Evidence for a major route for zinc uptake in human red blood cells: [ZN(HCO3)2CL]−influx through the [CI−/HCO3−] anion exchanger

Abstract

The initial rate of Zn²⁺ uptake in human red cells was measured by atomic absorption. A very important fraction of Zn²⁺ uptake was inhibited by DIDS with IC₅₀ = 0.3 (μ)M (and by furosemide and bumetanide with IC₅₀ of 200 and 500 μ M, respectively). DIDS–sensitive Zn²⁺ uptake exhibited the following properties: (1) It required the simultaneous presence of both external HCO₃− and Cl−. (2) In Cl− containing media, it was strongly stimulated by external HCO₃− following a sigmoidal (S–shaped) and saturable function, which was fitted by a Hanes equation, with n = 2 and an apparent dissociation constant (for external HCO₃−) of 5.3 ± 0.9 mM (mean ± SD of four experiments). The maximal rate of Zn²⁺ uptake at saturating HCO₃− concentrations was 50.7 ± 4.8 mmol (liter cells x h)⁻¹. (3) In HCO₃− containing media, it was strongly stimulated by external Cl⁻ following a Michaelis‐like equation with an apparent dissociation constant (for external Cl− of 88 ± 11 mM (mean ± SD of three experiments). 4) Bicarbonate‐stimulated Zn²⁺ uptake was inhibited by physiological concentrations of phosphate (sulfate was a much less potent inhibitor than phosphate). A kinetic analysis of the data strongly suggested that zinc was transported by the anion carrier in the form of the monovalent anion complex: [Zn(HCO₃)₂Cl]−.