Developmental aspects of renal β-amino acid transport. III. ontogeny of transport in isolated renal tubule segments

Isolated renal tubules were prepared from newborn and adult Sprague-Dawley rats. They were used to study the uptake and accumulation of the β-amino acid, taurine, by renal epithelium. Initial rate as well as steady-state kinetics were studied. Initial rate studies revealed heterogeneity of uptake in newborn and adult tubules. Slower uptake was present in the newborn in the low- affinity system. Slowed efflux was found in neonatal tissue. Newborn tubules in contrast to adult tubules demonstrated uptake under anaerobic conditions. Adult and newborn tissues showed decreased uptake of taurine when incubated with β -alanine. Physiologic taurinuria, be it in the rat or man, may be due to less rapid initial uptake and/or slowed efflux from renal epithelium. Speculation: β-Amino acid transport by newborn rat renal epithelium varies from that of adult rat renal epithelium. Although heterogeneity of uptake exists in both, newborn uptake by and efflux from renal epithelium is slower, and intracellular levels are higher in the newborn. Uptake differences may be examined by luminal membrane preparations; however, slowed efflux and higher intracellular levels suggest studies on intracellular components and basal lateral membranes are warranted.