Implication of alterations in intracellular calcium ion homoeostasis in the advent of paracetamol-induced cytotoxicity in primary mouse hepatocyte monolayer cultures

We have examined the fluctuation of free cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) using the fluorescent probe quin-2 during the cytotoxic response induced by low concentrations (100–250 μ ) of the model hepatotoxin paracetamol (APAP) in primary mouse hepatocyte cultures over 5 days. APAP-associated increases in [Ca²⁺]_i were recorded prior to APAP-associated cytotoxicity, and correlated with the subsequent loss of cell viability as measured by intracellular lactate dehydrogenase and K⁺ efflux. Co-incubation with promethazine (1 μ ) or ethyleneglycol-bis-(β-aminoethyl ether)-N,N,N′,N′-tetraacetic 0215 acid (4 m ) attenuated both the APAP-associated [Ca²⁺]_i changes and cytotoxicity. These results support the hypothesis that mobilization of intracellular Ca²⁺ may be an important early event in APAP-induced hepatotoxicity.     

CGP37157 modulates mitochondrial Ca homeostasis in cultured rat dorsal root ganglion neurons

The effects of 7-chloro-3,5-dihydro-5-phenyl-1H-4,1-benzothiazepine-2-on (CGP37157), an inhibitor of mitochondrial Na⁺/Ca²⁺ exchange, on depolarization-induced intracellular free Ca²⁺ concentration ([Ca²⁺]_i) transients were studied in cultured rat dorsal root ganglion neurons with indo-1-based microfluorimetry. A characteristic plateau in the recovery phase of the [Ca²⁺]_i transient resulted from mitochondrion-mediated [Ca²⁺]_i buffering. It was blocked by metabolic poisons and was not dependent on extracellular Ca²⁺. CGP37157 produced a concentration-dependent decrease in the amplitude of the mitochondrion-mediated plateau phase (IC₅₀=4±1 μM). This decrease in [Ca²⁺]_i was followed by an increase in [Ca²⁺]_i upon removal of the drug, suggesting that Ca²⁺ trapped in the matrix was released when the CGP37157 was removed from the bath. CGP37157 also inhibited depolarization-induced Ca²⁺ influx at the concentrations required to see effects on [Ca²⁺]_i buffering. Thus, CGP37157 inhibits mitochondrial Na⁺/Ca²⁺ exchange and directly inhibits voltage-gated Ca²⁺ channels, suggesting caution in its use to study [Ca²⁺]_i regulation in intact cells.     

Tetrabromobisphenol A (TBBPA), induces cell death in TM4 Sertoli cells by modulating Ca transport proteins and causing dysregulation of Ca homeostasis

Tetrabromobisphenol A (TBBPA) is a commonly used brominated flame retardant (BFR) utilized to reduce the flammability of a variety of products. Studies have indicated that a number of BFRs are becoming widely distributed within the environment and are bio-accumulating within organisms. There has been much speculation that a variety of phenolic pollutants (including compounds chemically related to TBBPA, such as bisphenol A) may cause endocrine disruption and Ca²⁺ dysregulation in cells involved in spermatogenesis. In this study we therefore investigate the effects of TBBPA on mouse TM4 Sertoli cells (essential for sperm development). Results show that TBBPA increases Ca²⁺ within these cells in the 5–60 μM concentration range (EC₅₀, 21 μM). TBBPA also causes cell death (LC₅₀, 18 μM) partly via apoptosis, involving Ca²⁺-dependent mitochondrial depolarisation. Studies on intracellular Ca²⁺ transporters shows that TBBPA can inhibit sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPases (SERCA) at low concentrations (IC₅₀, 0.4 to 1.2 μM) and also activate the Ryanodine receptor Ca²⁺ channel within the 0.4–4 μM concentration range. Therefore these studies suggest that the cytotoxic effects of TBBPA on cells is partly due to dysregulation of Ca²⁺ signalling, by directly affecting Ca²⁺ transport proteins.     

