Heterogeneity of chloride/base exchange in rabbit superficial and juxtamedullary proximal convoluted tubules

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Abstract

Active transcellular NaCl transport in the proximal convoluted tubule (PCT) is via apical parallel Na/H and Cl/base exchange. The mechanism of Cl/base exchange remains unclear. The present in vitro microperfusion study examined the mechanism of Cl/base exchange in superficial and juxtamedullary PCT by examining the rate of change in intracellular pH in response to luminal Cl removal. In superficial PCT the rate of Cl/base exchange was 24.0 ± 2.3 without formate, 36.4 ± 6.6 with 10 μM formate (P < 0.05), and 43.6 ± 2.8 pmol · mm-1 · min-1 (P < 0.001) with 1 mM luminal formate. Cl/base exchange was inhibited by luminal 4,4'-diisothiocyanostilbene-2,2'- disulfonic acid (DIDS) in the presence and absence of formate. In juxtamedullary PCT, Cl/base exchange was 22.2 ± 3.8 without formate and 25.0 ± 5.4 pmol · mm-1 · min-1 in the presence of 1 mM luminal formate [P = not significant (NS)]. Cl/base exchange was inhibited by luminal DIDS in juxtamedullary PCT. The rates of Cl/base exchange in both superficial and juxtamedullary PCT were not affected by 0.1 mM acetazolamide and 2 mM cyanide and were the same in the presence and absence of HCO3/CO2, consistent with Cl/OH rather than Cl/HCO3 exchange. To examine the effect of formate on PCT transport, tubules were perfused with a high-Cl solution without organics simulating late proximal tubular fluid. In superficial PCT net volume absorption (J(v)) was 0.00 ± 0.05 in the absence of formate and 0.14 ± 0.06 nl · mm-1 · min-1 in the presence of 1 mM formate (P < 0.05). In juxtamedullary PCT J(v) was 0.20 ± 0.08 in the absence of formate and 0.17 ± 0.07 nl · mm-1 · min-1 in the presence of 1 mM formate (P = NS). In conclusion, superficial PCT have both a Cl/OH and Cl/formate exchanger. Cl/formate exchange is present with physiological concentrations of formate. Addition of 1 mM formate stimulates Cl transport in superficial PCT, Juxtamedullary PCT have Cl/OH exchange but do not have Cl/formate exchange. Juxtamedullary PCT have Cl transport in the absence of formate, and the rate is not affected by formate.

Original languageEnglish (US)
Pages (from-to)F847-F853
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Volume268
Issue number5 37-5
DOIs
StatePublished - 1995

Keywords

  • formate
  • sodium chloride transport

ASJC Scopus subject areas

  • Physiology

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