Electrochemical Driving Forces in Intact Rat Liver

Recent observations suggest that the hepatic uptake of oleate may be sodium coupled. To assess the electrochemical forces driving fatty acid uptake, we used microelectrodes to monitor continuously the electrical potential difference across the plasma membrane in the perfused rat liver while simulta-neously monitoring the rate of tracer VHioleate uptake from 1 % albumin solutions. Isosmotic cation or anion substitution was used to vary the potential difference over the physiologic range. Depolarization of cells from-29 to-19 mV by substi-tuting gluconate for chloride reduced steady-state oleate up-take by 34%. Conversely, hyperpolarization of cells to-52 mV by substituting nitrate for chloride increased uptake by 41%. Replacement of perfusate sodium with choline depolarized the cells to-18 mV and reduced uptake by 58%, an amount greater than expected from the degree of depolarization alone. Oleate in higher concentrations (1.5 mM in 2 % albumin) de-polarized cells by 3 mV in the presence of sodium, but had no effect in sodium-free buffer. These results suggest that a por-tion of oleate uptake in the intact liver occurs by electrogenic sodium cotransport. Uptake appears to be driven by both the electrical and sodium chemical gradients across the plasma membrane