Mitochondria support inositol 1,4,5-trisphosphate-mediated Ca2+ waves in cultured oligodendrocytes.
We have examined the spatial and temporal nature of Ca2+ signals activated via the phosphoinositide pathway in oligodendrocytes and the cellular specializations underlying oligodendrocyte Ca2+ response characteristics. Cultured cortical oligodendrocytes were incubated with fluo 3 or fura 2, and digital video fluorescence microscopy was used to study the effect of methacholine on [Ca2+]i. Single peaks, oscillations, and steady-state plateau [Ca2+]i elevations were evoked by increasing agonist concentration. The peaks and oscillations were found to be Ca2+ wave fronts, which propagate via distinct amplification regions in the cell where the kinetics of Ca2+ release (amplitude and rate of rise of response) are elevated. Staining with 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolecarbocyanine++ + iodide (JC-1) and 3,3'-dihexyloxacarbocyanine iodide revealed that mitochondria are found in groups of three or more in oligodendrocyte processes and that the groups are distributed with considerable distance separating them. Cross-correlation analysis showed a high degree of correlation between sites where mitochondria are present and peaks in the amplitude and rate of rise of the Ca2+ response. Intramitochondrial Ca2+ concentration, measured using rhod 2, increased upon treatment with methacholine. Methacholine also evoked a rapid change in mitochondrial membrane potential as measured by the J-aggregate fluorescence of JC-1. Pretreatment with the mitochondrial inhibitors carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (1 microM, 2 min) or antimycin (2 microg/ml, 2 min) altered the methacholine-evoked Ca2+ response in most cells studied, responses being either markedly potentiated or inhibited. The results of this study demonstrate that stimulation of phosphoinositide-coupled muscarinic acetylcholinoceptors activates propagating Ca2+ wave fronts in oligodendrocytes and that the characteristics of these waves are dependent on mitochondrial location and function.
Simpson
P B
PB
Laboratory of Cellular and Molecular Neurophysiology, NICHD, National Institutes of Health, Bethesda, Maryland 20892-4495, USA. james@helix.nih.gov
Russell
J T
JT
D000818:Animals; D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002478:Cells, Cultured; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008564:Membrane Potentials; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D009836:Oligodendroglia / Q000378:metabolism*; D051381:Rats
C032456:antimycin; D002110:Caffeine; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000968:Antimycin A; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium