Evidence that ruthenium red disturbs the synaptic transmission in the rat hippocampal slices through interacting with sialic acid residues

The use of the Petri net method in the simulation modeling of mitochondrial swelling

Using photon correlation spectroscopy, which allows investigating changes in the hydrodynamic dia­meter of the particles in suspension, it was shown that ultrahigh concentrations of Ca2+ (over 10 mM) induce swelling of isolated mitochondria. An increase in hydrodynamic diameter was caused by an increase of non-specific mitochondrial membrane permeability to Ca ions, matrix Ca2+ overload, activation of ATP- and Ca2+-sensitive K+-channels, as well as activation of cyclosporin-sensitive permeability transition pore. To formalize the experimental data and to assess conformity of experimental results with theoretical predictions we developed a simulation model using the hybrid functional Petri net method.

Detection of glycomic alterations induced by overexpression of p-glycoprotein on the surfaces of L1210 cells using sialic acid binding lectins

P-glycoprotein (P-gp) overexpression is the most frequently observed cause of multidrug resistance in neoplastic cells. In our experiments, P-gp was expressed in L1210 mice leukemia cells (S cells) by selection with vincristine (R cells) or transfection with the gene encoding human P-gp (T cells). Remodeling of cell surface sugars is associated with P-gp expression in L1210 cells as a secondary cellular response. In this study, we monitored the alteration of cell surface saccharides by Sambucus nigra agglutinin (SNA), wheat germ agglutinin (WGA) and Maackia amurensis agglutinin (MAA). Sialic acid is predominantly linked to the surface of S, R and T cells via α-2,6 branched sugars that tightly bind SNA. The presence of sialic acid linked to the cell surface via α-2,3 branched sugars was negligible, and the binding of MAA (recognizing this branch) was much less pronounced than SNA. WGA induced greater cell death than SNA, which was bound to the cell surface and agglutinated all three L1210 cell-variants more effectively than WGA. Thus, the ability of lectins to induce cell death did not correlate with their binding efficiency and agglutination potency. Compared to S cells, P-gp positive R and T cells contain a higher amount of N-acetyl-glucosamine on their cell surface, which is associated with improved WGA binding. Both P-gp positive variants of L1210 cells are strongly resistant to vincristine as P-gp prototypical drug. This resistance could not be altered by liberalization of terminal sialyl residues from the cell surface by sialidase.

Intracranial V. cholerae sialidase protects against excitotoxic neurodegeneration

Converging evidence shows that GD3 ganglioside is a critical effector in a number of apoptotic pathways, and GM1 ganglioside has neuroprotective and noötropic properties. Targeted deletion of GD3 synthase (GD3S) eliminates GD3 and increases GM1 levels. Primary neurons from GD3S−/− mice are resistant to neurotoxicity induced by amyloid-β or hyperhomocysteinemia, and when GD3S is eliminated in the APP/PSEN1 double-transgenic model of Alzheimer's disease the plaque-associated oxidative stress and inflammatory response are absent. To date, no small-molecule inhibitor of GD3S exists. In the present study we used sialidase from Vibrio cholerae (VCS) to produce a brain ganglioside profile that approximates that of GD3S deletion. VCS hydrolyzes GD1a and complex b-series gangliosides to GM1, and the apoptogenic GD3 is degraded. VCS was infused by osmotic minipump into the dorsal third ventricle in mice over a 4-week period. Sensorimotor behaviors, anxiety, and cognition were unaffected in VCS-treated mice. To determine whether VCS was neuroprotective in vivo, we injected kainic acid on the 25th day of infusion to induce status epilepticus. Kainic acid induced a robust lesion of the CA3 hippocampal subfield in aCSF-treated controls. In contrast, all hippocampal regions in VCS-treated mice were largely intact. VCS did not protect against seizures. These results demonstrate that strategic degradation of complex gangliosides and GD3 can be used to achieve neuroprotection without adversely affecting behavior.

