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The Journal of Neuroscience, June 1, 2003, 23(11):4410-4419
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Elevation of Basal Intracellular Calcium as a Central Element in the Activation of Brain Macrophages (Microglia): Suppression of Receptor-Evoked Calcium Signaling and Control of Release Function
Anja Hoffmann,
Oliver Kann,
Carsten Ohlemeyer,
Uwe-Karsten Hanisch, and
Helmut Kettenmann
Department of Cellular Neurosciences, Max Delbrück Center for
Molecular Medicine, D-13092 Berlin, Germany
Microgliabrain macrophages are immune-competent cells of the CNS and
respond to pathologic events. Using bacterial lipopolysaccharide (LPS) as a
tool to activate cultured mouse microglia, we studied alterations in the
intracellular calcium concentration ([Ca 2+]i) and in
the receptor-evoked generation of transient calcium signals. LPS treatment led
to a chronic elevation of basal [Ca 2+]i along with a
suppression of evoked calcium signaling, as indicated by reduced [Ca
2+]i transients during stimulation with UTP and
complement factor 5a. Presence of the calcium chelator BAPTA prevented the
activation-associated changes in [Ca 2+]i and restored
much of the signaling efficacy. We also evaluated downstream consequences of a
basal [Ca 2+]i lifting during microglial activation and
found BAPTA to strongly attenuate the LPS-induced release of nitric oxide (NO)
and certain cytokines and chemokines. Furthermore, microglial treatment with
ionomycin, an ionophore elevating basal [Ca 2+]i,
mimicked the activation-induced calcium signal suppression but failed to
induce release activity on its own. Our findings suggest that chronic
elevation of basal [Ca 2+]i attenuates
receptor-triggered calcium signaling. Moreover, increased [Ca
2+]i is required, but by itself is not sufficient, for
release of NO and certain cytokines and chemokines. Elevation of basal [Ca
2+]i could thus prove a central element in the
regulation of executive functions in activated microglia.
Key words: BAPTA; C5a; CD88; fura-2; ionomycin; UTP
Received Nov 19, 2002;
revised January 29, 2003;
accepted February 27, 2003.
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