Binding of lanthanum ions and ruthenium red to synaptosomes and its effects on neurotransmitter release

Effects of in utero exposure to lanthanum on neurological behavior in rat offspring

The increasing use of rare-earth elements in various fields has raised concern from public heath perspective regarding their accumulation in human body. Long-term exposure to lanthanum, one of the frequently used rare-earth elements in biomedicine and agriculture, has been previously shown to exert neurotoxicity during development in rats; however, the effects of short-term exposure to lanthanum during gestation on neurobehavioral development in rat offspring is still not clear. The purpose of this study is to investigate the effects of intrauterine exposure to lanthanum on neurobehavioral development in rat offspring. Dams were orally exposed to 0, 2, 20, & 60 mg/kg BW of lanthanum nitrate from gestation day 7 to day 16. Morris water maze test, hindlimb strength test, nociceptive perception test, and grip strength test were conducted during postnatal day 61 to 66 in rat offspring. Blood lanthanum concentration and plasma neurotransmitters were measured after sacrifice. The results showed that intrauterine exposure to lanthanum nitrate significantly impaired memory and spatial learning in Morris water maze test. Lanthanum treatment dose-dependently increased blood lanthanum concentration in dams and pups. Lanthanum treatment significantly decreased hindlimb and grip strength and increased delay time in nociceptive response. Plasma neurotransmitter results showed that lanthanum treatment significantly decreased the level of acetylcholine and serotonin while increased the level of glutamate in rat offspring. These results suggest that short-term in utero exposure to lanthanum has potential adverse effects on neurodevelopment in rat offspring.

Clinical pharmacokinetics of the phosphate binder lanthanum carbonate

Lanthanum carbonate is considered to be the most potent of a new generation of noncalcium phosphate binders used to treat hyperphosphataemia in chronic kidney disease (CKD), a condition associated with progressive bone and cardiovascular pathology and a markedly elevated risk of death. Its phosphate-binding action involves ionic binding and precipitation of insoluble complexes within the lumen of the intestine, thereby preventing absorption of dietary phosphate. While pharmacokinetics have little relevance to the efficacy of lanthanum carbonate, they are of fundamental importance when it comes to evaluating safety. When administered as lanthanum carbonate, the oral bioavailability of lanthanum is low (approximately 0.001%). The small absorbed fraction is excreted predominantly in bile, with less than 2% being eliminated by the kidneys. Predictably, therefore, plasma exposure and pharmacokinetics have been shown to be similar in healthy human volunteers and CKD stage 5 patients. With almost complete plasma protein binding, free lanthanum concentrations in patients at steady state are <3 pg/mL. These properties greatly reduce systemic exposure, tissue deposition and the potential for adverse effects. While lanthanum has a variety of calcium-like actions in vitro, there is little or no evidence that these occur in vivo. This paradox is explained by the very low concentrations of circulating free lanthanum ions, which are many orders of magnitude lower than reported effect concentrations in vitro. Safety pharmacology and toxicology evaluations have failed to reveal any significant calcium-like actions in vivo, despite inclusion of high intravenous doses in some cases.Lanthanum carbonate has a low propensity to cause systemic drug interactions due to its poor absorption. However, the higher concentrations present in the gastrointestinal tract can form chelates with some drugs, such as fluoroquinolones, and reduce their absorption. The improved understanding of the pharmacokinetics of lanthanum that has emerged in recent years has helped to explain why the myriad of calcium-like effects described in vitro for lanthanum have little if any relevance in vivo. The pharmacokinetic investigations of lanthanum carbonate formed an important part of the stringent premarketing safety assessment process and have been influential in reassuring both regulators and physicians that the agent can be used safely and effectively in this vulnerable dialysis population.

Mitochondrial Ca2+ uniporter blockers influence activation-induced CBF response in the rat somatosensory cortex

