Phorbol 12-myristate, 13-acetate potentiates the action of the calcium ionophore in stimulating arachidonic acid release and production of phosphatidic acid in rabbit neutrophils

The addition of the tumor-promoting phorbol 12-myristate, 13-acetate to rabbit neutrophils greatly potentiates the effect of the calcium ionophore A23187 on 3H]-arachidonic acid release and 32P]-phosphatidic acid generation. At 5 X 10(-8) M A23187, the addition of 20 ng/ml PMA potentiates the action of the ionophore on 3H]-arachidonic acid release by 5-fold. At 5 X 10(-7) M A23187, PMA enhances 32P]-phosphatidic acid production by 1.5-fold. Incubation of the neutrophils with 5 X 10(-7) M ionophore for two minutes causes a significant increase in the 32P] phosphatidic acid production but does not affect the levels of 32P]-phosphatidylinositol or 32P]-phosphatidylinositol 4,5 bis-phosphate. In addition, increasing the sodium chloride concentrations in the suspending medium causes an increase in the level of phosphatidylinositol 4,5 bis-phosphate. These results suggest that the phorbol ester either acting directly or through the activation of protein kinase C modulates significantly the activities of the various forms of phospholipases, particularly A2, and/or increases the availability or amounts of their substrates.