Rapid kinetics of agonist-evoked changes in cytosolic free Ca2+ concentration in fura-2-loaded human neutrophils.
The initial kinetics of agonist-evoked rises in the cytosolic Ca2+ concentration [Ca2+]i were investigated in fura-2-loaded human neutrophils by stopped-flow fluorimetry. The rises in [Ca2+]i evoked by chemotactic peptide (fMet-Leu-Phe), platelet-activating factor and ADP all lagged behind agonist addition by 1-1.3 s. Lag times were not significantly different in the presence and in the absence of external Ca2+. Stimulation of the cells in the presence of extracellular Mn2+ resulted in a quench of fluorescence with a similar lag time to [Ca2+]i rise. The delay in onset of the rise in [Ca2+]i evoked by fMet-Leu-Phe was dependent on concentration, becoming longer at lower concentrations of agonist. These results indicate that both the agonist-evoked discharge of the intracellular Ca2+ stores and the generation of bivalent-cation influx lag behind agonist-receptor binding in neutrophils. Both pathways thus appear to be mediated by indirect mechanisms, rather than by a directly coupled process such as a receptor-operated channel. The temporal coincidence of the onset of store discharge with the commencement of bivalent-cation influx suggests that the two events may be causally linked.
Sage
S O
SO
Physiological Laboratory, University of Cambridge, U.K.
Pintado
E
E
Mahaut-Smith
M P
MP
Merritt
J E
JE
D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D007700:Kinetics; D009504:Neutrophils / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D001572:Benzofurans; D005456:Fluorescent Dyes; D002118:Calcium; D016257:Fura-2