Effects of mitochondrial calcium signaling blockade on neural activation-induced CBF response were studied in urethane-anesthetized rats. Ruthenium red (RuR), a nonspecific inhibitor of the mitochondrial calcium uniporter (MCU), and Ru360, a highly specific inhibitor of the MCU, were delivered intravenously (i.v.) or intracerebroventricularly (i.c.v.). Baseline cerebral blood flow (CBF) and cerebral hyperemic response to whisker stimulation were measured through a thinned skull over the somatosensory cortex using laser Doppler imaging (LDI). Ruthenium red or Ru360 did not alter the baseline CBF at all doses used. However, the hyperemic response, defined as the activation area and amplitude of CBF increase in response to mechanical whisker stimulation, was significantly reduced in the presence of either RuR or Ru360 delivered i.c.v. The hyperemic response reduced significantly with a dose of 14.5 nmol RuR (i.c.v.), showing a further decrease with 29 nmol RuR (i.c.v.). A comparable decrease in the hyperemic response was observed during treatment with a relatively lower dose of 4.5 and 9 nmol Ru360 (i.c.v.). Delivered intravenously, Ru360 significantly diminished the cerebral hyperemic response at doses greater than 80 microg/kg i.v., up to a dose of 320 microg/kg i.v. However, RuR (i.v.) had an opposite effect with an enhancement in the cerebral hyperemic response at all doses studied. Ruthenium red or Ru360 had no significant effect on the cerebral reactivity to hypercapnia, indicating that altered cerebral hyperemic response to whisker stimulation was predominantly neural. We conclude that mitochondrial calcium signaling through the MCU mediates neural activation-induced CBF response in vivo.

Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle

The sarco/endoplasmic reticulum (SR/ER) is the primary storage and release site of intracellular calcium (Ca2+) in many excitable cells. The SR is a tubular network, which in smooth muscle (SM) cells distributes close to cellular periphery (superficial SR) and in deeper aspects of the cell (deep SR). Recent attention has focused on the regulation of cell function by the superficial SR, which can act as a buffer and also as a regulator of membrane channels and transporters. Ca2+ is released from the SR via two types of ionic channels [ryanodine- and inositol 1,4,5-trisphosphate-gated], whereas accumulation from thecytoplasm occurs exclusively by an energy-dependent sarco-endoplasmic reticulum Ca2+-ATPase pump (SERCA). Within the SR, Ca2+ is bound to various storage proteins. Emerging evidence also suggests that the perinuclear portion of the SR may play an important role in nuclear transcription. In this review, we detail the pharmacology of agents that alter the functions of Ca2+ release channels and of SERCA. We describe their use and selectivity and indicate the concentrations used in investigating various SM preparations. Important aspects of cell regulation and excitation-contractile activity coupling in SM have been uncovered through the use of such activators and inhibitors of processes that determine SR function. Likewise, they were instrumental in the recent finding of an interaction of the SR with other cellular organelles such as mitochondria. Thus, an appreciation of the pharmacology and selectivity of agents that interfere with SR function in SM has greatly assisted in unveiling the multifaceted nature of the SR.

Enlargement and contracture of C2-ceramide channels

Ceramides are known to play a major regulatory role in apoptosis by inducing cytochrome c release from mitochondria. We have previously reported that ceramide, but not dihydroceramide, forms large and stable channels in phospholipid membranes and outer membranes of isolated mitochondria. C(2)-ceramide channel formation is characterized by conductance increments ranging from <1 to >200 nS. These conductance increments often represent the enlargement and contracture of channels rather than the opening and closure of independent channels. Enlargement is supported by the observation that many small conductance increments can lead to a large decrement. Also the initial conductances favor cations, but this selectivity drops dramatically with increasing total conductance. La(+3) causes rapid ceramide channel disassembly in a manner indicative of large conducting structures. These channels have a propensity to contract by a defined size (often multiples of 4 nS) indicating the formation of cylindrical channels with preferred diameters rather than a continuum of sizes. The results are consistent with ceramides forming barrel-stave channels whose size can change by loss or insertion of multiple ceramide columns.

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.

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.

Motor alterations and neuronal damage induced by intracerebral administration of Ruthenium red: effect of NMDA receptor antagonists and other anticonvulsant drugs

The effects of the intracerebroventricular (icv) and the intrahippocampal (ih) microinjection of the inorganic dye Ruthenium red (RuR) on motor activity, and the protective action of excitatory amino acid receptor antagonists and of GABAergic drugs, were studied in the rat. When administered icv, RuR produced intense tonic-clonic convulsions which were refractory to N-methyl-D-aspartate (NMDA) receptor antagonists and to diphenylhydantoin, whereas aminooxyacetic acid (AOA) and valproate only partially protected against seizure activity. The most notable motor effect of the ih RuR administration was the appearance of intense wet-dog shakes (WDS) behavior, which was remarkably attenuated by the icv or intraperitoneal (ip) administration of the NMDA receptor antagonists (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), CGP-37849, and MK-801, but not by their ih coinjection with RuR. Systemic AOA and valproate were also effective in reducing the number of WDS, whereas the non-NMDA receptor antagonist CNQX was ineffective. Light and electron microscopic observations of the RuR-injected brains revealed that the dye was highly concentrated in neuronal somas located in or near the injected areas. In the case of the CA1 region, remarkable damage of the pyramidal neurons was manifested by vacuolization, and 5-9 d after the injection notable cell loss and disruption of the CA1 cell layer organization was apparent. The results indicate that RuR penetrates selectively neuronal bodies and damage them, and suggest that the resulting motor alterations involve hyperactivity of glutamatergic neurotransmission.

