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

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.