Hypertonicity stimulates taurine uptake and transporter gene expression inCaco-2 cells

The osmoregulation of taurine transport in intestinal epithelial cells was investigated using human intestinal Caco-2 cells. The activity of taurine t ransport in the Caco-2 cells was increased by hypertonic conditions. This h ypertonicity-induced upregulation was dependent on both the culturing time and the osmotic pressure. Hypertonicity did not affect the activity of L-le ucinc, L-lysine, or L-glutamic acid transport, suggesting that osmoregulati on was specific to taurine transport. The intracellular taurine content of Caco-2 cells was also increased by culturing in a hypertonic medium. These hypertonicity-induced changes in the intracellular taurine content and tran sport activity were reversible. A kinetic analysis of taurine transport in the control and hypertonic cells suggested that the up-regulation was assoc iated with an increase in the amount of the taurine transporter. The mRNA l evel of the taurine transporter in hypertonic cells was markedly higher tha n that in the control cells, indicating that this osmotic regulation was du e to the increased expression of the taurine transporter gene. (C) 1999 Els evier Science B.V. All rights reserved.