Selective neurotoxicity of ruthenium red in primary cultures

The inorganic dye ruthenium red (RuR) has been shown to be neurotoxic in vivo when injected intracerebrally. In this work the toxicity of RuR was compared in primary cultures of rat cortical neurons, cerebellar granule neurons and cerebellar astroglia. Microscopic examination of the cultures revealed that RuR penetrates the somata of both types of neurons used and produces vacuolization and loss and fragmentation of neurites. In contrast, no RuR was seen inside cultured astrocytes and no morphological signs of damage were observed in these cells. RuR toxicity was also assessed by immunocytochemistry of alpha-tubulin and by biochemical measurement of the reduction of (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) by the cultured cells. The morphological alterations in the neurons were closely correlated with loss of tubulin immunoreactivity and particularly with a notable decrement in the ability to reduce MTT. Using the latter parameter, it was found that neuronal damage was independent of the age of the cultures, augmented progressively with time of incubation with RuR, from 8 to 24 h, and showed a clear dose-response curve from 20 to 100 microM RuR. Astrocytes showed only a slight decrease in MTT reduction after 24 h of incubation with 100 microM RuR. It is concluded that RuR seems to be toxic for neurons but not for astroglia, and that this selectivity is probably related to the ability of the neurons to internalize the dye. The possible mechanisms of RuR penetration and neuronal damage are discussed.

Involvement of calcium channels in depolarization-evoked release of adenosine from spinal cord synaptosomes

The potential involvement of L- and N-type voltage-sensitive calcium (Ca2+) channels and a voltage-independent receptor-operated Ca2+ channel in the release of adenosine from dorsal spinal cord synaptosomes induced by depolarization with K+ and capsaicin was examined. Bay K 8644 (10 nM) augmented release of adenosine in the presence of a partial depolarization with K+ (addition of 6 mM) but not capsaicin (1 and 10 microM). This augmentation was dose dependent from 1 to 10 nM and was followed by inhibition of release from 30 to 100 nM. Nifedipine and nitrendipine inhibited the augmenting effect of Bay K 8644 in a dose-dependent manner, but neither antagonist had any effect on release of adenosine produced by K+ (24 mM) or capsaicin (1 and 10 microM). omega-Conotoxin inhibited K(+)-evoked release of adenosine in a dose-dependent manner but had no effect on capsaicin-evoked release. Ruthenium red blocked capsaicin-induced release of adenosine but had no effect on K(+)-evoked release. Although L-type voltage-sensitive Ca2+ channels can modulate release of adenosine when synaptosomes are partially depolarized with K+, N-type voltage-sensitive Ca2+ channels are primarily involved in K(+)-evoked release of adenosine. Capsaicin-evoked release of adenosine does not involve either L- or N-type Ca2+ channels, but is dependent on a mechanism that is sensitive to ruthenium red.

Lack of effect of sumatriptan and UK-14,304 on capsaicin-induced relaxation of guinea-pig isolated basilar artery

1. The objectives of this study were to assess the effects of sensory neuropeptide antagonists and presynaptically acting receptor agonists on capsaicin-induced relaxations of guinea-pig isolated basilar artery (GPBA). 2. Capsaicin, human alpha-calcitonin gene-related peptide (CGRP) and substance P (SP) caused concentration-related relaxations of GPBA which had been pre-contracted with prostaglandin F2 alpha (PGF2 alpha). Responses to capsaicin were not modified by the peptidase inhibitors, phosphoramidon (1 microM) and bestatin (100 microM). 3. The relaxant responses to capsaicin were blocked in a selective manner by ruthenium red (3 microM) and by the CGRP antagonist, CGRP8-37 (1 microM). CGRP8-37 also selectively inhibited the relaxant effects of CGRP. 4. The selective NK1 receptor antagonist, GR82334 (10 microM), inhibited SP-induced relaxations but had little effect on capsaicin-induced relaxations. 5. The 5-HT1 receptor agonist, sumatriptan, produced small contractions of GPBA under conditions of resting tone. In the presence of PGF2 alpha, sumatriptan had no further contractile effect. Sumatriptan (0.3 and 3 microM) did not modify capsaicin-induced relaxations of GPBA. 6. The alpha 2-adrenoceptor agonist, UK-14,304 (0.1 microM), had no effect on basal or PGF2 alpha-induced tone. UK-14,304 did not modify capsaicin-induced relaxations. 7. These results suggest that capsaicin causes relaxation of GPBA via a release of CGRP. This process is amenable to blockade by CGRP8-37 and ruthenium red, but not to modulation by either sumatriptan or UK-14,304.

