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Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, and Gainesville Veterans Affairs Medical Center, Gainesville, Florida 32609
The cortical collecting duct (CCD) B cell possesses an apical
anion exchanger dissimilar to AE1, AE2, and AE3. The purpose of these
studies was to characterize this transporter more fully by examining
its regulation by CO2 and
HCO
3. We measured intracellular pH
(pHi) in single intercalated
cells of in vitro microperfused CCD using the fluorescent, pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein
(BCECF). In the absence of extracellular
CO2/HCO3,
luminal Cl removal caused
reversible intracellular alkalinization, identifying this transporter
as a Cl/base exchanger able
to transport bases other than HCO3. Adding extracellular
CO2/HCO3
decreased B cell pHi while
simultaneously increasing
Cl/base exchange activity.
Since intracellular acidification inhibits AE1, AE2, and AE3, we
examined mechanisms other than pHi
by which the stimulation occurred. These studies showed that B cell
apical anion exchange activity was
CO2 stimulated and carbonic
anhydrase dependent. Moreover, the stimulation was independent of
luminal bicarbonate, luminal pH or
pHi, and changes in buffer
capacity. We conclude that the B cell possesses an apical
Cl/base exchanger whose
activity is regulated by
CO2-stimulated, carbonic
anhydrase-dependent cytoplasmic HCO3 formation.
cortical collecting duct; intercalated cell; 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein
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