Luminal and Basolateral Membrane Transport of Glutathione in Isolated Perfused S1, S2, and S3Segments of the Rabbit Proximal Tubule

Abstract

Abstract. Lumen-to-bath and bath-to-lumen transport rates of glutathione (GSH) were measured in isolated perfused S1, S2, and S3segments of the rabbit proximal tubule. In lumen-to-bath experiments, the perfusion solution contained 4.6 μM3H-GSH with or without 1.0 mM acivicin. In all three segments perfused without acivicin, luminal disappearance rate (JDL) and bath appearance rate (JAB) of3H-GSH were 14.5 ± 0.5 and 2.2 ± 0.8 fmol/min per mm tubule length, respectively. With acivicin present,JDLandJABwere reduced to 1.3 ± 0.4 and 0.5 ± 0.3, respectively, with no differences among segments. Cellular concentrations of3H-GSH in S1, S2, and S3segments when acivicin was absent were 23.1 ± 2.0, 31.7 ± 11.4, and 143.5 ± 17.9 μM, respectively. With acivicin in perfusate, cellular concentrations were reduced but there was no change in the heterogeneity profile. In bath-to-lumen transport experiments (S2segments only), the bathing solution contained 2.3 μM3H-GSH.3H-GSH appearance in the lumen (JAL, fmol/min per mm) and cellular accumulation from the bath were studied with and without acivicin in the perfusate.JALvalues were 3.0 ± 0.2 and 0.2 ± 0.03 while cellular concentrations were 9.5 ± 1.0 and 6.1 ± 0.5 μM, respectively. It is concluded that: (1) GSH is primarily removed from the luminal fluid after degradation to glycine, cysteine, and glutamate, which are absorbed; (2) GSH can be absorbed intact at the luminal membrane; (3) the S3segment has the greatest GSH cellular concentration because its basolateral membrane has less capacity for cell-to-bath transport of GSH; and (4) GSH can be secreted intact from the peritubular compartment into the tubular lumen.