Capsazepine: a competitive antagonist of the sensory neurone excitant capsaicin

1. Capsazepine is a synthetic analogue of the sensory neurone excitotoxin, capsaicin. The present study shows the capsazepine acts as a competitive antagonist of capsaicin. 2. Capsazepine (10 microM) reversibly reduced or abolished the current response to capsaicin (500 nM) of voltage-clamped dorsal root ganglion (DRG) neurones from rats. In contrast, the responses to 50 microM gamma-aminobutyric acid (GABA) and 5 microM adenosine 5'-triphosphate (ATP) were unaffected. 3. The effects of capsazepine were examined quantitatively with radioactive ion flux experiments. Capsazepine inhibited the capsaicin (500 nM)-induced 45Ca2+ uptake in cultures of rat DRG neurones with an IC50 of 420 +/- 46 nM (mean +/- s.e.mean, n = 6). The 45Ca2+ uptake evoked by resiniferatoxin (RTX), a potent capsaicin-like agonist was also inhibited. (Log concentration)-effect curves for RTX (0.3 nM-1 microM) were shifted in a competitive manner by capsazepine. The Schild plot of the data had a slope of 1.08 +/- 0.15 (s.e.) and gave an apparent Kd estimate for capsazepine of 220 nM (95% confidence limits, 57-400 nM). 4. Capsazepine also inhibited the capsaicin- and RTX-evoked efflux of 86Rb+ from cultured DRG neurones. The inhibition appeared to be competitive and Schild plots yielded apparent Kd estimates of 148 nM (95% confidence limits, 30-332 nM) with capsaicin as the agonist and 107 nM (95% confidence limits, 49-162 nM) with RTX as agonist. 5. A similar competitive inhibition by capsazepine was seen for capsaicin-induced [14C]-guanidinium efflux from segments of adult rat vagus nerves (apparent Kd = 690 nM; 95% confidence limits, 63 nM-1.45 microM). No significant difference was noted in the apparent Kd estimates for capsazepine in assays on cultured DRG neurones and vagus nerve as shown by the overlap in the 95% confidence limits.6. Capsazepine, at concentrations up to 1O microM, had no significant effects on the efflux of 86Rb+ from cultured DRG neurones evoked either by depolarization with high (50 mM) K' solutions or by acidification of the external medium to pH 5.0-5.6. Similarly capsazepine had no significant effect on he depolarization (50 mM KCl)-induced efflux of [14C]-guanidinium from vagus nerve preparations.7. Ruthenium Red was also tested for antagonism against capsaicin evoked ['4C]-guanidinium release from vague nerves and capsaicin induced 45Ca2" uptake in cultures of DRG neurones. In contrast to capsazepine the inhibition by Ruthenium Red (10-500nM in DRG and 0.5-10microM in vagus nerve experiments) was not consistent with a competitive antagonism, but rather suggested a more complex,non-competitive inhibition.

Ruthenium red and capsaicin induce a neurogenic inflammatory response in the rabbit eye: effects of omega-conotoxin GVIA and tetrodotoxin

The effects of ruthenium red, an inorganic dye with known capsaicin antagonist properties, was investigated in the rabbit eye. At a dose of 0.24 nmol ruthenium red inhibited the inflammatory effects of capsaicin (1 or 8 nmol). Unexpectedly, when the dye was injected in doses ranging from 0.24 to 7.4 nmol, it caused an inflammatory response with constriction of the pupil (miosis) and a breakdown of the blood-aqueous barrier, leading to a rise intraocular pressure. Tetrodotoxin (30 nmol) inhibited the ruthenium red-induced rise in intraocular pressure but had less effect on the miotic response. The tachykinin antagonist spantide inhibited the miosis but had no effect on the rise in intraocular pressure. Ruthenium red induced an increase in substance P-like immunoreactivity and calcitonin gene-related peptide-like immunoreactivity in the aqueous humor. These levels were positively correlated with the rise in aqueous humor protein concentration. The ruthenium red-induced miosis and, to a less extent, the rise in intraocular pressure were inhibited by the Ca2+ channel-blocking agent omega-conotoxin GVIA (CTX), indicating a partial dependence on an influx of extracellular Ca2+. CTX also attenuated the miotic effect of capsaicin but had no effect on the capsaicin-induced rise in intraocular pressure. It is concluded that, in the rabbit eye, ruthenium red induces a neurogenic inflammatory response besides its capsaicin antagonist effects.

