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Isoform‐Specific Up‐Regulation by Ouabain of Na + ,K + ‐ATPase in Cultured Rat Astrocytes
Author(s) -
Hosoi Rie,
Matsuda Toshio,
Asano Shoichi,
Nakamura Hiroaki,
Hashimoto Hitoshi,
Takuma Kazuhiro,
Baba Akemichi
Publication year - 1997
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1997.69052189.x
Subject(s) - ouabain , cycloheximide , gene isoform , microbiology and biotechnology , biology , extracellular , astrocyte , calcineurin , intracellular , atpase , protein subunit , neuroglia , biochemistry , enzyme , chemistry , medicine , sodium , endocrinology , protein biosynthesis , central nervous system , transplantation , organic chemistry , gene
There are two α‐subunit isoforms (α1 and α2) and two β‐subunit isoforms (β1 and β2) of Na + ,K + ‐ATPase in astrocytes, but the functional heterodimer composition is not known. Ouabain (0.5–1.0 m M ) increased the levels of α1 and β1 mRNAs, whereas it decreased those of α2 and β2 mRNAs in cultured rat astrocytes. The increases in α1 and β1 mRNAs were observed at 6–48 h after addition of the inhibitor. Immunochemical analyses showed that ouabain increased α1 and β1, but not α2 and β2, proteins, and that the isoforms in control and ouabain‐treated cultures were of glial origin. Low extracellular K + and monensin (20 µ M ) mimicked the effect of ouabain on α1 mRNA. The ouabain‐induced increase in α1 mRNA was blocked by the protein synthesis inhibitor cycloheximide (10 µ M ), the intracellular Ca 2+ chelator 1,2‐bis(2‐aminophenoxy)ethane‐ N,N,N′,N′ ‐tetraacetic acid tetraacetoxymethyl ester (30 µ M ), and the calcineurin inhibitor FK506 (1 n M ). These findings indicate that chronic inhibition of Na + ,K + ‐ATPase up‐regulates the α1 and β1, but not α2 and β2, isoforms in astrocytes, suggesting a functional coupling of α1β1 complex. They also suggest that intracellular Na + , Ca 2+ , and calcineurin may be involved in ouabain‐induced up‐regulation of the enzyme in astrocytes.