Glycinergic mIPSCs in mouse and rat brainstem auditory nuclei: modulation by ruthenium red and the role of calcium stores

Spontaneous miniature inhibitory postsynaptic currents (mIPSCs) recorded in central neurons are usually highly variable in amplitude due to many factors such as intrinsic postsynaptic channel fluctuations at each release site, site-to-site variability between release sites, electrotonic attenuation due to variable dendritic locations of synapses, and the possibility of synchronous multivesicular release. A detailed knowledge of these factors is essential for the interpretation of mIPSC amplitude distributions and mean quantal size. We have studied glycinergic mIPSCs in two auditory brainstem nuclei, the rat anteroventral cochlear nucleus (AVCN) and the mouse medial nucleus of the trapezoid body (MNTB). Our previous results have demonstrated the location of glycinergic synapses on these neurons to be somatic, thus avoiding electrotonic complications. Spontaneous glycinergic mIPSCs were recorded from AVCN and MNTB neurons in brainstem slices, in the presence of TTX to block action potentials, and 6-cyano-7-nitroquinoxaline-2, 3-dione, (+/-)-2-amino-5-phosphonopentanoic acid and bicuculline to block glutamatergic and GABAergic synaptic currents. Ruthenium red (RuR), which was used to increase the frequency of mIPSCs, significantly changed the shape of most (90 %) mIPSC amplitude distributions by increasing the proportion of large-amplitude mIPSCs. The possibility was investigated (following previous evidence at GABAergic synapses) that large-amplitude glycinergic mIPSCs are due to synchronous multivesicular release initiated by presynaptic calcium sparks from ryanodine-sensitive calcium stores. Interval analysis of mIPSCs indicated that the number of potentially undetected (asynchrony < 0.5 ms) multivesicular mIPSCs was low in comparison with the number of large-amplitude mIPSCs. Ryanodine, thapsigargin and calcium-free perfusate did not reduce the frequency of large-amplitude mIPSCs (> 150 pA), arguing against a significant role for presynaptic calcium stores. Our results support previous evidence suggesting that RuR increases miniature postsynaptic current (mSC) frequency by a mechanism that does not involve presynaptic calcium stores. Our results also indicate that at glycinergic synapses in the AVCN and MNTB, site-to-site variability in mIPSC amplitude, rather than multivesicular release, is a major factor underlying the large range of amplitudes of glycinergic mIPSCs.

Effect of mitochondrial electron transport chain inhibitors on superoxide radical generation in rat hippocampal and striatal slices

In this study, we have compared the generation of superoxide radical in rat hippocampal and striatal slices in the presence of specific mitochondrial electron transport chain (ETC) inhibitors (complexes I and III) under control and depolarization conditions [incubation in artificial cerebrospinal fluid (ACSF) or depolarizing ACSF (dACSF), respectively]. Superoxide radical generation was increased in both ACSF- and dACSF-incubated hippocampal and striatal slices when rotenone and antimycin A were added to the incubation medium. The increase in superoxide radical was dependent on the concentration of ETC inhibitors under control, but not depolarization conditions. Rotenone was found to be more effective than antimycin A in producing superoxide radical from hippocampal and striatal slices. Our results also showed that hippocampal slices were more sensitive to ETC inhibitors compared with striatal slices. Thus, different regions of the brain seem to differ in their capacity to generate free radicals and vulnerability to oxidative stress conditions. This difference should be considered in developing therapeutic modalities against oxidative stress-related disorders and neurodegeneration.

