Mechanisms and kinetics of α-linolenic acid uptake in Caco-2 clone TC7

Abstract

The uptake kinetics of α-linolenic acid (18:3(n−3)), an essential fatty acid, were investigated in the human intestinal cell line Caco-2. Four clones (PD10, PF11, PD7 and TC7) from the heterogeneous parental Caco-2 cells population were used. After a screening step using isolated cells, the TC7 clone was selected for the study of α-linolenic acid uptake. [1- 14C]linolenic acid dissolved in 10 mM taurocholate was presented to the microvillus plasma membrane (apical side) of TC7 differentiated cells, grown on a semi-permeable polycarbonate membrane. The results show that the initial rate of uptake is not a linear function of the 18:3(n−3) monomer concentration in the incubation medium. In the monomer concentration range studied (0.2 to 36 μM) apical uptake was saturable and followed Michaelis–Menten kinetics ( V max=15.4±0.6 nmol/mg protein per min, K m=14.3±1.3 μM). In addition, it was temperature- and energy-dependent but was apparently unaffected by the sodium gradient and intracellular metabolic fate of 18:3(n−3). Excess of unlabeled saturated or unsaturated long chain fatty acids (C 16 to C 22) led to a 27–68% reduction of [1- 14C]linolenic acid uptake. Likewise basolateral uptake was saturable ( V max=4.9±0.7 nmol/mg protein per min, K m=8.7±2.9 μM). These facts argue in favour of the existence in these human intestinal cells of a carrier-mediated transport system for α-linolenic acid and probably other long chain fatty acids as well.