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

M. Ritter and F. Lang1
with a mathematical appendix by G. Grübl2 and H. G. Embacher2
1Institute for Physiology and 2Theoretical Physics Institute, University of Innsbruck,
A-6010 Innsbruck, Austria

(Received: January 2/Received after revision April 30/Accepted May 10, 1990)

Abstract. 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 tex2html_wrap_inline30 0.2 ktex2html_wrap_inline32cm2 and an intercellular coupling resistance (Rc ) of 6.1 tex2html_wrap_inline30 0.8 Mtex2html_wrap_inline32 were obtained at a mean potential difference across the cell membrane of -47.0 tex2html_wrap_inline30 0.6 mV. An increase of the extracellular K+ concentration from 5.4 to 20 mmol/l depolarized the cell membrane by 16.2 tex2html_wrap_inline30 0.5 mV and decreased Rm by 30.6 tex2html_wrap_inline30 3.0%; 1 mmol/l barium depolarized the cell membrane by 20.1 tex2html_wrap_inline30 1.1 mV and increased Rm by 75.9 tex2html_wrap_inline30 14.3%. Omission of extracellular bicarbonate and carbon dioxide at constant extracellular pH caused a transient hyperpolarization (up to -60.4 tex2html_wrap_inline30 1.4 mV), a decrease of Rm (by 75 tex2html_wrap_inline30 4.5%) and a decrease of Rc (by 23.1 tex2html_wrap_inline30 8.4%). The changes in Rm and Rc were probably the result of intracellular alkalosis. Cadmium ions (1 tex2html_wrap_inline72mol/l) led to a sustained, reversible hyperpolarization (to -64.8 tex2html_wrap_inline30 1.3 mV) and to a decrease of Rm (by 77.0 tex2html_wrap_inline30 2.7%); mercury ions (1 tex2html_wrap_inline72mol/l) cause a sustained hyperpolarization (to -60.1 tex2html_wrap_inline30 1.2 mV) and a decrease of Rm (by 76.3 tex2html_wrap_inline30 3.9%). Neither manoeuvre significantly altered Rc . We have previously shown that both cadmium and mercury hyperpolarize the cell membrane potential and increase its potassium selectivity; the decrease of the Rm observed in the present study indicates that these effects are due to an increase of the potassium-selective conductance of the cell membrane.

Key words. MDCK cells, Potassium conductance, Cell membrane potential, Cell membrane resistance, Barium, Cadmium, Mercury, Gap junctions.

Pflügers Arch 417, 29 - 36 (1990).