Influence of Platelet Activating Factor and a Nonmetabolizable Analogue on Superoxide Production by Bone Marrow Derived Macrophages

Serum‐free cultured macrophages could be stimulated for lucigenin‐dependent chemiluminescence by platelet activating factor (PAF) and phorbol myristate acetate (PMA). Stimulation with PMA resulted in a desensitization against PAF, whereas prestimulation with PAF had no influence on a following response caused by PMA. The PAF analogue, 1‐O‐octadecyl‐2‐O‐methyl‐ rac ‐glycero‐3‐phosphocholine (Et‐18‐OCH 3 ), did not induce chemiluminescence by itself and desensitized the cells against PAF, like substimulating concentrations of PAF. PAF and PMA responsiveness was rapidly modulated in a similar manner during adherence of the cells to polystyrene tubes. At higher concentrations, Et‐18‐OCH 3 as well as lysophosphatidylcholines potentiated PMA‐induced chemiluminescence. The PAF analogue was most effective. Although PMA‐induced chemiluminescence was stimulated at least 5‐fold by Et‐18‐OCH 3 , this compound Increased the PMA‐induced activation of protein kinase C only 1.39‐fold. The priming effect of Et‐18‐OCH 3 was not reduced in the absence of extracellular Ca 2+ and after cell membrane depolarisation.