Fig. 3. pH-dependent changes in HAF fluorescence. A salivary gland was incubated for 5 min with 30 µmol l^–1 HAF in PS in order to label the basolateral surface of the epithelial cells and was then superfused with PS of different pH as indicated. (A) HAF fluorescence upon excitation at 470 nm and 410 nm. (B) Ratio of the fluorescence signals obtained at the excitation wavelengths of 470 nm and 410 nm (F₄₇₀/F₄₁₀). Acidification is accompanied by a decrease in the ratio and alkalization by an increase in F₄₇₀/F₄₁₀.