Nitric oxide inhibits capacitative Ca2+ entry by suppression of mitochondrial Ca2+ handling

Characterization of endothelium-dependent and -independent processes in occipital artery of the rat: Relevance to control of blood flow to nodose sensory cells

Circulating factors access cell bodies of vagal afferents in nodose ganglia (NG) via the occipital artery (OA). Constrictor responses of OA segments closer in origin from the external carotid artery (ECA) differ from segments closer to NG. Our objective was to determine the role of endothelium in this differential vasoreactivity in rat OA segments. Vasoreactivity of OA segments (proximal segments closer to ECA, distal segments closer to NG) were examined in wire myographs. We evaluated (a) vasoconstrictor effects of 5-hydroxytryptamine (5-HT) in intact and endothelium-denuded OA segments in absence/presence of soluble guanylate cyclase (SGC) inhibitor ODQ, (b) vasodilator responses elicited by NO-donor MAHMA NONOate in intact or endothelium-denuded OA segments in absence/presence of ODQ, and (c) vasodilator responses elicited by endothelium-dependent vasodilator, acetylcholine (ACh), in intact OA segments in absence/presence of ODQ. Intact distal OA responded more to 5-HT than intact proximal OA. Endothelium denudation increased 5-HT potency in both OA segments, especially proximal OA. ODQ increased maximal responses of 5HT in both segments, particularly proximal OA. ACh similarly relaxed both OA segments, effects abolished by endothelial denudation and attenuated by ODQ. MAHMA NONOate elicited transient vasodilation in both segments. Effects of ODQ against ACh were segment-dependent whereas those against MAHMA NONOate were not. The endothelium regulates OA responsiveness in a segment-dependently fashion. Endothelial cells at the OA-ECA junction more strongly influence vascular tone than those closer to NG. Differential endothelial regulation of OA tone may play a role in controlling blood flow and access of circulating factors to NG.

Application of Genetically Encoded Fluorescent Nitric Oxide (NO•) Probes, the geNOps, for Real-time Imaging of NO• Signals in Single Cells

Nitric Oxide (NO•) is a small radical, which mediates multiple important cellular functions in mammals, bacteria and plants. Despite the existence of a large number of methods for detecting NO• in vivo and in vitro, the real-time monitoring of NO• at the single-cell level is very challenging. The physiological or pathological effects of NO• are determined by the actual concentration and dwell time of this radical. Accordingly, methods that allow the single-cell detection of NO• are highly desirable. Recently, we expanded the pallet of NO• indicators by introducing single fluorescent protein-based genetically encoded nitric oxide (NO•) probes (geNOps) that directly respond to cellular NO• fluctuations and, hence, addresses this need. Here we demonstrate the usage of geNOps to assess intracellular NO• signals in response to two different chemical NO•-liberating molecules. Our results also confirm that freshly prepared 3-(2-hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-propanamine (NOC-7) has a much higher potential to evoke change in intracellular NO• levels as compared with the inorganic NO• donor sodium nitroprusside (SNP). Furthermore, dual-color live-cell imaging using the green geNOps (G-geNOp) and the chemical Ca2+ indicator fura-2 was performed to visualize the tight regulation of Ca2+-dependent NO• formation in single endothelial cells. These representative experiments demonstrate that geNOps are suitable tools to investigate the real-time generation and degradation of single-cell NO• signals in diverse experimental setups.

TRPV1 activation counters diet-induced obesity through sirtuin-1 activation and PRDM-16 deacetylation in brown adipose tissue

Background/Objective

An imbalance between energy intake and expenditure leads to obesity. Increasing metabolism and thermogenesis in brown adipose tissue (BAT) can help in overcoming obesity. Here, we investigated the effect of activation of transient receptor potential vanilloid subfamily 1 (TRPV1) in the upregulation of thermogenic proteins in BAT to counter diet-induced obesity.

Subjects/Methods

We investigated the effect of dietary supplementation of capsaicin (TRPV1 agonist) on the expression of metabolically important thermogenic proteins in BAT of wild type and TRPV1^−/− mice that received either a normal chow or high fat (± capsaicin; TRPV1 activator) diet by immunoblotting. We measured the metabolic activity, respiratory quotient and BAT lipolysis.