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.

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.

Ruthenium red selectively inhibits oedema formation and increased blood flow induced by capsaicin in rabbit skin

It has been suggested that ruthenium red has a selective inhibitory effect on capsaicin-induced nociceptor stimulation. We have investigated the effect of ruthenium red on oedema formation and vasodilatation induced by intradermal (i.d.) injection of capsaicin in the rabbit in vivo. Responses induced by capsaicin were inhibited by ruthenium red, but responses induced by bradykinin, N-formyl-methionyl-leucyl-phenylalanine (FMLP), platelet activating factor (PAF), histamine and calcitonin gene-related peptide (CGRP) were not affected. These results suggest that ruthenium red selectively inhibits capsaicin-induced local plasma protein leakage and vasodilatation in the rabbit skin microvasculature.

Circling behavior induced by intranigral administration of ruthenium red and 4-aminopyridine in the rat

We have studied the effects of the unilateral intranigral microinjection of Ruthenium Red and 4-aminopyridine in the rat, as compared with that of muscimol. The three drugs produced contralateral turning when injected into the central nigra reticulata. Muscimol was the most effective but its effect disappeared in 3-4 h, whereas that of Ruthenium Red lasted for up to 3 days. When injected into the caudoventromedial nigra, Ruthenium Red produced intense ipsiversive turning, 4-aminopyridine weak ipsiversive turning and muscimol intense contraversive turning. Pretreatment with haloperidol (i.p.) abolished the effect of Ruthenium Red after injection into the caudoventromedial nigra but only partially reduced it after administration into the central nigra. The effect of muscimol, when injected into either of the nigral regions studied, was only slightly diminished by haloperidol. The release of [3H]GABA in slices of the Ruthenium Red-injected substantia nigra was not altered. Histological examination showed that the microinjected Ruthenium Red was located mainly inside the soma of nigral neurons. It is concluded that alterations of transmitter release are probably responsible for the circling behavior induced by 4-aminopyridine, but the effects of Ruthenium Red seem to be secondary to its penetration into the neuronal somas. Dopaminergic neurons seem to play an important role in the ipsilateral turning induced by Ruthenium Red when injected into the caudoventromedial nigra.

Ruthenium red antagonism of the effect of capsaicin on the motility of the isolated guinea-pig ileum

Ruthenium red (1 microM), an inorganic dye which blocks transmembrane calcium (Ca) fluxes in neural tissues, selectively reduced the capsaicin (1 microM)-induced contraction of the guinea-pig ileum and protected the sensory fibers from capsaicin-induced desensitization. The ruthenium red (0.5-1 microM) antagonism of capsaicin-induced inhibition of responses to mesenteric nerve stimulation or field stimulation in the isolated guinea-pig ileum was an example of a similar antagonism of the effect of capsaicin. In view of the known action of ruthenium red on the depolarization-coupled entry of Ca into synaptosomes and the release of transmitter, our results support the proposal that ruthenium red could antagonize the action of capsaicin on the peripheral terminals of sensory nerves by a similar mechanism, thereby suppressing transmitter release and preventing the establishment of desensitization.

Ruthenium red prevents capsaicin-induced neurotoxic action on sensory fibers of the guinea pig ileum

Capsaicin, a neurotoxin which impairs some primary afferent nerve fibers, was locally applied to the mesenteric nerve trunks of adult guinea pigs. The effect of capsaicin was studied on contractile responses of the ileum to mesenteric nerve stimulation (20 Hz). Exposure of the mesenteric nerve to capsaicin (1 microM) irreversibly abolished the contractile response to mesenteric nerve stimulation, without influencing the resting tension and spontaneous motility of the ileum. However, if the mesenteric nerve had been incubated in a Ca-free medium containing EGTA (0.1 mM) or pretreated with Ruthenium red (10 microM), capsaicin only partially inhibited (about 30%), but did not abolish, the contractile response to the mesenteric nerve stimulation, thus indicating protection from desensitization.

