Taurocholate depolarizes rat hepatocytes in primary culture by increasing cell membrane Na+ conductance |
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Authors: | Frank Wehner |
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Institution: | (1) Max-Planck-Institut für molekulare Physiologie, Postfach 102664, D-44026 Dortmund, Germany |
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Abstract: | Rat hepatocytes in primary culture were impaled with conventional microelectrodes. Addition of 5–100 mol/l taurocholate led to a slowly developing depolarization that was maximal at 50 mol/l (10.5±1.5 mV, n=15) and not reversible. The effect was Na+ dependent and decreased in cells preincubated with 1 mol/l taurocholate. Increasing external K+ tenfold depolarized the cells by 12.3±2.3 mV under control conditions and by 6.3±1.2 mV with 50 mol/l taurocholate present (n=7). Depolarization by 1 mmol/l Ba2+ was 7.6±0.8 mV and 6.0±0.7 mV (n=9) before and after addition of taurocholate, respectively. Cable analysis and Na+ substitution experiments reveal that this apparent decrease in K+ conductance reflects an actual increase in Na+ conductance: in the presence of taurocholate, specific cell membrane resistance decreased from 2.8 to 2.3 k · cm2 · Na+ substitution by 95% depolarized cell membranes by 8.9±2.9 mV (n=9), probably due to indirect effects on K+ conductance via changes in cell pH. With taurocholate present, the same manoeuvre changed membrane voltages by –0.8±2.6 mV. When Na+ concentration was restored to 100% from solutions containing 5% Na+, cells hyperpolarized by 3.5±3.6 mV (n=7) under control conditions and depolarized by 4.4±2.9 mV in the presence of taurocholate, respectively. In Cl– substitution experiments, there was no evidence for changes in Cl– conductance by taurocholate. These results show that taurocholate-induced membrane depolarization is due to an increase in Na+ conductance probably via uptake of the bile acid. |
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Keywords: | Rat hepatocytes Electrophysiology Membrane potentials Na+ conductance Bile acids Taurocholic acid |
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