Hepatic taurocholate uptake is electrogenic and influenced by transmembrane potential difference

S. D. Lidofsky, J. G. Fitz, R. A. Weisiger, B. F. Scharschmidt

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Uptake of the bile acid taurocholate by hepatocytes is coupled to Na+ influx. The stoichiometry of uptake, however, is uncertain, as is the influence of the transmembrane electrical potential difference (PD) on this process. In this study, we examined the relationship between taurocholate extraction and PD (measured using intracellular microelectrodes) in perfused liver, and we measured taurocholate-induced transport current in cultured hepatocytes using patch-clamp recording techniques. In the perfused liver under basal conditions, PD averaged -28.4 ± 0.6 (SE) mV, and extraction of 1, 50, and 300 μM taurocholate was 0.95 ± 0.02, 0.98 ± 0.01, and 0.41 ± 0.03, respectively. When the Na+ chemical gradient was decreased by replacing perfusate Na+ with choline, the membrane depolarized to -17.2 ± 1.1 mV, and taurocholate extraction markedly decreased at all taurocholate concentrations (P < 0.01). When perfusate Na+ concentration was held constant at 137 mM, membrane depolarization induced by substitution of gluconate for perfusate Cl- (-17.9 ± 0.6 mV) or Cl- for nitrate (-10.3 ± 2.1 mV) significantly decreased extraction of 300 μM taurocholate. Abrupt exposure to taurocholate produced a concentration-dependent membrane depolarization in the presence of Na+, but not in its absence (P < 0.001). In cultured hepatocytes, exposure to 100 μM taurocholate produced an inward current of -0.056 ± 0.016 pA/pF at a holding potential of -40 mV. This current was Na+ dependent, and it increased twofold as holding potential was changed from -20 to -50 mV. These observations indicate that Na+- taurocholate cotransport by hepatocytes is associated with net entry of positive charge, consistent with stoichiometry greater than 1:1, and that taurocholate uptake is directly influenced by variations in PD over the physiological range.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume264
Issue number3 27-3
StatePublished - 1993

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Taurocholic Acid
Membrane Potentials
Liver
Hepatocytes
Membranes
Microelectrodes
Patch-Clamp Techniques
Choline
Bile Acids and Salts
Nitrates

Keywords

  • bile acids
  • cultured hepatocytes
  • ion substitution
  • isolated perfused rat liver
  • membrane potential
  • patch clamp
  • sodium-coupled transport

ASJC Scopus subject areas

  • Physiology
  • Gastroenterology

Cite this

Hepatic taurocholate uptake is electrogenic and influenced by transmembrane potential difference. / Lidofsky, S. D.; Fitz, J. G.; Weisiger, R. A.; Scharschmidt, B. F.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 264, No. 3 27-3, 1993.

Research output: Contribution to journalArticle

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N2 - Uptake of the bile acid taurocholate by hepatocytes is coupled to Na+ influx. The stoichiometry of uptake, however, is uncertain, as is the influence of the transmembrane electrical potential difference (PD) on this process. In this study, we examined the relationship between taurocholate extraction and PD (measured using intracellular microelectrodes) in perfused liver, and we measured taurocholate-induced transport current in cultured hepatocytes using patch-clamp recording techniques. In the perfused liver under basal conditions, PD averaged -28.4 ± 0.6 (SE) mV, and extraction of 1, 50, and 300 μM taurocholate was 0.95 ± 0.02, 0.98 ± 0.01, and 0.41 ± 0.03, respectively. When the Na+ chemical gradient was decreased by replacing perfusate Na+ with choline, the membrane depolarized to -17.2 ± 1.1 mV, and taurocholate extraction markedly decreased at all taurocholate concentrations (P < 0.01). When perfusate Na+ concentration was held constant at 137 mM, membrane depolarization induced by substitution of gluconate for perfusate Cl- (-17.9 ± 0.6 mV) or Cl- for nitrate (-10.3 ± 2.1 mV) significantly decreased extraction of 300 μM taurocholate. Abrupt exposure to taurocholate produced a concentration-dependent membrane depolarization in the presence of Na+, but not in its absence (P < 0.001). In cultured hepatocytes, exposure to 100 μM taurocholate produced an inward current of -0.056 ± 0.016 pA/pF at a holding potential of -40 mV. This current was Na+ dependent, and it increased twofold as holding potential was changed from -20 to -50 mV. These observations indicate that Na+- taurocholate cotransport by hepatocytes is associated with net entry of positive charge, consistent with stoichiometry greater than 1:1, and that taurocholate uptake is directly influenced by variations in PD over the physiological range.

AB - Uptake of the bile acid taurocholate by hepatocytes is coupled to Na+ influx. The stoichiometry of uptake, however, is uncertain, as is the influence of the transmembrane electrical potential difference (PD) on this process. In this study, we examined the relationship between taurocholate extraction and PD (measured using intracellular microelectrodes) in perfused liver, and we measured taurocholate-induced transport current in cultured hepatocytes using patch-clamp recording techniques. In the perfused liver under basal conditions, PD averaged -28.4 ± 0.6 (SE) mV, and extraction of 1, 50, and 300 μM taurocholate was 0.95 ± 0.02, 0.98 ± 0.01, and 0.41 ± 0.03, respectively. When the Na+ chemical gradient was decreased by replacing perfusate Na+ with choline, the membrane depolarized to -17.2 ± 1.1 mV, and taurocholate extraction markedly decreased at all taurocholate concentrations (P < 0.01). When perfusate Na+ concentration was held constant at 137 mM, membrane depolarization induced by substitution of gluconate for perfusate Cl- (-17.9 ± 0.6 mV) or Cl- for nitrate (-10.3 ± 2.1 mV) significantly decreased extraction of 300 μM taurocholate. Abrupt exposure to taurocholate produced a concentration-dependent membrane depolarization in the presence of Na+, but not in its absence (P < 0.001). In cultured hepatocytes, exposure to 100 μM taurocholate produced an inward current of -0.056 ± 0.016 pA/pF at a holding potential of -40 mV. This current was Na+ dependent, and it increased twofold as holding potential was changed from -20 to -50 mV. These observations indicate that Na+- taurocholate cotransport by hepatocytes is associated with net entry of positive charge, consistent with stoichiometry greater than 1:1, and that taurocholate uptake is directly influenced by variations in PD over the physiological range.

KW - bile acids

KW - cultured hepatocytes

KW - ion substitution

KW - isolated perfused rat liver

KW - membrane potential

KW - patch clamp

KW - sodium-coupled transport

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