Ruthenium red inhibits selectively chromaffin cell calcium channels

The effect of Ruthenium red (RR) on ionic currents and catecholamine secretion was studied in chromaffin cells. This polycation inhibited 59 mM potassium-stimulated 45Ca2+ uptake in a concentration-dependent manner (IC50 = 5 +/- 0.2 microM). This effect was more evident at extracellular calcium concentrations over 1 mM and was not abolished by neuraminidase pretreatment. RR also inhibited potassium-stimulated catecholamine secretion (IC50 = 6 +/- 0.9 microM). These results were corroborated by patch-clamp in whole-cell recordings. RR inhibited chromaffin cell calcium currents (IC50 = 7 microM) without affecting significantly either sodium or potassium currents. Radioligand binding studies in adrenomedullary plasma membranes showed that RR inhibited [125I]omega-conotoxin GVIA binding but it had no effect on specific binding of [3H]nitrendipine. The effect of the RR on calcium currents was additive with the inhibitory effect observed with 10 microM nitrendipine. The residual dihydropyridine-resistant calcium current was inhibited with a potency similar to that determined under control conditions in the absence of nitrendipine. These results demonstrate that RR selectively inhibits calcium channels; however, this polycation was not selective for a particular calcium channel subtype.

Possible mechanism of ruthenium red antagonism of capsaicin-induced action in the isolated guinea pig ileum

Ruthenium red (3-5 microM) antagonism of the inhibitory effect of capsaicin (1 microM) on the contractile response to mesenteric nerve stimulation in the presence of hexamethonium (50 microM) and guanethidine (2 microM) was reversed significantly by sialic acid (2 mM) or neuraminidase (0.1 U/ml). These results suggested that ruthenium red at low concentrations inhibits the capsaicin-induced desensitization of activated Ca2+ influx into sensory nerves at least in part by binding to sialic acid residues.

Ruthenium red antagonism of the effects of capsaicin mediated by extrinsic sensory nerves on myenteric plexus neurons of the isolated guinea-pig ileum

The effects of Ruthenium red and its antagonism of capsaicin-induced action on the electrophysiological behavior of myenteric neurons were investigated with intracellular recording techniques in the isolated guinea-pig ileum. Ruthenium red antagonized dose-dependently (1-10 microM) a capsaicin-induced marked long-lasting slow depolarizing action associated with increased input resistance, during which the cells spiked repeatedly or displayed anodal break excitation. This action of capsaicin has been found to be mediated via a release of substance P from sensory nerve endings. The slow depolarizing response to exogenous substance P applied by pressure microejection, which mimicked the capsaicin-induced action, was not affected by Ruthenium red. Therefore, present results indicate that Ruthenium red antagonizes the specific effect of capsaicin on myenteric neurons by acting on the presynaptically located peripheral nerve terminals of sensory neurons and inhibiting the release of substance P. Electron-microscopic examination showed that the neurotoxic action of capsaicin towards extrinsic sensory nerve fibers was also dose-dependently (1-10 microM) protected by pretreatment of ruthenium red. Present results suggest that Ruthenium red inhibits a capsaicin-induced activation of cation channels at the cell membrane of sensory nerves.

Effects of neuropeptides, ruthenium red and neuraminidase on chemoreflexes mediated by afferents in the dog epicardium

1. Experiments were performed on anaesthetized, open-chest dogs to determine reflex effects on blood pressure and heart rate produced by stimulation of neural afferents of the left ventricular epicardium by local application of capsaicin, bradykinin, nicotine and the neuropeptides substance P (SP), neurokinin A (NKA), neurokinin B (NKB) and calcitonin gene-related peptide (CGRP). 2. Studies also included assessing whether reflexogenic actions of capsaicin, bradykinin and nicotine are influenced by epicardial treatment with either neuropeptides, Ruthenium Red or neuraminidase. 3. Epicardial application of either capsaicin (0.1-10 micrograms) or bradykinin (0.1-1 micrograms), consistently resulted in dose-related increases in blood pressure and heart rate, whereas reflex bradycardia and hypotensive effects were initiated by the application of nicotine (30-50 micrograms). 4. SP, NKA, NKB and CGRP caused marked hypotensive effects and tachycardia when injected intravenously (1 microgram), but failed to produce any cardiovascular response when applied to the epicardium of the left ventricle (0.1-1 microgram). Treatment of the heart surface with these neuropeptides (0.05-0.5 micrograms min-1) was also without any effect on the magnitude of reflex responses evoked by epicardial application of either capsaicin, bradykinin or nicotine. 5. Superfusion of the ventricular epicardium with Ruthenium Red (10-30 microM), a cationic dye known to have sialic acid as a molecular target, antagonized the reflexogenic effects of capsaicin but not those of bradykinin or nicotine. The reflex effects of capsaicin, but not those of bradykinin, were also sensitive to inhibition by epicardial treatment with neuraminidase, an enzyme which cleaves sialic acid residues from glycosides and sialoglycoproteins. 6. We conclude that neuropeptides which may be released from the peripheral endings of some cardiac sensory neurons neither directly activate nor sensitize spinal sympathetic and vagal afferents in the dog heart to the reflexogenic action of bradykinin, nicotine or capsaicin. 7. We further suggest that activation of the cardiac sympathetic chemoreflex by capsaicin involves its interaction with calcium-binding sialic acid moieties present on the surface of axons and/or terminals of chemosensitive sympathetic afferents distributed in the dog ventricular epicardium.