Results

CAP antagonized high fat diet (HFD)-induced obesity without decreasing energy intake in mice. HFD suppressed TRPV1 expression and activity in BAT and CAP countered this effect. HFD feeding caused glucose intolerance, hypercholesterolemia and decreased the plasma concentration of glucagon like peptide-1 and CAP countered these effects. HFD suppressed the expression of metabolically important thermogenic genes, ucp-1, bmp8b, sirtuin 1, pgc-1α and prdm-16 in BAT and CAP prevented this effect. CAP increased the phosphorylation of sirtuin 1 and induced an interaction between PPARγ with PRDM-16. Further, CAP treatment, in vitro, decreased the acetylation of PRDM-16, which was antagonized by inhibition of TRPV1 by capsazepine, chelation of intracellular Ca²⁺ by cell permeable BAPTA-AM or the inhibition of SIRT-1 by EX 527. Further, CAP supplementation, post HFD, promoted weight loss and enhanced the respiratory exchange ratio. CAP did not have any effect in TRPV1^−/− mice.

Conclusions

Our data show that activation of TRPV1 in BAT enhances the expression of SIRT-1, which facilitates the deacetylation and interaction of PPARγ and PRDM-16. These data suggest that TRPV1 activation is a novel strategy to counter diet-induced obesity by enhancing metabolism and energy expenditure.

The Role of Mitochondria in the Activation/Maintenance of SOCE: Store-Operated Ca2+ Entry and Mitochondria

Mitochondria extensively modify virtually all cellular Ca²⁺ transport processes, and store-operated Ca²⁺ entry (SOCE) is no exception to this rule. The interaction between SOCE and mitochondria is complex and reciprocal, substantially altering and, ultimately, fine-tuning both capacitative Ca²⁺ influx and mitochondrial function. Mitochondria, owing to their considerable Ca²⁺ accumulation ability, extensively buffer the cytosolic Ca²⁺ in their vicinity. In turn, the accumulated ion is released back into the neighboring cytosol during net Ca²⁺ efflux. Since store depletion itself and the successive SOCE are both Ca²⁺-regulated phenomena, mitochondrial Ca²⁺ handling may have wide-ranging effects on capacitative Ca²⁺ influx at any given time. In addition, mitochondria may also produce or consume soluble factors known to affect store-operated channels. On the other hand, Ca²⁺ entering the cell during SOCE is sensed by mitochondria, and the ensuing mitochondrial Ca²⁺ uptake boosts mitochondrial energy metabolism and, if Ca²⁺ overload occurs, may even lead to apoptosis or cell death. In several cell types, mitochondria seem to be sterically excluded from the confined space that forms between the plasma membrane (PM) and endoplasmic reticulum (ER) during SOCE. This implies that high-Ca²⁺ microdomains comparable to those observed between the ER and mitochondria do not form here. In the following chapter, the above aspects of the many-sided SOCE-mitochondrion interplay will be discussed in greater detail.

Fus1/Tusc2 is a novel regulator of mitochondrial calcium handling, Ca2+-coupled mitochondrial processes, and Ca2+-dependent NFAT and NF-κB pathways in CD4+ T cells

AIMS

Fus1 has been established as mitochondrial tumor suppressor, immunomodulator, and antioxidant protein, but molecular mechanism of these activities remained to be identified. Based on putative calcium-binding and myristoyl-binding domains that we identified in Fus1, we explored our hypothesis that Fus1 regulates mitochondrial calcium handling and calcium-coupled processes.

RESULTS

Fus1 loss resulted in reduced rate of mitochondrial calcium uptake in calcium-loaded epithelial cells, splenocytes, and activated CD4(+) T cells. The reduced rate of mitochondrial calcium uptake in Fus1-deficient cells correlated with cytosolic calcium increase and dysregulation of calcium-coupled mitochondrial parameters, such as reactive oxygen species production, ΔμH(+), mitochondrial permeability transition pore opening, and GSH content. Inhibition of calcium efflux via mitochondria, Na(+)/Ca(2+) exchanger significantly improved the mitochondrial calcium uptake in Fus1(-/-) cells. Ex vivo analysis of activated CD4(+) T cells showed Fus1-dependent changes in calcium-regulated processes, such as surface expression of CD4 and PD1/PD-L1, proliferation, and Th polarization. Fus1(-/-) T cells showed increased basal expression of calcium-dependent NF-κB and NFAT targets but were unable to fully activate these pathways after stimulation.

INNOVATION

Our results establish Fus1 as one of the few identified regulators of mitochondrial calcium handling. Our data support the idea that alterations in mitochondrial calcium dynamics could lead to the disruption of metabolic coupling in mitochondria that, in turn, may result in multiple cellular and systemic abnormalities.

CONCLUSION

Our findings suggest that Fus1 achieves its protective role in inflammation, autoimmunity, and cancer via the regulation of mitochondrial calcium and calcium-coupled parameters.

