Polarity of taurine transport in cultured renal epithelial cell lines: LLC-PK1 and MDCK.

We characterized taurine transport in two continuous renal epithelial cell lines: LLC-PK1, derived from the proximal tubule of the pig, and the Madin-Darby canine kidney (MDCK), which was originated from the distal tubule of the dog. In the LLC-PK1 cell line, taurine transport is greatest at the apical surface of the cell, whereas in the MDCK cell line taurine transport is greatest at the basolateral surface. Both apical and basolateral surfaces of LLC-PK1 and MDCK cells exhibit an adaptive response to the extracellular taurine concentration (medium taurine concentration). Only the basolateral surface of the MDCK cell responded to hyperosmolality with increased taurine accumulation. This indicates differential control of the beta-amino acid transport system by substrate and external tonicity. The function of the beta-amino acid transport system may be different depending on the cell. In the LLC-PK1 cell, there is net transepithelial movement of taurine and changes in transporter activity in response to supply of substrate. In contrast, taurine accumulation by the MDCK cell appears to be a mechanism for adaptation to osmotic stress.