Selective induction of alpha 1 isoform of (Na+ + K+)-ATPase by insulin/insulin-like growth factor-I in cultured rat astrocytes.
Treatment of cultured rat astrocytes with insulin increased (Na+ + K+)-ATPase activity expressed per protein or DNA by 1.6- to 2.1-fold, but did not affect Mg(2+)-ATPase and adenylate cyclase activities. Insulin treatment increased protein and DNA contents under the conditions, while it did not cause morphological differentiation as determined by a microscopic inspection. Insulin-like growth factor-I (IGF-I) had a similar effect on the enzyme activity in astrocytes: the effect of insulin was observed at supraphysiological concentrations, while that of IGF-I was observed at physiological concentrations. Insulin and IGF-I both stimulated DNA synthesis at the concentrations that caused an increase in enzyme activity. The effect was blocked by tyrosine kinase inhibitors such as genistein and herbimycin A and by cycloheximide. Western blot analysis showed that alpha 1 and alpha 2 isoforms of (Na+ + K+)-ATPase were present in cultured astrocytes and that insulin and IGF-I increased the content of the alpha 1 isoform but did not that of the alpha 2 isoform. Two components of ouabain inhibition were observed in the enzyme purified partially from cultured astrocytes, and treatment of the cells with IGF-I increased the ratio of the low-affinity component of the inhibition, indicating a selective increase in the activity of the alpha 1 isoform. These results indicate that insulin increases (Na+ + K+)-ATPase activity through an activation of IGF-I receptors and the increase is due to the selective induction of the alpha 1 isoform in cultured astrocytes.
Matsuda
T
T
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Osaka University, Japan.
Murata
Y
Y
Kawamura
N
N
Hayashi
M
M
Tamada
K
K
Takuma
K
K
Maeda
S
S
Baba
A
A
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002455:Cell Division; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000201:enzymology*; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D004790:Enzyme Induction; D005910:Glioma; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007527:Isoenzymes / Q000096:biosynthesis*; D007700:Kinetics; D009447:Neuroblastoma; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis* / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D014407:Tumor Cells, Cultured
D007328:Insulin; D007527:Isoenzymes; D010042:Ouabain; D007334:Insulin-Like Growth Factor I; D004247:DNA; D003513:Cycloheximide; D017301:Ca(2+) Mg(2+)-ATPase; D000262:Adenylyl Cyclases; D000254:Sodium-Potassium-Exchanging ATPase; D013936:Thymidine