Fig. 1.
Liver cytosol (LC) decreases nitric oxide (NO•) production by suppressing inducible nitric oxide synthase (iNOS) activity only when applied to the basolateral side. Filtered human LC (400 μg/ml) and cytomix were added together to culture medium of Caco-2 cells growing on collagen-coated dishes which were then incubated for 24 h at 37°C. A: NO2−/NO3− concentration in medium was measured by the Griess assay. B: iNOS protein expression was measured by Western blot analysis. C: the polarity of the suppressive effect of LC on NO• was investigated with mature Caco-2 monolayers 21 days after seeding on the permeable membranes. Filtered LC (400 μg/ml) and cytomix were added to either or both the apical and basolateral sides of the monolayer as indicated in the graph. The concentration of NO2−/NO3− was measured after 24 h of stimulation. The data shown here are representative of the same experiment, all of which were equivalent. *P < 0.05 vs. 0 h control.