Figure 4.

Effect of sodium, chloride, and potassium extracellular concentration on ZIP2 transport activity. (A) Changes in fluorescence intensity of Calcium 5 dye in response to Cd²⁺ perfusion (1 μM) measured in HEK293 cells transiently transfected with DsRed-Express2 and ZIP2 DNA constructs in KB buffer (pH 6.5) in which extracellular Na⁺ or Cl⁻ was replaced with equimolar NMDG, choline⁺, and K⁺ or gluconate salts, respectively. Data from two independent experiments were normalized to the mean ZIP2 activity at pH 6.5 and are represented as means ± SD (n = 8–12). (B) Uptake of ⁶³Zn²⁺ in the presence of 100 μM ZnCl₂ by ZIP2- and H₂O-injected X. laevis oocytes measured in ND96 (pH 6.0) in which extracellular Na⁺ was replaced with equimolar choline⁺ or K⁺. Data from two different batches of oocytes were normalized to the mean Zn²⁺ uptake by ZIP2 at pH 6.0 (403 ± 62 pmol oocyte^–1 min^–1) and are represented as means ± SD (6–12 oocytes). P values establish statistical differences between hZIP2-mediated Zn²⁺ uptake at pH 6.0 and the indicated experimental conditions.