The effect of hypoosmolarity on the electrical properties of Madin Darby canine kidney cells

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Abstract
The present study has been performed to test for the effect of hypotonic extracellular fluid on the electrical properties of Madin Darby canine kidney (MDCK)-cells. The volume of suspended MDCK-cell is 1,892±16 fl (n=8) in isotonic (298.7 mosmol/l) extracellular fluid. Exposure of the cells to hypotonic (230.7 mosmol/l) extracellular fluid is followed by cellular swelling to 2,269±18 fl (n=4) and subsequent volume regulatory decrease to 2,052±22 fl (n=4) within 512 s. Volume regulatory decrease is abolished by quinidine (1 mmol/l) and by lipoxygenase inhibitor nordihydroguaiaretic acid (50 μmol/l). The potential difference across the cell membrane averages −53.6±0.9 mV (n=49) in isotonic extracellular perfusates. Reduction of extracellular osmolarity depolarizes the cell membrane by +25.7±0.8 mV (n=67), reduces the apparent potassium selectivity of the cell membrane, from 0.55±0.07 (n=9) to 0.09±0.01 (n=26), and increases the apparent chloride selectivity from close to zero to 0.34±0.02 (n=21). Potassium channel blocker barium (1 mmol/l) depolarizes the cell membrane by +15.2±1.1 mV (n=13). In the presence of barium, reduction of extracellular osmolarity leads to a further depolarization by +14.0±1.4 mV (n=12). Addition of chloride channel blocker anthracene-9-COOH (1 mmol/l) leads to a hyperpolarization of the cell membrane by −6.7±2.2 mV (n=11). In the presence of anthracene-9-COOH, reduction of the extracellular osmolarity leads to a depolarization by +22.4±1.7 mV (n=11). Application of 1 mmol/l quinidine depolarizes the cell membrane to −6.6±0.5 mV (n=8) and virtually abolishes the effect of reduced extracellular osmolarity on cell membrane potential. Nordihydroguaiaretic acid (50 μmol/l), a substance known to inhibit lipoxygenase, increases steady state cell membrane potential in isotonic extracellular fluid to −58.8±1.8 mV (n=10) and blunts the depolarizing effect of hypotonic extracellular fluid (+5.4±1.5 mV,n=10). In conclusion, exposure of MDCK-cells to hypotonic media depolarizes the cell membrane by activation of a conductive pathway, which is insensitive to both barium and anthracene-9-COOH. The conductive pathway is possibly activated by leucotrienes.