EFFECT OF ALPHA-FETOPROTEIN AND ALBUMIN ON THE UPTAKE OF POLYUNSATURATED FATTY-ACIDS BY RAT HEPATOMA-CELLS AND FETAL-RAT HEPATOCYTES

The uptake of polyunsaturated fatty acids by rat hepatoma cells and fetal hepatocytes has been studied using albumin and alpha-fetoprotein (AFP) as carrier proteins. Both types of cells took up linoleic (18:2 (n - 6)) and linolenic (18:3(n - 3)) fatty acids at the same rate when they were added complexed either to albumin or AFP at a 1:1 molar ratio. At 37-degrees-C a greater incorporation of arachidonic acid (20:4(n - 6)) and mainly docosahexaenoic acid (22:6(n - 3)) was observed when these acids were bound to albumin (6.5 nmol 20:4(n - 6); 6.4 nmol 22:6(n - 3)/million cells) as compared to AFP (5.5 nmol 20:4(n - 6); 4.3 nmol 22:6 (n - 3)/million cells). The 20:4(n - 6) and 22:6(n - 3) uptake seems to be inversely related to the apparent association constants (k'a) between these fatty acids and both proteins (1.3 and 1.5. 10(-7) M-1 20:4(n - 6) and 22:6(n - 3) for albumin; 6.4 and 54.0. 10(-7) M-1 20:4(n - 6) and 22:6(n - 3) for AFP). Experiments carried out at 4-degrees-C indicated that binding of 20:4(n - 6) (0.83 nmol/million cells in presence of albumin; 2.16 nmol/million cells in presence of AFP) and 22:6(n - 3) (0.83 nmol/million cells in presence of albumin; 1.32 nmol/million cells in presence of AFP) by cell membranes was also inversely related to the k'a of these proteins. At 4-degrees-C, the k'a of AFP and albumin for 20:4(n - 6) and 22:6(n - 3) changed considerably (12.7 and 9.6. 10(-7) M-1 20:4(n - 6) and 22:6(n - 3) for albumin; 3.9 and 14.6. 10(-7) M-1 20:4(n - 6) and 22:6(n - 3) for AFP) with respect to the k'a calculated at 37-degrees-C. Hence, k'a values were higher for albumin and lower for AFP than the corresponding values at 37-degrees-C. It was concluded that uptake by cells and interaction of fatty acids with cell membranes depend mainly on the k'a of fatty acids and carrier proteins at equilibrium.