Localization of the membrane defect in transepithelial transport of taurine by parallel studies in vivo and in vitro in hypertaurinuric mice.

Abstract

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.

Characteristics of taurine transport in freshly isolated rat hepatocytes.

“…Moreover in mammals, the presence of active taurine transport was reported in brain (22), heart (23) and kidney (24).…”

Taurine Transport in the in Vitro Perfused Human Placenta

“…Taurine has been shown to be actively transported in several different tissues (Table 1) by the B-amino acid carrier or "B" carrier (6,7). This carrier system has been described as a sodium-dependent, saturable system (9)(10)(11)(12)(13)(14) that is dependent on cellular respiration and temperature (15) as well as an external chloride gradient (16).…”

Developmental Aspects of Renal β-Amino Acid Transport II. Ontogeny of Uptake and Efflux Processes and Effect of Anoxia

“…The first uptake system had an apparent Km of 0.1-0.2 mM and the second system values of 13-15 mM, akin to those concentrations found in the mouse (9). The first site is saturable and could serve to facilitate transport in the concentration range of taurine found in rat plasma, 200-400 mmole/liter (2,9). The second transport site is similar to the nonsaturable taurine transport system found in Erhlich ascites cells and rat jejenum by Christensen et al (10).…”

“…Segal and associates (20,23,27) have been unable to confirm the frnding that transport systems emerge with age using both Sprague-Dawley and Long-Evans rats (24). The pattern of transport processes for taurine accumulation in slices from immature and adult animals would obviously be informative in view of the increased taurinuria of young animals described in the preceding paper (9).…”

“…Taurine accumulation by adult rat and mouse slices is sodiumdependent at both transport skes and only other /3-amino acids, of all amino acids examined, inhibited the uptake of taurine in a competitive fashion at both sites (7)(8)(9). Thus, an examination of these conditions is germaine.…”