Injection of Xenopus oocytes with mRNA from cultured neurons induces new currents and susceptibility to the damaging action of ruthenium red

The Role of Ruthenium Red as a Partial Agonist in Caffeine-Induced Neurotoxicity in Cerebellar Granular Cell Culture of Rats

Caffeine is widely spread and well known as a mild stimulant of the central nervous system. The present study tested the role of caffeine and Ruthenium red on the intact neuronal cells alone and Ruthenium red in caffeine-induced neurotoxicity. One-day-old newborn rats were used to obtain cerebellar cell cultures. Caffeine at a concentration of 1 mM was found to be most toxic. Dead cell scores were 5.9 +/- 0.8 for control, and 56.2 +/- 3.4 for caffeine (p < .001). Ruthenium red alone has also caused the reduction in neuronal cell number 36.1 +/- 4.5 for 10(-5) and 47 +/- 2.7 for 10(-6) M concentrations (p < .001 for both). Interestingly Ruthenium red used in caffeine-induced neurotoxicity has partly diminished the number of dead cells 28.7 +/- 3.2 for 10(-5) and 23.8 +/- 2.27 for 10(-6) M concentrations (p < .001for both). The results suggest that both Ruthenium red and caffeine are neurotoxic alone but, in combination, the neurotoxicity may be reduced through partial agonistic action.

Ruthenium red inhibits TASK-3 potassium channel by interconnecting glutamate 70 of the two subunits

TASK channels are highly pH-sensitive two-pore-domain background potassium channels expressed in the central nervous system and in some peripheral tissues. Their current can be regulated by receptor-mediated activation of phospholipase C and also by pharmacological means. We have reported previously that the cationic dye, ruthenium red (RR), inhibited homodimeric TASK-3 (kcnk9), whereas TASK-1 (kcnk3) homodimer and TASK-1/TASK-3 heterodimer were not affected by this compound. In the present study, we identify the molecular determinant of the RR-mediated TASK-3 inhibition. Mutation of the negatively charged Glu 70 of TASK-3 to Arg (E70R) or Cys (E70C) abolished the inhibitory action of RR. When two TASK-3 coding sequences were concatenated, and the entire homodimer was expressed as a single polypeptide chain, the resulting tandem channel was also sensitive to RR. Mutation of Glu 70 in either the first (E70R) or the second (E465R) linked subunit prevented the action of the inhibitor. Together with the Hill coefficient of 1.0 for TASK-3 inhibition, these data indicate that simultaneous binding of one polycationic RR molecule to Glu 70 of both subunits is required for the inhibitory action. The pivotal role of this residue in the inhibitory mechanism of RR is confirmed by the gained RR sensitivity of the mutant TASK-1 in which Lys 70 was changed to Glu. Our results indicate that RR inhibits TASK-3 by tethering its two subunits and identify amino acid 70 as a possible target for designing selective inhibitors against the different TASK channels.

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

Ruthenium red (RR) is a polycationic dye that induces neuronal death in vivo and in primary cultures. To characterize this neurotoxic action and to determine the mechanisms involved, we have analyzed the ultrastructural alterations induced by RR in rat cortical neuronal cultures and measured its effect on cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and on mitochondrial function. RR produced a dose-dependent, progressive disruption of neurites and plasma membrane of neuronal somata after 8-24 hr of incubation. RR caused also an elevation of both the basal [Ca(2+)](i) and its maximal levels after K(+) depolarization. Mitochondrial oxidative function, assessed by reduction of 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and by changes in dihydrorhodamine-123 fluorescence, was significantly diminished after treatment with RR, both in cultured neurons and in isolated brain mitochondria. La(3+) did not prevent but rather potentiated RR-induced cell death. Glutamate receptor antagonists also failed to prevent RR neurotoxicity. Apoptotic electron microscope images were not observed, and protein synthesis inhibitors did not show any protective effect. It is concluded that RR penetrates neurons and that its neurotoxic damage probably is due to intracellular Ca(2+) dishomeostasis and disruption of mitochondrial oxidative function. These results enhance our understanding of the intracellular mechanisms underlying neuronal death.