Oxalate transport by anion exchange across rabbit ileal brush border.

Abstract

This study demonstrates the presence of oxalate transporters on the brush border membrane of rabbit ileum. We found that an inside alkaline (pH = 8.5 inside, 6.5 outside) pH gradient stimulated I14Cloxalate uptake 10-fold at 1 min with a fourfold accumulation above equilibrated uptake at 5 min. 1 mM 4,4'-disothiocyanostilbene-2,2'-disulfonate (disodium salt; DIDS) profoundly inhibited the pH-gradient stimulated oxalate uptake. Using an inwardly directed K+ gradient and valinomycin, we found no evidence for potential sensitive oxalate uptake. In contrast to Cl:HCO3 exchange, HCO3 did not stimulate oxalate uptake more than was seen with a pH gradient in the absence of HCO3. An outwardly directed Cl gradient (50 mM inside, 5 mM outside) stimulated oxalate uptake 10-fold at 1 min with a fivefold accumulation above equilibrated uptake. Cl-stimulated oxalate uptake was largely inhibited by DIDS. Addition of K+ and nigericin only slightly decreased the Cl gradient-stimulated oxalate uptake, which indicates that this stimulation was not primarily due to the Cl gradient generating an inside alkaline pH gradient via Cl:OH exchange. Further, an outwardly directed oxalate gradient stimulated 36CI uptake. These results suggested that both oxalate:OH and oxalate:Cl exchange occur on the brush border membrane. To determine if one or both of these exchanges were on contaminating basolateral membrane, the vesicle preparation was further fractionated into a brush border and basolateral component using sucrose density gradient centrifugation. Both exchangers localized to the brush border component. A number of organic anions were examined (outwardly directed gradient) to determine if they could stimulate oxalate and Cl uptake. Only formate and oxaloacetate were found to stimulate oxalate and Cl uptake. An inwardly directed Na gradient only slightly stimulated oxalate uptake, which was inhibited by DIDS.

Ileal oxalate absorption and urinary oxalate excretion are enhanced in Slc26a6 null mice

“…The observation of basal net oxalate secretion in WT mouse ileum agrees with previous findings of basal net oxalate secretion in the rat (14) and rabbit (6,20) ileum under similar experimental conditions. In contrast to this phenomenon of basal net oxalate secretion in the small bowel, the distal colon of rats and rabbits typically exhibits basal net oxalate absorption (12,15).…”

“…In contrast, net oxalate transport in the mouse ileum was not as dramatically altered by a cAMP analog as frequently observed in the other species (6,11,13,15). Previous studies of oxalate transport across isolated, short-circuited epithelia (11)(12)(13) and isolated ileal brush-border membrane vesicles (19,20) have implicated a variety of anion exchange systems as mediators of transmembrane oxalate flux. However, the apparent multiplicity of exchangers and possible exchange modes (2,25,27) has made it difficult to assign a specific function to any one exchanger.…”

“…From studies of isolated, short-circuited intestinal epithelia from rats and rabbits, it is clear that transepithelial oxalate transport occurs passively through paracellular pathways and actively (secondarily) through transcellular pathways in a vectorial manner that produces net absorption or net secretion of oxalate in a segment-specific fashion (6,12,13,15). The latter studies, and others employing membrane vesicles prepared from rabbit distal ileum (19,20), suggested that transmembrane oxalate transport across the apical and basolateral membrane is mediated by one or more distinct anion exchange systems (antiporters) that exhibit varying degrees of stilbene sensitivity. The apparent multiplicity of exchangers at a given membrane, the variety of possible cotransport partners (exchange modes), and the general inability to identify a single specific exchanger (beyond stilbene sensitivity or exchange modes) have hampered a completely satisfactory explanation of net oxalate absorption or secretion by intestinal or renal epithelia.…”

Molecular characterization of the murine Slc26a6 anion exchanger: functional comparison with Slc26a1

“…Thus there is evidence for DIDS-sensitive Cl Ϫ /oxalate, OH Ϫ /oxalate, and formate/oxalate exchange in brush-border vesicles from rabbit ileum (20), and Slc26a6 is heavily expressed in small intestine (Fig. 2).…”

Oxalate: From the Environment to Kidney Stones

“…Evidence for transcellular absorption of oxalate in the intestine with regard to other anions came from observations that oxalate and Cl -share a common anion transport system in the rabbit ileum and colon, which was inhibited by the stilbene derivatives SITS and DIDS (102,103). In the rabbit colon, which is an important site for oxalate uptake and/or excretion, oxalate transport is mediated by Na + -, Cl --, and HCO 3 --dependent pathways (104,105).…”