Determination of cell membrane resistance in cultured renal epithelioid (MDCK) cells: effects of cadmium and mercury ions.

Previous studies have indicated that the cell membrane of Madin Darby Canine Kidney (MDCK) cells is hyperpolarized by a number of hormones and trace elements, in parallel with an enhancement of potassium selectivity. Without knowledge of the cell membrane resistance (Rm), however, any translation of potassium selectivity into potassium conductance remains equivocal. The present study was performed to determine the Rm of MDCK cells by cellular cable analysis. To this end, three microelectrodes were impaled into three different cells of a cell cluster; current was injected via one microelectrode and the corresponding voltage deflections measured by the other two microelectrodes. In order to extract the required specific resistances, the experimental data were analysed mathematically in terms of an electrodynamical model derived from Maxwell's equations. As a result, a mean Rm of 2.0 +/- 0.2 k omega cm2 and an intercellular coupling resistance (Rc) of 6.1 +/- 0.8 M omega were obtained at a mean potential difference across the cell membrane of -47.0 +/- 0.6 mV. An increase of the extracellular K+ concentration from 5.4 to 20 mmol/l depolarized the cell membrane by 16.2 +/- 0.5 mV and decreased Rm by 30.6 +/- 3.0%; 1 mmol/l barium depolarized the cell membrane by 20.1 +/- 1.1 mV and increased Rm by 75.9 +/- 14.3%. Omission of extracellular bicarbonate and carbon dioxide at constant extracellular pH caused a transient hyperpolarization (up to -60.4 +/- 1.4 mV), a decrease of Rm (by 75 +/- 4.5%) and a decrease of Rc (by 23.1 +/- 8.4%).(ABSTRACT TRUNCATED AT 250 WORDS)