Binding of the anion-exchange inhibitor 3Hz-labeled 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid (DIDS) to highly purified luminal and basolateral beef kidney tubular membranes was characterized. Specific binding of [3H2]DIDS is present in both luminal and basolateral membranes. Scatchard analysis revealed a Kd for [3Hz]DIDS of 5.5 pM and 19.3 pM and a maximal number of binding sites of 10.9 nmol and 31.7 nmol DIDS/mg protein in basolaterdl and luminal membranes, respectively. To assess the role of this putative anion exchanger on transport we measured 3 5 S 0 4 uptake by luminal and basolateral membranes. In both luminal and basolateral membranes sulfate uptake was significantly greater in the presence of an outward-directed C1 gradient, OH gradient or HCOJ gradient than in the absence of these gradients. There was an early anion-dependent sulfate uptake of five to ten times the equilibrium uptake at 60 min. The sulfate taken in could be released by lysis of the vesicles indicating true uptake and not binding of sulfate. No significant difference in SO4 uptake was found in the presence and in the absence of valinomycin, indicating that the anion exchanger is electroneutral. The anion-dependent sulfate uptake was completely inhibited by either DIDS or furosemide in both luminal and basolateral membranes. Dixon analysis of HC03-dependent SO4 uptake by luminal membranes in the presence of different concentrations of DIDS revealed a Ki for DIDS of 20 pM. The similar values of the Kd for [3H2]DIDS binding and the Ki for DIDS inhibition of SO4 uptake might suggest an association between DIDS binding and the inhibition of SO4 transport. In addition, an inward-directed Na gradient stimulated sulfate uptake in luminal but not in basolateral membranes. The Na-dependent sulfate uptake in luminal membranes was also inhibited by DIDS. We conclude that, in addition to the well-known Na-dependent sulfate uptake in luminal membranes, there exists an anion exchanger in both basolateral and luminal membranes capable of sulfate transport. . Lucci and Warnock [6] have shown inhibition of volume reabsorption by furosemide and 4-acetamido-4-isothiocyano-2,2'-stilbene disulfonic acid (SITS) when added to the luminal perfusion solution in microperfusion studies of superficial proximal convoluted tubules of rat. In addition, the disulfonic stilbene SITS has been shown to inhibit H C 0 3 and fluid reabsorption by the proximal tubule when added only to the peritubular fluid [7], and to inhibit SO, transport when added to either bath or perfusate [8]. Taken together these data suggest the existence of an anion exchanger in both the luminal and in the peritubular side of the proximal tubular cell. Therefore, the purpose of the present study was to characterize specific binding of [3H2]DIDS by highly purified luminal and basolateral renal tubular membranes and to assess the role of this Correspondence to Z . Talor, Section of Nephrology (m/c 793)
A patient who ingested carburetor fluid developed methanol intoxication followed by hypouricemia, hypophosphatemia, glycosuria, and hyperchloremic metabolic acidosis. Renal clearances of phosphate, uric acid, glucose, and bicarbonate were found to be elevated indicating the presence of Fanconi's syndrome. The authors postulate that the Fanconi's syndrome observed in our patient was the result of the organic solvents present in the mixture.
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