Yoon M, Jung H, Lee H, Park T. 2001. Beta-alanine induced down-regulation of the taurine transporter activity in the human colon carcinoma cell line (HT-29). J Korean Soc Food Sci Nutr 30(2):314–319.
In the present study, effects of -alanine, a known taurine antagonist for its structural similarity, on the adaptive regulation and kinetic behavior of the taurine transporter were investigated in the HT-29, human colon carcinoma cell line. Pretreatment of the cell with -alanine(10mM) for varying periods from 3 to 30 hrs significantly reduced the taurine uptake compared to the value for control cells. This decrease in the taurine transporter activity was dependent on the incubation time with -alanine, and the maximal down-regulation of the transporter activity was observed in cells pretreated with -alanine for 24 hrs (25% of the control value, p<0.01). The taurine transporter appears to bind exclusively with -alanine in the HT-29 cells since the same concentration of -alanine added in the culture medium for 24 hrs did not influence the taurine uptake. Kinetic analyses of the taurine transporter activity was performed in the HT-29 cell line with varying taurine concentration (5~60M) in the uptake medium. Active taurine uptake was significantly lower in -alanine pretreated cells compared to the value for control cells in the range of taurine concentration used in the experiment (p<0.001). The cells pretreated with -alanine showed a 50% lower maximal velocity (Vmax, 1.72.0 nmole.mg .), and a 99% higher Michaelis constant (Km, 40.37.6M) than the control values (3.31.9 nmole.mg ., and 20.32.1M, respectively). These results on kinetic data suggest that -alanine induced down-regulation of the taurine transporter activity was associated with decreases in both maximal velocity and affinity of the transporter.