Exchangers chloride-bicarbonate

Figure 11 Schematic of mucosal membrane sodium-proton exchanger and chloride-bicarbonate exchanger responsible for pH homeostasis in enterocyte cytosol. Microclimate pH is maintained by mucosal slowing of proton diffusion away from the lumenal membrane.

The chloride-bicarbonate exchanger mediates antiport of the anions CF and... 

The Chloride-Bicarbonate Exchanger Catalyzes Electroneutral Cotransport of Anions across the Plasma Membrane... 

FIGURE 11-33 Chloride-bicarbonate exchanger of the erythrocyte membrane. This cotransport system allows the entry and exit of HCOf without changes in the transmembrane electrical potential. Its role is to increase the C02-carrying capacity of the blood. 

The human genome has genes for three closely related chloride-bicarbonate exchangers, all with the same predicted transmembrane topology. Erythrocytes... 

Figure 2. Bulk calcium transport by the osteoclast. Net acid transport is driven by the vacuolar-type H+-ATPase with a specialized large membrane subunit. Transport is balanced by chloride transport, probably involving both a chloride channel (CLIC-5) and a chloride bicarbonate antiporter (CLCN7). Supporting transport processes include chloride-bicarbonate exchange. Insertion of transporters is specific for subcellular locations and involves interaction of transporters with specific cytoskeletal components, including actin (See Colour Plate 29)...

FIGURE 2.27 The parietal cell in the acid-producing slate. The large circles represent membrane-bound proteins. The apical membrane contains the H,K-ATPase and the KCI transporter shown in Figme 2.26- Also shown is cytoplasmic carbonic anhydrase and the chloride-bicarbonate exchanger in the basal membrane of the cell. The terms "apical" and "basal" refer to opposite sides of the plasma membrane of epithelial cells. 

Knickelbein, R. G Aronson, P, S., and Dobbins, J. W. (I9ftft). Membrane distribution of sodium -hydrogen and chloride-bicarbonate exchanges in crypt and villus cell membranes from rabbit ileum. /. Cbn. Iniwsl. 82,2158-2163. 

Ptacek That is linked to 2q. There was another beautiful candidate gene, which encodes a chloride/bicarbonate exchanger. There is a good physiological argument about how this gene could cause that disease. As so many great hypotheses do, it went down in flames. 

When the erythrocytes reach the lungs and the carbon dioxide concentration decreases as the carbon dioxide leaves the lungs, the whole process reverses. Since the passage of blood through the alveoli of the lungs may take less than a second, it is fortunate that the chloride/bicarbonate exchange occurs in less than a second. Otherwise, not all the bicarbonate formed in the tissues would be eliminated as carbon dioxide when the cells return to the lungs. 

In this section, we will analyze an example of the physiological utility of two channels that have been discussed already the sodium/proton exchanger and the chloride/bicarbonate exchanger. Several mammalian cells use these channels to protect themselves against cell shrinkage due to increases in medium osmolality. To be consistent, we will continue to use the lymphocyte as our cell, recognizing that other cells may adopt different variations of these two channel mechanisms. 

Figure 7b, Changes in cell pH during regulatory volume decrease (RVD) followed by regulatory volume increase (RVI) in lymphocytes, only sodium/proton excharigers were functional (square). Both sodium/proton exchangers and chloride/bicarbonate exchangers were functional (diamond).

Figure 7d. Changes in cell pH after lymphocytes suspended in isosmotic medium were resuspended in 1.5 isosmotic medium. Both the sodium/proton exchangers and the chloride/bicarbonate exchangers were functional. At 7.5 min, the sodium/proton exchanger was turned off, but the chloride icarbonate exchanger was functional.

Formation of carbonic acid from HjO and CO2 is a relatively slow process, but within the corpuscles it is speeded up by the presence of the enzyme carbonic anhydrase. As a result the concentration of bicarbonate ions rises more rapidly in the corpuscles than in the plasma and some of them leave the corpuscles in exchange for chloride ions. This chloride-bicarbonate exchange ensures that a large fraction of the acidic CO2 produced in the tissues is carried as plasma bicarbonate. Consequently there is very little increase in the acidity of venous blood. 

Greco, F. A. Solomon, A. K. Kinetics of chloride-bicarbonate exchange across the human red blood cell membrane. J. Membr. Biol. 1997, 159, 197-208. 

Calafut, T. M. Dix, J. A. Chloride-bicarbonate exchange through the human red cell ghost membrane monitored by the fluorescent probe 6-methoxy-A-(3-sulfopropyl)quinolinium. Anal. Biochem. 1995, 230, 1-7. 

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