Mechanism of the increase in cation permeability of human erythrocytes in low-chloride media. Involvement of the anion transport protein capnophorin.

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Abstract
When human erythrocytes are suspended in low-Cl- media (with sucrose replacing Cl-), there is large increase in both the net efflux and permeability of K+. A substantial portion (> 70% with Cl- < 12.5 mM) of this K+ eflfux is inhibited by the anion exchange inhibitor DIDS (4,4''-diisothiocyanostilbene-2,2''-disulfonic acid). This inhibition cannot be explained as an effect of DIDS on net Cl- permeability (PCl) and membrane potential, but rather represents a direct effect on the K+ permeability. When cells are reacted with DIDS for different times, the inhibition of K+ efflux parallels that of Cl- exchange, which strongly indicates that the band 3 anion exchange protein (capnophorin) mediates the net K+ flux. Since a noncompetitive inhibitor of anion exchange, niflumic acid, has no effect on net K+ efflux, the net K+ flow does not seem to involve the band 3 conformational change that mediates anion exchange. The data suggest that in low-Cl- media, the anion selectivity of capnorphorin decreases so that it can act as a very low-conductivity channel for cations. Na+ and Rb+, as well as K+, can utilize this pathway.