Transport and metabolism of palmitate in the rat liver. Net flux and unidirectional fluxes across the cell membrane.

The unidirectional fluxes of palmitate across the liver cell membrane and metabolic uptake rates were measured employing the multiple-indicator dilution technique. The following results were obtained: (1) Influx and net uptake rates do not vary proportionally to each other when albumin and palmitate concentrations are varied. (2) Efflux is significant for albumin concentrations in the range between 1.5 and 500 microM. (3) At 150 microM albumin net uptake rates are proportional to the total (bound plus free) extracellular palmitate concentration in the range from 10 to 600 microM; the dependence of influx rates on the palmitate concentration is rather concave up. (4) When albumin and palmitate are both varied at an equimolar ratio, pseudo-saturation appears in the net uptake rates; the influx rates also show pseudo-saturation, but with a declining tendency at the higher concentrations. (5) The intracellular palmitate concentration is strongly influenced by albumin. At very low concentrations of the protein (1.5 microM) the intracellular concentration is practically equal to the extracellular one; at physiological albumin concentrations, however, the intracellular palmitate concentration is less than 2% of the extracellular one. (6) Saturation of net uptake with respect to the intracellular palmitate concentration was not observed with concentrations up to 46 microM.

Octanoate transport in the isolated, perfused rat liver.

The multiple indicator dilution technique was used to investigate octanoate transport in the isolated, perfused rat liver. The form of the octanoate outflow profiles depends on albumin concentration. The steady-state intracellular octanoate concentration and the rate of uptake increase when the albumin concentration is decreased. At physiological albumin concentrations, the intracellular concentration of octanoate is only 7% of the extracellular concentration. Exchange between the intra- and extracellular space, however, is very rapid, irrespective of the albumin concentration and consequently exchange is not rate limiting for metabolism.

The influence of albumin on palmitate transport in the isolated perfused rat liver.

Unidirectional fluxes (influx and efflux) and the net flux of palmitate across the hepatocyte membrane were measured in the intact rat liver employing the multiple indicator dilution technique. At albumin concentrations in the range between 0.1 and 0.5 mM the influx rate was 2.3 times greater than that of the net flux. The rate of efflux was somewhat higher than the net flux, indicating that palmitate undergoes an exchange process across the liver cell membranes with efflux to the extracellular albumin site being significant. At lower albumin concentrations, however, the influx/net flux ratio approached unity, implying that transport becomes a rate-limiting factor for metabolism.

Octanoate transport in the isolated, perfused rat liver

The multiple indicator dilution technique was used to investigate octanoate transport in the isolated, perfused rat liver. The form of the octanoate outflow profiles depends on albumin concentration. The steady-state intracellular octanoate concentration and the rate of uptake increase when the albumin concentration is decreased. At physiological albumin concentrations, the intracellular concentration of octanoate is only 7% of the extracellular concentration. Exchange between the intra-and extracellular space, however, is very rapid, irrespective of the albumin concentration and consequently exchange is not rate limiting for metabolism

The influence of albumin on palmitate transport in the isolated perfused rat liver

Unidirectional fluxes (influx and efflux) and the net flux of palmitate across the hepatocyte membrane were measured in the intact rat liver employing the multiple indicator dilution technique. At albumin concentrations in the range between 0.1 and 0.5 mM the influx rate was 2.3 times greater than that of the net flux. The rate of efflux was somewhat higher than the net flux, indicating that palmitate undergoes an exchange process across the liver cell membranes with efflux to the extracellular albumin site being significant. At. lower albumin concentrations, hower, the influx/net flux approached unit, implying that transport becomes a rate-limiting factor for metabolism