Enhanced aspartate release from hippocampal slices of epileptic (El) mice

The release of putative neurotransmitters [aspartate, glutamate, and gamma-aminobutyric acid (GABA)] was studied in hippocampal slices from adult normal C57BL/6J (B6) and El (epileptic) mice. The El mice, a genetic model of temporal lobe epilepsy, had an average of 86 seizures. Sets of B6 and El hippocampal slices (400 microns thick) were incubated in a series of normal and high potassium (60 mM) buffers in the presence or absence of calcium. The calcium-dependent and calcium-independent potassium-induced release of amino acids was compared in each mouse strain. Release of endogenous amino acids was measured using liquid chromatography with electrochemical detection and was expressed as picomoles of amino acid released per milliliter of incubation buffer per minute of incubation per slice +/- SEM. No significant differences were found between the El and B6 mice for the calcium-dependent potassium-evoked release of glutamate (18.20 +/- 2.62 and 15.41 +/- 3.56), or GABA (17.28 +/- 2.90 and 12.73 +/- 1.37), respectively. Aspartate release, however, was significantly higher in the El mice (6.62 +/- 0.69) than in the B6 mice (3.31 +/- 0.72). These findings suggest that enhanced aspartate release may be related to seizure expression in El mice.

Ruthenium red as a capsaicin antagonist

Definition of the physiological and pharmacological properties of primary afferent neurons by the use of capsaicin and its analogues (e.g. resiniferatoxin) has represented one of the most active areas of research of the last decade (1-4 for reviews). In the past 3 years many important advancements have been made in this field, dealing with: a) discovery of the capsaicin (or 'vanilloid' receptor (5); b) discovery of capsazepine as a competitive receptor antagonist at the vanilloid receptor (6); c) definition of the cation channel coupled with the vanilloid receptor and the ionic basis for excitation and "desensitization" of primary afferents by capsaicin and related substances (7,8) and d) discovery of ruthenium red as a functional capsaicin antagonist. The aim of the present article is to briefly review the pharmacology of ruthenium red as a capsaicin antagonist and attempting to define the usefulness and the limits of this substance as a tool in sensory neuron research.

Calcium regulation of neuronal differentiation: the role of calcium in GM1-mediated neuritogenesis

