Fig. 5. Assembly state of V-ATPase in control and 5-hydroxytryptamine (5-HT)-stimulated salivary glands. The glands were homogenized and separated by high-speed centrifugation into a pellet fraction (P) and a supernatant (S). The relative distribution of various proteins between the two fractions was then probed by western blot analysis. Upon stimulation with 5-HT, the amount of the V₁ component proteins (subunits A and E) increases within the pellet and diminishes in the supernatant. No significant change in response to 5-HT stimulation is observed in the distribution of integral membrane proteins (Na⁺/K⁺-ATPase -subunit; V₀ component proteins, subunits a and d), of -tubulin or of the total amount of protein between both fractions. Values represent the mean ± S.D. of six independent experiments. Asterisks indicate a significant difference (P<0.001).