Inhibition of Golgi apparatus-mediated secretion by cinnamic acid derivatives

Two test systems have been utilized for screening potential inhibitors of Golgi apparatus function. In one system we measured formation of external polysaccharide droplets by the outer cap cells of maize roots. The droplets, direct products of the Golgi apparatus, were quantitated by visual estimates of droplet size compared to known standards. In the second system, we monitored secretory granule formation in the parotid gland of the rat, an activity also mediated by the Golgi apparatus. Parotid gland slices were stimulated with epinephrine to achieve 90% release of granules. The ability of the Golgi apparatus to package new secretory granules was then tested by incubating degranulated gland slices in the presence of putative inhibitors followed by restimulation with epinephrine. The amounts of alpha-amylase or (3H)leucine labeled proteins secreted into the medium were used as measures of secretory granule formation. The phenolic acid cinnamic acid and a related compound scopoletin were found to show substantial inhibition of secretion in both test systems.