Cultures of mouse Neuro-2a neuroblastoma cells treated with 3-6 mM extracellular Ca2+ exhibited enhanced neurite extension characterized by increased neurite numbers and lengths. The ganglioside GM1 potentiated the effect of extracellular Ca2+ by increasing further the number and length of the neurites formed in response to exogenous Ca2+. Maximal neuritic numbers were achieved with 4 mM Ca2+ while the longest neurites were observed in medium containing 4-6 mM Ca2+. Stimulation of the Ca2+ influx with the ionophore A23187 or the amino acid taurine also enhanced neurite formation and GM1 potentiated these actions. Transmission electron microscopy revealed numerous microtubules and neurofilaments in neurites and microfilaments with the spine-like processes along fine neuritic branches and in the filopodia of growth cones. Neuritic varicosities and growth cones contained a variety of vesicles. All of these structures were increased in the presence of GM1 and were increased further by extracellular Ca2+ or A23187. The ability of GM1 to enhance neuritogenesis was diminished by EGTA or Ruthenium red. Similarly, the effect of GM1 was diminished or abolished by Ca2+ channel blockers such as CdCl2 or LaCl3. X-ray microprobe analysis revealed that GM1 alone enhanced intracellular levels of total ionic and membrane bound Ca2+, perhaps accounting for the increased neuritogenesis observed under conditions in which Ca2+ was manipulated. The present study suggest that the neuritogenic action of GM1 is Ca2+ dependent.

ATP-induced synaptic potentiation in hippocampal slices

The purpose of this study was to investigate the influence of different adenosine triphosphate (ATP) concentrations (ranging from 400 nM to 250 microM) on hippocampal potentials recorded from pyramidal neurons. ATP applied at a concentration of 400 nM induced a 100% increase in the size of the population spike (potentiation). The potential started to increase 30-60 s after ATP application, reached a maximum after 20 min, and remained potentiated for longer than 1.5 h. Washing the slices with fresh Ringer solution did not reverse the effect. ATP applied at a concentration of 50-150 microM, temporarily depressed the potential. This depression, however, was transient, as the potential gradually recovered by itself and reached a value higher than that observed before ATP application. ATP applied at the concentration of 250 microM caused a long-lasting depression of the potential. The potential was not restored by washing the slices, but recovered after addition of 0.7 microM 3,4-diaminopyridine. These data show a concentration-dependent mode of ATP action on hippocampal neurons and suggest a role for ATP in regulating synaptic efficiency.

Ruthenium red selectively inhibits capsaicin-induced release of calcitonin gene-related peptide from the isolated perfused guinea pig lung

In the present study the influence of Ruthenium red on capsaicin- and bradykinin-evoked neuropeptide release from primary afferent neurons was investigated in the guinea pig. Perfusion of the isolated guinea pig lung in vitro with a capsaicin (1 microM)-containing physiological salt solution increased the amount of calcitonin gene-related peptide-like immunoreactivity (CGRP-IR) in the outflow more than 20-fold. Ruthenium red (RR: 1 microM, 10 microM) dose-dependently reduced capsaicin-induced release of CGRP-IR. Addition of bradykinin (1 microM) to the perfusate induced a 3-fold increase of CGRP-IR in the outflow, which was not significantly reduced by 10 microM RR. These results suggest that RR represents a rather specific antagonist of capsaicin's action on sensory neurons.

Stimulation-dependent release of adenosine triphosphate from hippocampal slices

Schaffer collaterals of rat and mouse hippocampal slices were stimulated with bursts of pulses (300 Hz for 50 ms, 2-s intervals) for 30-s which caused a stable increase in the size of the population spike known as long-term potentiation. The release of adenosine triphosphate (ATP) was measured with a luciferase-luciferine system and the light emitted was recorded with a photomultiplier placed beneath a modified slice chamber. ATP release was observed shortly after the start of stimulation and was quantified by comparison with the response of standard solutions of ATP. No ATP release was observed in a Ca2+ free solution or after low frequency stimulation (1 Hz). Glutamate (2 mM), applied without electrical stimulation, did not evoke ATP release. Also, the glutamate receptor blocker, kynurenic acid (10 mM), did not block ATP release. It is concluded that ATP is released from electrically stimulated hippocampal slices from presynaptic nerve terminals in a calcium-dependent fashion and may play a role in the modulation of synaptic efficiency.