The 'efferent' function of capsaicin-sensitive nerves: ruthenium red discriminates between different mechanisms of activation

We have investigated the ability of Ruthenium Red, an inorganic dye with calcium entry blocking properties, to interfere with the 'efferent' function of capsaicin-sensitive sensory nerves. These nerves were activated in the guinea-pig isolated bronchus (atropine in the bath) or left atria (reserpine-pretreated animals, atropine in the bath) by electrical field stimulation or with capsaicin. Both stimuli produced a contraction of the bronchus and a positive inotropic response in the atria, responses which are mediated by endogenous neuropeptides (tachykinins in the bronchus, calcitonin gene-related peptide in the atria) released from sensory nerves. Ruthenium Red (10 microM for 20 min in both cases) selectively inhibited the responses produced by the administration of capsaicin, while leaving the responses to electrical field stimulation unaffected. Likewise, the bronchoconstrictor response to exogenous neurokinin A and the atrial positive inotropic response to calcitonin gene-related peptide were unaffected by Ruthenium Red. A prejunctional site of action of Ruthenium Red was confirmed in release experiments where the dye strongly inhibited the capsaicin-evoked outflow of calcitonin gene-related peptide, which is taken as a marker of activation in sensory nerves. Together with other observations, these findings support the concept that there are two independent mechanisms for activating the 'efferent' function of sensory nerves, one of which is activated by capsaicin and is Ruthenium Red-sensitive but omega-conotoxin-resistant, while the other is activated by propagated action potentials (field stimulation) and is omega-conotoxin-sensitive and Ruthenium Red-resistant.

Effect of ruthenium red on responses mediated by activation of capsaicin-sensitive nerves of the rat urinary bladder

(1) Topical administration of Ruthenium Red (10-100 microM in saline) to the serosal surface of the urinary bladder in urethane-anesthetized rats prevented the motor response of the urinary bladder to topical administration of capsaicin and protected the sensory fibers from capsaicin desensitization, but had no effect on the volume-evoked contractions (micturition reflex). At 1 mM increased bladder capacity and decreased amplitude of micturition contraction were observed. (2) At 100 microM, topical Ruthenium Red prevented the blood pressure rise produced by topical administration of capsaicin onto the bladder but did not affect the blood pressure rise produced by sudden bladder distension in spinal rats. (3) After intrathecal administration, Ruthenium Red (80-800 ng/rat) produced a long lasting inhibition of the micturition reflex in urethane-anesthetized rats, this effect being evident in both vehicle- or capsaicin- (50 mg/kg s.c. 4 days before) pretreated rats. At 800 ng/rat, intrathecal Ruthenium Red did not affect the blood pressure rise produced by topical administration of capsaicin onto the rat bladder nor that produced by bladder distension. (4) These findings provide further evidence that Ruthenium Red acts quite selectively as a "capsaicin antagonist" preventing both reflex and "efferent" responses activated by peripherally administered capsaicin. By contrast, sensory impulse generation by a natural stimulus such as bladder distension is apparently unaffected by Ruthenium Red. The marked inhibition of the micturition reflex observed after intrathecal administration of Ruthenium Red does probably not involve an interaction with primary afferents in the spinal cord.

The effects of ruthenium red on the response of guinea-pig ileum to capsaicin

Ruthenium red has recently been found to inhibit the effects of capsaicin on peripheral terminals of sensory neurones. Thus the effects of ruthenium red on the responses of the guinea-pig isolated ileum to capsaicin, acetylcholine (ACh), substance P (SP) and nicotine were investigated. Ruthenium red, 5 mumol/l, abolished responses to capsaicin 1.5 mumol/l and nicotine 2 mumol/l, and shifted the concentration-response lines to ACh and SP to the right. Pretreatment of ileum preparations with ruthenium red, 12.5 mumol/l for 2 min, prevented desensitization of ileum responses to capsaicin tested 30 min later. Tetrodotoxin, 1 mumol/l, abolished the response to capsaicin on control preparations and those pretreated with atropine, 5 mumol/l, ruthenium red, 12.5 mumol/l or spantide, 10 mumol/l. It is proposed that capsaicin acts via a specific receptor coupled to a receptor-operated membrane calcium channel, and that ruthenium red binds irreversibly to the calcium channel part of the complex but reversibly to some other site which prevents the action or binding of capsaicin at its specific receptor.

