Flow cytometric calcium flux assay: evaluation of cytoplasmic calcium kinetics in whole blood leukocytes.
In leukocytes, as in many other cell types, cytoplasmic calcium ([Ca(2+)](i)) changes play a key role in a series of pathways leading to activation. Here we describe a flow cytometric method allowing the simultaneous kinetic analysis of changes in [Ca(2+)](i) in the three types of leukocytes, i.e. monocytes, granulocytes and lymphocytes. Heparinised whole blood was diluted in phosphate buffered saline with Ca(2+) and 1 mM sodium pyruvate and incubated with the Ca(2+) indicator fluo3-acetoxymethyl ester. Leukocytes were identified by labelling with the phycoerythrin-conjugated antibody against CD45, the leukocyte common antigen. Resuspension of the cells in PBS with or without Ca(2+) allowed us to detect the origin of Ca(2+) changes. During flow cytometric analysis only CD45-positive cells were counted and monocytes, granulocytes and lymphocytes were evaluated separately. Baseline fluorescence of the fluo3-Ca(2+)-complex was determined and changes in [Ca(2+)](i) after stimulation with the calcium ionophore A23187 or the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) were recorded over a time period of 150 s. Stimulation with A23187 resulted in a rise in [Ca(2+)](i) in all three leukocyte subpopulations. This rise was sustained in the presence of extracellular Ca(2+) (Ca(2+)(ex)) but had a transient character in the absence of Ca(2+)(ex). For fMLP, [Ca(2+)](i) changes occurred only in monocytes and granulocytes and were transient irrespective of the presence or absence of Ca(2+)(ex). In conclusion, the present method is a simple, fast and easy tool to analyse in vitro [Ca(2+)](i) changes over time in leukocytes under physiologically relevant conditions, without the need for their isolation or the lysis of erythrocytes. The whole blood approach allows a continuous interaction between the different leukocyte subpopulations and other blood components and a minimum of preparative manipulations avoids artefactual activation of the cells. A distinction can be made between Ca(2+) release from the intracellular stores and the entry of Ca(2+) from outside the cell. The approach allows to evaluate the effect of various agonists on [Ca(2+)](i) changes in leukocytes, with physiological, patho-physiological or therapeutic purposes.
Schepers
Eva
E
Renal Division, Department of Internal Medicine, University Hospital Gent, De Pintelaan 185, 9000 Gent, Belgium. Eva.Schepers@UGent.be
Glorieux
Griet
G
Dhondt
Annemieke
A
Leybaert
Luc
L
Vanholder
Raymond
R
D000814:Aniline Compounds / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000819:agonists / Q000032:analysis*; D020013:Calcium Signaling; D005434:Flow Cytometry / Q000379:methods*; D005456:Fluorescent Dyes / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D017493:Leukocyte Common Antigens / Q000378:metabolism; D007962:Leukocytes / Q000187:drug effects / Q000378:metabolism*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D014966:Xanthenes / Q000494:pharmacology
D000814:Aniline Compounds; D005456:Fluorescent Dyes; D014966:Xanthenes; C059715:Fluo-3; D000001:Calcimycin; D009240:N-Formylmethionine Leucyl-Phenylalanine; D017493:Leukocyte Common Antigens; C516769:PTPRC protein, human; D002118:Calcium