A B S T R A C T We investigated the mechanism of taurinuria in three inbred strains of mice: A/J, a normal taurine excretor (taut+) ; and two hypertaurinuric (taut) strains, C57BL/6J and PRO/Re. Plasma taurine is comparable in the three strains (-0.5 mM), but taurinuria is 10-fold greater in tau'-animals. Fractional reabsorption of taurine is 0.967±0.013 (mean±SD) in A/J); and 0.839±0.08 and 0.787+0.05 in C57BL/6J and PRO/Re, respectively. Taurine concentration in renal cortex intracellular fluid (free of urine contamination) is similar in the three strains. Taurine reabsorption is inhibited by fi-alanine, in taut`and taut' strains. These in vivo findings reveal residual taurine transport activity in the taut' phenotype and no evidence for impaired efflux at basilar membranes as the cause of impaired taurine reabsorption.Cortex slices provide information about uptake of amino acids at the antiluminal membrane. Taurine behaves as an inert metabolite in mouse kidney cortex slices. Taurine uptake by slices is active and, at < 1 mM, is greater than normal in taut' slices. Concentration-dependent uptake studies reveal more than one taurine carrier in taut+ and taut' strains. The apparent K. values for uptake below 1 mM are different in taut' and taut`slices (-0.2 mM and 0.7 mM, respectively); the apparent K. values above 1 mM taurine are similar in taut and taut' slices. Efflux from slices in all strains is the same (0.0105-0.0113 Amol min-lfg-1 wet wt), but taut' tissue retains about 10% more radioactivity over the period of efflux. P-Alanine is actively metabolized in mouse kidney.

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