title: Taurocholate depolarizes rat hepatocytes in primary culture by increasing cell membrane Na+ conductance.
abstract: Rat hepatocytes in primary culture were impaled with conventional microelectrodes. Addition of 5-100 mumol/l taurocholate led to a slowly developing depolarization that was maximal at 50 mumol/l (10.5 +/- 1.5 mV, n = 15) and not reversible. The effect was Na+ dependent and decreased in cells preincubated with 1 mumol/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 mumol/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 omega x cm2 x 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.
authors.affiliation: Max-Planck-Institut für molekulare Physiologie, Dortmund, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Wehner
mesh_terms: D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013656:Taurocholic Acid / Q000494:pharmacology*
chemical_list: D018118:Chloride Channels; D015221:Potassium Channels; D015222:Sodium Channels; D002034:Bumetanide; D013656:Taurocholic Acid