Study on pathogenesis of urolithiasis with special reference to oxalate handling in biomembranes

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In this study we investigated mechanisms of oxalate transport in red blood cell membrane, intestinal and renal epithelial membranes which relate to oxalate absorption and excretion.1. Oxalate influx rate in red blood cell membrane increased in calcium oxalate stone formers compared to that in healthy controls. This influx was inhibited by an inhibitor of anion exchange system such as DIDS.2. There are oxalate : OH^- exchange and oxalate : HCO_3^- exchange systems both in the brush border membrane vesicles of the intraluminal side and in the basolateral membrane vesicles of the contraluminal side, in the renal proximal tubule Oxalate : OH^- exchange system shares the common transport pathway with oxalate : HCO_3^- exchange system.3. Oxalate absorption is accelerated by an increment of sodium concentration in the intestinal epithelial cells, suggesting the existence of sodium-oxalate cotransport system in the intestine. This result coincides with the fact that urinary oxalate excretion is exaggerated by adding sodium chloride during oxalate loading test.An increased oxalate influx rate in red blood cell membrane in calcium oxalate stone formers may share the common abnormality in biomembrane with the intestinal epithelium where oxalate absorption increases and with the renal epithelium where oxalate excretion increases.Further investigations are required to analyse an abnormal transporter of oxalate within cells in calcium oxalate stone formers.