Heterogeneity of the beta-amino-preferring transport system in rat kidney cortex. Differential influence of glutathione oxidation.

Taurine, a naturally found beta-amino acid, is inert in rat renal cortex slices. Its active accumulation by slices is abolished by anaerobiosis, a strongly acidic media or the removal of Na+. Concentration-dependent uptake studies reveal more than one taurine carrier: the apparent Km value for uptake below 1.1 mM is 0.4 mM and the apparent Km value above 1.1 mM is 14.5 mM. Of all amino acids tested only beta-alanine, another beta-compound, inhibited uptake. The oxidizing agent diamide was used to lower the concentration of GSH in rat cortex slices. The ability to accumulate taurine by the low Km system was decreased in diamide-treated slices, but not by the high Km system. Diamide was found to greatly augment efflux of taurine taken up from lower concentrations but not from higher concentrations. GSH in the media prevented this diamide-induced inhibition of uptake and enhanced efflux at lower taurine concentrations. A possible mechanism of diamide inhibition of uptake is that intracellular GSH depletion leads to greatly enhanced efflux of taurine, thus preventing uptake.