DEXAMETHASONE AND LIPOPOLYSACCHARIDE REGULATION OF TAURINE TRANSPORT IN CACO-2 CELLS

Intracellular enterocytic levels of the immunomodulator taurine decrea se significantly in response to trauma and surgical insult. The effect of physiological stress on enterocyte taurine uptake is unknown. The aim of this study was to compare taurine transport under basal and str essed conditions using the human intestinal Caco-2 cell line in vitro. Caco-2 cells were incubated with 10 nM [1,2-H-3]taurine at 37 degrees C and 5% CO2 and taurine uptake was examined over the range of 0.1-10 mu M to determine kinetic parameters of the transporter. The culture medium was then supplemented with dexamethasone and/or lipopolysacchar ide (LPS) and taurine uptake was calculated as picomoles per milligram protein per hour. Statistics were by unpaired Student's t test. Tauri ne uptake was hyperbolically related to taurine concentration and obey ed Michaelis-Menten kinetics with a K-m of 5.27 +/- 0.95 mu M and V-ma x of 1125.43 +/- 130.9 pmole/mg protein/ hour, Dexamethasone (1-1000 m u M) significantly reduced taurine uptake by up to 66.15%. LPS (1 mu g /ml) impaired transport of taurine by 15.7%, and in combination with d examethasone (100 mu M) by 42.4%. All results are mean of at least thr ee experiments and P < 0.05. We have established that taurine uptake b y enterocytes is downregulated by dexamethasone. This may relate to th e decreased intestinal levels of taurine observed in trauma and surger y patients. Further study may elucidate mechanisms whereby homeostasis of enterocyte taurine might be maintained during sepsis. (C) 1997 Aca demic Press.