title: Characteristics of the anion transport system in sea turtle erythrocytes.
abstract: Erythrocytes of Kemp's ridley sea turtle (Lepidochelys kempi) contain a 100- to 105-kDa protein that is reactive with a monoclonal antibody to the membrane domain of human erythrocyte band 3. Based on inhibition of membrane HCO(3-)-Cl- exchange with 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), sea turtle erythrocytes were found to contain 4 x 10(6) copies of band 3 per cell. Unidirectional HCO3- transfer, specifically HCO3- out----in-Cl-in----out exchange, where subscript in----out represents transfer from inside to outside and subscript out----in represents transfer from outside to inside, was characterized by a maximal exchange rate of 1.0-1.1 nmol.cm-2.s-1, substrate affinity coefficients of 0.1-0.2 mM for HCO3- and 1.6 mM for Cl-, and an apparent inhibition constant for SITS of 0.6-1.0 microM (10 degrees C, pH 7.6). Under physiological conditions (30 degrees C, pH 7.4), the rate of net HCO3- transfer (i.e., the difference between HCO3- in----out-Cl-out----in and HCO3- out----in-Cl-in----out) was 1.13 nmol. cm-2.s-1 for cells subjected to a 5-mM decrement in CO2 content. This yields a rate coefficient for the "physiological" anion shift in sea turtle blood of 1.7 s-1, indicating that the anion shift may require 2.6 s to reach 99% completion in vivo. The erythrocyte anion shift appears to be a potential rate-limiting step for capillary CO2 exchange in these turtles.
authors.affiliation: Pulmonary Research Laboratories, University of Texas Medical Branch, Galveston 77550.
authors.forename: E K
authors.initials: EK
authors.lastname: Stabenau
authors.forename: C G
authors.initials: CG
authors.lastname: Vanoye
authors.forename: T A
authors.initials: TA
authors.lastname: Heming
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000302:isolation & purification / Q000378:metabolism; D001798:Blood Proteins / Q000302:isolation & purification; D002245:Carbon Dioxide / Q000097:blood; D002352:Carrier Proteins / Q000097:blood* / Q000302:isolation & purification; D027963:Chloride-Bicarbonate Antiporters; D004591:Electrophoresis, Polyacrylamide Gel; D004912:Erythrocytes / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008565:Membrane Proteins / Q000097:blood; D008962:Models, Theoretical; D014426:Turtles / Q000097:blood*
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D001798:Blood Proteins; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D008565:Membrane Proteins; D002245:Carbon Dioxide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid