Platelet-Activating Factor Stimulates Receptor-Mediated Formation of Reactive Oxygen Intermediates in Human Monocytes

Abstract

Stimulation of production of reactive oxygen intermediates (ROD was examined in human peripheral blood monocytes by l-minol<lependent chemilnmlnescence. The dose~response curve characterizing the dependence of ROI production on the concentration of platelet-activating fac~ tot (PAF) showed that stimulation occurred within a concentration range of 2 X 10-9M to 5 X 10-6M, Transformation of the dose-response curve to an Eadie-Hofstee plot indicated that the process is characterized by two K m values. The Km value corresponding to the highaffinity branch of the curve is 1.3 + 0.14 nM. In the same cells, the dissociation constant for the [SH]PAF/receptor complex was determined. The K d value was 0.8 d-0.1 nM, which agreed quite well with the high-affinity K m value obtained in the Eadie-Hofstee plot. The data indicate that stimulation of ROI generation is mediated through PAF binding at specific receptor sites at nanomolar PAF concentrations. Along with the specific receptor-mediated ROI generation, a nonspecific effect of PAF at a high concentration was demonstrated.