Leukotriene B4 mobilizes calcium without the breakdown of polyphosphoinositides and the production of phosphatidic acid in rabbit neutrophils.

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Abstract
The addition of fMet-Leu-Phe, leukotriene B4, or arachidonic acid to rabbit neutrophils causes a rise in the level of intracellular free Ca measured by the fluorescent dye quin-2. The Ca response is rapid and dose-dependent with an ED50 of 0.12 .+-. 0.05 nM for leukotriene B4, 0.20 .+-. 0.02 nM for fMet-Leu-Phe, and 320 .+-. 30 nM for arachidonic acid. However, unlike fMet-Leu-Phe, leukotriene B4 at concentrations up to 70 nM does not cause a significant breakdown of any of the phosphoinositides or the generation of phosphatidic acid, arachidonic acid, or 1,2-diacylglycerol. The addition of arachidonic acid causes little (< 20%) production of phosphatidic acid. The dose-response curve of the generation of phosphatidic acid by fMet-Leu-Phe is shifted to the right when compared with that for Ca mobilization. Although similar in many respects, there are important qualitative differences between the mechanisms of action of these 2 chemotactic factors. Ca mobilization by leukotriene B4 is not mediated by the breakdown of any of the phosphoinositides. Ca mobilization by leukotriene B4, arachidonic acid and possibly fMet-Leu-Phe is not mediated by the generation of phosphatidic acid.