Insulin stimulates transepithelial sodium transport by activation of a protein phosphatase that increases Na-K ATPase activity in endometrial epithelial cells.
The objective of this study was to investigate the effects of insulin and insulin-like growth factor I on transepithelial Na(+) transport across porcine glandular endometrial epithelial cells grown in primary culture. Insulin and insulin-like growth factor I acutely stimulated Na(+) transport two- to threefold by increasing Na(+)-K(+) ATPase transport activity and basolateral membrane K(+) conductance without increasing the apical membrane amiloride-sensitive Na(+) conductance. Long-term exposure to insulin for 4 d resulted in enhanced Na(+) absorption with a further increase in Na(+)-K(+) ATPase transport activity and an increase in apical membrane amiloride-sensitive Na(+) conductance. The effect of insulin on the Na(+)-K(+) ATPase was the result of an increase in V(max) for extracellular K(+) and intracellular Na(+), and an increase in affinity of the pump for Na(+). Immunohistochemical localization along with Western blot analysis of cultured porcine endometrial epithelial cells revealed the presence of alpha-1 and alpha-2 isoforms, but not the alpha-3 isoform of Na(+)-K(+) ATPase, which did not change in the presence of insulin. Insulin-stimulated Na(+) transport was inhibited by hydroxy-2-naphthalenylmethylphosphonic acid tris-acetoxymethyl ester [HNMPA-(AM)(3)], a specific inhibitor of insulin receptor tyrosine kinase activity, suggesting that the regulation of Na(+) transport by insulin involves receptor autophosphorylation. Pretreatment with wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase as well as okadaic acid and calyculin A, inhibitors of protein phosphatase activity, also blocked the insulin-stimulated increase in short circuit and pump currents, suggesting that activation of phosphatidylinositol 3-kinase and subsequent stimulation of a protein phosphatase mediates the action of insulin on Na(+)-K(+) ATPase activation.
Deachapunya
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Department of Physiology, University of Minnesota, St. Paul, Minnesota 55108, USA.
Palmer-Densmore
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O'Grady
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SM
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D015153:Blotting, Western; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D004594:Electrophysiology; D004717:Endometrium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D020536:Enzyme Activators / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D005260:Female; D007150:Immunohistochemistry; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D010042:Ouabain / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013268:Stimulation, Chemical; D013552:Swine
D020536:Enzyme Activators; D007328:Insulin; D015221:Potassium Channels; C013407:benzamil; D010042:Ouabain; D007334:Insulin-Like Growth Factor I; D000584:Amiloride; D012964:Sodium; D010749:Phosphoprotein Phosphatases; D000254:Sodium-Potassium-Exchanging ATPase