Hepatic efflux of glutathione by the perfused rat liver: Role of membrane potential difference

T. L. Wright, J. G. Fitz, Thomas D Boyer

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Abstract

Glutathione (GSH) is released into hepatic sinusoids by a carrier-mediated process. The importance of transmembrane potential difference (PD) as a driving force for hepatic efflux of GSH from isolated perfused rat liver was investigated. The membrane PD measured using intracellular microelectrodes as PD was altered over the physiological range by ion substitution in the perfusate. The effect of a change in membrane PD on the rate of efflux of GSH into the perfusate was determined. Because GSH carries a net negative charge at physiological values of pH, we predicted that hyperpolarization of cells would increase efflux, whereas depolarization would decrease efflux. Three different manipulations were used to depolarize the hepatocyte membrane to a similar degree, and variable effects on GSH efflux were observed. Substitution of Cl with gluconate in the perfusate depolarized the hepatocyte but had no effect on GSH efflux, whereas substitution of Na with choline in the perfusate increased GSH efflux to 110% of basal values. Perfusion with K+ inhibited GSH efflux by 21%. The latter two manipulations were associated with evidence of hepatic injury. Hyperpolarization of the hepatocyte also had variable effects on GSH efflux. Substitution of Cl with nitrate in the perfusate transiently increased the membrane PD and decreased GSH efflux, whereas perfusion with glucagon caused a sustained increase in membrane PD but did not alter GSH efflux rates. None of the latter manipulations was associated with hepatic injury and thus no consistent relationship between membrane PD and sinusoidal efflux of GSH was demonstrated. We conclude that in the isolated perfused rat liver, efflux of GSH is not driven directly by membrane PD.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume255
Issue number5
StatePublished - 1988
Externally publishedYes

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Membrane Potentials
Glutathione
Liver
Hepatocytes
Perfusion
Wounds and Injuries
Microelectrodes
Choline
Glucagon
Nitrates
Ions
Membranes

ASJC Scopus subject areas

  • Physiology
  • Gastroenterology

Cite this

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title = "Hepatic efflux of glutathione by the perfused rat liver: Role of membrane potential difference",
abstract = "Glutathione (GSH) is released into hepatic sinusoids by a carrier-mediated process. The importance of transmembrane potential difference (PD) as a driving force for hepatic efflux of GSH from isolated perfused rat liver was investigated. The membrane PD measured using intracellular microelectrodes as PD was altered over the physiological range by ion substitution in the perfusate. The effect of a change in membrane PD on the rate of efflux of GSH into the perfusate was determined. Because GSH carries a net negative charge at physiological values of pH, we predicted that hyperpolarization of cells would increase efflux, whereas depolarization would decrease efflux. Three different manipulations were used to depolarize the hepatocyte membrane to a similar degree, and variable effects on GSH efflux were observed. Substitution of Cl with gluconate in the perfusate depolarized the hepatocyte but had no effect on GSH efflux, whereas substitution of Na with choline in the perfusate increased GSH efflux to 110{\%} of basal values. Perfusion with K+ inhibited GSH efflux by 21{\%}. The latter two manipulations were associated with evidence of hepatic injury. Hyperpolarization of the hepatocyte also had variable effects on GSH efflux. Substitution of Cl with nitrate in the perfusate transiently increased the membrane PD and decreased GSH efflux, whereas perfusion with glucagon caused a sustained increase in membrane PD but did not alter GSH efflux rates. None of the latter manipulations was associated with hepatic injury and thus no consistent relationship between membrane PD and sinusoidal efflux of GSH was demonstrated. We conclude that in the isolated perfused rat liver, efflux of GSH is not driven directly by membrane PD.",
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year = "1988",
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T1 - Hepatic efflux of glutathione by the perfused rat liver

T2 - Role of membrane potential difference

AU - Wright, T. L.

AU - Fitz, J. G.

AU - Boyer, Thomas D

PY - 1988

Y1 - 1988

N2 - Glutathione (GSH) is released into hepatic sinusoids by a carrier-mediated process. The importance of transmembrane potential difference (PD) as a driving force for hepatic efflux of GSH from isolated perfused rat liver was investigated. The membrane PD measured using intracellular microelectrodes as PD was altered over the physiological range by ion substitution in the perfusate. The effect of a change in membrane PD on the rate of efflux of GSH into the perfusate was determined. Because GSH carries a net negative charge at physiological values of pH, we predicted that hyperpolarization of cells would increase efflux, whereas depolarization would decrease efflux. Three different manipulations were used to depolarize the hepatocyte membrane to a similar degree, and variable effects on GSH efflux were observed. Substitution of Cl with gluconate in the perfusate depolarized the hepatocyte but had no effect on GSH efflux, whereas substitution of Na with choline in the perfusate increased GSH efflux to 110% of basal values. Perfusion with K+ inhibited GSH efflux by 21%. The latter two manipulations were associated with evidence of hepatic injury. Hyperpolarization of the hepatocyte also had variable effects on GSH efflux. Substitution of Cl with nitrate in the perfusate transiently increased the membrane PD and decreased GSH efflux, whereas perfusion with glucagon caused a sustained increase in membrane PD but did not alter GSH efflux rates. None of the latter manipulations was associated with hepatic injury and thus no consistent relationship between membrane PD and sinusoidal efflux of GSH was demonstrated. We conclude that in the isolated perfused rat liver, efflux of GSH is not driven directly by membrane PD.

AB - Glutathione (GSH) is released into hepatic sinusoids by a carrier-mediated process. The importance of transmembrane potential difference (PD) as a driving force for hepatic efflux of GSH from isolated perfused rat liver was investigated. The membrane PD measured using intracellular microelectrodes as PD was altered over the physiological range by ion substitution in the perfusate. The effect of a change in membrane PD on the rate of efflux of GSH into the perfusate was determined. Because GSH carries a net negative charge at physiological values of pH, we predicted that hyperpolarization of cells would increase efflux, whereas depolarization would decrease efflux. Three different manipulations were used to depolarize the hepatocyte membrane to a similar degree, and variable effects on GSH efflux were observed. Substitution of Cl with gluconate in the perfusate depolarized the hepatocyte but had no effect on GSH efflux, whereas substitution of Na with choline in the perfusate increased GSH efflux to 110% of basal values. Perfusion with K+ inhibited GSH efflux by 21%. The latter two manipulations were associated with evidence of hepatic injury. Hyperpolarization of the hepatocyte also had variable effects on GSH efflux. Substitution of Cl with nitrate in the perfusate transiently increased the membrane PD and decreased GSH efflux, whereas perfusion with glucagon caused a sustained increase in membrane PD but did not alter GSH efflux rates. None of the latter manipulations was associated with hepatic injury and thus no consistent relationship between membrane PD and sinusoidal efflux of GSH was demonstrated. We conclude that in the isolated perfused rat liver, efflux of GSH is not driven directly by membrane PD.

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