Endothelial mitochondria--less respiration, more integration

Lining the inner surface of the circulatory system, the vascular endothelium accomplishes a vast variety of specialized functions. Even slight alterations of these functions are implicated in the development of certain cardiovascular diseases that represent major causes of morbidity and mortality in developed countries. Endothelial mitochondria are essential to the functional integrity of the endothelial cell as they integrate a wide range of cellular processes including Ca²⁺ handling, redox signaling and apoptosis, all of which are closely interrelated. Growing evidence supports the notion that impairment of mitochondrial signaling in the endothelium is an early event and a causative factor in the development of diseases such as atherosclerosis or diabetic complications. In this review, we want to outline the significance of mitochondria in both physiology and pathology of the vascular endothelium.

Thiamine and oxidants interact to modify cellular calcium stores

Diminished thiamine (vitamin B1) dependent processes and oxidative stress accompany Alzheimer's disease (AD). Thiamine deficiency in animals leads to oxidative stress. These observations suggest that thiamin may act as an antioxidant. The current experiments first tested directly whether thiamin could act as an antioxidant, and then examined the physiological relevance of the antioxidant properties on oxidant sensitive, calcium dependent processes that are altered in AD. The first group of experiments examined whether thiamin could diminish reactive oxygen species (ROS) or reactive nitrogen species (RNS) produced by two very divergent paradigms. Dose response curves determined the concentrations of t-butyl-hydroperoxide (t-BHP) (ROS production) or 3-morpholinosydnonimine ((SIN-1) (RNS production) to induce oxidative stress within cells. Concentrations of thiamine that reduced the RNS in cells did not diminish the ROS. The second group of experiments tested whether thiamine alters oxidant sensitive aspects of calcium regulation including endoplasmic reticulum (ER) calcium stores and capacitative calcium entry (CCE). Thiamin diminished ER calcium considerably, but did not alter CCE. Thiamine did not alter the actions of ROS on ER calcium or CCE. On the other hand, thiamine diminished the effect of RNS on CCE. These data are consistent with thiamine diminishing the actions of the RNS, but not ROS, on physiological targets. Thus, both experimental approaches suggest that thiamine selectively alters RNS. Additional experiments are required to determine whether diminished thiamine availability promotes oxidative stress in AD or whether the oxidative stress in AD brain diminishes thiamine availability to thiamine dependent processes.

Effect of uncoupling endothelial nitric oxide synthase on calcium homeostasis in aged porcine endothelial cells

AIMS

The requirement of endothelial NO synthase (NOS3) calcium to produce NO is well described, although the effect of NO on intracellular calcium levels [Ca(2+)](i) is still confusing. Therefore, NO and [Ca(2+)](i) cross-talk were studied in parallel in endothelial cells possessing a functional or a dysfunctional NO pathway.

METHODS AND RESULTS

Dysfunctional porcine endothelial cells were obtained either in vitro by successive passages or in vivo from regenerated endothelium 1 month after coronary angioplasty. Activity of NOS3 was characterized by conversion of arginine to citrulline, BH(4) intracellular availability, cGMP, and superoxide anion production. Imaging of the Ca(2+) indicator FURA 2-AM was recorded and sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) pump activity was analysed by (45)Ca(2+) uptake into cells. In endothelial cells with a functional NO pathway, NOS3 inhibition increased [Ca(2+)](i) and, conversely, an NO donor decreased it. In aged cells with an uncoupled NOS3 as shown by the reduced BH(4) level, the increase in superoxide anion and the lower production of cGMP and the decrease in NO bioavailability were linearly correlated with the increase in basal [Ca(2+)](i). Moreover, when stimulated by bradykinin, the calcium response was reduced while its decay was slowed down. These effects on the calcium signalling were abolished in calcium-free buffer and were similarly induced by SERCA inhibitors. In aged cells, NO improved the reduced SERCA activity and tended to normalize the agonist calcium response.

CONCLUSION

In control endothelial cells, NO exerts a negative feedback on cytosolic Ca(2+) homeostasis. In aged cells, uncoupled NOS3 produced NO that was insufficient to control the [Ca(2+)](i). Consequently, under resting conditions, SERCA activity decreased and [Ca(2+)](i) increased. These alterations were reversible as exogenous NO, in a cGMP-independent way, refilled intracellular calcium stores, reduced calcium influx, and improved the agonist-evoked calcium response. Therefore, prevention of the decrease in NO in dysfunctional endothelium would normalize the calcium-dependent functions.

