Sodium ion mediated regulation of Na/K-ATPase gene expression in vascular smooth muscle cells.
OBJECTIVE
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 isoforms in cultured rat vascular smooth muscles cells.


METHODS
Na/K-ATPase alpha and beta isoform mRNA expression was evaluated by northern blot analysis. The alpha 1 subunit content was determined by ELISA. A luciferase reporter gene assay was performed to study whether the alpha 1 promoter might contain Na+ responsive elements.


RESULTS
Na/K-ATPase alpha 1 and beta 1 isoform mRNAs, but not alpha 2 and alpha 3 isoform mRNAs, were expressed in cultured rat vascular smooth muscle cells. Exposure of the cells to 10 microM veratridine, an Na+ channel activator, resulted in two- and threefold increases in alpha 1 and beta 1 mRNA accumulation, respectively, with a maximum at 60 min. The veratridine induced alpha 1 and beta 1 mRNA accumulation was still observed even in the absence of extracellular Ca2+. The increase in alpha 1 mRNA accumulation caused by 10 microM veratridine was associated with a significant increase in alpha 1 subunit protein accumulation. Transfection experiments with chimeric plasmids containing 5'-flanking sequences of alpha 1 isoform gene and luciferase reporter gene showed that 10 microM veratridine caused a threefold increase in luciferase activity.


CONCLUSIONS
These results suggest that Na+ stimulates the transcription of Na/K-ATPase alpha 1 and beta 1 isoform genes in vascular smooth muscle cells. The transfection study further supports the premise that Na+ responsive elements are located within the 5'-flanking sequences of alpha 1 isoform gene.
Jichi Medical School, Tochigi, Japan.
K
K
Yamamoto
U
U
Ikeda
K
K
Okada
T
T
Saito
K
K
Kawakami
K
K
Shimada
D000818:Animals; D015152:Blotting, Northern; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D007477:Ions; D007527:Isoenzymes; D008156:Luciferases / Q000378:metabolism; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics*; D014162:Transfection; D014701:Veratridine / Q000494:pharmacology
D007477:Ions; D007527:Isoenzymes; D012333:RNA, Messenger; D014701:Veratridine; D012964:Sodium; D008156:Luciferases; D000254:Sodium-Potassium-Exchanging ATPase