Fig. 3. Bafilomycin A₁-sensitive and ouabain-sensitive ATPase activity in homogenized salivary glands. (A) Dose–response curve for the effect of bafilomycin A₁ on the total ATPase activity within the homogenate. Values represent the means ± S.D. of 4–11 experiments for each concentration. Half-maximal inhibition (IC₅₀) is reached at approximately 3 nmol l^–1 bafilomycin A₁. (B) Effect of 5-hydroxytryptamine (5-HT) on total ATPase activity, bafilomycin-sensitive ATPase activity and ouabain-sensitive ATPase activity. Values represent the mean ± S.D. of 5–16 experiments; asterisks indicate a significance level of P<0.001. In 5-HT-stimulated salivary glands, bafilomycin-sensitive ATPase activity is enhanced by a factor of approximately 2, whereas ouabain-sensitive ATPase activity does not change significantly.