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Hypertonicity in fused Madin-Darby canine kidney cells: transient rise in NaHCO3 followed by sustained KCl accumulation
Authors:L. Wojnowski  H. Oberleithner
Affiliation:(1) Department of Physiology, University of Würzburg, Röntgenring 9, W-8700 Würzburg, Federal Republic of Germany
Abstract:
We investigated mechanisms of regulatory volume increase in fused Madin-Darby canine kidney (MDCK) cells, a cell line originally derived from renal collecting duct. The intracellular ion concentrations as well as the concentration of the volume marker tetramethylammonium+ were measured by means of ion-selective microelectrodes. Application of hypertonic Ringer bicarbonate solution (+150 mmol/l mannitol) resulted in cell shrinkage to 84±2% of the initial cell volume (shrinkage expected for an ideal osmometer = 66%), indicating a significant regulatory volume increase. During the first 90 s of the hypertonic stress, a transient increase in intracellular Na+ and HCO3concentrations was observed. It was followed by a sustained increase in intracellular K+ and Cl concentrations. Ouabain (0.1 mmol/l) as well as amiloride (1 mmol/l) reduced K+ accumulation significantly, whereas the H+ /K+-ATPase inhibitor SCH 28080 had no effect. Hypertonic stress hyperpolarized the cell membrane potential by 19±2 mV, owing to the decrease of the ratio of Cl conductance to K+ conductance of the cell membrane. We conclude: (a) acute hypertonic stress activates Na+/H+ exchange in MDCK cells; (b) transient alteration of intracellular Na+ and pH stimulates Na+/K+-ATPase and Cl/HCO3exchange, both leading to the sustained intracellular accumulation of KCl; (c) a high intracellular KCl concentration is maintained by the partial reversion of the Cl/K+ conductance ratio of the plasma membrane.
Keywords:Hyperosmolarity  Volume regulation  MDCK cells  Na+/H+ antiporter  Na+/K+-ATPase  Renal medulla
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