Characterization of Ca2+ Signalling in Postnatal Mouse Retinal Ganglion Cells: Involvement of OPA1 in Ca2+ Clearance

Purpose: The regulation of Ca2+ 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 Ca2+ reuptake. Methods: We first described the Ca2+ 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 Ca2+ in cells transfected with the OPA1 small interfering ribonucleic acids (siRNAs). Results: In control RGCs, K+-evoked [Ca2+](i) increase was blocked by the Ca2+ channel antagonists (Ni2++ Cd2+) and GABA(A) receptor agonist muscimol-induced [Ca2+](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 Ca2+-ATPase pumps of the intracellular Ca2+ stores, induced an increase in [Ca2+] i while ryanodine or caffeine had no effect on resting [Ca2+](i). Spontaneous Ca2+ 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 Ca2+ 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 Ca2+ homeostasis and cell survival in RGCs, suggesting a possible patho-physiological mechanism involved in inherited optic neuropathies.