Oxalate:OH exchange across rat renal cortical brush border membrane

We demonstrated the presence of oxalate:OH exchange in rat renal brush border membrane. Transient concentrative uptake of oxalate ("overshoot") was observed in the presence of an inside alkaline (pH = 8.5 inside, 6.5 outside) pH gradient, but this pH gradient-stimulated oxalate uptake was abolished by 1 mM DIDS, indicating that DIDS-sensitive and -insensitive oxalate uptake mechanisms were present. The DIDS-sensitive oxalate uptake was temperature-dependent and saturable with a Km of 0.0365 mM and a Vmax of 1.38 nmol.30 second-1.mg protein-1. In addition, oxalate was transported into the osmotically active internal space. In the presence of the pH gradient, a change in transmembrane potential had no effect on pH gradient-stimulated oxalate uptake. Oxalate was exchanged for OH and this exchange was sensitive to inhibition by DIDS. Inhibition by DIDS, furosemide and probenecid facilitated the distinction of oxalate:OH exchange from formate:Cl and oxalate:Cl exchange. In preparation of our brush border membrane vesicles, no apparent SO4:HCO3 exchange was present. These data indicate that oxalate:OH exchange occurs on the brush border membrane.