Hepatic transport of a fluorescent stearate derivative

electrochemical driving forces in intact rat liver

J. G. Fitz, N. M. Bass, R. A. Weisiger

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Abstract

We determined the effect of varying the transmembrane Na+ electrochemical gradient on extraction of a fluorescent derivative of stearate, 12-N-methyl-7-nitrobenzo-2-oxa-1,3,-diazol-amino stearate (NBD-stearate), by the isolated perfused rat liver. Membrane potential difference (PD) of individual hepatocytes and extraction of NBD-stearate were measured simultaneously under basal conditions and during changes in PD induced by perfusate ion substitutions. Under basal conditions, PD averaged -30 ± 1 mV, and extraction of 10 μM NBD-stearate from 1% albumin solutions averaged 0.54 ± 0.03. Fluorescence microscopy indicated that uptake exhibited a declining portal-to-central gradient in the presence but not absence of Na+. Substitution of nitrate for Cl- hyperpolarized PD to -59 mV and increased extraction to 131% of control values. Withdrawal of nitrate and substitution of gluconate for Cl- depolarized PD to -3 and -15 mV, respectively, and decreased extraction to 63 and 73% of control values. Substitution of choline for Na+ eliminated the out-to-in Na+ gradient, depolarized PD to -16 mV, and decreased extraction to 27% of control values, an effect greater than expected for membrane depolarization alone. Uptake of NBD-stearate was saturable and caused Na+-dependent membrane depolarization at higher concentrations (300 μM). These studies indicate that uptake of NBD-stearate occurs in large part by an efficient Na+-dependent mechanism compatible with electrogenic Na+-fatty acid cotransport.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume261
Issue number1 24-1
StatePublished - 1991

Fingerprint

Stearates
Liver
Nitrates
Membranes
Choline
Fluorescence Microscopy
Individuality
Membrane Potentials
Hepatocytes
Albumins
Fatty Acids
12-N-methyl-7-nitrobenzo-2-oxa-1,3-diazolamino stearate
Ions

Keywords

  • Carrier-mediated transport
  • Electrogenic transport
  • Isolated perfused rat liver
  • Lobular gradient
  • Long-chain fatty acid
  • Membrane potential difference
  • Microelectrodes
  • Sodium-coupled transport

ASJC Scopus subject areas

  • Physiology
  • Gastroenterology

Cite this

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title = "Hepatic transport of a fluorescent stearate derivative: electrochemical driving forces in intact rat liver",
abstract = "We determined the effect of varying the transmembrane Na+ electrochemical gradient on extraction of a fluorescent derivative of stearate, 12-N-methyl-7-nitrobenzo-2-oxa-1,3,-diazol-amino stearate (NBD-stearate), by the isolated perfused rat liver. Membrane potential difference (PD) of individual hepatocytes and extraction of NBD-stearate were measured simultaneously under basal conditions and during changes in PD induced by perfusate ion substitutions. Under basal conditions, PD averaged -30 ± 1 mV, and extraction of 10 μM NBD-stearate from 1{\%} albumin solutions averaged 0.54 ± 0.03. Fluorescence microscopy indicated that uptake exhibited a declining portal-to-central gradient in the presence but not absence of Na+. Substitution of nitrate for Cl- hyperpolarized PD to -59 mV and increased extraction to 131{\%} of control values. Withdrawal of nitrate and substitution of gluconate for Cl- depolarized PD to -3 and -15 mV, respectively, and decreased extraction to 63 and 73{\%} of control values. Substitution of choline for Na+ eliminated the out-to-in Na+ gradient, depolarized PD to -16 mV, and decreased extraction to 27{\%} of control values, an effect greater than expected for membrane depolarization alone. Uptake of NBD-stearate was saturable and caused Na+-dependent membrane depolarization at higher concentrations (300 μM). These studies indicate that uptake of NBD-stearate occurs in large part by an efficient Na+-dependent mechanism compatible with electrogenic Na+-fatty acid cotransport.",
keywords = "Carrier-mediated transport, Electrogenic transport, Isolated perfused rat liver, Lobular gradient, Long-chain fatty acid, Membrane potential difference, Microelectrodes, Sodium-coupled transport",
author = "Fitz, {J. G.} and Bass, {N. M.} and Weisiger, {R. A.}",
year = "1991",
language = "English (US)",
volume = "261",
journal = "American Journal of Physiology - Heart and Circulatory Physiology",
issn = "0363-6135",
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TY - JOUR

T1 - Hepatic transport of a fluorescent stearate derivative

T2 - electrochemical driving forces in intact rat liver

AU - Fitz, J. G.

