Alterations of intracellular calcium homeostasis and mitochondrial function are involved in ruthenium red neurotoxicity in primacy cortical cultures

Ruthenium red (RR) is a polycationic dye that induces neuronal death in viv o and in primary cultures. To characterize this neurotoxic action and to de termine the mechanisms involved, we have analyzed the ultrastructural alter ations induced by RR in rat cortical neuronal cultures and measured its eff ect on cytoplasmic Ca2+ concentration ([Ca2+](i)) and on mitochondrial func tion. RR produced a dose-dependent, progressive disruption of neurites and plasma membrane of neuronal somata after 8-24 hr of incubation. RR caused a lso an elevation of both the basal [Ca2+](i) and its maximal levels after K + depolarization. Mitochondrial oxidative function, assessed by reduction o f 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and by chang es in dihydrorhodamine-123 fluorescence, was significantly diminished after treatment with RR, both in cultured neurons and in isolated brain mitochon dria. La3+ did not prevent but rather potentiated RR-induced cell death. Gl utamate receptor antagonists also failed to prevent RR neurotoxicity. Apopt otic electron microscope images were not observed, and protein synthesis in hibitors did not show any protective effect. It is concluded that RR penetr ates neurons and that its neurotoxic damage probably is due to intracellula r Ca2+ dishomeostasis and disruption of mitochondrial oxidative function. T hese results enhance our understanding of the intracellular mechanisms unde rlying neuronal death. (C) 2000 Wiley-Liss, Inc.