Acid-base effects on intestinal Na(+) absorption and vesicular trafficking.
We examined for vesicular trafficking of the Na(+)/H(+) exchanger (NHE) in pH-stimulated ileal and CO(2)-stimulated colonic Na(+) absorption. Subapical vesicles in rat distal ileum were quantified by transmission electron microscopy at x27,500 magnification. Internalization of ileal apical membranes labeled with FITC-phytohemagglutinin was assessed using confocal microscopy, and pH-stimulated ileal Na(+) absorption was measured after exposure to wortmannin. Apical membrane protein biotinylation of ileal and colonic segments and Western blots of recovered proteins were performed. In ileal epithelial cells incubated in HCO/Ringer or HEPES/Ringer solution, the number of subapical vesicles, the relative quantity of apical membrane NHE isoforms 2 and 3 (NHE2 and NHE3, respectively), and apical membrane fluorescence under the confocal microscope were not affected by pH values between 7.1 and 7.6. Wortmannin did not inhibit pH-stimulated ileal Na(+) absorption. In colonic epithelial apical membranes, NHE3 protein content was greater at a PCO(2) value of 70 than 21 mmHg, was internalized when PCO(2) was reduced, and was exocytosed when PCO(2) was increased. We conclude that vesicle trafficking plays no part in pH-stimulated ileal Na(+) absorption but is important in CO(2)-stimulated colonic Na(+) absorption.
Charney
Alan N
AN
Nephrology Section, Veterans Affairs Medical Center, New York University School of Medicine, New York 10010, USA. alan.charney@med.va.gov
Egnor
Richard W
RW
Alexander-Chacko
Jesline
J
Cassai
Nicholas
N
Sidhu
Gurdip S
GS
D000143:Acids / Q000494:pharmacology*; D000468:Alkalies / Q000494:pharmacology*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002245:Carbon Dioxide / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D018699:Coated Vesicles / Q000187:drug effects / Q000378:metabolism; D003106:Colon / Q000378:metabolism / Q000648:ultrastructure; D022162:Cytoplasmic Vesicles / Q000187:drug effects / Q000378:metabolism*; D004705:Endocytosis / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007082:Ileum / Q000378:metabolism / Q000648:ultrastructure; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects / Q000378:metabolism; D000077191:Wortmannin
D000143:Acids; D000468:Alkalies; D000730:Androstadienes; C513110:Slc9a2 protein, rat; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D002245:Carbon Dioxide; D012964:Sodium; D000077191:Wortmannin