Halide transport patterns of apical anion exchange in rabbit cortical collecting duct intercalated cells

To investigate halide selectivity patterns of cortical collecting duct (CCD) intercalated cells (ICs), intracellular pH (pHi) was measured in perfused rabbit outer CCD ICs in Na(+)-free, HCO-3-buffered, 115 mM Cl solutions. Apical anion exchange activity was measured as the dpH/dt after lumen Cl- replacement with gluconate. The perfusate was randomly changed to equimolar Br-, F-, or I-. Addition of Br- to the lumen in place of gluconate caused a brisk acidification similar to that with Cl- return. The acidification rate with I- replacement was only approximately 25% of that seen with Cl- readdition, and F- substitution resulted in a small alkalinization. In a separate protocol, each halide was substituted for lumen Cl-. Replacement of lumen Cl- with Br- resulted in intracellular acidification, whereas F- substitution caused an increase in pHi similar to that with gluconate. A slower rate of alkalinization was seen with I-. Separate tubules were perfused and bathed in Cl(-)-free gluconate solutions for 10 min, and then either Cl- or Br- was returned to the lumen. Similar rates of acidification were found with either Cl- or Br- return. Taken together, the results show that, at a halide concentration of 115 mM, the halide selectivity transport pattern of the apical anion exchanger of CCD ICs is Cl- = Br- > I- > F-.