Agonist-induced calcium flux, phosphoinositide metabolism, aggregation and enzyme secretion in human neutrophils.
Formyl-methionyl-leucyl-phenylalanine (FMLP), platelet activating factor (PAF) and leukotriene B4 (LTB4) are potent activators of human neutrophils. Using human neutrophils prelabelled with the fluorescent indicator dye, Quin 2, or with [32P]-orthophosphate, we examined the effects of these stimuli on intracellular free calcium concentration, [Ca2+]i, and on various indices of phosphoinositide metabolism, including [32P]-phosphatidic acid (PtdA) formation. The concentration-dependence of the observed changed in [Ca2+]i or [32P]-PtdA were then compared to stimulus-induced aggregation and enzyme release (beta-N-acetylglucosaminidase (NAG) and lysozyme). FMLP, PAF and LTB4 caused a concentration-dependent elevation of [Ca2+]i, aggregation and enzyme release. However, unlike FMLP and PAF, LTB4 (less than or equal to 2.5 microM) did not cause significant formation of [32P]-PtdA. The concentration response curves for agonist-induced elevation of [Ca2+]i lie to the left of those for aggregation and enzyme release. FMLP and PAF also caused an elevation of [Ca2+]i at concentrations lower than those required to elicit [32P]-PtdA formation. These observations suggest that [Ca2+]i elevation per se cannot mediate human neutrophil functional responses to FMLP, PAF and LTB4. Consequently there may exist other mediator(s) that act in concert with [Ca2+]i or are triggered by [Ca2+]i elevation to promote human neutrophil activation. Both the elevation of [Ca2+]i and the formation of these putative mediator(s) in response to LTB4 apparently occur independently of inositol phospholipid hydrolysis.
Rossi
A G
AG
Department of Pharmacology, University of Glasgow, Scotland, UK.
McMillan
R M
RM
MacIntyre
D E
DE
D000328:Adult; D002118:Calcium / Q000378:metabolism*; D002449:Cell Aggregation / Q000187:drug effects; D006801:Humans; D007975:Leukotriene B4 / Q000494:pharmacology*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000494:pharmacology*
D010716:Phosphatidylinositols; D010972:Platelet Activating Factor; D007975:Leukotriene B4; D009240:N-Formylmethionine Leucyl-Phenylalanine; D002118:Calcium