Acid-base effects on intestinal Na+ absorption and vesicular trafficking

• Published in: American Journal of Physiology: Cell Physiology 2002-09, Vol.283 (3), p.C971-C979
• Main Authors: Charney, Alan N, Egnor, Richard W, Alexander-Chacko, Jesline, Cassai, Nicholas, Sidhu, Gurdip S
• Format: Article
• Language: English
• Subjects: Acids - pharmacology; Alkalies - pharmacology; Androstadienes - pharmacology; Animals; Biological Transport - drug effects; Biological Transport - physiology; Carbon Dioxide - pharmacology; Cell Membrane - metabolism; Coated Vesicles - drug effects; Coated Vesicles - metabolism; Colon - metabolism; Colon - ultrastructure; Cytoplasmic Vesicles - drug effects; Cytoplasmic Vesicles - metabolism; Endocytosis - drug effects; Exocytosis - drug effects; Hydrogen-Ion Concentration - drug effects; Ileum - metabolism; Ileum - ultrastructure; Intestinal Absorption - drug effects; Intestinal Absorption - physiology; Intestinal Mucosa - drug effects; Intestinal Mucosa - metabolism; Intestinal Mucosa - ultrastructure; Male; Rats; Sodium - metabolism; Sodium-Hydrogen Exchanger 3; Sodium-Hydrogen Exchangers - drug effects; Sodium-Hydrogen Exchangers - metabolism
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00079.2002

1  Nephrology Section and 2  Department of Pathology, Veterans Affairs Medical Center, New York University School of Medicine, New York, New York 10010 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 ×27,500 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 P CO 2 value of 70 than 21 mmHg, was internalized when P CO 2 was reduced, and was exocytosed when P CO 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. rat; ileum; colon; electrolyte transport