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 HCO3--Cl- exchange with 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), sea turtle erythrocytes were found to contain 4 x 106 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 μM (10°C, pH 7.6). Under physiological conditions (30°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.
|Original language||English (US)|
|Journal||American Journal of Physiology - Regulatory Integrative and Comparative Physiology|
|Issue number||5 30-5|
|State||Published - Dec 1 1991|
- Anion exchange
- Band 3
ASJC Scopus subject areas