Effect of a phospholipase A2 with cardiotoxin-like properties, from Bungarus fasciatus snake venom, on calcium-modulated potassium currents

, , , and . Effect of a phospholipase A₂ with cardiotoxin-like properties, from Bungarus fasciatus snake venom, on calcium-modulated potassium currents. Toxicon 27, 1339–1349, 1989.—The action of a 16,300mol. wt phospholipase A₂ with cardiotoxin-like properties from Bungarus fasciatus venom on membrane electrical properties of two human cell types was examined in vitro by using tight-seal whole-cell recording methods. Epithelial cells exhibited a voltage-and Ca²⁺-activated K⁺current; the sensitivity for voltage activation of the K⁺ current was enhanced by increasing free Ca²⁺ in the recording pipette from 10⁻⁸ M to 2 × 10⁻⁶ M. In contrast, peripheral blood lymphocytes possessed voltage-activated K⁺ currents that were inhibited by increasing intracellular Ca²⁺.

Exposure of either preparation to B.fasciatus toxin (0.2–5 × 10⁻⁶ M) for up to 30 min in the bath did not alter membrane leakage current, as judged by the maintenance of low pre-treatment values over the range of − 140mV to − 40mV. However, the sensitivity for voltage activation of the K⁺ current was enhanced in the epithelial cells even at the lowest concentrations tested. In contrast to the results with epithelial cells, toxin exposure inhibited the activation of voltage-activated K⁺ currents in human lymphocytes, suggesting a specific increase in intracellular Ca²⁺ levels in both cell types.

The fluorescent probe indo-1/AM was used to monitor cytoplasmic Ca²⁺ levels. Exposure of either lymphocytes or epithelial cells to toxin (10⁻⁶ M) resulted in a transient increase in Ca²⁺. However, while the Ca²⁺ response to toxin was transient, K-channel modulation by the toxin appeared to be irreversible over the experimental time course. The longer-lasting modulation of Ca²⁺-regulated K⁺ channels may reflect an irreversible action of the B.fasciatus phospholipase A₂ on a Ca²⁺-dependent regulatory process.     

Ca dependence of the response of three adenosine type receptors in rat hepatocytes

The effect of three different receptor-specific adenosine agonists on the rate of ureagenesis by isolated rat hepatocytes and the dependence on the external free Ca²⁺ concentration ([Ca²⁺]_e) were investigated. In the presence of high [Ca²⁺]_e all adenosine receptor agonists increased ureagenesis to similar levels. However, with low [Ca²⁺]_e the effects of each agonist varied as follows: (i) the adenosine A₁ receptor agonist, 2-chloro-N⁶-cyclopentyl-adenosine, increased ureagenesis depending partially on [Ca²⁺]_e, (ii) the adenosine receptor A₂ agonist, 2-p-(-2-carboxy-ethyl) phenethylamino-5′-N-ethylcarboxyamido adenosine hydrochloride, increased ureagenesis independently of [Ca²⁺]_e and (iii) in contrast, the adenosine receptor A₃ agonist N⁶-2-(-4-aminophenyl) ethyladenosine, increased ureagenesis only in the presence of high [Ca²⁺]_e. The adenosine receptor A₁ antagonist, 1-allyl-3,7-dimethyl-8-phenyl xanthine, inhibited the effect of the adenosine receptor A₁ agonist on ureagenesis, but not the effect of the adenosine A₂ or A₃ receptor agonists. The adenosine A₂ receptor antagonist, 3,7-dimethyl-1-propargylxanthine, inhibited only the effect of the adenosine A₂ receptor agonist. Thus, in addition to A₁ and A₂ type adenosine receptors, rat hepatocytes possess an A₃-like adenosine receptor which responds to the addition of an adenosine A₃ agonist by accelerating ureagenesis a [Ca²⁺]_e dependent manner. Moreover, it was observed that in the presence of extracellular Ca²⁺ each agonist increased [Ca²⁺]_i and this effect was inhibited by the appropriate specific antagonist.     

