FIGURE 3.

Comparison of cytosolic and mitochondrial Zn²⁺. A and B, cytosolic resting Zn²⁺ concentrations from 46 individual cells (A, ●) and mitochondrial resting Zn²⁺ concentrations from 10 individual cells (B, ■) as a function of sensor expression. In the cytosol, there is a wide variation in sensor expression from cell to cell, whereas the variation is markedly reduced in mitochondria. C, representative traces of the cytosolic (●), and mitochondrial (■) Cys₂His₂ sensor. Resting ratios are established at the start, followed by treatment with 150 μm TPEN to obtain R_min, and 2 mm ZnCl₂, 15 μm digitonin (●) or 2 mm Zn²⁺, 15 μm digitonin, 25 μm pyrithione (■) to obtain R_max. The number of R_max data points we can collect is limited by the fact that the R_max experimental conditions are toxic to the cells.