Mitochondria and Ca(2+) signaling: old guests, new functions

Mitochondria are ancient endosymbiotic guests that joined the cells in the evolution of complex life. While the unique ability of mitochondria to produce adenosine triphosphate (ATP) and their contribution to cellular nutrition metabolism received condign attention, our understanding of the organelle's contribution to Ca(2+) homeostasis was restricted to serve as passive Ca(2+) sinks that accumulate Ca(2+) along the organelle's negative membrane potential. This paradigm has changed radically. Nowadays, mitochondria are known to respond to environmental Ca(2+) and to contribute actively to the regulation of spatial and temporal patterns of intracellular Ca(2+) signaling. Accordingly, mitochondria contribute to many signal transduction pathways and are actively involved in the maintenance of capacitative Ca(2+) entry, the accomplishment of Ca(2+) refilling of the endoplasmic reticulum and Ca(2+)-dependent protein folding. Mitochondrial Ca(2+) homeostasis is complex and regulated by numerous, so far, genetically unidentified Ca(2+) channels, pumps and exchangers that concertedly accomplish the organelle's Ca(2+) demand. Notably, mitochondrial Ca(2+) homeostasis and functions are crucially influenced by the organelle's structural organization and motility that, in turn, is controlled by matrix/cytosolic Ca(2+). This review intends to provide a condensed overview on the molecular mechanisms of mitochondrial Ca(2+) homeostasis (uptake, buffering and storage, extrusion), its modulation by other ions, kinases and small molecules, and its contribution to cellular processes as fundamental basis for the organelle's contribution to signaling pathways. Hence, emphasis is given to the structure-to-function and mobility-to-function relationship of the mitochondria and, thereby, bridging our most recent knowledge on mitochondria with the best-established mitochondrial function: metabolism and ATP production.

Ferulic acid with ascorbic acid synergistically extenuates the mitochondrial dysfunction during beta-adrenergic catecholamine induced cardiotoxicity in rats

Disruption of mitochondria and free radical mediated tissue injury have been reported during cardiotoxicity induced by isoproterenol (ISO), a beta-adrenergic catecholamine. The present study was designed to investigate the effect of the combination of ferulic acid (FA) and ascorbic acid (AA) on the mitochondrial damage in ISO induced cardiotoxicity. Induction of rats with ISO (150 mg/kg b.wt., i.p.) for 2 days resulted in a significant decrease in the activities of respiratory chain enzymes (NADH dehydrogenase and cytochrome c-oxidase), tricarboxylic acid cycle enzymes (isocitrate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, alpha-ketoglutarate dehydrogenase), mitochondrial antioxidants (GPx, GST, SOD, CAT, GSH), cytochromes (b, c, c1, aa3) and in the level of mitochondrial phospholipids. A marked elevation in mitochondrial lipid peroxidation, mitochondrial levels of cholesterol, triglycerides and free fatty acids were also observed in ISO intoxicated rats. Pre-co-treatment with the combination of FA (20 mg/kg b.wt.) and AA (80 mg/kg b.wt.) orally for 6 days significantly enhanced the attenuation of these functional abnormalities and restored normal mitochondrial function when compared to individual drug treated groups. Mitigation of ISO induced biochemical and morphological changes in mitochondria were more pronounced with a combination of FA and AA rather than the individual drug treated groups. Transmission electron microscopic observations also correlated with these biochemical parameters. Hence, these findings demonstrate the synergistic ameliorative potential of FA and AA on mitochondrial function during beta-adrenergic catecholamine induced cardiotoxicity and associated oxidative stress in rats.

Synergistic salubrious effect of ferulic acid and ascorbic acid on membrane-bound phosphatases and lysosomal hydrolases during experimental myocardial infarction in rats

Altered membrane integrity has been suggested as a major factor in the development of cellular injury during myocardial necrosis. The present study was designed to investigate the effect of the combination of ferulic acid (FA) and ascorbic acid (AA) on lysosomal hydrolases and membrane-bound phosphatases during isoproterenol (ISO) induced myocardial necrosis in rats. Induction of rats with 1SO (150 mg/kg b.wt, i.p.) for 2 days resulted in a significant increase in the activities of lysosomal hydrolases (beta-D-glucuronidase, beta-D-galactosidase, beta-D-N-acetylglucosaminidase, acid phosphatase and cathepsin-D) in the heart and serum. A significant increase in plasma lactate level, cardiac levels of sodium, calcium and a decrease in cardiac level of potassium was also observed, which was paralleled by abnormal activities of membrane-bound phosphatases (Na(+)-K(+) ATPase, Ca(2+) ATPase and Mg(2+) ATPase) in the heart of ISO-administered rats. Pre-co-treatment with the combination of FA (20 mg/kg b.wt) and AA (80 mg/kg b.wt) orally for 6 days significantly attenuated these abnormalities and restored the levels to near normalcy when compared to individual drug treated groups. The combination of FA and AA preserved the membrane integrity by mitigating the oxidative stress and associated cellular damage more effectively when compared to individual treatment groups. In our study, the protection conferred by FA and AA might be through the nitric oxide pathway and by their ability of quenching free radicals. In conclusion, these findings indicate the synergistic modulation of lysosomal hydrolases and membrane phosphatases by the combination of FA and AA.

