Modulation of tight junction formation in clone 4 MDCK cells by fatty acid supplementation

Abstract

Clone 4 MDCK cells, which generate a transepithelial electrical resistance (TER) of greater than 2,000 omega.cm2, were used to examine the role of membrane lipids in the barrier function of tight junctions. Phospholipid acyl groups were modified by supplementing cells grown in serum-free medium with 18:1(n-9), 18:3(n-3), or 18:3(n-6) complexed to albumin. Although both of these polyunsaturated fatty acids depress the melting point of membrane phospholipids, only 18:3(n-6) contributes significantly to eicosanoid production. Saturation indices of the phospholipids of cells supplemented with albumin alone, 18:1(n-9), 18:3(n-3), or 18:3(n-6) were 0.77, 0.78, 1.81, and 1.65, respectively. After trypsinization or removal of Ca2+, cells supplemented with 18:3(n-6) required longer periods of time to reestablish TER than did nonsupplemented cells or those incubated with 18:3(n-3) or 18:1(n-9). In contrast to MDCK strains I and II, clone 4 MDCK cells required continuous protein synthesis not only to reseal preexisting junctions after the addition of Ca2+ to Ca2+-depleted monolayers, but also to maintain steady-state TER. The rate of decay of TER in the presence of 1 microgram/ml of cycloheximide was 1.5 times greater in cells supplemented with either of the two 18:3 isomers than it was in nonsupplemented controls or in cells supplemented with 18:1(n-9). No significant difference was observed in the steady-state TER or selectivity of the tight junctions after fatty acid supplementation. These results suggest that there is a change in the dynamics of junction formation, rather than an alteration in their intrinsic properties.(ABSTRACT TRUNCATED AT 250 WORDS)