PLD and neutrophil function

The first experiments implicating a role for PLD activity in neutrophil function were performed by Cockcroft and colleagues (Cockcroft Stutchfield, 1989 Cockcroft, 1992) who measured phosphatidic acid accumulation in cells whose membrane phospholipids or ATP were radiolabelled. These experiments showed that phosphatidic acid accumulation during cell activation did not derive from DAG, but rather was directly generated from a phospholipid. Phosphatidic acid production from DAG (generated by PLC) 

These approaches have been used to show conclusively that the initial, low formation of DAG that occurs during activation with soluble agonists comes from PLC activity, and that the later, more sustained generation of DAG comes from PLD activity. Such experiments have also shown that primary alcohols can inhibit the activity of the NADPH oxidase under some conditions. When neutrophils are pretreated with cytochalasin B, primary alcohols are potent inhibitors of 02 secretion, and the kinetics of phosphatidic acid formation are rapid, peaking within about 20 s and coinciding with oxidase activation. However, in the absence of cytochalasin B, primary alcohols have little effect on the initiation of O2 secretion, but decrease the duration of oxidase activity they also inhibit the later phase of luminol chemiluminescence, which is largely intracellular, and the kinetics of phosphatidic acid formation closely parallel the kinetics of this intracellular oxidase activity (Fig. 6.20). Thus, in cytochalasin-treated cells, PLD is activated rapidly, and this activation is required for 02 secretion in the absence of cytochalasin, PLD is activated more slowly and its function is not for the activation of the oxidase, but rather for sustained (and intracellular) activity. 

Primary alcohols inhibit the up-regulation of CR3 (complement receptor) molecules on the plasma membrane during neutrophil activation, indicating that PLD products are required for the translocation of specific granules, 

The enzyme phosphatidate phosphohydrolase can be inhibited by propranolol, although this inhibitor is not completely specific. Thus, propranolol treatment of neutrophils results in the increased formation of phosphati-dic acid and the decreased formation of DAG. There is increasing evidence 

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