Differential gel electrophoresis and transgenic mitochondrial calcium reporters demonstrate spatiotemporal filtering in calcium control of mitochondria

Mitochondria must adjust both their intracellular location and their metabolism in order to balance their output to the needs of the cell. Here we show by the proteomic technique of time series difference gel electrophoresis that a major result of neuroendocrine stimulation of the Drosophila renal tubule is an extensive remodeling of the mitochondrial matrix. By generating Drosophila that were transgenic for both luminescent and fluorescent mitochondrial calcium reporters, it was shown that mitochondrial calcium tracked the slow (minutes) but not the rapid (<1 s) changes in cytoplasmic calcium and that this resulted in both increased mitochondrial membrane polarization and elevated cellular ATP levels. The selective V-ATPase inhibitor, bafilomycin, further enhanced ATP levels, suggesting that the apical plasma membrane V-ATPase is a major consumer of ATP. Both the mitochondrial calcium signal and the increase in ATP were abolished by the mitochondrial calcium uniporter blocker Ru360. By using both mitochondrial calcium imaging and the potential sensing dye JC-1, the apical mitochondria of principal cells were found to be selectively responsive to neuropeptide signaling. As the ultimate target is the V-ATPase in the apical plasma membrane, this selective activation of mitochondria is clearly adaptive. The results highlight the dynamic nature and both spatial and temporal heterogeneity of calcium signaling possible in differentiated, organotypic cells and provide a new model for neuroendocrine control of V-ATPase.

GEA3162, a nitric oxide-releasing agent, activates non-store-operated Ca2+ entry and inhibits store-operated Ca2+ entry pathways in neutrophils through thiol oxidation

We demonstrated that 5-amino-3-(3,4-dichlorophenyl)1,2,3,4-oxatriazolium (GEA3162), a nitric oxide (NO)-releasing agent, stimulated [Ca2+]i rise in rat neutrophils. This Ca2+ response was prevented by the thiol reducing agents, 2-mercaptoethanol, N-acetyl-L-cysteine, dithiothreitol, 2,3-dimercaptopropane-1-sulfonic acid (DMPS) and tris-(2-carboxyethyl)phosphine (TCEP), but slightly reduced by the antioxidant, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox). GEA3162 also increased the formation of cellular reactive oxygen intermediates and decreased the cellular content of low molecular thiols. These responses were greatly reduced by Trolox, dithiothreitol and N-acetyl-L-cysteine. GEA3162 stimulated the protein tyrosine phosphorylation in neutrophils. The [Ca2+]i rise caused by formyl-Met-Leu-Phe (fMLP) and cyclopiazonic acid (CPA) was suppressed by GEA3162. TCEP prevented the inhibition of fMLP-induced [Ca2+]i rise by GEA3162. In the absence of external Ca2+, GEA3162 inhibited the CPA-induced [Ca2+]i rise, whereas it only slightly affected the fMLP-induced mobilization of the Ca2+ store. Application of GEA3162 after the stimulation with fMLP or CPA suppressed the robust Ca2+ entry followed by the readdition of Ca2+ into medium. Moreover, the Ca2+ entry was more susceptible to inhibition by treatment with GEA3162 prior to than after the fMLP stimulation. GEA3162 had no effect on the mitochondrial membrane potential. GEA3162 induced actin reorganization and condensed filament network at the cell periphery. These results indicate that GEA3162 exerted both the stimulation of Ca2+ entry and the inhibition of the store-operated Ca2+ entry in rat neutrophils. The dual effects of GEA3162 on the regulation of the external Ca2+ entry are mainly through the thiol modification of target protein(s) residing on the outside of the plasma membrane.

Effects of nitric oxide donors on cybrids harbouring the mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) A3243G mitochondrial DNA mutation

Reactive nitrogen and oxygen species (O2*-, H2O2, NO* and ONOO-) have been strongly implicated in the pathophysiology of neurodegenerative and mitochondrial diseases. In the present study, we examined the effects of nitrosative and/or nitrative stress generated by DETA-NO {(Z)-1-[2-aminoethyl-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate}, SIN-1 (3-morpholinosydnonimine hydrochloride) and SNP (sodium nitroprusside) on U87MG glioblastoma cybrids carrying wt (wild-type) and mutant [A3243G (Ala3243-->Gly)] mtDNA (mitochondrial genome) from a patient suffering from MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes). The mutant cybrids had reduced activity of cytochrome c oxidase, significantly lower ATP level and decreased mitochondrial membrane potential. However, endogenous levels of reactive oxygen species were very similar in all cybrids regardless of whether they carried the mtDNA defects or not. Furthermore, the cybrids were insensitive to the nitrosative and/or nitrative stress produced by either DETA-NO or SIN-1 alone. Cytotoxicity, however, was observed in response to SNP treatment and a combination of SIN-1 and glucose-deprivation. The mutant cybrids were significantly more sensitive to these insults compared with the wt controls. Ultrastructural examination of dying cells revealed several characteristic features of autophagic cell death. We concluded that nitrosative and/or nitrative stress alone were insufficient to trigger cytotoxicity in these cells, but cell death was observed with a combination of metabolic and nitrative stress. The vulnerability of the cybrids to these types of injury correlated with the cellular energy status, which were compromised by the MELAS mutation.

