title: Hypertonicity in fused Madin-Darby canine kidney cells: transient rise in NaHCO3 followed by sustained KCl accumulation.
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 HCO3- concentrations 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-/HCO3- exchange, exchange, 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.
authors.affiliation: Department of Physiology, University of Würzburg, Federal Republic of Germany.
authors.forename: L
authors.initials: L
authors.lastname: Wojnowski
authors.forename: H
authors.initials: H
authors.lastname: Oberleithner
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002460:Cell Line; D004285:Dogs; D017506:H(+)-K(+)-Exchanging ATPase; D006982:Hypertonic Solutions / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D007477:Ions; D007668:Kidney / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D011189:Potassium Chloride / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D017693:Sodium Bicarbonate; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013997:Time Factors
chemical_list: D001639:Bicarbonates; D006982:Hypertonic Solutions; D007093:Imidazoles; D007477:Ions; D000644:Quaternary Ammonium Compounds; C035235:Sch 28080; D010042:Ouabain; D011189:Potassium Chloride; D017693:Sodium Bicarbonate; D012964:Sodium; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D000254:Sodium-Potassium-Exchanging ATPase; C027917:tetramethylammonium