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1.
钙离子(Ca2+)是细胞内重要的第二信使,其主要储存在内质网和线粒体中,参与调控细胞多种生理功能及维持内质网、线粒体功能。内质网和线粒体对钙离子的摄取与释放直接影响胞内钙离子水平的变化,继而影响细胞正常生理功能。病理条件下,细胞内钙离子稳态失衡,可引发细胞生理功能异常并进一步影响内质网、线粒体功能。非酒精性脂肪肝(NAFLD)是临床常见病和多发病,其主要病理特征是:肝脏脂肪样变性、内质网应激、线粒体损伤和非特异性炎性反应等。其中持续的内质网应激及线粒体功能障碍是NAFLD发生发展的重要诱因。而细胞内钙稳态的变化可直接导致内质网及线粒体功能异常,继而影响NAFLD的发生发展。本文主要从钙稳态的主要影响因素以及钙稳态变化与NAFLD的关系两方面进行阐述,为寻求和研发防治NAFLD的药物提供新的方向。 相似文献
2.
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. 相似文献
3.
Oluseye A. Ogunbayo Pei F. Lai Thomas J. Connolly Francesco Michelangeli 《Toxicology in vitro》2008,22(4):943-952
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. 相似文献
4.
López JJ Jardín I Bobe R Pariente JA Enouf J Salido GM Rosado JA 《Biochemical pharmacology》2008,75(11):2157-2164
Ca2+ mobilization regulates a wide variety of cellular functions. Platelets posses agonist-releasable Ca2+ stores in acidic organelles where sarcoendoplasmic reticulum Ca2+-ATPase-3 (SERCA) pump is involved in store refilling. Stromal interaction molecule 1 (STIM1), which has been presented as a central regulator of platelet function, is a Ca2+ sensor of the intracellular Ca2+ stores. Here we present that STIM1 is required for acidic store refilling. Electrotransjection of cells with anti-STIM1 (Y231–K243) antibody, directed towards a cytoplasmic sequence of STIM1, significantly reduced acidic store refilling, which was tested by remobilizing Ca2+ from the acidic stores using 2,5-di-(t-butyl)-1,4-hydroquinone (TBHQ) after a brief refilling period that followed thrombin stimulation. Platelet treatment with thrombin or thapsigargin in combination with ionomycin, to induce extensive Ca2+ store depletion, resulted in a transient increase in the interaction between STIM1 and SERCA3, reaching a maximum 30 s after stimulation. The coupling between STIM1 and SERCA3 was abolished by electrotransjection with anti-STIM1 antibody. The interaction between STIM1 and SERCA3 induced by thrombin or by treatment with thapsigargin plus ionomycin is reduced in platelets from type 2 diabetic patients, as well as Ca2+ reuptake into the acidic Ca2+ stores. These findings provide evidence for a role of STIM1 in acidic store refilling in platelets probably acting as a Ca2+ sensor and regulating the activity of SERCA3. This action is impaired in platelets from type 2 diabetics, which might lead to the enhanced cytosolic Ca2+ concentration observed and, therefore, in platelet hyperactivity. 相似文献
5.
Gurpreet S Ratra Winston A Morgan Jenny Mullervy Christopher J Powell Matthew C Wright 《Toxicology》1998,130(2-3):79-93
Methapyrilene (MP) is an unusual hepatotoxin in that it causes periportal necrosis in rats. The mechanism of acute methapyrilene hepatotoxicity has, therefore, been investigated in cultured male rat hepatocytes. Addition of methapyrilene to rat hepatocytes resulted in a time- and dose-dependent loss in cell viability between 4 and 8 h of incubation as judged by cellular enzyme leakage. The cytochrome P450 (CYP) inhibitor metyrapone protected against methapyrilene-mediated toxicity suggesting that MP is metabolised by CYP for toxicity. The concentration-dependent protection from methapyrilene toxicity afforded by metyrapone correlated with an inhibition of microsomal CYP2C11-associated androstenedione 16 hydroxylase activity, and hepatocytes prepared from hypophysectomised rats (containing reduced levels of microsomal immunodetectable CYP2C11 and associated androstenedione 16 hydroxylase activity) showed resistance to the toxic effects of methapyrilene. These data suggest that the toxicity of methapyrilene is predominantly dependent on the CYP2C11 isoform. Treatment of hepatocytes with a toxic concentration of MP caused oxidative stress as indicated by increases in NADP+ levels within 2 h and cellular thiol oxidation as evidenced by a reduction—but not complete loss—in glutathione levels. Methapyrilene hepatotoxicity was associated with an early loss in mitochondrial function, as indicated by mitochondrial swelling and significant losses in cellular ATP within 2 h. Co-incubation of methapyrilene-treated hepatocytes with inhibitors of inner mitochondrial transition permeability pore opening—cyclosporin A or the thiol reductant dithiothreitol—abrogated cell death suggesting that pore opening and loss of mitochondrial Ca2+ homeostasis play a significant role in methapyrilene-mediated cell death. Co-incubation of methapyrilene-treated hepatocytes with the phenylalkylamine calcium channel blocker verapamil—but not by treating cells in a nominally calcium-free medium—also abrogated cell death, suggesting that if Ca2+ is involved in cell killing then it is dependent on an intracellular Ca2+ pool. Pre-treatment of hepatocytes for 1 h with verapamil—to inhibit intracellular Ca2+ pool filling—increased the potency of verapamil protection against methapyrilene toxicity by approximately 100-fold. Taken together, these data indicate that methapyrilene intoxication leads to mitochondrial disfunction and suggest a critical role for a loss of mitochondrial Ca2+ homeostasis in this model of hepatocyte death. 相似文献
6.
