Polarized nature of taurine transport in LLC-PK1 and MDCK cells: Further characterization of divergent transport models.

Taurine transport was measured in cultured epithelial cells-LLC-PK1 and MDCK-grown on permeable membrane supports. Taurine transport by LLC-PK1 cells was greater on the apical surface compared to the basolateral surface. MDCK cells exhibited greater taurine uptake from the basolateral side. Transepithelial taurine flux was in the direction of apical to basolateral in the LLC-PK1 monolayers. There was no net transepithelial movement of taurine in the MDCK monolayers. Efflux of taurine from the apical and the basolateral membrane surfaces of LLC-PK1 cell monolayers was stimulated by externalβ-alanine but not L-alanine. Efflux of taurine from MDCK cell monolayers was stimulated byβ-alanine on the basolateral surface. While the competitive inhibitor guainidinoeithane sulfonate (GES) competitively inhibited taurine uptake to a similar degree on the apical and basolateral surface of LLC-PK1 cell monolayers, GES had a more potent inhibitory effect on the basolateral taurine uptake in MDCK cells when compared to its inhibition of apical taurine transport. We conclude that there are characteristic differences in transport of taurine by apical and basolateral surfaces of LLC-PK1 and MDCK cells which may be the consequence of asymmetric distribution or unique structural properties of the taurine transporter.