WORTMANNIN INHIBITS MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVATION-INDUCED BY PLATELET-ACTIVATING-FACTOR IN GUINEA-PIG NEUTROPHILS

Stimulation of guinea pig neutrophils with platelet-activating factor (PAF) caused a rapid and transient activation of mitogen-activated pro tein kinase (MAPK). Wortmannin, an inhibitor of phosphatidylinositol 3 -kinase, partially (similar to 50%) inhibited PAF-induced MAPK activat ion. Half-maximal inhibition was observed with 200-300 nM wortmannin, while it did not inhibit phorbol ester-induced MAPK activation. Neutro phils preloaded with 2-bis-(O-aminophenoxy)ethane-N,N,N',N'-tetraaceti c acid acetoxymethyl ester (BAPTA/AM) failed to raise cytosolic Ca2+ c oncentrations toward PAF, while they still responded to PAF with a 40- 50% activation of MAPK. However, when cells were treated with BAPTA/AM and wortmannin in combination, the MAPK activation was completely inh ibited. These results suggest that PAF activates MAPK through two dist inct pathways in guinea pig neutrophils, one Ca2+-dependent, and the o ther Ca2+-independent but wortmannin-sensitive.