苦参碱对阿霉素所致H9c2心肌细胞损伤的保护作用及与线粒体Na+-K+-ATP酶、Ca2+-ATP酶关系的研究

目的：研究苦参碱对阿霉素所致H9c2心肌细胞损伤的保护作用及其机制。方法：将H9c2心肌细胞培养,取2~3代细胞进行试验,共分为4组。对照组：接受生理盐水作为干预因素;阿霉素组：接受0.5 mg·L^-1阿霉素作为损伤模型;苦参碱+阿霉素组：接受0.5 mg·L^-1阿霉素和不同浓度苦参碱（50,150,200 mg·L^-1）作为干预因素;苦参碱组：接受不同浓度苦参碱（50,150,200 mg·L^-1）作为干预因素。以上各组相应干预24 h后,应用流式细胞仪检测H9c2心肌细胞凋亡水平,应用分光光度法检测线粒体Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶活性,利用JC-1法检测线粒体膜电位。结果：与阿霉素组相比,苦参碱+阿霉素组H9c2心肌细胞凋亡显著减少、线粒体Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶活性显著升高（P<0.05）、线粒体膜电位显著改善。结论：苦参碱对阿霉素所致H9c2心肌细胞有保护作用,减轻心肌细胞凋亡,改善线粒体膜电位、提高线粒体Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶活性。     

Fluorescent estimation on cytotoxicity of methylmercury in dissociated rat cerebellar neurons: its comparison with ionomycin

To study the cellular basis of the neurotoxicity of methylmercury, the effects of methylmercury on dissociated rat cerebellar neurons were examined using a flow cytometer, a confocal laser microscope and three fluorescent dyes, fluo-3 for monitoring the changes in intracellular Ca²⁺ concentration ([Ca²⁺]_i) and for detecting live neurons, ethidium for assessing the neurons that are dead or have compromised membranes, and 5-chloromethylfluorescein (CMF) for estimating the cellular content of nonprotein thiols. Methylmercury at concentrations of 1 μM or greater increased the [Ca²⁺]_i of almost all neurons. Prolonged exposure to methylmercury (3 and 10 μM) produced a further increase in [Ca²⁺]_i, in association with compromising membranes in some neurons. Thereafter, methylmercury induced blebs on membranes of some neurons with increased [Ca²⁺]_i. Methylmercury at concentrations of 0.3 μM or greater dose-dependently decreased the cellular content of nonprotein thiols. Results suggest that methylmercury may induce the loss of membrane integrity through destabilized Ca²⁺ homeostasis and oxidative stress in mammalian brain neurons.     

Influence of the carcinogenic oestrogen diethylstilboestrol on the intracellular calcium level in C6 rat glioma cells

The synthetic oestrogen diethylstilboestrol (DES) causes a dose-dependent elevation of the cytoplasmic Ca²⁺ concentration in C6 rat glioma cells. This Ca²⁺ rise is caused neither by Ca²⁺ influx nor by release from the Ca²⁺ stores of the endoplasmic reticulum. Therefore it seems likely that DES mobilizes Ca²⁺ from a mitochondrial source. The DES-induced Ca²⁺ signal is remarkably similar to the one induced by the tumour promotor thapsigargin. As this compound causes leakage of calcium from the endoplasmic reticulum it seems possible that DES induces a similar leakage from mitochondrial Ca²⁺ stores. It remains to be established whether the DES-mediated rise in intracellular calcium is causally related to the tumour-promoting properties of this compound.     

Opposite effects of Bay k 8644 and nicardipine on the inhibitory effect of Ca on rat myometrium

The effect of Ca²⁺ on the oxytocin-induced, sustained contraction of rat uterine muscle in Ca-free medium after prolonged incubation with 3 mM EGTA (Ca-free contraction) was investigated. A micromolar concentration of Ca²⁺ caused phasic contraction followed by relaxation while a submicromolar concentration caused relaxation only. Cumulative addition of Ca²⁺ (10⁻⁸-3×10⁻⁶ M) caused dose-dependent relaxation (Ca reversal). This relaxation was inhibited by nicardipine and enhanced by Bay k 8644, and the effects of these two drugs were potentiated in 45.6 mM K⁺ medium. It is concluded that the inhibitory effect of Ca²⁺ on Ca-free contraction is caused by the influx of a minute amount of Ca²⁺. Thus, Ca²⁺ has dual actions in the cell: activation at concentrations higher than 10⁻⁶ M, and inhibition alone at concentrations lower than 10⁻⁷ M.     