In a wide variety of cells, activation of certain surface membrane receptors results in a rise in intracellular Ca2+ due to release of intracellular Ca2+ stores, and to an increased rate of Ca2+ entry. James Putney summarizes some current ideas about the mechanisms by which Ca2+-mobilizing receptors act. The intracellular Ca2+ release is believed to result from the action of inositol 1,4,5-trisphosphate, generated as a result of the activation by receptors of a polyphosphoinositide-specific phospholipase C. Evidence suggests that a guanine nucleotide-dependent regulatory protein may mediate this activation. The regulation of Ca2+ entry is less well understood, but may involve a mechanism whereby the emptying of the (1,4,5)IP3-sensitive pool secondarily activates Ca2+ influx across the plasma membrane. 相似文献
7.
G. Maurice Briggs James P. Morgan Judith K. Gwathmey 《European journal of pharmacology》1989,170(3):281-284
Phasic release of calcium from the sarcoplasmic reticulum occurs in all mammalian cardiac preparations when the intracellular calcium concentration is sufficiently high. The phasic calcium release is often sufficient to trigger electrophysiological responses and aftercontractions. These can be detrimental to normal cardiac function. We induced phasic calcium release in ferret papillary muscles loaded with the calcium indicator aequorin. Development of phasic calcium release was associated with an increase in resting and peak [Ca2+]i. Inhibiting sodium channels with yohimbine reduced resting [Ca2+]i and prevented phasic calcium release. We propose a mechasism where by reduced [Na+]i, and the subsequent increased efflux of calcium via sodium/calcium exchange reduced [Ca2+]i. 相似文献
8.
9.
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. 相似文献
10.
Resin acids from bleached wood pulp are toxic to fish. 12,14-Dichlorodehydroabietic acid (12,14-Cl2DHA) raises cytoplasmic Ca2+ in synaptosomes and blocks neural GABAA receptors; however, the underlying mechanism remains unclear in these earlier rodent studies. 12,14-Cl2DHA (50 μM) almost completely blocked native GABAA currents (rat cortical cultures) but had no significant effect on picrotoxin-sensitive recombinant human receptors in oocytes (1, β2 and γ2L: the most prevalent isoforms in mammalian brain). In oocytes, 12,14-Cl2DHA failed to produce a calcium-activated chloride current, in contrast to the calcium ionophore ionomycin (10 μM). However, in cultured cortical pyramidal cells, both ionomycin and 12,14-Cl2DHA produced chloride-selective currents of similar magnitude (presumably secondary to Ca2+ release). 12,14-Cl2DHA was unable to stimulate phosphate labelling of [3H]-inositol in mouse synaptosomes, indicating that the study compound does not cause Ca2+ release via an IP3 mechanism. Calcium pump ATPase inhibition also seems unlikely since thapsigargin did not elevate free calcium in synaptosomes. 12,14-Cl2DHA clearly blocks GABAA currents indirectly: we infer that its toxicity may be secondary to the elevations in cytoplasmic Ca2+ via an unidentified recognition site (or receptor) found in neuronal cells. 相似文献
11.
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. 相似文献
12.
