title: Mitochondrial calcium ion and membrane potential transients follow the pattern of epileptiform discharges in hippocampal slice cultures.
abstract: Emerging evidence suggests that mitochondrial dysfunction contributes to the pathophysiology of epilepsy. Recurrent mitochondrial Ca2+ ion load during seizures might act on mitochondrial membrane potential (DeltaPsim) and proton motive force. By using electrophysiology and confocal laser-scanning microscopy, we investigated the effects of epileptiform activity, as induced by low-Mg2+ ion perfusion in hippocampal slice cultures, on changes in DeltaPsim and in mitochondrial Ca2+ ion concentration ([Ca2+]m). The mitochondrial compartment was identified by monitoring DeltaPsim in the soma and dendrites of patched CA3 pyramidal cells using the mitochondria-specific voltage-sensitive dye rhodamine-123 (Rh-123). Interictal activity was accompanied by localized mitochondrial depolarization that was restricted to a few mitochondria in small dendrites. In contrast, robust Rh-123 release into the cytosol was observed during seizure-like events (SLEs), indicating simultaneous depolarization of mitochondria. This was critically dependent on Ca2+ ion uptake and extrusion, because inhibition of the mitochondrial Ca2+ ion uniporter by Ru360 and the mitochondrial Na+/Ca2+ ion exchanger by 7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one but not the inhibitor of mitochondrial permeability transition pore, cyclosporin A, decreased the SLE-associated mitochondrial depolarization. The Ca2+ ion dependence of simultaneous mitochondrial depolarization suggested enhanced Ca2+ ion cycling across mitochondrial membranes during epileptiform activity. Indeed, [Ca2+]m fluctuated during interictal activity in single dendrites, and these fluctuations spread over the entire mitochondrial compartment during SLEs, as revealed using mitochondria-specific dyes (rhod-2 and rhod-ff) and spatial frequency-based image analysis. These findings strengthen the hypothesis that epileptic activity results in Ca2+ ion-dependent changes in mitochondrial function that might contribute to the neuronal injury during epilepsy.
authors.affiliation: Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences, 1525 Budapest, Hungary. mozsafa@gmx.net
authors.forename: Richard
authors.initials: R
authors.lastname: Kovács
authors.forename: Julianna
authors.initials: J
authors.lastname: Kardos
authors.forename: Uwe
authors.initials: U
authors.lastname: Heinemann
authors.forename: Oliver
authors.initials: O
authors.lastname: Kann
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002998:Clonazepam / Q000031:analogs & derivatives / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation; D004827:Epilepsy / Q000503:physiopathology*; D005456:Fluorescent Dyes; D006624:Hippocampus / Q000166:cytology; D021621:Imaging, Three-Dimensional / Q000379:methods; D066298:In Vitro Techniques; D007474:Ion Exchange; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D018613:Microscopy, Confocal / Q000379:methods; D008928:Mitochondria / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D013841:Thiazepines / Q000494:pharmacology
chemical_list: D005456:Fluorescent Dyes; D013841:Thiazepines; D002998:Clonazepam; C079032:CGP 37157; D002118:Calcium