Effect of caffeine and reduced temperature (20 degrees C) on the organization of the pre-Golgi and the Golgi stack membranes

Electron microscopy study of the Golgi structure revealed a vesicularization of the Golgi stack in the presence of 10 mM caffeine at 20~ These small vesicles remained as tight clusters at the perinuclear site where the Golgi complex is normally localized. This result is in agreement with the immunofluorescence observations with man II. Since the perinuclear localization of the Golgi complex in the cell is dependent on the integrity of the microtubules (Thyberg and Moskalewski, 1985; Kreis, 1990) , it is unlikely that caffeine at 20~ would act through disrupting the microtubular network. This is further supported by the fact that also in caffeine-treated cells the BFA-induced tubular, microtubuledependent structures were able to form. One possible explanation for the caffeineinduced vesicularization of the Golgi stack could be that when the transport from the ER to the Golgi complex is inhibited, while the vesicular recycling in the Golgi stack is still occurring, the Golgi stack ultimately becomes vesicularized.