Sarcoplasmic reticulum Ca2+ release channel ryanodine receptor (RyR2) plays a crucial role in aconitine-induced arrhythmias

The present study established a model of RyR₂ knockdown cardiomyocytes and elucidated the role of RyR₂ in aconitine-induced arrhythmia. Cardiomyocytes were obtained from hearts of neonatal Sprague–Dawlay rats. siRNAs were used to down-regulate RyR₂ expression. Reduction of RyR₂ expression was documented by RT-PCR, western blot, and immunofluorescence. Ca²⁺ signals were investigated by measuring the relative intracellular Ca²⁺ concentration, spontaneous Ca²⁺ oscillations, caffeine-induced Ca²⁺ release, and L-type Ca²⁺ currents. In normal cardiomyocytes, steady and periodic spontaneous Ca²⁺ oscillations were observed, and the baseline [Ca²⁺]_i remained at the low level. Exposure to 3 μM aconitine increased the frequency and decreased the amplitude of Ca²⁺ oscillations; the baseline [Ca²⁺]_i and the level of caffeine-induced Ca²⁺ release were increased but the L-type Ca²⁺ currents were inhibited after application of 3 μM aconitine for 5 min. In RyR₂ knockdown cardiomyocytes, the steady and periodic spontaneous Ca²⁺ oscillations almost disappeared, but were re-induced by aconitine without affecting the baseline [Ca²⁺]_i level; the level of caffeine-induced Ca²⁺ release was increased but L-type Ca²⁺ currents were inhibited. Alterations of RyR₂ are important consequences of aconitine-stimulation and activation of RyR₂ appear to have a direct relationship with aconitine-induced arrhythmias. The present study demonstrates a potential method for preventing aconitine-induced arrhythmias by inhibiting Ca²⁺ leakage through the sarcoplasmic reticulum RyR₂ channel.     

Effects of Induction and Inhibition of Cytochromes P450 on the Hepatotoxicity of Methapyrilene

The mechanisms by which the antihistamine drug methapyrilenecauses acute periportal hepatotoxicity in rats are not yet elucidated.This study investigated the effects of modulators of cytochromeP450 (CYP) activity on the hepatotoxicity of methapyrilene andalso the effect of methapyrilene on hepatic CYP. Pretreatmentof male Han Wistar rats with ß-naphthoflavone, phenobarbitone,butylated hydroxytoluene, piperonyl butoxide, Aroclor 1254,or cobalt protoporphyrin IX, agents known to modify hepaticCYP, all afforded some degree of protection against a hepatotoxicdose of methapyrilene (150 mg/kg x 3 days p.o.), as assessedby clinical chemistry and histology. Total hepatic CYP depletionby cobalt protoporphyrin IX treatment indicated CYP-mediatedbioactivation was a prerequisite for methapyrilene-induced hepatotoxicity.Protection against hepatic damage was strongly associated withß-naphthoflavone induction of CYP1A and phenobarbitone-associatedCYP2B induction. However, the role of CYP3A, which is constitutivelyexpressed in the liver and induced by piperonyl butoxide, butylatedhydroxytoluene, or Aroclor 1254, was unclear. Modulation ofFAD monooxgenase activity by methimazole pretreatment was notassociated with increased methapyrilene-induced hepatotoxicity.Methapyrilene treatment alone specifically decreased microsomalenzyme activity markers for CYP2C11, CYP3A, and CYP2A and pretreatmentwith all the hepatic enzyme-inducing agents specifically preventedthe loss of CYP2C11. Together this suggested that CYP2C11 wasresponsible for the suicide substrate bioactivation of methapyrileneand the toxicologic outcome largely relied upon an abundanceof detoxifying enzymes present in the liver.     

Effects of Ca channel blockers on Ca loading induced by metabolic inhibition and hyperkalemia in cardiomyocytes

The effects of the L-type (nifedipine and verapamil) and the T-type (mibefradil) Ca²⁺ channel blockers on the increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) induced by NaCN metabolic inhibition and hyperkalemia were examined in chicken cardiomyocytes using fluorescence imaging with Fura-2. NaCN induced a slow and sustained rise in [Ca²⁺]_i, which was not affected by pretreating the cells for 5 min with nifedipine, verapamil, or mibefradil at 100 nM or 10 μM. Pretreatment of the cells with 10 μM nifedipine, verapamil, or mibefradil for 5 min remarkably inhibited the K⁺-induced increase in [Ca²⁺]_i. These inhibitory effects diminished after 48-h pretreatment with nifedipine or verapamil but not with mibefradil. Ryanodine also induces an increase in [Ca²⁺]_i, and this effect was enhanced by 48-h pretreatment of the cells with 10 μM verapamil but not with 10 μM mibefradil. We conclude that the NaCN-induced increase in [Ca²⁺]_i is independent of the Ca²⁺ influx though the L-type or T-type Ca²⁺ channels. Chronic inhibition of the L-type Ca²⁺ channels but not T-type channels may enhance the ryanodine receptor-mediated Ca²⁺ release, which may be responsible for the development of tolerance to their inhibitory effects on K⁺-induced increase in [Ca²⁺]_i.     

