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Molecular Medicine and Renal Units, Beth Israel Deaconess Medical Center, Boston 02215; and Departments of Medicine and Cell Biology, Harvard Medical School, Boston, Massachusetts 02215
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.
chloride-bicarbonate exchange; weak acids; Xenopus oocytes; isotopic flux; pH-sensitive microelectrodes
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