Chelation of endogenous membrane calcium inhibits gamma-aminobutyric acid uptake in synaptosomes

In a previous work, we have demonstrated that calcium chelators induce the release of gamma-aminobutyric acid (GABA) from synaptosomes in a Na+ -dependent manner and that this release is blocked by cations such as Mg2+, La3+, and ruthenium red. In the present study, we show that treatment of synaptosomes with 0.1 mM EGTA in the absence of both Ca2+ and Mg2+ inhibits the sodium-dependent high-affinity uptake of [3H]GABA by about 50%. This inhibition increased to about 65% with 1.5 mM EGTA, and it was completely prevented by an excess of Ca2+ or by 1.2 mM Mg2+. In contrast, when EDTA was used as a chelator, Mg2+ was unable to reverse the inhibition. The inhibitory effect of 0.1 mM EGTA was also prevented by 250 microM La3+ or by 20 microM ruthenium red. In the absence of chelators and the presence of Ca2+ and Mg2+, 50 microM and 200 microM La3+ inhibited GABA uptake by about 20 and 50%, respectively, whereas 20 microM ruthenium red produced a nonsignificant 25% inhibition and nifedipine was without effect. It is concluded that the membrane-surface negative charges, probably those of the sialic acid molecules that have been implicated in the functioning of the GABA carrier, must be neutralized by endogenous Ca2+ or by another cation in order to permit the adequate function of the transporter. The inhibition by La3+ in the absence of the chelators could be explained by a binding of this cation to the Na+ sites on the GABA carrier.

Interactions between alpha-latrotoxin and trivalent cations in rat striatal synaptosomal preparations

The interactions between alpha-latrotoxin (alpha-LTx), a neurosecretagogue purified from the venom of the black widow spider, and the trivalent cations Al3+, Y3+, La3+, Gd3+, and Yb3+ were investigated in rat striatal synaptosomal preparations. All trivalent cations tested were inhibitors of alpha-LTx-induced [3H]dopamine [( 3H]DA) release (order of potency: Yb3+ greater than Gd3+ approximately Y3+ greater than La3+ greater than Al3+). Only with Al3+ could inhibition of [3H]DA release be attributed to a block of 125I-alpha-LTx specific binding to synaptosomal preparations. The inhibitory effect of trivalent ions was reversible provided synaptosomes were washed with buffer containing EDTA. Trivalent ions also inhibited alpha-LTx-induced [3H]DA release at times when alpha-LTx-stimulated release was already evident. alpha-LTx-induced synaptosomal membrane depolarization was blocked by La3+, but not affected by Gd3+, Y3+, and Yb3+. alpha-LTx-stimulated uptake of 45Ca2+ was inhibited by all trivalent cations tested. These results demonstrate that there exist at least three means by which trivalent cations can inhibit alpha-LTx action in rat striatal synaptosomal preparations: (1) inhibition of alpha-LTx binding (Al3+); (2) inhibition of alpha-LTx-induced depolarization (La3+); and (3) inhibition of alpha-LTx-induced 45Ca2+ uptake (Gd3+, Y3+, Yb3+, La3+).

Relationship of dihydropyridine binding sites with calcium-dependent neurotransmitter release in synaptosomes

In the present work, we have studied the effect of ruthenium red (RuR), La3+ and 4-aminopyridine (4-AP) on the specific binding of (+)-[3H]PN200-110 to synaptosomes, as well as the effect of nitrendipine, nifedipine, and BAY K 8644 on gamma-[3H]aminobutyric acid [( 3H]GABA) release induced by potassium depolarization and by 4-AP in synaptosomes. Scatchard plots indicated that neither RuR nor 4-AP modifies the KD and Bmax of [3H]PN200-110 specific binding, whereas La3+ decreased the Bmax by about 25%; when the effect of the drugs on the total binding of PN200-110 was studied, a similar inhibition by La3+ was found. The calcium antagonists, nitrendipine and nifedipine, did not affect at all the potassium-stimulated release of [3H]GABA nor its release induced by 4-AP. The calcium agonist BAY K 8644 failed to affect both the spontaneous and the potassium-stimulated GABA release. Our results suggest that the binding sites of dihydropyridines in presynaptic membranes are not related to the calcium channels involved in neurotransmitter release with which RuR, La3+, and 4-AP interact.

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.

Protective action of ruthenium red toward capsaicin desensitization of sensory fibers

In the rat isolated urinary bladder, exposure to capsaicin (1 microM) produced a contraction thought to involve neuropeptide(s) release from sensory nerves. A second application of the drug had no motor effect indicating desensitization. The establishment of the desensitized state requires the presence of extracellular calcium. In the presence of Ruthenium red 9RR, 30 nM-10 microM) the first response to capsaicin was reduced and a concentration-dependent protection from capsaicin desensitization was observed. RR up to 10 microM had no inhibitory effect toward contractions produced by exogenous substance P nor by electrical stimulation of efferent nerves.

