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  • Title: HCO3-/Cl- exchange across the human erythrocyte membrane: effects of pH and temperature.
    Author: Obaid AL, Crandall ED.
    Journal: J Membr Biol; 1979 Oct 05; 50(1):23-41. PubMed ID: 41100.
    Abstract:
    Changes in extracellular pH (PH0) in red cell suspensions were monitored in a stopped-flow rapid reaction apparatus under conditions where dpH0/dt was determined by the rate of HCO3-/Cl- exchange across the membrane. Experiments were performed at 5 degrees C less than T less than 40 degrees C using either untreated cells or cells exposed to 0.11 mM SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid). Although SITS exposure reduced the rate of exchange by 90%, both untreated and SITS-treated cells are similarly affected by changes in pH0 and temperature. The rate of HCO3-/Cl- exchange exhibits a minimum at about pH0 5 and a maximum at about pH0 7.4 at all temperatures. A transition temperature of 17 degrees C was observed in the Arrhenius relationship for all pH0. The activation energies (Ea) in kcal/mol are 19.6 below and 11.7 above 17 degrees C for 5 less than pH0 less than 8. These findings, similar to those reported for Cl- self-exchange, suggest that: (i) a change in the rate-limiting step for HCO3-/Cl- exchange occurs at 17 degrees C, possibly due to an altered interaction between the transport pathway and membrane lipids; (ii) the carrier system can be titrated by either H+ or SITS from the outside of the membrane, but the untitrated sites continue to transport normally; (iii) the pH0 dependence of the rate of exchange is consistent with the titratable carrier having its most alkaline pK in the range expected for amino groups; and (iv) below pH0 5, the nature of the exchange is markedly altered.
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