Translocation of fatty acids across the basolateral rat liver plasma membrane is driven by an active potential-sensitive sodium-dependent transport system.
In previous studies it was shown that hepatocellular uptake of fatty acids is mediated by a specific fatty acid binding membrane protein. To determine now directly the driving forces for their entry into hepatocytes, the uptake of a representative long chain fatty acid, [3H]oleate, by basolateral rat liver plasma membrane vesicles was examined. Influx of oleate was stimulated by increasing the Na+ concentration of the medium. In the presence of an inwardly directed Na+ gradient (NaSCN, NaNO3, NaCl) oleate was accumulated during the initial uptake phase (20 s) at a concentration of 1.4-1.9-fold that at equilibrium (overshoot). This activation of influx was not observed after replacement of Na+ by Li+, K+, or choline+. Na+-dependent oleate uptake was significantly stimulated by creation of a negative intravesicular potential, either by altering the accompanying anions or by valinomycin-induced K+ diffusion potentials, suggesting an electrogenic transport mechanism. Na+-dependent fatty acid uptake was temperature dependent, with maximal overshoots occurring at 37 degrees C, and revealed saturation kinetics with a Km of 83.1 nM and Vmax of 2.9 nmol X min-1 X mg protein-1. These studies demonstrate that the carrier-mediated hepatocellular uptake of fatty acids represents an active potential-sensitive Na+-fatty acid cotransport system.
D000200:Action Potentials; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D008099:Liver / Q000166:cytology* / Q000378:metabolism; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism; D009994:Osmolar Concentration; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors; D014634:Valinomycin / Q000494:pharmacology
D005227:Fatty Acids; D009829:Oleic Acids; D014634:Valinomycin; D019301:Oleic Acid; D012964:Sodium