Oligomycin inhibits Na+,K+-ATPase activity by stabilizing the Na+ occlusion but not the K+ occlusion. To locate the binding domain of oligomycin on Na+,K+-ATPase, the tryptic-digestion profile of Na+,K+-ATPase was compared with the profile of Na+ occlusion within the digested Na+,K+-ATPase in the presence of oligomycin. The Na+ occlusion profile is responsible for the digestion profile of the -subunit, which is the catalytic subunit of the ATPase. The effect of oligomycin on chimeric Ca2+-ATPase activity was examined. The chimera used, in which the 163 N-terminal amino acids of chicken sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 1 were replaced with the 200 N-terminal amino acids of the chicken Na+,K+-ATPase 1-subunit, partially retains the Na+-dependent characteristics of Na+,K+-ATPase, because the chimeric Ca2+-ATPase activity is activated by Na+ but inhibited by ouabain, a specific inhibitor of Na+,K+-ATPase (Ishii, T., Lemas, M.V., Takeyasu, K., 1994, Proc. Natl. Acad. Sci. U. S. A., 91, 6103–6107). Oligomycin depressed the activation by Na+ of the chimeric Ca2+-ATPase activity. These findings suggest that the 200 N-terminal amino acids of the Na+,K+-ATPase -subunit include a binding domain for oligomycin. 相似文献
13.
Verapamil, diltiazem, nisoldipine and felodipine, calcium antagonist drugs with different chemical structures, were studied for their effects on activities of sarcoplasmic reticulum (SR) isolated from dog cardiac and rabbit skeletal muscles. Nisoldipine and felodipine exerted biphasic actions on both cardiac and skeletal SR Ca2+-ATPase with maximum activation of 40–60% occurring at 20–40 μM for nisoldipine and 30–40% occurring at 15–30 μM for felodipine. At higher drug concentrations, Ca2+-ATPase was inhibited. In the presence of oxalate the maximum activation of the Ca2+ uptake rates at 5–20 μM nisoldipine were 30–50% for cardiac SR and 80–100 μM of the drug were 300–500% for skeletal SR. Felodipine inhibited the rate of Ca2+ uptake by dog cardiac SR, but activated Ca2+ uptake by rabbit skeletal SR with a maximum of 30–50% at 12–25 μM. At higher concentrations of the two drugs the rate of Ca2+ uptake was inhibited. In the absence of oxalate, i.e., limited tranport, nisoldipine shortened the duration of time that Ca2+ was bound to the cardiac and skeletal SR, while the rate of release of Ca2+ from skeletal SR was stimulated. Felodipine at low concentrations similarly caused a premature release of Ca2+ from skeletal SR at a rapid rate; at high concentrations both drugs did not alter Ca2+ binding but delayed Ca2+ release. Unlike nisoldipine and felodipine, verapamil and diltiazem inhibited the rates of Ca2+ transport both in cardiac and skeletal SR. The two drugs inhibited Ca2+-ATPase in cardiac SR but activated the enzyme in skeletal SR. Thus, these drugs caused complex and different effects on cardiac and skeletal SR, possibly resulting from perturbations of the lipid environment of the SR Ca2+-ATPase. 相似文献
14.
Endoh M 《European journal of pharmacology》2004,500(1-3):73-86
The force–frequency relationship (FFR) is an important intrinsic regulatory mechanism of cardiac contractility. The FFR in most mammalian ventricular myocardium is positive; that is, an increase in contractile force in association with an increase in the amplitude of Ca2+ transients is induced by elevation of the stimulation frequency, which reflects the cardiac contractile reserve. The relationship is different depending on the range of frequency and species of animal. In some species, including rat and mouse, a ‘primary-phase’ negative FFR is induced over the low-frequency range up to approximately 0.5–1 Hz (rat) and 1–2 Hz (mouse). Even in these species, the FFR over the frequency range close to the physiological heart rate is positive and qualitatively similar to that in larger mammalian species, although the positive FFR is less prominent. The integrated dynamic balance of the intracellular Ca2+ concentration ([Ca2+]i) is the primary cellular mechanism responsible for the FFR and is determined by sarcoplasmic reticulum (SR) Ca2+ load and Ca2+ flux through the sarcolemma via L-type Ca2+ channels and the Na+-Ca2+ exchanger. Intracellular Na+ concentration is also an important factor in [Ca2+]i regulation. In isolated rabbit papillary muscle, over a lower frequency range (<0.5 Hz), an increase in duration rather than amplitude of Ca2+ transients appears to be responsible for the increase in contractile force, while over an intermediate frequency range (0.5–2.0 Hz), the amplitude of Ca2+ transients correlates well with the increase in contractile force. Over a higher frequency range (>2.5 Hz), the contractile force is dissociated from the amplitude of Ca2+ transients probably due to complex cellular mechanisms, including oxygen limitation in the central fibers of isolated muscle preparations, while the amplitude of Ca2+ transients increases further with increasing frequency (‘secondary-phase’ negative FFR). Calmodulin (CaM) may contribute to a positive FFR and the frequency-dependent acceleration of relaxation, although the role of calmodulin has not yet been established unequivocally. In failing ventricular myocardium, the positive FFR disappears or is inverted and becomes negative. The activation and overexpression of cardiac sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) is able to reverse these abnormalities. Frequency-dependent alterations of systolic and diastolic force in association with those of Ca2+ transients and diastolic [Ca2+]i levels are excellent indicators for analysis of cardiac excitation-contraction coupling, and for evaluating the severity of cardiac contractile dysfunction, cardiac reserve capacity and the effectiveness of therapeutic agents in congestive heart failure. 相似文献
15.