Capsaicin stimulates the non-store-operated Ca2+ entry but inhibits the store-operated Ca2+ entry in neutrophils

Rat neutrophils express the mRNA encoding for transient receptor potential (TRP) V1. However, capsaicin-stimulated [Ca2+]i elevation occurred only at high concentrations (> or = 100 microM). This response was substantially decreased in a Ca2+-free medium. Vanilloids displayed similar patterns of Ca2+ response with the rank order of potency as follows: scutigeral>resiniferatoxin>capsazepine>capsaicin=olvanil>isovelleral. Arachidonyl dopamine (AAD), an endogenous ligand for TRPV1, failed to desensitize the subsequent capsaicin challenge. Capsaicin-induced Ca2+ response was not affected by 8-bromo-cyclic ADP-ribose (8-Br-cADPR), the ryanodine receptor blocker, but was slightly attenuated by 1-[6-[17beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U-73122), the inhibitor of phospholipase C-coupled processes, 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole (SKF-96365), the blocker of receptor-gated and store-operated Ca2+ (SOC) channels, 2-aminoethyldiphenyl borate (2-APB), the blocker of D-myo-inositol 1,4,5-trisphospahte (IP3) receptor and Ca2+ influx, and by ruthenium red, a blocker of TRPV channels, and enhanced by the Ca2+ channels blocker, cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL-12330A) and Na+-deprivation. In addition, capsaicin had no effect on the plasma membrane Ca2+-ATPase activity or the production of nitric oxide (NO) and reactive oxygen intermediates (ROI) or on the total thiols content. Capsaicin (> or = 100 microM) inhibited the cyclopiazonic acid (CPA)-induced store-operated Ca2+ entry (SOCE). In the absence of external Ca2+, the robust Ca2+ entry after subsequent addition of Ca2+ was decreased by capsaicin in CPA-activated cells. Capsaicin alone increased the actin cytoskeleton, and also increased the actin filament content in cell activation with CPA. These results indicate that capsaicin activates a TRPV1-independent non-SOCE pathway in neutrophils. The reorganization of the actin cytoskeleton is probably involved in the capsaicin inhibition of SOCE.

Topics on the Na+/Ca2+ Exchanger: Responses of Na+/Ca2+ Exchanger to Interferon-γ and Nitric Oxide in Cultured Microglia

The Na(+)/Ca(2+) exchanger (NCX) plays a role in regulation of intracellular Ca(2+) levels, but little is known about the functional role of NCX in microglia. To clarify the role of NCX in microglia, we studied the responses of NCX to pathological conditions such as interferon-gamma or nitric oxide (NO) exposure. Treatment with interferon-gamma caused a biphasic increase in NCX activity. The delayed increase in NCX activity was accompanied by increases in the mRNA and protein levels. Pharmacological studies show that protein kinase C and tyrosine kinase are involved in the transient and delayed increases in NCX activity, and the extracellular signal-regulated protein kinase is involved in the delayed increase in NCX activity. On the other hand, NO causes apoptotic cell death in cultured microglia. We observed, using the specific NCX inhibitor SEA0400, that NO activates NCX activity and NCX is involved in NO-induced depletion of Ca(2+) in the endoplasmic reticulum (ER), leading to ER stress. These results suggest that NCX is involved in the regulation of Ca(2+) levels in the ER. The responses of NCX to interferon-gamma and NO implies that NCX plays a key role in microglial function.

