Involvement of Na+,K(+)ATPase in the mitogenic effect of insulin-like growth factor-I on cultured rat astrocytes.
We have previously reported that insulin/insulin-like growth factor (IGF)-I induced the alpha 1 isoform of Na+,K(+)-ATPase in cultured astrocytes. In this study the effects of insulin/IGF-I on Na+,K(+)-ATPase activity and cell proliferation were examined in astrocytes cultured under the various conditions, to test the possible involvement of the enzyme activity in the mitogenic action of IGF-I on astrocytes. Insulin increased Na+,K(+)-ATPase activity and stimulated cell proliferation in subconfluent astrocytes (cultured for 7-14 days in vitro). In contrast, these effects were not observed in confluent cells (cultured for 28 days). Furthermore, insulin stimulated neither the enzyme activity nor [3H]thymidine incorporation in astrocytes preincubated in fetal calf serum-free medium for 2 days (quiescent cells) and treated with dibutyryl cyclic AMP (differentiated cells). The increases in Na+,K(+)-ATPase activity and expression of the alpha 1 mRNA preceded the mitogenic effect. 125I-IGF-I binding experiment showed that all the cells used here had similar binding characteristics. The insulin-induced increase in enzyme activity was not affected by 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), and it was observed even in Ca(2+)-free medium. The stimulation by IGF-I of [3H]thymidine incorporation was attenuated by ouabain and a low external K+ level. These findings suggest that stimulation of Na+,K(+)-ATPase activity is involved in the mitogenic action of IGF-I on cultured astrocytes.
Matsuda
T
T
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Osaka University, Japan.
Murata
Y
Y
Tanaka
K
K
Hosoi
R
R
Hayashi
M
M
Tamada
K
K
Takuma
K
K
Baba
A
A
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007546:Isoquinolines / Q000494:pharmacology; D008934:Mitogens / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013936:Thymidine / Q000378:metabolism
D007328:Insulin; D007546:Isoquinolines; D008934:Mitogens; D010879:Piperazines; D010042:Ouabain; D003994:Bucladesine; D007334:Insulin-Like Growth Factor I; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D004247:DNA; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D013936:Thymidine