4-acetamido-4--isothiocyanatostilbene-2-2--disulfonic-acid and formic-acid

We examined the effects of formate and oxalate on the rate of fluid absorption (Jv) in the rat proximal convoluted tubule in situ. Proximal tubules were microperfused with a high-Cl-, low-HCO3- Ringer solution (pH 6.7), and the peritubular capillaries were perfused with a standard Ringer solution (pH 7.4), simulating conditions in the late proximal tubule. Jv, a measure of transtubular NaCl absorption under these conditions, was calculated from the change in luminal [3H]inulin. Addition of formate in the physiological range (500 microM) to the luminal perfusate increased Jv by 45%; addition of 500 microM formate to both luminal and capillary perfusates increased Jv by 57%. Similarly, addition of oxalate in the physiological range (5 microM) to the luminal perfusate increased Jv by 37%; addition of 5 microM oxalate to both luminal and capillary perfusates increased Jv by 57%. The stimulatory effects of formate and oxalate perfused in the lumen and capillaries were not additive. Addition of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS, 0.1 mM) to the luminal perfusate had no effect on baseline Jv measured in the absence of added formate and oxalate but completely abolished the increment in Jv induced by formate and oxalate. Addition of the Cl(-)-channel blocker diphenylamine-2-carboxylate (DPC, 0.2 mM) to the capillary perfusate had no effect on baseline Jv but completely abolished the increment in Jv induced by formate and oxalate.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Absorption; Animals; Chlorides; Formates; Ion Exchange; Kidney Tubules, Proximal; Male; ortho-Aminobenzoates; Oxalates; Perfusion; Rats; Rats, Inbred Strains; Sodium Chloride

The present in vitro microperfusion study examined whether apical membrane chloride transport is mediated by chloride-base exchange in the rabbit proximal convoluted (PCT) and proximal straight tubule (PST) by examining the effect of the addition of luminal chloride on intracellular pH. Intracellular pH was measured fluorometrically using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. In PCT initially perfused without chloride, changing the luminal perfusate to a high chloride (148 mM)-low bicarbonate (5 mM) solution simulating late proximal tubular fluid produced a cell acidification (7.56 +/- 0.06 to 7.52 +/- 0.06, P less than 0.02) when 1 mM formate was present in the perfusate and bathing solution. This acidification was inhibited by 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. This chloride-base exchange was not observed in the absence of formate, and neither acetate nor lactate produced the cell acidification observed with formate. Because the Na+-H+ antiporter could blunt a pH change, 2 mM amiloride was added to the luminal perfusate. While addition of luminal chloride produced a small cell acidification in the absence of formate (7.63 +/- 0.06 to 7.60 +/- 0.05, P less than 0.05), a much greater cell acidification was observed in the presence of 1 mM formate (7.69 +/- 0.05 to 7.58 +/- 0.06, P less than 0.01). Chloride-base exchange was only detected in the presence of formate in the PST. These studies demonstrate apical membrane chloride-base exchange in the presence of formate in the rabbit proximal tubule consistent with chloride-formate exchange.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Bicarbonates; Chlorides; Formates; Hydrogen-Ion Concentration; Kidney Tubules, Proximal; Rabbits

We evaluated the mechanisms of chloride transport in microvillus membrane vesicles isolated from the rabbit renal cortex. The presence of Cl-formate exchange was confirmed. Outward gradients of oxaloacetate, HCO3, acetate, lactate, succinate, sulfate, and p-aminohippurate (PAH) stimulated the rate of Cl uptake minimally (less than 25%) or not at all. However, an outward gradient of oxalate stimulated Cl uptake by 70%, and an outward Cl gradient induced uphill oxalate uptake, indicating Cl-oxalate exchange. Moreover, an outward formate gradient induced uphill oxalate uptake, indicating formate-oxalate exchange. Studies of inhibitor and substrate specificity indicated the probable operation of at least two separate anion exchangers in mediating Cl transport. The Cl-formate exchanger accepted Cl and formate as substrates, had little or no affinity for oxalate, was sensitive to inhibition by furosemide, and was less sensitive to inhibition by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). The Cl (formate)-oxalate exchanger also accepted Cl and formate as substrates but had high affinity for oxalate, was highly sensitive to inhibition by DIDS, and was less sensitive to inhibition by furosemide. The Cl-formate exchanger was electroneutral, whereas the Cl (formate)-oxalate exchanger was electrogenic. We conclude that at least two separate anion exchangers mediating Cl transport are present on the luminal membrane of the rabbit proximal tubule cell. These exchangers may play important roles in mediating transtubular Cl and oxalate transport in this nephron segment.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Anions; Biological Transport; Cell-Free System; Chlorides; Formates; Furosemide; Kidney Cortex; Microvilli; Oxalates; Rabbits