Effects of Anion-Transport Inhibitors on NaCl Reabsorption in the Rat Superficial Proximal Convoluted Tubule

Abstract

A B S T R A C T The effects of anion-transport inhibitors on volume reabsorption, and total CO2 concentrations were examined by in vivo microperfusion of superficial proximal convoluted tubules of rats. The luminal perfusion solution was a high-chloride, lowbicarbonate solution like that in the in vivo late proximal tubule. The anion-transport inhibitors were only added to the luminal perfusion solutions.In tubules perfused with the control high-chloride solution, the rate of volume reabsorption (J,) was 2.3±0.2 nl/mm min (n = 18), and the collected total CO2 concentration was 4.0±0.3 mM. Furosemide (3 mM) caused a marked reduction in volume reabsorption to 0.8±0.3 nl/mmmin (n = 20) and only a slight increase in the total CO2 concentration of collected samples of perfusate (7.8±0.5 mM). 0.8 mM acetazolamide caused a more pronounced rise in the collected total CO2 concentrations to 10.7±0.5 mM but only a slight fall in J, to 1.7±0.3 nl/mm-min (n = 19). Hence, we inferred that inhibition of carbonic anhydrase only partially accounted for the inhibition of J, by furosemide. 4-acetamido-4'-iso-thiocyanato-stilbene-2,2'-disulphonic acid (0.1 mM), a well-characterized inhibitor of erythrocyte anion exchange mechanisms, also reduced J, to 1.6±0.3 nl/mm min (n = 15) without changing the total CO2 concentrations of the collected perfusates (3.6±0.4 mM). The effect of 4-acetamidoA4'-iso-thiocyanato-stilbene-2,2'-disulphonicPortions of this work were presented at the 10th Annual

Activation of the apical Na+/H+exchanger NHE3 by formate: a basis of enhanced fluid and electrolyte reabsorption by formate in the kidney

“…Inhibition of the apical Na ϩ /H ϩ exchanger by amiloride analogs inhibits Na ϩ and Cl Ϫ reabsorption in the kidney proximal tubule. The presence of disulfonic stilbenes, inhibitors of Cl Ϫ /base exchanger, inhibits Na and Cl reabsorption (23,44). These results support a model of coordinated regulation of Na ϩ /H ϩ and Cl Ϫ /base exchangers in the kidney proximal tubule.…”

Apical membrane chloride/base exchange in the rat proximal convoluted tubule.

“…Lucci and Warnock (8) effect apical membrane NaCI absorption. Baum (30) found no effect of luminal chloride removal on cell pH in the rabbit PST.…”

“…absorption (8). Subsequent studies in isolated apical membrane vesicles have disagreed with respect to the presence or absence of C1/OH exchange (9)(10)(11)(12)(13)(14)(15).…”

Mechanism of apical and basolateral Na(+)-independent Cl-/base exchange in the rabbit superficial proximal straight tubule.

“…In contrast, Yoshitomi and Hoshi ( 19) demonstrated apical Cl-/base exchange in Triturus proximal tubules by measuring intracellular Cl-activity. An inhibitory effect of luminal stilbenes on electroneutral proximal tubule NaCl reabsorption has been observed in several studies, suggesting a role for apical Cl-/base exchange (20)(21)(22). Against a role for apical Cl-/HCO-(but not incompatible with Cl-/ OH-) exchange was the finding that the carbonic anhydrase inhibitor methazolamide failed to alter Jcj in the rat proximal convoluted tubule (23).…”