Heptachlor epoxide induces a non-capacitative type of Ca2+ entry and immediate early gene expression in mouse hepatoma cells

The effects of the organochlorine (OC) liver tumor promoter heptachlor epoxide (HE) and a related non-tumor promoting OC, delta-hexachlorocyclohexane (δ-HCH), on the dynamics of intracellular calcium (Ca²⁺) were investigated in mouse 1c1c7 hepatoma cells. HE induced a non-capacitative, Ca²⁺ entry-like phenomenon, which was transient and concentration-dependent with 10 and 50 μM HE. The plasma membrane Ca²⁺ channel blocker SKF-96365 antagonized this HE-induced Ca²⁺ entry. δ-HCH failed to induce Ca²⁺ entry, rather it antagonized the HE-induced Ca²⁺ entry. Both HE and δ-HCH induced Ca²⁺ release from endoplasmic reticulum (ER) at treatment concentrations as low as 10 μM; at 50 μM, the former induced 5× as much Ca²⁺ release as the latter. The HE-induced Ca²⁺ release from the ER was antagonized using the IP₃ receptor/channel blocker xestospongin C, suggesting that HE induces ER Ca²⁺ release through the IP₃ receptor/channel pore. These results show that the effect of HE on cellular Ca²⁺ mimics that of mitogens such as epidermal and hepatocyte growth factors. They also provide insight into the similarities and differences between tumorigenic and non-tumorigenic OCs, in terms of the mechanisms and the extent of the [Ca²⁺]_i increased by these agents.     

Gas6 rescues cortical neurons from amyloid beta protein-induced apoptosis

Gas6, a product of the growth-arrest-specific gene 6, protects neurons from serum deprivation-induced apoptosis. Neuronal apoptosis is also caused by amyloid β protein (Aβ), whose accumulation in the brain is a characteristic feature of Alzheimer’s disease. Aβ induces Ca²⁺ influx via L-type voltage-dependent calcium channels (L-VSCCs), leading to its neurotoxicity. In the present study, we investigated effects of Gas6 on Aβ-induced cell death in primary cultures of rat cortical neurons. Aβ caused neuronal cell death in a concentration- and time-dependent manner. Gas6 significantly prevented neurons from Aβ-induced cell death. Gas6 ameliorated Aβ-induced apoptotic features such as the condensation of chromatin and the fragmentation of DNA. Prior to cell death, Aβ increased influx of Ca²⁺ into neurons through L-VSCCs. Gas6 significantly inhibited the Aβ-induced Ca²⁺ influx. The inhibitor of L-VSCCs also suppressed Aβ-induced neuronal cell death. The present cortical cultures contained few non-neuronal cells, indicating that Gas6 affected the survival of neurons directly, but not indirectly via non-neuronal cells. In conclusion, we demonstrate that Gas6 rescues cortical neurons from Aβ-induced apoptosis. Furthermore, the present study indicates that inhibition of L-VSCC contributes to the neuroprotective effect of Gas6.     

Glucose action `beyond ionic events'' in the pancreatic β cell

For normal glucose homeostasis, insulin release by the pancreatic β cell is vital. Until recently, it was thought that glucose-induced ionic events, such as closure of the ATP-sensitive K⁺ (K_ATP) channels, membrane depolarization, activation of the -type voltage-dependent Ca²⁺ channels, Ca²⁺ influx and elevation of cytosolic free Ca²⁺, constitute the main signalling pathway in β-cell stimulus–secretion coupling. However, since the discovery of ‘non-ionic' glucose actions in the β cell by the Aizawa and Henquin laboratories in 1991, data have accumulated that strongly indicate the physiological relevance of this signalling pathway. In this review, Toru Aizawa and colleagues discuss how the K_ATP channel–Ca²⁺ hypothesis was formulated, what was overlooked in the hypothesis, and then provide a comprehensive view of stimulus–secretion coupling in the β cell, with an emphasis on non-ionic glucose actions.     