The antagonism induced by ruthenium red of the actions of capsaicin on the peripheral terminals of sensory neurons: further studies

Ruthenium Red, an inorganic dye which blocks transmembrane calcium (Ca) fluxes in neural tissues, reduced the capsaicin-induced release of substance P-like immunoreactivity from muscle strips of the guinea-pig urinary bladder in a concentration-dependent (30 nM - 3 microM) manner, and protected the sensory fibers from capsaicin-induced densensitization. A similar antagonism of the actions of capsaicin was observed in functional experiments (capsaicin-induced contraction of the isolated guinea-pig bladder or inhibition of twitches of the isolated rat vas deferens). In view of its established action on the depolarization-coupled entry of Ca into synaptosomes and the secretion of transmitter, we propose that Ruthenium Red could antagonize the action of capsaicin on the peripheral terminals of sensory nerves by a similar mechanism, thereby suppressing transmitter secretion and preventing the establishment of desensitization.

Altered response of fibroblasts from aged and Alzheimer donors to drugs that elevate cytosolic free calcium

Previous studies demonstrate that resting intracellular calcium in cultured skin fibroblasts declines due to in vivo aging and is further depressed by Alzheimer's disease. These data suggest that altered calcium homeostasis may underlie the deficits in cell function (e.g., cell spreading) that also occur in these cells. Depressed cytosolic free calcium in fibroblasts from aged and Alzheimer donors can be elevated by various drug treatments. 3,4-Diaminopyridine, serum, N-formyl-methionyl-leucyl-phenylalanine and bradykinin increased cytosolic free calcium transiently although the rate of the increase was slower and the magnitude of the rise was less in cells from aged and Alzheimer donors when compared to young donors. Four minutes after N-formyl-methionyl-leucyl-phenylalanine or bradykinin treatment cytosolic free calcium returned to resting levels in all six cell lines. Six minutes after either serum or 3,4-diaminopyridine treatments, however, cytosolic free calcium in cells from aged and Alzheimer donors remained elevated at concentrations similar to the resting calcium level in young cells. Bradykinin and serum were effective in the absence of extracellular calcium but 3,4-diaminopyridine and N-formyl-methionyl-leucyl-phenylalanine were not. These demonstrate that dynamic, as well as resting calcium homeostasis, is altered in cultured skin fibroblasts from aged and Alzheimer donors.

Increased retention of calcium in the dendrites of long-term potentiated CA1 neurons of the hippocampal slice. A combined electrophysiological and electron histochemical study

In view of the importance of calcium in the induction of long-term potentiation (LTP), experiments were carried out to localize calcium at the electron microscopic level in the CA1 region of guinea pig hippocampal slices, following high-frequency stimulation of the Schaffer collaterals. Apart from the ultrastructural localization, a semi-quantitative method was used to count the calcium-containing deposits in electron micrographs. Significantly more calcium-containing deposits were seen in the dendrites of the stratum radiatum in slices with LTP than in those without it. A moderate increase of the extradendritic deposits was observed, too. The calcium content of the deposits was determined by means of EGTA incubation and X-ray analysis. The presented results, together with the relevant literature data, underline the importance of calcium-activated processes in postsynaptic structures probably involved in the generation of LTP.

Calcium and the aging nervous system

Many aspects of calcium homeostasis change with aging. Numerous calcium compartments complicate studies of altered calcium regulation. However, age-related decreases in calcium permeation across membranes and mobilization from organelles may be a common fundamental change. Deficits in ion movements appear to lead to altered coupling of calcium-dependent biochemical and neurophysiological processes and may lead to pathological and behavioral changes. The calcium-associated changes during aging probably do not occur with equal intensity in all cell types or in different parts of the same cell. Thus, cells or compartments with a high proportion of calcium activated processes would be more sensitive to diminished calcium availability. These age-related changes may predispose the brain to the development of age-related neurological disorders. The effects of decreased ion movement may be further aggravated by an age-related decline in other calcium-dependent processes. Depression of some of these calcium-dependent functions appears physiologically significant, since increasing calcium availability ameliorates age-related deficits in neurotransmission and behavior. A better understanding of the interactions between calcium homeostasis and calcium-dependent processes during aging will likely help in the design of more effective therapeutic strategies.