Cell proliferation depends on mitochondrial Ca2+ uptake: inhibition by salicylate

Store-operated Ca2+ entry (SOCE) is a ubiquitous Ca2+ influx pathway involved in control of multiple cellular and physiological processes including cell proliferation. Recent evidence has shown that SOCE depends critically on mitochondrial sinking of entering Ca2+ to avoid Ca2+-dependent inactivation. Thus, a role of mitochondria in control of cell proliferation could be anticipated. We show here that activation of SOCE induces cytosolic high [Ca2+] domains that are large enough to be sensed and avidly taken up by a pool of nearby mitochondria. Prevention of mitochondrial clearance of the entering Ca2+ inhibited both SOCE and cell proliferation in several cell types including Jurkat and human colon cancer cells. In addition, we find that therapeutic concentrations of salicylate, the major metabolite of aspirin, depolarize partially mitochondria and inhibit mitochondrial Ca2+ uptake, as revealed by mitochondrial Ca2+ measurements with targeted aequorins. This salicylate-induced inhibition of mitochondrial Ca2+ sinking prevented SOCE and impaired cell growth of Jurkat and human colon cancer cells. Finally, direct blockade of SOCE by the pyrazole derivative BTP-2 was sufficient to arrest cell growth. Taken together, our results reveal that cell proliferation depends critically on mitochondrial Ca2+ uptake and suggest that inhibition of tumour cell proliferation by salicylate may be due to interference with mitochondrial Ca2+ uptake, which is essential for sustaining SOCE. This novel mechanism may contribute to explaining the reported anti-proliferative and anti-tumoral actions of aspirin and dietary salicylates.

Modulatory role of lotus-seed milk fermented product on gastrointestinal motility and absorption in mice

AIM: To explore the modulatory role of lotus-seed milk fermented product (LMFP) on gastrointestinal motility and absorption function in mice.

METHODS: Mice were divided into groups by the ran-domized complete weight-block design and treated with distilled water, different drugs and different conc-entrations of LMFP accordingly. L-arginine was intrape-ritoneally injected into the mice to observe the state of gastric emptying, small intestinal propelling, and the nitric oxide (NO) concentration in gastric homogenate; Compound Diphenoxylate was used to establish the mouse model of constipation, and the time, weight, quantity and the water content of black feces were measured; Reserpine was subcutaneously injected into the mice to calculate the small intestinal propellant rate and the content of uric xylose.

RESULTS: The delay of gastric emptying was positive-ly correlated with the NO concentration (r = 0.475, P = 0.001). As compared with those in the l-arginine model group, the volumns of phenol red leaving in the stomach of 250, 500 mL/L LMFP groups and Dom-peridone group were significantly decreased (22.78±6.95%, 27.12±5.73%, 22.82±5.63% vs 34.76±9.15%, P<0.05) and the NO concentration of gastric homogenate in 250 mL/L LMFP group and Domperido-ne group were lower (26.13±4.95 µmol/g pro, 26.33±4.06 µmol/g pro vs 38.33±9.82 µmol/g pro, P<0.05). The volumns of phenol red leaving in the distal 3 small intestinal segments of 500 mL/L, 750 mL/L LMFP group and Domperidone group were markedly higher, and the volumns leaving in the distal 4 small intestinal segments in 750 mL/L LMFP group and Domperidone group were also notably increased (P<0.05), in comparison with those in the model group. The time of black feces excreted was reduced and the water content of the feces were significantly increased in 250, 500, 750 mL/L LMFP groups than those in the model group (133.63±18.28, 113.25±26.25, 141.75±25.95 min vs 175.50±24.04 min, P<0.05). The weights of black feces in 250 and 500 mL/L LMFP groups were increased than those in the model group (0.68±0.16, 0.82±0.23 g vs 0.37±0.13 g, P<0.05). As compared with that in the reserpine model group, the propellant rate of powdered charcoal in pure LMFP (1 000 mL/L) group was lower (79.93±14.52% vs 97.64±5.68%, P = 0.002), while the uric xylose level in 500 mL/L, pure LMFP group were higher (10.54±2.48, 12.24±2.15 mg vs 7.86±1.71 mg, P<0.05).

CONCLUSION: LMFP regulate can regulate the gastr-ointestinal motility in a bidirectional way, and it can ease the constipation and improve the absorption function of small intestine.

Distinct effects of N-ethylmaleimide on formyl peptide- and cyclopiazonic acid-induced Ca2+ signals through thiol modification in neutrophils