Antamanide Prevents Bradykinin-lnduced Filamin Translocation by Inhibiting Extracellular Calcium Influx

Bradykinin-induced paracellular gap formation in cultured endothelial cells (ECs) is preceded by cytoskeletal rearrangement. Actin binding proteins, such as nonmuscle filamin, perform a pivotal role in modulating actin organization. In response to bradykinin treatment, EC filamin translocates from the cell periphery to the cytosol within 1 min and the dynamics of filamin translocation parallel intracellular Ca²⁺ increases. Intracellular Ca²⁺ increases are essential for bradykinin-induced filamin translocation. In this study, we examine the role of extracellular Ca²⁺ influx in mediating bradykinin-induced filamin translocation. Several K⁺ channel blockers, including antamanide, tetraethylam-monium chloride (TEA), and charybdotoxin (CTX), are evaluated. All of these agents inhibit extracellular Ca²⁺ influx with minimal or partial inhibition of intracellular Ca²⁺ release. Bradykinin-induced filamin translocation is prevented by pretreatment with these K⁺ channel blockers. Moreover, incubation of ECs in high-K⁺ saline inhibits bradykinin-induced extracellular Ca²⁺ influx as well as filamin translocation. To examine the efficacy of antamanide as an anti-inflammatory drug that affects filamin translocation, bradykinin-induced paracellular gap formation is quantified and compared in the presence or absence of antamanide pretreatment. Antamanide does not completely block bradykinin-induced gap formation; however, a significant attenuation is observed. This suggests that extracellular Ca²⁺ influx is required for bradykinin-induced filamin translocation, which in part regulates microvascular EC barrier function, and that antamanide may be a useful anti-inflammatory agent.     

Homologous and heterologous desensitisation of somatostatin-induced increases in intracellular Ca and inositol 1,4,5-trisphosphate in CHO-K1 cells expressing human recombinant somatostatin sst5 receptors

The mechanisms responsible for somatostatin (SRIF)-induced increases in intracellular Ca²⁺ concentration ([Ca²⁺]_i) and subsequent desensitisation were studied in CHO-K1 cells expressing human sst₅ receptors (CHOsst₅ cells). To study the nature of the desensitisation, interactions with uridine triphosphate (UTP) were examined. SRIF (pEC₅₀ 7.10) and UTP (pEC₅₀ 5.14) caused concentration-dependent increases in [Ca²⁺]_i but the SRIF maximum was about 40% of that to UTP. SRIF-, but not UTP-, induced increases in [Ca²⁺]_i were transient and abolished by pertussis toxin. SRIF and UTP caused sustained increases in Ins(1,4,5)P₃ but the SRIF maximum was about 30% of that to UTP. Removal of [Ca²⁺ ]_e attenuated the SRIF-induced peak rise in [Ca²⁺]_i but had no effect on the peak increases in Ins(1,4,5)P₃. UTP-induced increases in [Ca²⁺]_i and Ins(1,4,5)P₃ were attenuated in the absence of [Ca²⁺]_e. Following pre-exposure to SRIF (1 μM) or UTP (100 μM) for 5 min, subsequent SRIF responses were desensitised. Similar results were obtained in the absence of [Ca²⁺]_e. Pre-exposure to SRIF had no effect on subsequent responses to UTP but in the absence of [Ca²⁺]_e, responses to UTP were attenuated. The results suggest that SRIF but not UTP-induced increases in [Ca²⁺]_i in CHOsst₅ cells are mediated by pertussis toxin sensitive G proteins and are caused by an entry of extracellular Ca²⁺ and release from an Ins(1,4,5)P₃ sensitive Ca²⁺ store. Homologous or heterologous desensitisation of agonist-induced increases in [Ca²⁺]_i could be demonstrated in the presence or absence of extracellular Ca²⁺ respectively, and the latter appeared to involve depletion of a common intracellular Ca²⁺ store.     

