevation was r eached at 60 min in both cases. The ouabain-induced alpha1 mRNA accumu lation was still observed in the Ca2+-free culture medium. Exposure of cardiocytes to 10 muM monensin in the absence of extracellular Ca2+ a lso resulted in a threefold increase in alpha1 mRNA accumulation. The increased alpha1 mRNA expression by 1 mM ouabain was associated with a fourfold increase in alpha1 subunit protein accumulation. Transfectio n experiments with chimeric plasmids containing 5'-flanking sequences of alpha1, alpha2, and alpha3 isoform genes and a luciferase reporter gene revealed that 1 mM ouabain caused a twofold increase in luciferas e activity in each alpha system. These results suggest that Na + direc tly regulates Na,K-ATPase gene expression in cardiocytes. The transfec tion study further supports the premise that Na+-responsive elements a re located within the 5'-flanking sequences of each alpha isoform gene .