Platelet-activating factor induced Ca(2+) signaling in human microglia.
Increases in intracellular Ca(2+) concentration in human microglial cells in response to platelet-activating factor (PAF) were studied using Ca(2+)-sensitive fluorescence microscopy. In normal physiological solution (PSS), PAF-induced transient increases in [Ca2+](i) which recovered to baseline values within 200 s. Application of PAF in zero-Ca(2+) solution caused the peak response to be decreased to a value near 20% of that recorded in PSS suggesting a primary contribution of Ca(2+) influx for the [Ca2+](i) increase in PSS. To investigate PAF-induced Ca(2+) influx, the contents of intracellular stores were modulated using the SERCA blocker cyclopiazonic acid (CPA). The Ca(2+) signal induced by CPA (10 microM) in zero-Ca(2+) solution showed a peak response about 20% of the amplitude in the presence of external Ca(2+), suggesting the latter response included significant contributions from store-operated Ca(2+) entry. The influx of divalent cations with PAF or CPA was directly measured using Mn(2+) quenching of the fluorescence signal. Although both PAF and CPA induced a similar degree of Mn(2+) influx over time, the PAF effect was very rapid, whereas the CPA action was delayed and only evident about 200 s after application. Overall, the results show that the primary source of the PAF-induced increase of [Ca2+](i) in human microglia was the influx of Ca(2+) from the extracellular space and intracellular Ca(2+)-release contributed only a small part of the total Ca(2+) signal. Nevertheless, Ca(2+)-release induced by PAF (or CPA) serves as an important factor in controlling Ca(2+) entry presumably mediated by activation of store-operated-Ca(2+) channels.
Wang
X
X
Department of Pharmacology and Therapeutics, Department of Medicine, The University of British Columbia, 2176 Health Sciences Mall, Vancouver, BC, Canada.
Bae
J H
JH
Kim
S U
SU
McLarnon
J G
JG
D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008345:Manganese / Q000378:metabolism; D017628:Microglia / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008856:Microscopy, Fluorescence; D010972:Platelet Activating Factor / Q000494:pharmacology*
D005456:Fluorescent Dyes; D007211:Indoles; D010972:Platelet Activating Factor; D008345:Manganese; D002118:Calcium; D016257:Fura-2; C000543:cyclopiazonic acid