Development aspects of renal beta-amino acid transport II. Ontogeny of uptake and efflux processes and effect of anoxia.

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 (less than 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 mumoles/ml ICF/120 min at four ages. The second uptake mode had an apparent Km2 = 12-16 mM and a Vmax of 45 mumoles/ml ICF/120 min. Efflux of taurine was reduced in slices from younger animals possibly accounting for taurinuria. Only other beta-amino acids inhibited accumulation. Anoxia inhibited uptake at high concentration ( greater than 1.0 mM) at each age, but taurine accumulation at low concentrations ( less than 0.4 mM) was relatively protected from anoxia in neonatal ( less than 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 maturation events in renal tubular amino acid transport.