In cerebellar cultures, comprising predominantly granule neurones, dihydropyridine (DHP) Ca2+ agonists were potent stimulators of voltage-sensitive 45Ca2+ uptake. Their effect was maximal in partially depolarized cells; at 15 mM Ke+ half maximal stimulation occurred at about 5 × 10−8 M BAY K 8644 and 10−7 M(+)-(S)-202 791. Organic Ca2+ antagonists were effective inhibitors of voltage-sensitive calcium entry into granule cells: the order of potency in blocking uptake induced by sub-maximal concentration of K+ and BAY K 8644 was nifedipine > (−)-202 791 > D600. BAY K 8644 also stimulated the release of glutamate, the transmitter of the granule cells, from depolarized cells. Granule cells are therefore a class of neurones whose responsiveness to organic Ca2+ effectors is similar to that of cardiac and smooth muscle. The discrepant findings on the effect of calcium effectors in various preparations of nervous tissues may thus reflect a differential distribution of voltage-sensitive Ca2+ channels in different neuronal cell types. 相似文献
16.
In rat ventricular muscles, ryanodine (10–30 nM) evoked tension oscillation in the relaxation phase of an isometric twitch (relaxation oscillations) and an increase of tonic tension (ryanodine contracture). Both events were more pronounced in Ca2+-loaded rat muscles due to the addition of 0.5 μM adrenaline, an increase in the Ca2+ concentration in the solution and high muscle activity. The ryanodine-induced tension oscillations were comparable to those triggered by caffeine in this species. In both cases, blockers of the release of Ca2+ from the sarcoplasmic reticulum, namely tetracaine and dantrolene, abolished the relaxation oscillations and the ryanodine contracture. The results suggest that the ability of low concentrations of ryanodine to facilitate the release of Ca2+ from the sarcoplasmic reticulum, as shown recently in biochemical experiments, makes a direct contribution to triggering the relaxation oscillations and the ryanodine contracture in intact ventricular muscles. The Ca2+ load of the sarcoplasmic reticulum appears to be essential for the manifistation of the ryanodine Ca2+-releasing activity in rat ventricular muscles. 相似文献
17.
Abstract: It has been suggested recently that disturbances of endoplasmic reticulum calcium homeostasis plays a major role in ischaemic cell injury of the brain. Depletion of endoplasmic reticulum calcium stores induces suppression of the initiation process of protein synthesis, a prominent feature of ischaemic cell damage. The benzoic acid derivative 3,4,5-trimethoxybenzoic acid 8-diethylamino-octyl ester (TMB-8), an established inhibitor of calcium release from endoplasmic reticulum, would be an ideal tool for elucidating the role of endoplasmic reticulum dysfunction in this pathological process. The present investigation was performed to study the effects of TMB-8 on neuronal metabolism (cytoplasmic calcium activity, ATP levels and protein synthesis) using hippocampal slices and primary neuronal cell cultures. In addition, we investigated whether the rise in cytoplasmic calcium activity and the suppression of protein synthesis induced by endoplasmic reticulum calcium pool depletion, is reversed by this agent. Exposure of neurones to TMB-8 (100 μM) induced a small transient increase in cytoplasmic calcium activity ([Ca2+]i), whereas a second dose of TMB-8 (200 μM) produced a marked and sustained rise in [Ca2+]i. The increase in [Ca2+]i evoked by blocking endoplasmic reticulum Ca2+-ATPase was only transiently suppressed and then aggravated by TMB-8. The dose-dependent suppression of protein synthesis by TMB-8, observed both in neuronal cultures and hippocampal slices, indicates that TMB-8 has a pathological effect on neuronal metabolism. This inhibition was not reversed after washing-off of the drug. TMB-8 did not reverse the inhibition of protein synthesis evoked by caffeine, which depletes endoplasmic reticulum calcium stores by activating the ryanodine receptor. The results indicate that TMB-8 is not a suitable investigative tool for blocking in neuronal cell cultures the depletion of endoplasmic reticulum calcium stores and the suppression of protein synthesis induced by endoplasmic reticulum calcium pool depletion. 相似文献
18.
