Characterization of Ca2+ signalling in postnatal mouse retinal ganglion cells: involvement of OPA1 in Ca2+ clearance.
OBJECTIVE
The regulation of Ca(2+) entry and removal is a fine-tuned process which remains not well understood in mouse retinal ganglion cells (RGCs). The latter are known to be sensitive to dysfunctions of mitochondria, organelles playing a pivotal role in Ca(2+) reuptake.


METHODS
We first described the Ca(2+) signals of RGCs in response to varied drugs with Fura-2 imaging, and secondly tested the role of optic atrophy 1 or OPA1, the gene responsible for Autosomal Dominant Optic Atrophy, on mitochondrial ability to capture intracellular Ca(2+) in cells transfected with the OPA1 small interfering ribonucleic acids (siRNAs).


RESULTS
In control RGCs, K(+)-evoked [Ca(2+)](i) increase was blocked by the Ca(2+) channel antagonists (Ni(2+)+ Cd(2+)) and GABA(A) receptor agonist muscimol-induced [Ca(2+)](i) responses were attenuated by the GABA(A) receptor antagonists, picrotoxin and gabazine. We also prove the presence of NMDA and AMPA/Kainate (glutamate receptor agonists) responsive receptors in this model. Application of cyclopiazonic acid, an inhibitor of Ca(2+)-ATPase pumps of the intracellular Ca(2+) stores, induced an increase in [Ca(2+)](i) while ryanodine or caffeine had no effect on resting [Ca(2+)](i). Spontaneous Ca(2+) oscillations in contacting neurons highlighted the importance of cross-talks between RGCs during maturation. The mitochondrial respiration uncoupler, carbonyl cyanide 3-chlorophenylhydrazone (CCCP), induced robust raises of intracellular Ca(2+) after K(+) application, with a more pronounced effect in cells silenced for OPA1, which could lead to cell death.


CONCLUSIONS
Our results indicate an important role of OPA1 in mitochondrial dependent Ca(2+) homeostasis and cell survival in RGCs, suggesting a possible patho-physiological mechanism involved in inherited optic neuropathies.
Dayanithi
Govindan
G
Institut des Neurosciences de Montpellier, INSERM U583, Montpellier, France.
Chen-Kuo-Chang
Murielle
M
Viero
Cedric
C
Hamel
Christian
C
Muller
Agnès
A
Lenaers
Guy
G
D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D058787:GABA-A Receptor Antagonists; D020558:GTP Phosphohydrolases / Q000502:physiology*; D006706:Homeostasis; D007211:Indoles / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D018091:Receptors, AMPA / Q000378:metabolism; D011963:Receptors, GABA-A / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000378:metabolism*; D014162:Transfection
D002121:Calcium Channel Blockers; D058787:GABA-A Receptor Antagonists; D007211:Indoles; D034741:RNA, Small Interfering; D018091:Receptors, AMPA; D011963:Receptors, GABA-A; D016194:Receptors, N-Methyl-D-Aspartate; D020558:GTP Phosphohydrolases; C498809:Opa1 protein, mouse; D000252:Calcium-Transporting ATPases; D011188:Potassium; D002118:Calcium; D016257:Fura-2; C000543:cyclopiazonic acid