Influence of platelet activating factor and a nonmetabolizable analogue on superoxide production by bone marrow...

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-OCH3), 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-OCH3 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-OCH3, this compound increased the PMA-induced activation of protein kinase C only 1.39-fold. The priming effect of Et-18-OCH3 was not reduced in the absence of extracellular Ca2+ and after cell membrane depolarisation.