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 language | English (US) |
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Pages (from-to) | G83-G91 |
Journal | American Journal of Physiology - Gastrointestinal and Liver Physiology |
Volume | 261 |
Issue number | 1 24-1 |
DOIs | |
State | Published - 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)