Fig. 6. Effects of acetazolamide and concanamycin A on 5-HT-induced pH_i changes. (A) Bath application of 500 µmol l^–1 acetazolamide causes a cytoplasmic acidification, whereas 10 nmol l^–1 5-HT, applied in the presence of acetazolamide, produces an alkalinization. (B) In the presence of acetazolamide, 10 µmol l^–1 8-CPT-cAMP induces an intracellular alkalinization. (C,D) Inhibition of the apical V-ATPase by 1 µmol l^–1 concanamycin A causes a small acidification. In preparations in which 10 nmol l^–1 5-HT induces a monophasic acidification (C), this pH change is almost unaffected by concanamycin A. When 10 nmol l^–1 5-HT induces a multiphasic pH change, concanamycin A blocks the alkalizing response component (D). (E) Acetazolamide and concanamycin A applied together cause additive acidifications, and 10 nmol l^–1 5-HT causes an alkalinization in the presence of these two inhibitors (E). The alkalinization produced by 10 nmol l^–1 5-HT in the presence of acetazolamide is significantly (P<0.05) smaller when the V-ATPase is simultaneously inhibited by concanamycin A (F). Data in F are means ± s.e.m., N=9.