AU - Bass, N. M.

AU - Weisiger, R. A.

PY - 1991

Y1 - 1991

N2 - We determined the effect of varying the transmembrane Na+ electrochemical gradient on extraction of a fluorescent derivative of stearate, 12-N-methyl-7-nitrobenzo-2-oxa-1,3,-diazol-amino stearate (NBD-stearate), by the isolated perfused rat liver. Membrane potential difference (PD) of individual hepatocytes and extraction of NBD-stearate were measured simultaneously under basal conditions and during changes in PD induced by perfusate ion substitutions. Under basal conditions, PD averaged -30 ± 1 mV, and extraction of 10 μM NBD-stearate from 1% albumin solutions averaged 0.54 ± 0.03. Fluorescence microscopy indicated that uptake exhibited a declining portal-to-central gradient in the presence but not absence of Na+. Substitution of nitrate for Cl- hyperpolarized PD to -59 mV and increased extraction to 131% of control values. Withdrawal of nitrate and substitution of gluconate for Cl- depolarized PD to -3 and -15 mV, respectively, and decreased extraction to 63 and 73% of control values. Substitution of choline for Na+ eliminated the out-to-in Na+ gradient, depolarized PD to -16 mV, and decreased extraction to 27% of control values, an effect greater than expected for membrane depolarization alone. Uptake of NBD-stearate was saturable and caused Na+-dependent membrane depolarization at higher concentrations (300 μM). These studies indicate that uptake of NBD-stearate occurs in large part by an efficient Na+-dependent mechanism compatible with electrogenic Na+-fatty acid cotransport.

AB - We determined the effect of varying the transmembrane Na+ electrochemical gradient on extraction of a fluorescent derivative of stearate, 12-N-methyl-7-nitrobenzo-2-oxa-1,3,-diazol-amino stearate (NBD-stearate), by the isolated perfused rat liver. Membrane potential difference (PD) of individual hepatocytes and extraction of NBD-stearate were measured simultaneously under basal conditions and during changes in PD induced by perfusate ion substitutions. Under basal conditions, PD averaged -30 ± 1 mV, and extraction of 10 μM NBD-stearate from 1% albumin solutions averaged 0.54 ± 0.03. Fluorescence microscopy indicated that uptake exhibited a declining portal-to-central gradient in the presence but not absence of Na+. Substitution of nitrate for Cl- hyperpolarized PD to -59 mV and increased extraction to 131% of control values. Withdrawal of nitrate and substitution of gluconate for Cl- depolarized PD to -3 and -15 mV, respectively, and decreased extraction to 63 and 73% of control values. Substitution of choline for Na+ eliminated the out-to-in Na+ gradient, depolarized PD to -16 mV, and decreased extraction to 27% of control values, an effect greater than expected for membrane depolarization alone. Uptake of NBD-stearate was saturable and caused Na+-dependent membrane depolarization at higher concentrations (300 μM). These studies indicate that uptake of NBD-stearate occurs in large part by an efficient Na+-dependent mechanism compatible with electrogenic Na+-fatty acid cotransport.

KW - Carrier-mediated transport

KW - Electrogenic transport

KW - Isolated perfused rat liver

KW - Lobular gradient

KW - Long-chain fatty acid

KW - Membrane potential difference

KW - Microelectrodes

KW - Sodium-coupled transport

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M3 - Article

VL - 261

JO - American Journal of Physiology - Heart and Circulatory Physiology

JF - American Journal of Physiology - Heart and Circulatory Physiology

SN - 0363-6135

IS - 1 24-1

ER -