Stimulus–secretion coupling in rabbit neutrophils is not mediated by phosphatidylinositol breakdown

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Abstract
In common with other cells which use intracellular Ca2+ to mediate specific cell function, the rate of metabolism of phosphatidylinositol (PI) increases in rabbit neutrophiles, stimulated with specific agonists. This is normally measured as the incorporation of radioactive phosphate or inositol into PI, but these reactions are presumed to be secondary processes following the initial breakdown of pre-existing PI to diaclyglycerol. The radioactive labels are incorporated during the stepwise resynthesis of PI via phosphatidic acid (PA). In the sequence of biochemical events, starting with the binding of the ligand to a receptor and finally resulting in the expression of cellular activity, the breakdown of PI is an early event immediately directed by activation of the receptor. This could then control the increase in cytoplasmic Ca2+ and other processes dependent on this. An analysis of the temporal relationship between these phospholipid changes and cell stimulation is reported. In neutrophils, PI breakdown and PA labeling are both consequences and not causes of a rise in intracellular Ca2+.