Hepatic transport of a fluorescent stearate derivative: electrochemical driving forces in intact rat liver

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

Research output: Contribution to journalArticle

17 Scopus citations

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)
Pages (from-to)G83-G91
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume261
Issue number1 24-1
DOIs
StatePublished - Jan 1 1991

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
  • Hepatology
  • Gastroenterology
  • Physiology (medical)

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