Saccharomyces cerevisiae Cells Produce Platelet-activating Factor in Response to Calcium Ionophore A23187

Abstract

Synthesis of platelet-activating factor (PAF) was stimulated by the treatment of cells with the calcium ionophore A23187 in Saccharomyces cerevisiae. The amount of PAF production increased A23187-concentration- and time-dependently. The maximum PAF synthesis was observed when the yeast cells were treated with 2 μM of A23187 for 5 min, and the PAF amount decreased at the higher concentrations of A23187 and/or for the longer incubation time. Treatment of the cells with 1 mM of PMSF (phenylmethylsulfonyl fluoride), an inhibitor of PAF catabolism, resulted in transient accumulation of PAF ; however, at more than 2mM of PMSF, PAF production was reduced. Synthesized PAF was not released into the extracellular fraction and was found to be cell-associated. In the absence of A23187 or CaCl₂, and in the presence of EGTA, a Ca²⁺ -chelator, no new synthesis of PAF was observed. These results suggested A23187-induced PAF production was Ca²⁺ dependent, and proceed via PAF remodeling pathway. PAF synthesis in response to A23187 was not detectable in the yeast cells in the logarithmic phase, but increased and reached maximum in the stationary phase of the cell growth. These tindings suggest that PAF is related to yeast cell growth.