Inhibitory effect of ionized free intracellular calcium enhanced by ruthenium red and m-chloro-carbonylcyanide phenyl hydrazon on the evoked release of acetylcholine

In order to understand the relationship between the free ionized calcium concentration in the axon terminals and the transmitter release we have investigated the effect of ruthenium red (RuR) and m-chloro-carbonylcyanide phenyl hydrazon (CCCP), mitochondrial uncoupler agents on the liberation of acetylcholine from myenteric plexus of guinea-pig ileum. Both compounds are able to enhance intracellular free Ca2+. In the presence of RuR and CCCP the spontaneous release of radioactivity from isolated myenteric-plexus preparation, previously loaded with (methyl-3H)-choline chloride was significantly enhanced while that evoked by electrical stimulation was decreased. Atropine did not affect the electrically evoked release in the presence of CCCP, indicating that in the effect of CCCP the presynaptic muscarinic receptors mediated negative feedback modulation does not play any role. Our findings are consistent with the hypothesis that the enhanced level of intracellular free Ca2+ enhances the spontaneous while depresses the electrically evoked release of transmitter.

Effect of lanthanum on the release of acetylcholine from the myenteric plexus and on its activation by ouabain and electrical stimulation

The effect of lanthanum ions (La3+) on the release of acetylcholine (ACh) from longitudinal muscle strips of the guinea pig ileum with the myenteric plexus attached was investigated. After an exposure of the tissue to 2 mM LaCl3 for 18 min the rate of ACh release was increased approximately eightfold and the increased release lasted for more than 100 min. The augmented release of ACh was accompanied by enhanced synthesis. At the end of the experiments (102 min after LaCl3 had been removed), when the release of ACh was still more than six times higher than in controls, the content of ACh was the same in La3+-treated and untreated tissues. Electrical field stimulation failed to cause a further increase in the release of ACh from La3+-pretreated preparations whereas ouabain released considerable more ACh when compared to controls. It is concluded from this difference that electrical stimulation and ouabain release ACh from different pools.

Calcium dependence of baclofen- and GABA-induced depression of responses to transmural stimulation in the guinea-pig isolated ileum

Both baclofen and gamma-aminobutyric acid (GABA) induced a dose-dependent depression of cholinergic twitch contractions in the transmurally stimulated guinea-pig isolated ileum. Over a range of 0.6-2.4 mM Ca2+, the degree of depression was inversely related to the Ca2+ concentration, with an increased sensitivity and sinistral shift of the dose-response curve at lower Ca2+ concentrations. Partial occupation of Ca2+ channels by Ruthenium Red (0.1 microM) also potentiated the depressive responses to baclofen and GABA. It is concluded that these agonists, acting through GABAB receptors, limit the availability of Ca2+ required for neurotransmitter release in myenteric motor nerves.

Differential calcium dependence of gamma-aminobutyric acid and acetylcholine release in mouse brain synaptosomes

The dependence of gamma-aminobutyric acid (GABA) and acetylcholine (ACh) release on Ca2+ was comparatively studied in synaptosomes from mouse brain, by correlating the influx of 45Ca2+ with the release of the transmitters. It was observed that exposure of synaptosomes to a Na+-free medium notably increases Ca2+ entry, and this condition was used, in addition to K+ depolarization and the Ca2+ ionophore A23187, to stimulate the influx of Ca2+ and the release of labeled GABA and ACh. The effect of ruthenium red (RuR) on these parameters was also investigated. Of the three experimental conditions used, the absence of Na+ in the medium proved to be the most efficient in increasing Ca2+ entry. RuR inhibited by 60-70% the influx of Ca2+ stimulated by K+ depolarization but did not affect its basal influx or its influx stimulated by the absence of Na+ or by A23187. The release of ACh was stimulated by K+ depolarization, absence of Na+ in the medium, and A23187 in a strictly Ca2+-dependent manner, whereas the release of GABA was only partially dependent on the presence of Ca2+ in the medium. The extent of stimulation of ACh release was related to the extent of Ca2+ entry, whereas no such correlation was observed for GABA. In the presence of Na+, RuR did not affect the release of the transmitters induced by A23187. In the absence of Na+, paradoxically RuR notably enhanced the release of both ACh and GABA induced by A23187, in a Ca2+-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)