Rabbit ileal brush-border membrane Cl-HCO3 exchanger is activated by an internal pH-sensitive modifier site

• Published in: The American journal of physiology Vol. 259; no. 4 Pt 1; pp. G666 - G670
• Main Authors: Mugharbil, A, Knickelbein, R G, Aronson, P S, Dobbins, J W
• Format: Journal Article
• Language: English
• Published: United States 01-10-1990
• Subjects: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid - analogs & derivatives; 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid - pharmacology; Animals; Bicarbonates - metabolism; Biological Transport, Active; Carrier Proteins - metabolism; Chlorides - metabolism; Hydrogen-Ion Concentration; Ileum - metabolism; Intestinal Mucosa - metabolism; Membrane Potentials; Microvilli - metabolism; Microvilli - physiology; Rabbits
• ISSN: 0002-9513
• DOI: 10.1152/ajpgi.1990.259.4.G666

The purpose of these studies was to look for evidence of a pH-sensitive modifier site on the Cl-HCO3 exchanger on the brush-border membrane in rabbit ileum utilizing membrane vesicles. When internal pH and HCO3 were increased, Cl uptake was stimulated in a sigmoidal fashion consistent with a modifier effect. Increasing internal HCO3 alone did not have a similar effect, and increasing pH alone in the absence of HCO3 resulted in very little uptake of Cl. These results suggested that OH was a poor substrate for the exchanger but that it "activated" the transport of HCO3. Further evidence for this hypothesis was provided by the observation that increasing internal pH also stimulated Cl-Cl exchange. Altering the membrane potential with K and valinomycin had no effect on Cl uptake at high internal pH, suggesting no change in the 1:1 coupling ratio for Cl-HCO3 exchange at high internal pH. These studies provide evidence that there is an internal pH-sensitive modifier site on the Cl-HCO3 exchanger.