Abstract
The role of changes in cytosolic free calcium (Ca) in the activation sequence of the human neutrophil has been monitored by means of the fluorescent probe Quin2. "Complete" secretagogues such as the chemotactic peptide f-Met-Leu-Phe and aggregated IgG, as well as the "incomplete" secretagogue concanavalin A, elicited prompt rises in cytosolic Ca. The rise in cytosolic Ca was in all cases one of the earliest measurable events, consistent with the hypothesis that increments in cytosolic free Ca serve as a signal to activate subsequent physiological responses. The source of cytosolic Ca is principally intracellular, since removal of extracellular Ca had little effect on the rise in cytosolic Ca. Although increments in cytosolic Ca may be essential for neutrophil activation, they are evidently not sufficient; chemotactic levels of f-Met-Leu-Phe elicited optimal increments in cytosolic Ca without triggering degranulation, O-2 generation, and aggregation. Some other factor, associated with high levels of receptor occupancy, must be required for secretion. The tumor promoter phorbol myristate acetate was an exceptional stimulus, since it elicited degranulation, aggregation, and O-2 generation without triggering a rise in cytosolic Ca. Finally, an efflux of Ca is initiated which serves to maintain low intracellular levels of Ca.
Highlights
The role of changes in cytosolicfree calcium (Ca) in omission from the medium or by addition of EGTA,l reduces the activation sequence of the human neutrophil has but does not entirely abolish aggregation, degranulation, or beenmonitoredbymeansofthefluorescentprobe the generation of 02 in response to a variety of stimuli, Quina
Quin2 remains in the cytoplasm optimal increments in cytosolicCa without triggering and hasbeen shown to serve as a rapid and sensitive indicator degranulation, 0;generation, and aggregation
The tumor Ca as a second messenger in this system
Summary
Tactic peptide f-Met-Leu-Phe and aggregated IgG, as Many workers have demonstrated enhanced Ca uptake by well as the “incomplete” secretagogue concanavalAin, activated neutrophils [9,10,11,12], fulfilling thethird criterion. Some of changes in cytoplasmic free Ca in f-Met-Leu-Phe-activated other factor, associated with high levels of receptor cells [16].This finding fulfillsthe fourthcriterion establishing occupancy, must be required for secretion. To establish a role for calcium as a second messenger possible that PMA may bypass the Ca mobilizing segments mediating the action of ligands such as f-Met-Leu-Phe, im- of the activation by directly activating a protein kinase C mune complexes, C5a,and concanavalin A on the neutrophil, [17]. The abbreviations used are: EGTA, ethylene glycol bis(8-aminoethyl ether)-N,N,N,’,N”tetraacetic acid; f-Met-Leu-Phe, N-formyl methionyl leucyl phenylalanine; PMA, phorbol myristate acetate; conA, concanavalin A; IgG, immunoglobulin G; Hepes, N-2-hydroxyethylpiperazine-N”2-ethanesulfonicacid; %, superoxide anion
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