Fig. 8. Comparison of Ca²⁺ elevations evoked by membrane depolarization with 57 mM and 110 mM K⁺. (A) Averaged fura-2 fluorescence ratios (F340/F380) measured in single PC12 cells stimulated with 57 mM K⁺ (white triangles) or with 110 mM K⁺ (black triangles). Fluorescence images were acquired every 15 seconds. Superfusion was switched from physiological buffer (containing 4 mM K⁺) to high K⁺ depolarization buffer at 1.85 minutes. The symbols indicate the mean fluorescence ratio of 16 (57 mM K⁺) and 14 cells (110 mM K⁺). (B) Analysis of Ca²⁺ responses induced by 57 mM K⁺ and 110 mM K⁺ from experiments such as the one shown in A. The bars show the average response (± s.d.) of 4 (57 mM K⁺) and 3 (110 mM K⁺) experiments (7-16 cells per experiment).