Contraluminal sulfate transport in the proximal tubule of the rat kidney

Abstract

In order to study the specificity for the contraluminal sulfate transport system the inhibitory potency of sulfate esters and sulfonate compounds on the³⁵SO ²⁻₄ influx from the interstitium into cortical tubular cells in situ has been determined. The following was found: 1. From 10 sulfate monoesters tested 9 inhibited contraluminal sulfate influx with an app.K _i between 0.6 and 6 mmol/l; the two sulfate diesters tested, however, did not. 2. Out of 8 aliphatic sulfonate compounds only three, having a NH- or OH-group in a suitable position, exerted a moderate inhibition (app.K _i ca. 2–6 mmol/l). 3. Amongst 14 benzene sulfonates tested only 2 compounds (5-nitrobenzene-sulfonate and 2-hydroxy-5-nitrobenzenesulfonate) inhibited with aK _i<5 mmol/l. 4. Out of 10 naphthalene sulfonates tested 8 inhibited with aK _i<5; the highest inhibition was seen with the NH-containing 8-anilinonaphthalene-1-sulfonate (ANS), but no inhibition with 2 compounds containing an amino group. 5. From the polycyclic sulfonates pyrene-3-sulfonate and anthracene-1-sulfonate inhibited with aK _i of approximately 2 mmol/l, while no inhibition was seen with anthracene-2-sulfonate. 6. Out of 4 amino-sulfonates tested benzene-1-amino-sulfonate and a similar benzyl-analog inhibited with aK _i of 1 mmol/l and smaller; cyclohexyl-1-amino-sulfonate (cyclamate), however, inhibited only slightly (app.K _i of 6 mmol/l). The data indicate that sulfate monoesters are well accepted by the contraluminal sulfate transport system. The affinity of sulfonate compounds to this system depends on neighbouring OH-groups −NH-groups, meta-positioned electronegative groups or a hydrophobic moiety in an appropriate position.