Effect of pH on membrane potential and K+ conductance in cultured rat hepatocytes

J. G. Fitz, T. E. Trouillot, B. F. Scharschmidt

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Abstract

We have investigated the effects of extracellular (pH(o)) and intracellular (pH(i)) pH on membrane potential difference (PD) and cell conductance (g(cell)) in rat hepatocytes in primary culture. PD and pH(i) were measured continuously by using intracellular microelectrodes and the pH-sensitive fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxy fluorescein (BCECF), respectively, during abrupt changes in the pH(o) or ionic composition of extracellular perfusate. In the presence of 25 mM HCO3̄, PD, g(cell), and pH(i) averaged (± SE) -32 ± 1 mV, 16.4 ± 1.0 nS, and 7.32 ± 0.01, respectively. The transference number for K+ (t(K+)), which reflects the fractional contribution of K+ conductance to g(cell), averaged 0.36 ± 0.03. Exposure to 1 mM Ba2+ produced membrane depolarization and decreased t(K+) by ~ 90%. Lowering pH(o) consistently decreased pH(i), decreased g(cell) (~ 30 nS per unit change in pH(i)), and depolarized PD. Increasing pH(o) had opposite effects, but the changes in g(cell) were generally greater with intracellular acidification than alkalinization. The decrease in PD produced by lowering pH(o) was associated with a decrease in t(K+) or 73 ± 2% and was inhibited by Ba2+. Exposure to butyrate or withdrawal of NH4 +, which lowered pH(i) without changing pH(o), also caused depolarization of PD and a decrease in g(cell) that was inhibited by Ba2+. These observations indicate that the PD of hepatocytes is strongly influenced by pH(i), with or without changes in pH(o), and they further suggest that the effects of pH on PD are mediated through changes in plasma membrane K+ conductance.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume257
Issue number6
StatePublished - 1989

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Membrane Potentials
Hepatocytes
Butyrates
Microelectrodes
Fluorescein
Fluorescent Dyes

Keywords

  • 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein
  • barium
  • ion transport
  • microelectrodes

ASJC Scopus subject areas

  • Physiology
  • Gastroenterology

Cite this

Effect of pH on membrane potential and K+ conductance in cultured rat hepatocytes. / Fitz, J. G.; Trouillot, T. E.; Scharschmidt, B. F.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 257, No. 6, 1989.

Research output: Contribution to journalArticle

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abstract = "We have investigated the effects of extracellular (pH(o)) and intracellular (pH(i)) pH on membrane potential difference (PD) and cell conductance (g(cell)) in rat hepatocytes in primary culture. PD and pH(i) were measured continuously by using intracellular microelectrodes and the pH-sensitive fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxy fluorescein (BCECF), respectively, during abrupt changes in the pH(o) or ionic composition of extracellular perfusate. In the presence of 25 mM HCO3̄, PD, g(cell), and pH(i) averaged (± SE) -32 ± 1 mV, 16.4 ± 1.0 nS, and 7.32 ± 0.01, respectively. The transference number for K+ (t(K+)), which reflects the fractional contribution of K+ conductance to g(cell), averaged 0.36 ± 0.03. Exposure to 1 mM Ba2+ produced membrane depolarization and decreased t(K+) by ~ 90{\%}. Lowering pH(o) consistently decreased pH(i), decreased g(cell) (~ 30 nS per unit change in pH(i)), and depolarized PD. Increasing pH(o) had opposite effects, but the changes in g(cell) were generally greater with intracellular acidification than alkalinization. The decrease in PD produced by lowering pH(o) was associated with a decrease in t(K+) or 73 ± 2{\%} and was inhibited by Ba2+. Exposure to butyrate or withdrawal of NH4 +, which lowered pH(i) without changing pH(o), also caused depolarization of PD and a decrease in g(cell) that was inhibited by Ba2+. These observations indicate that the PD of hepatocytes is strongly influenced by pH(i), with or without changes in pH(o), and they further suggest that the effects of pH on PD are mediated through changes in plasma membrane K+ conductance.",
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AU - Trouillot, T. E.

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N2 - We have investigated the effects of extracellular (pH(o)) and intracellular (pH(i)) pH on membrane potential difference (PD) and cell conductance (g(cell)) in rat hepatocytes in primary culture. PD and pH(i) were measured continuously by using intracellular microelectrodes and the pH-sensitive fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxy fluorescein (BCECF), respectively, during abrupt changes in the pH(o) or ionic composition of extracellular perfusate. In the presence of 25 mM HCO3̄, PD, g(cell), and pH(i) averaged (± SE) -32 ± 1 mV, 16.4 ± 1.0 nS, and 7.32 ± 0.01, respectively. The transference number for K+ (t(K+)), which reflects the fractional contribution of K+ conductance to g(cell), averaged 0.36 ± 0.03. Exposure to 1 mM Ba2+ produced membrane depolarization and decreased t(K+) by ~ 90%. Lowering pH(o) consistently decreased pH(i), decreased g(cell) (~ 30 nS per unit change in pH(i)), and depolarized PD. Increasing pH(o) had opposite effects, but the changes in g(cell) were generally greater with intracellular acidification than alkalinization. The decrease in PD produced by lowering pH(o) was associated with a decrease in t(K+) or 73 ± 2% and was inhibited by Ba2+. Exposure to butyrate or withdrawal of NH4 +, which lowered pH(i) without changing pH(o), also caused depolarization of PD and a decrease in g(cell) that was inhibited by Ba2+. These observations indicate that the PD of hepatocytes is strongly influenced by pH(i), with or without changes in pH(o), and they further suggest that the effects of pH on PD are mediated through changes in plasma membrane K+ conductance.

AB - We have investigated the effects of extracellular (pH(o)) and intracellular (pH(i)) pH on membrane potential difference (PD) and cell conductance (g(cell)) in rat hepatocytes in primary culture. PD and pH(i) were measured continuously by using intracellular microelectrodes and the pH-sensitive fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxy fluorescein (BCECF), respectively, during abrupt changes in the pH(o) or ionic composition of extracellular perfusate. In the presence of 25 mM HCO3̄, PD, g(cell), and pH(i) averaged (± SE) -32 ± 1 mV, 16.4 ± 1.0 nS, and 7.32 ± 0.01, respectively. The transference number for K+ (t(K+)), which reflects the fractional contribution of K+ conductance to g(cell), averaged 0.36 ± 0.03. Exposure to 1 mM Ba2+ produced membrane depolarization and decreased t(K+) by ~ 90%. Lowering pH(o) consistently decreased pH(i), decreased g(cell) (~ 30 nS per unit change in pH(i)), and depolarized PD. Increasing pH(o) had opposite effects, but the changes in g(cell) were generally greater with intracellular acidification than alkalinization. The decrease in PD produced by lowering pH(o) was associated with a decrease in t(K+) or 73 ± 2% and was inhibited by Ba2+. Exposure to butyrate or withdrawal of NH4 +, which lowered pH(i) without changing pH(o), also caused depolarization of PD and a decrease in g(cell) that was inhibited by Ba2+. These observations indicate that the PD of hepatocytes is strongly influenced by pH(i), with or without changes in pH(o), and they further suggest that the effects of pH on PD are mediated through changes in plasma membrane K+ conductance.

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