The role of Ca2+ in the generation of spontaneous astrocytic Ca2+ oscillations.
Astrocytes in the rat thalamus display spontaneous [Ca(2+)](i) oscillations that are due to intracellular release, but are not dependent on neuronal activity. In this study we have investigated the mechanisms involved in these spontaneous [Ca(2+)](i) oscillations using slices loaded with Fluo-4 AM (5 microM) and confocal microscopy. Bafilomycin A1 incubation had no effect on the number of spontaneous [Ca(2+)](i) oscillations indicating that they were not dependent on vesicular neurotransmitter release. Oscillations were also unaffected by ryanodine. Phospholipase C (PLC) inhibition decreased the number of astrocytes responding to metabotropic glutamate receptor (mGluR) activation but did not reduce the number of spontaneously active astrocytes, indicating that [Ca(2+)](i) increases are not due to membrane-coupled PLC activation. Spontaneous [Ca(2+)](i) increases were abolished by an IP3 receptor antagonist, whilst the protein kinase C (PKC) inhibitor chelerythrine chloride prolonged their duration, indicating a role for PKC and inositol 1,4,5,-triphosphate receptor activation. BayK8644 increased the number of astrocytes exhibiting [Ca(2+)](i) oscillations, and prolonged the responses to mGluR activation, indicating a possible effect on store-operated Ca(2+) entry. Increasing [Ca(2+)](o) increased the number of spontaneously active astrocytes and the number of transients exhibited by each astrocyte. Inhibition of the endoplasmic reticulum Ca(2+) ATPase by cyclopiazonic acid also induced [Ca(2+)](i) transients in astrocytes indicating a role for cytoplasmic Ca(2+) in the induction of spontaneous oscillations. Incubation with 20 microM Fluo-4 reduced the number of astrocytes exhibiting spontaneous increases. This study indicates that Ca(2+) has a role in triggering Ca(2+) release from an inositol 1,4,5,-triphosphate sensitive store in astrocytes during the generation of spontaneous [Ca(2+)](i) oscillations.
Parri
H R
HR
School of Biosciences, Cardiff University, Museum Avenue, PO Box 911, CF10 3US, Wales, Cardiff, UK. parri@cardiff.ac.uk
Crunelli
V
V
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D000891:Anti-Infective Agents, Local / Q000494:pharmacology; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001896:Boron Compounds / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020013:Calcium Signaling; D004148:Dioxolanes / Q000494:pharmacology; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives* / Q000494:pharmacology; D018613:Microscopy, Confocal / Q000295:instrumentation / Q000379:methods; D018408:Patch-Clamp Techniques / Q000379:methods; D011687:Purines / Q000494:pharmacology; D051381:Rats; D012433:Ryanodine / Q000494:pharmacology; D013788:Thalamus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013849:Thimerosal / Q000494:pharmacology; D014966:Xanthenes / Q000378:metabolism
D000814:Aniline Compounds; D000891:Anti-Infective Agents, Local; D001896:Boron Compounds; D002120:Calcium Channel Agonists; D004148:Dioxolanes; D004791:Enzyme Inhibitors; C409648:Fluo 4; D011687:Purines; D014966:Xanthenes; C104068:4-(2-amino-6-chloro-9H-purin-9-yl)-1,3-dioxolane-2-methanol; D012433:Ryanodine; D013849:Thimerosal; D002110:Caffeine; D008734:Methoxyhydroxyphenylglycol; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium; C010117:3,4-dihydroxyphenylglycol