title: Activation of the Na+-K+ pump by hyposmolality through tyrosine kinase-dependent Cl- conductance in Xenopus renal epithelial A6 cells.
abstract: 1. We studied the regulatory mechanism of Na+ transport by hyposmolality in renal epithelial A6 cells. 2. Hyposmolality increased (1) Na+ absorption, which was detected as an amiloride-sensitive short-circuit current (INa), (2) Na+-K+ pump activity, (3) basolateral Cl- conductance (Gb,Cl), and (4) phosphorylation of tyrosine, suggesting an increase in activity of protein tyrosine kinase (PTK). 3. A Cl- channel blocker, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), which abolished Gb, Cl, blocked the INa by inhibiting the Na+-K+ pump without any direct effect on amiloride-sensitive Na+ channels. Diminution of Gb,Cl by Cl- replacement with a less permeable anion, gluconate, also decreased the hyposmolality-increased Na+-K+ pump activity. 4. The PTK inhibitors tyrphostin A23 and genistein induced diminution of the hyposmolality-stimulated Gb,Cl, which was associated with attenuation of the hyposmolality-increased Na+-K+ pump activity. 5. Taken together, these observations suggest that: (1) hyposmolality activates PTK; (2) the activated PTK increases Gb,Cl; and (3) the PTK-increased Gb,Cl stimulates the Na+-K+ pump. 6. This PTK-activated Gb,Cl-mediated signalling of hyposmolality is a novel pathway for stimulation of the Na+-K+ pump.
authors.affiliation: Lung Biology, Hospital for Sick Children Research Institute, Department of Paediatrics and Institute of Medical Science, University of Toronto Faculty of Medicine, Toronto, Ontario, Canada M5G 1X8.
authors.forename: N
authors.initials: N
authors.lastname: Niisato
authors.forename: Y
authors.initials: Y
authors.lastname: Marunaka
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D018118:Chloride Channels / Q000502:physiology*; D004232:Diuretics / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism*; D007038:Hypotonic Solutions; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D009579:Nitrobenzoates / Q000494:pharmacology; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D018118:Chloride Channels; D004232:Diuretics; D004791:Enzyme Inhibitors; D007038:Hypotonic Solutions; D009579:Nitrobenzoates; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D014443:Tyrosine; D010042:Ouabain; D000584:Amiloride; D011505:Protein-Tyrosine Kinases; D000254:Sodium-Potassium-Exchanging ATPase