SACCHAROMYCES-CEREVISIAE CELLS PRODUCE PLATELET-ACTIVATING-FACTOR IN RESPONSE TO CALCIUM IONOPHORE A23187

Synthesis of platelet-activating factor (PAF) was stimulated by the tr eatment of cells with the calcium ionophore A23187 in Saccharomyces ce revisiae. The amount of PAF production increased, A23187-concentration - and time-dependently. The maximum PAF synthesis was observed when th e yeast cells were treated with 2 mu M of A23187 for 5 min, and the PA F amount decreased at the higher concentrations of A23187 and/or for t he longer incubation time. Treatment of the cells with 1 mM of PMSF (p henylmethylsulfonyl fluoride), an inhibitor of PAF catabolism, resulte d in transient accumulation of PAF; however, at more than 2 mM of PMSF , PAF production was reduced. Synthesized PAF was not released into th e extracellular fraction and was found to be cell-associated. In the a bsence of, A23187 or CaCl2, and in the presence of EGTA, a Ca2+-chelat or, no new synthesis of PAF was observed. These results suggested A231 87-induced PAF production was Ca2+ dependent, and proceed via PAF remo deling pathway. PAF synthesis in response to A23187 was not detectable in the yeast cells in the logarithmic phase, but increased and reache d maximum in the stationary phase of the cell growth. These findings s uggest that PAF is related to yeast cell growth.