Hypoxanthine Uptake in Isolated Rat Renal Cortical Tubule Fragments

John W. Foreman; Stanton Segal

doi:10.1172/JCI109361

Hypoxanthine Uptake in Isolated Rat Renal Cortical Tubule Fragments

John W. Foreman and Stanton Segal

Published April 1, 1979 - More info

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Abstract

Isolated renal tubule fragments prepared from adult Sprague-Dawley rats were used to study the cellular uptake of hypoxanthine. This uptake was rapid, reaching a steady state after 30 min of incubation. Analysis of the intracellular pool during the initial uptake and at the steady state revealed a concentration gradient of hypoxanthine consistent with active transport, although only one-third of the transported hypoxanthine remained unmetabolized. The remainder of the transported hypoxanthine was converted to inosine and inosinic acid, but detectable conversion to uric acid was not noted. A kinetic analysis of uptake revealed that two systems for cellular entry of hypoxanthine existed with K_m1 = 0.005 and K_m2 = 0.80 mM. Hypoxanthine uptake at physiologic concentrations was oxygen, sodium, and temperature dependent, but the addition of metabolic fuels and alteration of the medium pH over the range of from 6.1 to 7.4 had no effect. Adenine, guanine, and inosine inhibited the uptake of hypoxanthine via the low-K_m system which mediates the majority of uptake at physiologic levels. Xanthine, uric acid, and probenecid inhibited uptake via the high-K_m system, but did not affect uptake via the low-K_m system. The data indicate that hypoxanthine at physiologic levels is transported into the renal tubule cell via a system different from that for other oxypurines.