PARACELLULAR CALCIUM-TRANSPORT ACROSS CACO-2 AND HT29 CELL MONOLAYERS

Intestinal calcium absorption has been shown to include two processes, a saturable transcellular movement and a non-saturable paracellular p athway. The potential utility of cell monolayers for studying transepi thelial intestinal calcium transport has already been demonstrated; ho wever, simultaneous evaluation of the contribution of the saturable tr anscellular and of the non-saturable paracellular processes to the tot al transepithelial transport has not yet been attempted. The aim of th is study was to investigate the contribution both of transcellular and paracellular transport processes to the total transepithelial calcium transport in two cell culture monolayers. Caco-2 cells and a clone de rived from HT29 cells (HT29-C1.19A), two cell lines derived from colon adenocarcinomas which are known to be able to exhibit typical enteroc ytic differentiation, were used. Cell monolayers were grown on a perme able support and used after 15 days of culture when these cells expres s enterocytic differentiation and high transepithelial resistance. Iso topic transport rate measurements were performed in the absence of a c hemical gradient. The paracellular route was evaluated using [H-3]mann itol. Calcium and [H-3]mannitol transport rates across cell monolayers were not significantly different. Augmentation of calcium uptake by 2 00 mM sorbitol did not significantly increase calcium or mannitol tran sepithelial transport; however, calcium accumulation in the cells was increased by about 200%. Modulation of the monolayer permeability by a ddition of 10 nM vasoactive intestinal polypeptide (VIP) or 0.5 mM car bachol treatment, which respectively increased and decreased the trans epithelial resistance, consequently modified calcium and mannitol tran sport in a parallel manner, Our results show that Caco-2 and HT29-C1.1 9A cell monolayers are good models for studying the calcium paracellul ar transport pathway.