Physiological significance of taurine and the taurine transporter in intestinal epithelial cells

Taurine transport in human intestinal epithelial Caco-2 cells was down-regu lated by culturing the cells in taurine-containing media and was upregulate d in a taurine-free medium. This adaptive regulation was associated with ch anges in both the Vmax and Km values of taurine transport. A change in the mRNA level of the taurine transporter (TAUT) in this regulation was also ob served. The presence of such a regulatory mechanism for maintaining the int racellular taurine content at a certain level suggests that taurine plays a n important role in the intestinal cell functions. The intracellular taurin e content was increased when Caco-2 cells were exposed to a hypertonic stre ss. TAUT was up-regulated via the increased expression of TAUT mRNA in the hypertonic cells, suggesting that taurine serves as an osmolyte and protect s the cells from osmotic stress. Similar up-regulation of TAUT was observed in the small intestine of water-deprived rats.