Human erythrocyte anion permeabilities measured under conditions of net charge transfer

Abstract

The permeability of the human erythrocyte to anions was measured under conditions of net charge transfer: for Cl- and .**GRAPHIC**. ions, at 37.degree. C, this permeability is 5 orders of magnitude too small to account for the rate of the electroneutral anion exchange which is responsible for the chloride, or Hamburger, shift. The method is an indirect one in which the ionophore, valinomycin, is used to increase the erythrocyte K+ permeability: in the absence of permeant cation externally, the rate of the resulting K+ efflux may be limited by the slowness of the accompanying anion efflux, allowing the true anion permeability to be estimated. The average Cl- permeability estimated in ACD[acid citrate dextrose]-stored erythrocytes (7 experiments) and erythrocytes from fresh blood (2 experiments) was 2.1 .times. 10-8 cm/s at 37.degree. C and pH 7.4: this may also be expressed as a Cl- conductance of about 1.0 .times. 10-5 .OMEGA.-1 cm-2. The apparent activation energy for net efflux of Cl- was 3.9 kJ/mole (16.4 kcal/mole). In fresh cells, the ratios of Cl-, .**GRAPHIC**. Br- and I- permeabilities (or conductances) were 1:0.8:1.5:5. The 3 halide ions follow Eisenman''s Sequence I, representing a binding site of low field strength.