Cellulaire (URA 1 130 CNRSI, FPdPration des Ldboratoires de Riologie, L)@pdrlernerit de Recherrhc For?darrienLd/e, Centre d'€tudes ,h!uc/eaire>,
3804 I Grenohlc cedcx, France
The effect of the trimethylxanthine, caffeine, was examined on the growth and endocytosis pathways of the vegetative amoebae of the cellular slime inold Dirtyostelium disc-oiclcum. Cafieine at concentrations of 1.5-3 niM was found to inhibit axenic growth, fluid-phase piriocytosis, and secretion of lysosornal enzymes. Cell vidbility was unaffected by incubation for 16 hours with 5 m M caffeine but decreased markedly thereafter. t'hagocytosis ot the bacterium Etrherichid coli by Diclyosteliurn amoebae was also inhibited by caffeine, although at concentralions twofold to threefold highrr. C3feine rapidly entered into amoebae to reach an equilibrium between extracellular and intracellulcu concentrations, and it was not appreciably metabolized by Uictyosteliurn. Inhibition of growth and enclocytosis was reversible upon removal of thc drug and was partially counteracted by 10 m M adenwine. As caffeine discharged intracellular calcium stores in Llictyostelium (Abe et al., 1988), its inhibitory effect on endocytosis could result from the perturbation o i calcium homeostasis. In agreement with h i s hypothesis, the cation La' ' (10 LM), a Ca'+-transport inhibitor, also strongly reduced fluid-phase pinocvtosis Several important cellular mechanisms have been found to be caffeine sensitive in the slime mold Dictyostelium discoideunz. Among the previously studied ef- fects that are either directly caused or potentiated by caffeine is sensitization to ultraviolet irradiation or alkylating agents (Payez and Deering, 1972; Liwerant and Peirera Da Silva, 1975;Hoetzer and Deering, 1980). Another example of a caffeine-sensitive system is the extensively characterized adenylate cyclase pathway (for review, Janssens and Van Haastert, 1987) upon which caffeine has different effects, depending on the experimental conditions. In starving Dietyostelium amoebae, it prevents the stimulation of adenylate cyclase activity by extracellular cyclic adenosine monophosphate (AMP) and the subsequent release of cyclic AMP (Brenner and Thoms, 1984). Caffeine is therefore a classical inhibitor of the cyclic AMP relay system in Dict.yostelium amoebae during the differentiation program (