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

Publisher Website
Google Scholar
Abstract
Summary: Renal cortex slices from newborn, 2-week, and 4-week-old Sprague-Dawley rats had reduced initial rates of taurine uptake compared to adult slices after short (< 30 min) incubation periods. From birth onward, steady-state accumulation occurred by at least two sodium-dependent uptake systems. The first system had an “apparent Km1” = 0.1 mM and a Vmax varying from 1.8 to 5.1 μmoles/ml ICF/120 min at four ages. The second uptake mode had an apparent Km2 = 12–16 mM and a Vmax of 45 μmoles/ml ICF/120 min. Efflux of taurine was reduced in slices from younger animals possibly accounting for taurinuria. Only other β-amino acids inhibited accumulation. Anoxia inhibited uptake at high concentrations (> 1.0 mM) at each age, but taurine accumulation at low concentrations (< 0.4 mM) was relatively protected from anoxia in neonatal (< 36 hr of age) tissue. Preincubation in taurine-free medium for 120 min enhanced low concentration, but not high concentration uptake in neonatal and 2-week slices. After preincubation in dibutyryl cyclic AMP (dbcAMP) enhanced uptake of taurine was found in adult cortex, but not in neonatal cortex. The ontogeny of renal taurine transport in cortex slices appeared to involve faster initial uptake rates and faster efflux as well as greater dependence on aerobic metabolism with maturation. Age-related differences in the response to preincubation and cyclic nucleotides were also indicative of maturational events in renal tubular amino acid transport. Speculation: Taurinuria found in the immature rat may involve decreased initial uptake rates and/or decreased efflux, but heterogeniety of transport processes across the antiluminal membrane was apparent at birth. Preincubation in taurine-free medium increased the rate of taurine accumulation by immature cortex, but changes in transport processes across the brush border membrane may account for the decrease in taurinuria found after the age of 2 weeks.