UNCOUPLING EFFECT OF POLYUNSATURATED FATTY-ACID DEFICIENCY IN ISOLATED RAT HEPATOCYTES - EFFECT ON GLYCEROL METABOLISM

The effects of a 4-week deficiency in polyunsaturated fatty acids (PUF A) in isolated rat hepatocytes have been investigated for oxidative ph osphorylation and fatty acid, dihydroxyacetone (DHA) or glycerol metab olism. Oxygen uptake was significantly increased (by 20%) with or with out fatty acid addition (octanoate or oleate) in the PUFA-deficient gr oup compared with controls. The effect persisted after oligomycin addi tion but not after that of potassium cyanide, leading to the conclusio n that, in these intact cells, the mitochondria were uncoupled. The PU FA-deficient group exhibited a significant decrease in the cytosolic A TP/ADP ratio, whereas the mitochondrial ratio was not affected. PUFA d eficiency led to a 16% decrease in DHA metabolism owing to a 34% decre ase in glycerol kinase activity; the significant decrease in the ATP/A DP ratio was accompanied by an increase in the fractional glycolytic f lux. In contrast, glycerol metabolism was significantly enhanced in th e PUFA-deficient group. The role of the glycerol 3-phosphate dehydroge nase step in this stimulation was evidenced in hepatocytes perifused w ith glycerol and octanoate in the presence of increased concentrations of 2,4-dinitrophenol (Dnp) : uncoupling with Dnp led to an enhancemen t of glycerol metabolism, as found in PUFA deficiency, although it was more pronounced than in controls. The matrix/cytosol gradients for re dox potential and ATP/ADP ratio were lower in cells from PUFA-deficien t rats, suggesting a decreased mitochondrial membrane potential in acc ordance with the uncoupling effect. Moreover, a doubling of the mitoch ondrial glycerol 3-phosphate dehydrogenase activity in the PUFA-defici ent group compared with controls led us to conclude that the activatio n of glycerol metabolism is the consequence of two mitochondrial effec ts: uncoupling and an increase in glycerol 3-phosphate dehydrogenase a ctivity.