Contraluminal sulfate transport in the proximal tubule of the rat kidney

In order to evaluate the specificity for the contraluminal sulfate transport system the inhibitory potency of phenol- and sulfonphthaleins, of sulfamoyl-compounds (diuretics) as well as diphenylamine-2-carboxylates (Cl- channel blockers) on the 35SO4(2-) influx from the interstitium into cortical tubular cells in situ has been determined. The following was found: 1) Phenolsulfonphthalein (phenol-red) inhibited with an app. Ki-value of 1.7 mmol/l, while analogs which had additional Br-atoms in position 3 and/or 5, i.e. bromphenol-blue, bromcresol-purple and bromcresol-green, inhibited with an apparent Ki of 0.1 and 0.5 mmol/l respectively. 2) Phenolphthalein and tetrabromphenolphthalein did not inhibit, while the disulfonate dyes bromsulfalein, fuchsin acid and indigocarmine inhibited with a Ki between approximately equal to 1 and 3 mmol/l. The highest inhibitory potency in this class of compounds was seen with orange G (app. Ki 0.07 mmol/l). The monosulfonate dyes tested, fluorescein-sulfonate and orange I inhibited moderately with an app. Ki of approximately equal to mmol/l. 3) The 3-sulfamoyl compounds inhibited to a varying degree, when they had a neighbouring -NH-group (furylmethylamino-group), i.e. in position 6 to the COOH or SO3H-group, or when they had a phenoxy-group in position 4. 4) 4-sulfamoylbenzoate and the related compounds probenecid, acetazolamide and hydrochlorothiazide inhibited with an app. Ki between 4 and 7 mmol/l. 5) All diphenylamine-2-carboxylate analogs inhibited with an app. Ki between 3 and 5 mmol/l, even when the -NH-group was replaced by an = O-group or the benzene ring was replaced by a pyrimidine ring, but not when it was replaced by a thiophen ring.(ABSTRACT TRUNCATED AT 250 WORDS)