Stephen C. Bondy 《Neurotoxicology and teratology》1989,11(6):527-531
Calcium is important in many intracellular regulatory processes. However, the maintenance of low levels of this cation within the cytosol is essential for maintenance of cell viability, in view of the large concentration gradient of ionic calcium across the plasma membrane. The expenditure of energy is needed to maintain intracellular calcium concentration [Ca2+]i at normal levels. In addition, the integrity of the limiting membrane is also vital for this function. Thus, any disruption of membrane characteristics or of mitochondrial anabolic processes may lead to deleterious levels of [Ca2+]i. The toxicity of a wide range of unrelated agents may, therefore, be in part due to elevation of cytosolic calcium. This general event may synergize with the more selective harmful properties of a compound, thus adversely affecting cell metabolism. The capacity now exists to measure levels of [Ca2+]i in isolated cells or organelles such as synaptosomes. The use of such in vitro models can be of value in the evaluation of the neurotoxic potential of compounds. This method, in conjunction with the use of pharmacological agents known to act at specific sites, and with the use of radioactive calcium in translocation studies, also has utility in the delineation of the biochemical mode of action of neurotoxic agents. 相似文献
19.
We have previously shown that although glutamate alone has no effects on viability of mouse hypothalamic GT1–7 cells, it clearly enhances Pb2+-induced cytotoxicity. It is likely that Pb2+ must enter cells to exert most of its toxic effects. Pb2+ is known to substitute for Ca2+ in many cellular processes. Therefore, we studied the uptake mechanisms of Pb2+ into GT1–7 neuronal cells with a special focus on the role of extracellular calcium (Ca2+), voltage-sensitive calcium channels (VSCCs) and glutamate. Basal uptake of Pb2+ (1 μM or 10 μM), i.e. without any external stimulus, clearly increased in nominally Ca2+-free buffer and was partially abolished by 13 mM Ca2+ when compared to uptake in the presence of a physiological concentration of extracellular Ca2+ (1.3 mM). Depolarization by 25 mM K+, or antagonists of VSCCs, verapamil (10 μM) or flunarizine (10 μM) had no clear effect on basal Pb2+ uptake. Glutamate (1 mM) increased Pb2+ uptake, but only when cells were treated with 1 μM Pb2+ in the presence of 1.3 mM Ca2+. Our data suggest that Pb2+ competes for the same cellular uptake pathways with Ca2+, although not via VSCCs. In addition, enhancement of Pb2+-induced neurotoxicity by glutamate may be due to increased neuronal uptake of Pb2+. 相似文献
20.
Gregory R Monteith Yewlan Wanigasekara Basil D Roufogalis 《Journal of pharmacological and toxicological methods》1998,40(4):183-190
Significant progress has been achieved in elucidating the role of the plasma membrane Ca2+-ATPase in cellular Ca2+ homeostasis and physiology since the enzyme was first purified and physiology since the enzyme was first purified and cloned a number of years ago. The simple notion that the PM Ca2+-ATPase controls resting levels of [Ca2+]CYT has been challenged by the complexity arising from the finding of four major isoforms and splice variants of the Ca2+ pump, and the finding that these are differentially localized in various organs and subcellular regions. Furthermore, the isoforms exhibit differential sensitivities to Ca2+, calmodulin, ATP, and kinase-mediated phosphorylation. The latter pathways of regulation can give rise to activation or inhibition of the Ca2+ pump activity, depending on the kinase and the particular Ca2+ pump isoform. Significant progress is being made in elucidating subtle and more profound roles of the PM Ca2+-ATPase in the control of cellular function. Further understanding of these roles awaits new studies in both transfected cells and intact organelles, a process that will be greatly aided by the development of new and selective Ca2+ pump inhibitors. 相似文献