Effect of sea nettle (Chrysaora quinquecirrha) venom on isolated rat aorta

, and . Effect of sea nettle (Chrysaora quinquecirrha) venom on isolated rat aorta. Toxicon 26, 1209–1212, 1988.—The venom from sea nettle (Chrysaora quinquecirrha) (1–10μg/ml) produced an irreversible contraction of the isolated rat aortic ring that was slow in onset, increased with time, and reached maximum in about 10–20 min. The contraction was not inhibited by pretreatment with phenoxybenzamine, atropine, indomethacin, tetrodotoxin, ouabain, low Na⁺ or Na⁺-free medium, however, it was markedly decreased by the Ca²⁺ channel blockers, nifedipine and verapamil. In Ca²⁺-free medium, no increase in tension was produced by the venom. It is concluded that sea nettle venom causes a contraction of the rat aortic ring by increasing Ca²⁺ influx through the voltage-dependent Ca²⁺ channels.     

Stimulus-evoked glutamate release is diminished by acute exposure to uranium in vitro

Uranium is used in civilian applications, in the manufacture of nuclear fuel, and by the military for munitions and armament, but little information is available on its neurotoxicity. Neurological dysfunctions have been observed after chronic exposure in both animals and humans, but the actions of acute exposure on amino acid neurotransmission have not been investigated. The following study was performed to examine the effects of uranyl ion (UO₂^+ 2) on hippocampal glutamatergic and GABAergic function as possible bases for the neurotoxicity and to assess the direct effects on the exocytotic process. Nominal UO₂^+ 2 concentrations were applied to superfused hippocampal synaptosomes to permit estimation of the metal's potency on endogenous transmitter release in the presence and absence of Ca^+ 2. K⁺-evoked glutamate release was diminished in the range of 10 nM–316 μM UO₂^+ 2, resulting in an IC₅₀ of 1.92 μM. In contrast, the potency of UO₂^+ 2 to decrease stimulated GABA release was reduced, producing an IC₅₀ ≈ 2.6 mM. In the absence of Ca^+ 2 in the superfusion medium there was no systematic change in the magnitude of glutamate or GABA release, suggesting that UO₂^+ 2 does not possess Ca^+ 2-mimetic properties. The inhibitory potency of UO₂^+ 2 on glutamate release is similar to the potencies of other multivalent metal ions, suggesting by inference an action exerted on voltage-sensitive Ca^+ 2 channels. The bases for the reduced potency to inhibit GABA release is not known, but differential sensitivity to other heavy metals has been reported for glutamate and GABA neurotransmission. These findings indicate a profile of neurotoxicity not unlike that of other metal ions, and indicate the importance of extending subsequent studies to chronic exposure models.     

Propafenone and disopyramide enhance post-ischemic contractile and metabolic recovery of perfused hearts

The effects of sodium channel blockers, propafenone and disopyramide, on post-ischemic contractile dysfunction of perfused rat hearts were examined. Isolated hearts were subjected to 35 min ischemia, followed by 60 min reperfusion with and without administration of either drug during 3 min of pre-ischemia. Ischemia/reperfusion induced complete cardiac dysfunction, rise in left ventricular end-diastolic pressure, increase in perfusion pressure, accumulation of Na⁺ and Ca²⁺ and loss of K⁺ and Mg²⁺, and release of creatine kinase and purine nucleosides and bases from the heart. These observations suggest that ischemia/reperfusion in the current study induces cardiac cell necrosis or an increase in cell membrane permeability to ions, substrates and macromolecules. Treatment of perfused hearts with either propafenone at concentrations ranging from 5 to 70 μM, or disopyramide at concentrations of 100 μM or higher resulted in a pronounced contractile recovery of the heart, associated with suppression of reperfusion-induced tissue ion alteration and inhibition of reperfusion-induced release of creatine kinase and purine nucleosides and bases. Ischemic insult itself caused tissue Na⁺ accumulation and K⁺ loss without any change in tissue Ca²⁺ and Mg²⁺. The alterations in the electrolytes were attenuated by treatment with either agent. The results suggest that prevention of ischemia- and reperfusion-induced ionic disturbance of cardiac cells by propafenone and disopyramide plays a role in the improvement of post-ischemic contractile dysfunction.