Fig. 1.

Intracellular cAMP elevation causes a reversible luminal pH change that depends on V-ATPase activity. The apical membrane was labeled with pH-sensitive dye HAF, and the F₄₇₀/F₄₁₀ fluorescence ratio was measured during bath application of 10 mM cAMP (A), 200 μM Sp-cAMPS (B), or 100 μM forskolin (C and D). All substances led to a reversible acidification on the luminal side of the salivary glands, as indicated by the decrease in the F₄₇₀/F₄₁₀ ratio. (D) Preincubation with 1 μM concanamycin A abolishes the response to forskolin.