Adaptive regulation of taurine transport in two continuous renal epithelial cell lines

Abstract

Taurine is actively transported by a beta-amino acid transporter located on the proximal tubule apical surface. We have characterized taurine transport into confluent monolayers of two continuous renal epithelial cell lines: LLC-PK1, a cell of porcine proximal tubular origin, and the Madin-Darby canine kidney cell line (MDCK) of distal origin. Taurine uptake is linear up to 90 minutes in LLC-PK1 cells and 180 minutes in MDCK cells. This process is highly dependent upon Na+ as the cation and either Cl- or Br- as the anion. Taurine uptake is inhibited by another beta-amino acid, beta-alanine, to a greater extent than the alpha-analog, L-alanine or other alpha-amino acids. Incubation of cell monolayers with taurine-free medium (0 microM taurine) induces an increase in Na(+)-dependent taurine uptake when compared to cells exposed to standard medium (50 microM taurine). When cells were incubated in medium containing high taurine (500 microM), uptake was decreased as compared to control cells. This adaptive response is evident by 12 hours in both cell lines and is the result of changes in the apparent transport maximum (Jmax) rather than the apparent Km for taurine. The changes in transport observed after manipulation of medium taurine concentration were not associated with differences in taurine efflux. In summary, taurine is transported by a beta-specific, Na-Cl dependent process in both renal epithelial cell lines. Although the factors which regulate taurine transport are not known, an increased transport maximum is observed in cells which have been taurine-starved, and a decreased Jmax is seen in cells supplied with excess taurine.(ABSTRACT TRUNCATED AT 250 WORDS)

Taurine behaves as an osmolyte in Madin-Darby canine kidney cells. Protection by polarized, regulated transport of taurine.

“…When MDCK cells are cultured on plastic tissue culture dishes in defined medium lacking taurine, their rate of uptake of taurine is increased to two times the rate in cells grown in defined medium containing 50 ,M taurine (12). To examine the polarity of the effect of medium taurine on taurine uptake, we added 50 MAM taurine to the medium 2 d after seeding cells on filters.…”

“…The activity of the cotransporter in the brush border ofthe proximal tubule contributes to whole-body homeostasis of taurine: activity increases in animals fed diets deficient in taurine-and sulfur-containing amino acids (6,12,22). The cotransporter has not been identified in other segments of the nephron.…”

“…Furthermore, the same level of increased of taurine content was observed in the inner medulla when rats were prevented from drinking for 4 d. The taurine content ofthe inner medulla returned to control levels after hydration (T. Nakanishi, unpublished results). Taurine transport in MDCK cells grown on plastic tissue culture dishes has been characterized recently ( 12), but the location of the transporter in the cells and regulation by hypertonicity was not examined.…”

“…High intracellular taurine concentrations in tissues reported to have limited capacity for taurine biogenesis (7) indicate that taurine is probably taken up against a concentration gradient from extracellular fluid where its concentration is 50,uM (8). Na+-dependent taurine transport has been well characterized in many tissues (9)(10)(11)(12)(13)(14)(15)(16). The transporter has a far higher affinity for a-amino acids than for a-amino acids (6), and is unusual in that chloride is also required (13,(17)(18)(19)(20).…”

The Relative Roles of External Taurine Concentration and Medium Osmolality in the Regulation of Taurine Transport in LLC-PK1 and MDCK Cells

“…Taurine transport is regulat ed by the dietary intake of taurine in the rat (6), by the extrac ellular concentration in kidney cells in culture (7), and by medium osmolality in MD CK cells (8). We have previousl y demon strated that taurine transport in both MDCK and LLC-PK1 cells is increased after incubation of cell monolayers in taurin e-free medium and is decreased after incubation of cells in high levels of extracellular taurine (8).…”