β-Amino Acid Transport in Isolated Tubule Segments

Abstract

Using taurine as a model substrate, β-amino acid transport in isolated rat renal cortical tubule segments as studied. Heterogeneity of taurine accumulation was found in tubule segments and has previously been measured in renal cortex slices. In contrast to studies in cortical slices, initial rate kinetics could also be determined, and demonstrated uptake by two systems. Efflux of taurine from tubule cells was measured and showed 50% remaining in tubule segments after 30 min incubation in taurine-free medium. Concentrative uptake was prevented by NaCN and iodoacetate. Incubation with other β-amino acids resulted in decreased taurine accumulation. An important although unexpected finding was decreased taurine uptake by isolated tubules in the presence of Krebs-Ringer phosphate and Tris-HCl buffer as compared to Krebs-Ringer bicarbonate buffer. Isolated tubule preparations provide a rapid means of assessing β-amino acid transport including initial rate kinetics. However, when using tubules to study uptake, the buffer medium may play a critical role.

Fasting Reverses the Renal Adaptation to Altered Dietary Sulfur Amino Acid Intake

“…Transport studies were performed in isolated renal cortex tubules, as previously described (14,15). Minced cortex was digested in 0.375% collagenase I1 (Wor-thington, N.J.) at room temperature in Krebs -Ringer bicarbonate medium.…”

“…Tissue and medium were constantly gassed with 95% 02:5% CO,. Concentrative uptake studies were performed as described (14,15). Concentration-dependent uptake was measured using unlabeled taurine in concentrations ranging from 0.009 to 20 mM plus 1.0 pCi of [1-I4C] taurine.…”

“…Concentration-dependent uptake was measured using unlabeled taurine in concentrations ranging from 0.009 to 20 mM plus 1.0 pCi of [1-I4C] taurine. Initial rate kinetics was measured after 5 min of incubation, as it has previously been established that taurine uptake reaches steady state after 20 min incubation (9,14,15).…”

“…Uptake of taurine was measured by determining distribution ratio ( c p d m l ICF to c p d m l of medium). The percentage of trapped medium in the pellet was determined using radiolabeled polyethylene glycol, as previously described (14). Since polyethylene glycol can be used as a marker of the extracellular fluid (ECF), the proportion of ECF in a pellet can be derived.…”

The Influence of Hypotaurine on Taurine Transport in Isolated Renal Cortex Tubules

“…Taurine uptake was determined by a previously described method (4)(5)(6) and tissue was incubated in Krebs -Ringer bicarbonate medium gassed continuously with 95% 0,-5% CO,. was used to separate tubules and all glassware used was freshly siliconized.…”