Chloride/formate exchange with formic acid recycling: a mechanism of active chloride transport across epithelial membranes

Proc Natl Acad Sci U S A. 1985 Sep;82(18):6362-5. doi: 10.1073/pnas.82.18.6362.

Abstract

The pathways for transport of Cl- and formate in microvillus membrane vesicles isolated from rabbit renal cortex were evaluated. An outward formate gradient stimulated the uptake of Cl-, and an outward Cl- gradient stimulated the uptake of formate, indicating Cl-/formate exchange. In addition, an inside alkaline pH gradient induced the accumulation of formate, consistent with nonionic diffusion of formic acid. Although an inward Na+ gradient also stimulated uphill formate accumulation, suggesting Na+/formate cotransport, this effect was abolished when ionophores were used to prevent the generation of a transmembrane pH gradient, indicating an indirect coupling of formic acid transport to Na+/H+ exchange. An inside alkaline pH gradient only minimally stimulated the uptake of 82Br-, used as tracer for Cl-, confirming the absence of appreciable Cl-/OH- exchange. However, the same pH gradient in the presence of a physiologic formate concentration (0.2 mM) markedly stimulated 82Br- influx. These data suggest that Cl-/formate exchange with recycling of formic acid by nonionic diffusion is a potential mechanism for active Cl- absorption across the luminal membrane in the proximal tubule and perhaps in other epithelia.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Biological Transport, Active
  • Bromides / metabolism
  • Cell Membrane / metabolism
  • Chlorides / metabolism*
  • Epithelium / metabolism
  • Formates / metabolism*
  • Hydrogen-Ion Concentration
  • Kidney Cortex / metabolism
  • Kidney Tubules, Proximal / metabolism*
  • Male
  • Microvilli / metabolism*
  • Rabbits
  • Sodium / metabolism

Substances

  • Bromides
  • Chlorides
  • Formates
  • formic acid
  • Sodium