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The Journal of Neuroscience, June 1, 2003, 23(11):4737-4745
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Transient Receptor Potential Channel Activation Causes a Novel Form of [Ca 2+]i Oscillations and Is Not Involved in Capacitative Ca 2+ Entry in Glial Cells
Maurizio Grimaldi,
Marina Maratos, and
Ajay Verma
Department of Neurology, Uniformed Services University of the Health
Sciences, Bethesda, Maryland 20814
Astrocytes express transient receptor potential channels (TRPCs), which
have been implicated in Ca 2+ influx triggered by
intracellular Ca 2+ stores depletion, a phenomenon known
as capacitative Ca 2+ entry. We studied the properties
of capacitative Ca 2+ entry in astrocytes by means of
single-cell Ca 2+ imaging with the aim of understanding
the involvement of TRPCs in this function. We found that, in astrocytes,
capacitative Ca 2+ entry is not attributable to TRPC
opening because the TRPC-permeable ions Sr2+ and
Ba2+ do not enter astrocytes during capacitative Ca
2+ entry. Instead, natively expressed
oleyl-acetyl-glycerol (OAG) (a structural analog of DAG) -sensitive TRPCs,
when activated, initiate oscillations of cytosolic Ca 2+
concentration ([Ca 2+]i) pharmacologically
and molecularly consistent with TRPC3 activation. OAG-induced [Ca
2+]i oscillations are not affected by
inhibition of inositol trisphosphate (InsP3) production or blockade
of the InsP3 receptor, therefore representing a novel form of [Ca
2+]i signaling. Instead, high [Ca
2+]i inhibited oscillations, by closing the
OAG-sensitive channel. Also, treatment of astrocytes with antisense against
TRPC3 caused a consistent decrease of the cells responding to OAG. Exogenous
OAG but not endogenous DAG seems to activate TRPC3. In conclusion, in glial
cells, natively expressed TRPC3s mediates a novel form of Ca
2+ signaling, distinct from capacitative Ca
2+ entry, which suggests a specific signaling function
for this channel in glial cells.
Key words: astrocyte; transient receptor potential channel; store-operated Ca 2+ channels; [Ca 2+]i oscillations; capacitative Ca 2+ entry; C6 glioma cells
Received Dec. 2, 2002;
revised Mar. 12, 2003;
accepted Mar. 12, 2003.
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