Transport of oxalate across the rabbit papillary surface epithelium

The renal papilla and pelvic recesses of the mammalian kidney are thought to be the anatomical sites of initial kidney stone formation. We studied oxalate transport across the renal papillary surface epithelium.

In vitro oxalate transport across the papillary surface epithelium was studied by dissecting it off of the papilla and mounting it in a modified Ussing chamber. Experiments were conducted using physiological Ringer's solution at 37C. Removal or appearance of radioactive oxalate from the solution bathing the apical papillary surface epithelium surface was used as a measure of transepithelial transport.

When only the papillary surface epithelium apical surface was exposed to oxalate (17 micromol./l.), the apical to basolateral flux of oxalate was 7.1 +/- 1.5 nmol./cm.2 per hour. When only the basolateral side was perfused with oxalate, the basolateral to apical oxalate flux was 1.6 +/- 0.7 nmol./cm.2 per hour. When the apical and basolateral surfaces were exposed to oxalate, a net apical to basolateral flux of oxalate was 3.0 +/- 0.7 nmol./cm.2 per hour. There was almost complete inhibition of apical to basolateral oxalate transport when the experiments were conducted at 20C. Absorption of oxalate across the papillary surface epithelium was decreased by the addition of 1 mM. 4, 4'-diisothiocyanatsostilbene-2,2'-disulphonic acid (DIDS), independent of sodium, but reduced by the presence of chloride in the apical solution. Increasing the pH of the apical solution from 7. 4 to 7.8 also resulted in a significant decrease in papillary surface epithelium oxalate uptake.

Rabbit papillary surface epithelium demonstrates oxalate absorption by mechanisms that may be similar to those described previously for renal and colonic epithelia. Absorption of oxalate across the papillary surface epithelium may have a role in the prevention of initial calcium oxalate stone formation within the pelvic recesses.