Insulin stimulates transepithelial sodium transport by activation of a protein phosphatase that increases Na-K ATPase activity in endometrial epithelial cells

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Abstract

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 α-1 and α-2 isoforms, but not the α-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.

Original languageEnglish (US)
Pages (from-to)561-574
Number of pages14
JournalJournal of General Physiology
Volume114
Issue number4
DOIs
StatePublished - Oct 1999

Keywords

  • Amiloride
  • Epithelial ion transport
  • Insulin-like growth factor I
  • Membrane transport
  • Ouabain

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