Fig. 4. Spatiotemporal analysis of pH changes at the luminal surface evoked by 30 nmol l^–1 5-HT. (A) Series of pseudocolour images of the F₄₇₀/F₄₁₀ ratio in a salivary gland with HAF in the apical membrane. The squares in the first image indicate the areas selected to generate the graph. +5-HT, beginning of the 5-HT stimulus; –5-HT, washout of 5-HT. Note that the F₄₇₀/F₄₁₀ ratio laterally along the salivary gland tube (asterisks) is not linked to pH because it results from cellular autofluorescence rather than HAF fluorescence. Only F₄₇₀/F₄₁₀ in the mid-region of the salivary gland results from HAF and thus relates to luminal surface pH. Image intervals, 50 s; scale bar, 50 µm. (B) Time course of 5-HT-induced changes in luminal surface pH in four different regions along a salivary gland (squares in A).