Activation of human granulocytes by arachidonic acid: its use and limitations for investigating granulocyte functions

The effects of arachidonic acid on human granulocytes (polymorphonuclear neutrophil leukocytes, PMN) were examined with respect to early events associated with activation of the superoxide (O2-)-generating system and its reactivation with other stimuli after the addition of fatty acid-free bovine serum albumin. As with other stimuli, O2- production occurred after a lag that was dependent on the amount of arachidonic acid used. Although the lag, rate, and extent of O2- production were dose dependent, at all concentrations used, the duration of O2- production was four to six minutes. As previously described, when fatty acid-free albumin was added one minute after stimulation of PMN by arachidonic acid, O2- production ceased immediately. The O2(-)-generating system could then be reactivated by the addition of either phorbol myristate acetate (PMA), concanavalin A, or serum-treated zymosan. In previously activated cells, the lag time for reactivation was shorter and the rate of O2- production greater with PMA. PMN membrane potential was depolarized by arachidonic acid. This depolarization was not reversed with the addition of albumin. PMN cytoplasts were also capable of reversible activation by arachidonic acid in a manner identical to whole cells. Divalent cations were found to be necessary for the activation of PMN by arachidonic acid. In the absence of calcium, arachidonic acid caused rapid lysis of the cells, as manifested by the release of lactic acid dehydrogenase. We were unable to measure later events in PMN stimulated by arachidonic acid since even in the presence of divalent cations lactic acid dehydrogenase was released from the cells after five minutes of incubation. We conclude that, in addition to its ability to activate PMN, arachidonic acid is toxic to the cells and cannot be used to study late events in granulocyte activity, and, in the absence of calcium, it may be difficult to interpret its action as a stimulant of the oxidase.