Osmoregulatory Alterations in Taurine Uptake by Cultured Human and Bovine Lens Epithelial Cells

Abstract

Schafer, Grant D., Osmoregulatory Alterations in Taurine Uptake by Cultured Human and Bovine Lens Epithelial Cells. Master of Science (Biomedical Sciences), July, 2002, 47 pp., 3 tables, 12 figures, bibliography, 43 titles. Purpose. Using cultured human lens epithelial cells (HLECs) and bovine lens epithelial cells (BLECs) and the nature of the relationship between taurine-concentrating capability and intracellular polyol accumulation or extracellular hypertonicity. Methods. The kinetic characteristics of taurine accumulation based upon the measurement in vitro [3H]-taurine uptake were compared in cultured HLECs and BLECs pre-exposed to either galactose-supplemented medium or extracellular hypertonicity. Results: The capacity to accumulate [3H]-taurine was significantly lowered after chronic (20 hour) incubation of cultured BLECs in 40 mmol/l galactose in contrast to HLECs. Inhibition of the intracellular taurine transport site appeared to be noncompetitive as there was a marked reduction in the Vmax without significant alteration in the Km. Galactitol content in BLECs exceeded five times that found in HLECs. The coadministration of the aldose reductase inhibitor, sorbinil with 40 mmol/l galactose completely prevented the inhibitory effect of galactose on [3H]-taurine uptake. Acute expression (3 hours) of HLECs and BLECs to a range of 10 to 40 mmol/l galactitol or 10 to 40 mmol/l galactose plus sorbinil-supplemented medium suggested by Dixon plot analysis that neither galactitol nor galactose interacted with the extracellular taurine transport site. In contrast, [3H]-taurine accumulation was markedly elevated in both HLECs and BLECs after chronic exposure to galactose-free medium made hyperosmotic by supplementation with sodium chloride. The enhanced taurine uptake capacity involved an increase in Vmax without significant change in the Km value. Conclusions: These results demonstrate lens epithelial cells express a taurine transporter protein capable of active uptake but predisposed to inhibition by intracellular galactitol when the sugar alcohol is present in high enough concentration to interfere with cell metabolism. Furthermore, lens epithelial cells respond to hypertonic stress by raising taurine transport activity.