FIGURE 4.

Ectopically expressed ZnR/GPR39 in HEK293 cells is regulated by extracellular acidic pH. A, pH dependence of ZnR responses was determined in HEK293 cells transfected with hGPR39 that were loaded with Fura-2. Representative traces after application of Zn²⁺ (200 μm) and ATP (25 μm) at pH 6.5 and 7.4 are shown. B, averaged initial rates of Zn²⁺-dependent Ca²⁺ rise at the indicated Zn²⁺ concentrations applied in Ringer's solution at pH 6.5 (gray bars) versus pH 7.4 (black bars; n = 3, *, p < 0.05). Note that the response of ZnR/GPR39 is attenuated to about 50% at pH 6.5 that over the whole range of Zn²⁺ concentrations.