FIGURE 3.

ZnR-dependent activation of AKT and ERK1/2 and up-regulation of NHE transport are eliminated at extracellular acidic pH. A and B, AKT and ERK1/2 phosphorylation in HT29 cells was monitored after application of Zn²⁺ (100 μm, 10 min) in Ringer's solution at pH 7.4 or 6.5. Immunoblots using antibodies against phospho- or total-AKT (A) and ERK1/2 (B) are shown (upper panels). Phosphorylated protein levels were normalized to the total protein and are presented as the percentage of the phosphorylation induced by Zn²⁺ at pH 7.4 (lower panels; n = 4; *, p < 0.05). C, ZnR-dependent up-regulation of NHE activity was monitored in HT29 cells using the NH₄Cl prepulse paradigm. Intracellular pH was monitored in BCECF-loaded cells, and the recovery rates from internal acidification upon the addition of Na⁺-containing Ringer's solution were monitored. Rates were compared between cells pretreated with Zn²⁺ (100 μm, 2 min) applied in Ringer's solution at the indicated pH or in control cells that were incubated in Zn²⁺-free Ringer's solution at pH 7.4. Representative traces (left panel) and the averaged recovery rates (right panel) are shown. n = 3; *, p < 0.05.