Regulation of AE2 anion exchanger by intracellular pH: critical regions of the NH2-terminal cytoplasmic domain

Abstract

The role of intracellular pH (pHi) in regulation of AE2 function in Xenopus oocytes remains unclear. We therefore compared AE2-mediated 36Cl− efflux from Xenopus oocytes during imposed variation of extracellular pH (pHo) or variation of pHi at constant pHo. Wild-type AE2-mediated 36Cl−efflux displayed a steep pHo vs. activity curve, with pHo(50) = 6.91 ± 0.04. Sequential NH2-terminal deletion of amino acid residues in two regions, between amino acids 328 and 347 or between amino acids 391 and 510, shifted pHo(50) to more acidic values by nearly 0.6 units. Permeant weak acids were then used to alter oocyte pHi at constant pHo and were shown to be neither substrates nor inhibitors of AE2-mediated Cl−transport. At constant pHo, AE2 was inhibited by intracellular acidification and activated by intracellular alkalinization. Our data define structure-function relationships within the AE2 NH2-terminal cytoplasmic domain, which demonstrates distinct structural requirements for AE2 regulation by intracellular and extracellular protons.