Acid/base transporters in human duodenal enterocytes.
BACKGROUND
Duodenal mucosal bicarbonate secretion serves as a key defensive factor against mucosal injury. The purpose of the present study was to isolate human proximal duodenal enterocytes and identify their inherent acid/base transporters that participate in duodenal alkaline secretion.


METHODS
Biopsy specimens were obtained from the duodenal bulb in 18 healthy volunteers. Individual duodenal epithelial cells were isolated by means of a combination of calcium chelation and collagenase. Intracellular pH (pHi) was measured by the pH-sensitive dye BCECF and dynamic fluorescence ratio imaging.


RESULTS
Cytologic and histologic examination confirmed that isolated cells were of epithelial origin. In HCO3--free media, pHi recovery after acidification with NH4Cl was amiloride-sensitive and Na+-dependent, indicating the presence of an Na+/H+ exchanger. pHi recovery after acidification was significantly enhanced by the presence of HCO3-, showing the presence of an HCO3--dependent recovery mechanism (that is, a base loader/acid extruder). HCO3--dependent recovery required external Na+ yet was Cl-- and amiloride-insensitive, characteristic of an NaHCO3 cotransporter. In the presence of HCO3-, a Cl--dependent anion exchanger serving as a base extruder was shown, indicative of a Cl-/HCO3- exchanger.


CONCLUSIONS
Human duodenal enterocytes contain at least three acid/base transporters: an Na+/H+ exchanger that serves as to extrude acid, an NaHCO3 cotransporter that functions as base loader, and a Cl-/HCO3- exchanger that operates as a base extruder.
Ainsworth
M A
MA
Dept. of Medicine, University of California San Diego Medical Center, USA.
Hogan
D L
DL
Rapier
R C
RC
Amelsberg
M
M
Dreilinger
A D
AD
Isenberg
J I
JI
D000136:Acid-Base Equilibrium; D000328:Adult; D017920:Antiporters / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism; D001706:Biopsy; D002352:Carrier Proteins / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters; D004386:Duodenum / Q000166:cytology / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013997:Time Factors
D017920:Antiporters; D001639:Bicarbonates; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers