Human monocytes maintained in culture acquire functional responsiveness to platelet-activating factor that is independent of increases in protein tyrosine phosphorylation.
1. Acute (day 0) stimulation with platelet-activating factor (PAF) did not elicit superoxide anion (O2-) generation from adherent monocytes. However, by day 2 of culture, PAF induced an increase in O2- generation that was inhibited by pretreatment with the PAF receptor antagonist WEB 2086. 2. The lack of effect of PAF on O2- generation was not due to the absence of receptors, as PAF stimulated an increase in tyrosine phosphorylation and intracellular calcium ([Ca2+]i) on both days 0 and 2 of culture. 3. Pretreatment with the protein tyrosine kinase inhibitor methyl 2,5-dihydroxycinnamate inhibited PAF-induced tyrosine phosphorylation; however, this inhibitor failed to inhibit PAF-induced O2- generation. In contrast, pretreatment with the protein kinase C inhibitor staurosporine had no effect on PAF-induced tyrosine phosphorylation, but did inhibit PAF-induced O2- generation. 4. These results indicate that monocytes maintained in culture acquire a functional response to PAF through a mechanism that appears to be independent of PAF receptor expression, coupling to increases in [Ca2+]i or tyrosine phosphorylation.
Grigoriadis
G
G
Bernard O'Brien Institute of Microsurgery, Fitzroy, Victoria, Australia.
Stewart
A G
AG
D001381:Azepines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured / Q000187:drug effects; D006801:Humans; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010766:Phosphorylation; D010972:Platelet Activating Factor / Q000494:pharmacology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D014230:Triazoles / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism*
D001381:Azepines; D010972:Platelet Activating Factor; D010975:Platelet Aggregation Inhibitors; D014230:Triazoles; C052518:WEB 2086; D014443:Tyrosine; D010100:Oxygen; D002118:Calcium