Figure 5. Effects of pH on the endogenous and FrZIP2-dependent zinc uptake activities in MDCK cells.

(A) Zinc uptake rate was assayed in MDCK-Vec (black bars) and MDCK-FrZIP2 cells (grey bars) with 1.5 μM ZnCl₂ plus 0.03 μCi ⁶⁵Zn²⁺ in uptake buffer adjusted to the indicated pH. Values are means±S.E.M. (n=3). Significant differences between experimental groups were tested using non-parametric ANOVA followed by post-hoc test. *P<0.05, significant differences from control values. (B) Effects of pH on free Zn²⁺ concentration and the endogenous zinc uptake activities. (C) Effects of pH on free Zn²⁺ concentration and the FrZIP2-mediated zinc uptake activity that was calculated by subtracting MDCK-Vec rates from the corresponding MDCK-FrZIP2 values. The free zinc concentration in uptake buffer with different pH values was analysed with MINEQL+ software.