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

An interesting question was whether caffeine and reduced temperature would inhibit also the BFA-induced retrograde movement of the Golgi membranes. In the presence of 10 mM caffeine at 20~ BFA was able to redistribute at least part of the cellular man II to the ER with nearly similar kinetics than with BFA only at 20~ Interestingly, caffeine did seem to slow down the rate by which BFA treatment results in the disappearance of any recognizable Golgi complex by a factor of ~1.6. Nevertheless, already after a 60-min chase in the presence of caffeine at 20~ 68% of the cells showed labeling in the ER and long tubular structures emanating from the Golgi complex. These results show that caffeine does not inhibit the BFA-induced retrograde Golgi-to-ER transport, although the traffic in the opposite (ER-to-Golgi) direction, is inhibited. Also, since caffeine at 20~ did not inhibit the BFA-induced retrograde movement of Golgi membranes, known to be inhibited by the GTP-,y-S (Tan et al., 1992) , it seems unlikely that the effect of caffeine would be due to caffeine mimicking GTP-3,-S.