In this study, we demonstrate that N-ethylmaleimide (NEM), a cell permeable thiol-alkylating agent, enhanced the [Ca2+]i rise caused by stimulation with cyclopiazonic acid (CPA), a sarcoplasmic-endoplasmic reticulum Ca2+-ATPase inhibitor, in rat neutrophils. In addition, NEM attenuated the formyl-Met-Leu-Phe (fMLP)-induced [Ca2+]i rise whether NEM was added to cells prior to or after fMLP stimulation. Moreover, application of NEM after fMLP activation in the absence of external Ca2+ inhibited the Ca2+ signal upon addition of Ca2+ to the medium. Similar patterns were also obtained by using 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), a cell impermeable dithiol-oxidizing agent, which replaced NEM in the CPA- and fMLP-induced [Ca2+]i rise experiments. Treatment with dithiothreitol (DTT), a cell permeable dithiol-reducing agent, N-acetyl-l-cysteine (NAC), a cell permeable monothiol-reducing agent, and tris-(2-carboxyethyl)phosphine (TCEP), a cell impermeable reductant without a thiol group, all rescued the fMLP-induced Ca2+ signal from NEM. Rat neutrophils express the mRNA encoding for transient receptor potential (TRP) C6, inositol trisphosphate receptor (IP3R) 2 and IP3R3. NEM had no effect on the mitochondrial membrane potential. NEM could restore the polarization and F-actin accumulation of fMLP-treated cells to those of the control. In the absence of external Ca2+, NEM rendered the CPA-induced [Ca2+]i elevation persistently but inhibited the fMLP-induced Ca2+ spike, which was reversed by tris-(2-cyanoethyl)phosphine (TCP), a cell permeable reductant without a thiol group. DTNB did not affect the Ca2+ spike caused by fMLP. These results indicate that through protein thiol oxidation, NEM affects the receptor-activated and the store depletion-derived Ca2+ signals in an opposing manner.

Modulation of mitochondrial Ca2+ by nitric oxide in cultured bovine vascular endothelial cells

In the present study, we used laser scanning confocal microscopy in combination with fluorescent indicator dyes to investigate the effects of nitric oxide (NO) produced endogenously by stimulation of the mitochondria-specific NO synthase (mtNOS) or applied exogenously through a NO donor, on mitochondrial Ca2+ uptake, membrane potential, and gating of mitochondrial permeability transition pore (PTP) in permeabilized cultured calf pulmonary artery endothelial (CPAE) cells. Higher concentrations (100–500 μM) of the NO donor spermine NONOate (Sper/NO) significantly reduced mitochondrial Ca2+ uptake and Ca2+ extrusion rates, whereas low concentrations of Sper/NO (<100 μM) had no effect on mitochondrial Ca2+ levels ([Ca2+]mt). Stimulation of mitochondrial NO production by incubating cells with 1 mM l-arginine also decreased mitochondrial Ca2+ uptake, whereas inhibition of mtNOS with 10 μM l- N5-(1-iminoethyl)ornithine resulted in a significant increase of [Ca2+]mt. Sper/NO application caused a dose-dependent sustained mitochondrial depolarization as revealed with the voltage-sensitive dye tetramethylrhodamine ethyl ester (TMRE). Blocking mtNOS hyperpolarized basal mitochondrial membrane potential and partially prevented Ca2+-induced decrease in TMRE fluorescence. Higher concentrations of Sper/NO (100–500 μM) induced PTP opening, whereas lower concentrations (<100 μM) had no effect. The data demonstrate that in calf pulmonary artery endothelial cells, stimulation of mitochondrial Ca2+ uptake can activate NO production in mitochondria that in turn can modulate mitochondrial Ca2+ uptake and efflux, demonstrating a negative feedback regulation. This mechanism may be particularly important to protect against mitochondrial Ca2+ overload under pathological conditions where cellular [NO] can reach very high levels.

Oral L-arginine supplementation ameliorates urinary risk factors and kinetic modulation of Tamm-Horsfall glycoprotein in experimental hyperoxaluric rats

BACKGROUND

Oral supplementation of l-arginine (l-arg) is found to be beneficial in many kidney disorders. We determined whether l-arg supplementation safeguards the renal epithelial cell damage induced by hyperoxaluria with excretion of urinary marker enzymes and lithogenic salts with special reference to Tamm-Horsfall glycoprotein (THP).

METHODS

Hyperoxaluria was induced by 0.75% ethylene glycol (EG) in drinking water. l-Arg was co-supplemented at the dose of 1.25 g/kg b.w. orally for 28 days. At the end of experimental period, 24-h urine samples were collected in all the experimental groups. Isolation and purification of THP was carried in rat urine and were subjected to spectrophotometric crystallization assay and calcium-(14)C-oxalate binding studies. Determination of the lithogenic risk factors like calcium, oxalate, phosphorus, citrate, and marker enzymes such as lactate dehydrogenase (LDH) and gamma-glutamyltransferase (gamma-GT) were carried out in the collected urine sample.

RESULTS

Urinary excretion of calcium and oxalate was significantly increased in EG-treated rats. In l-arg supplemented hyperoxaluric rats, these concentrations were significantly (p<0.001) decreased when compared to that of hyperoxaluric rats, and were moderately elevated from that of control rats. The activities of urinary marker enzymes, both LDH and gamma-GT were 2-fold increased in EG-treated rats, when compared to control rats, but these values were maintained near normal in l-arg supplemented EG-treated rats. Citrate excretion was enhanced in the l-arg co-supplemented hyperoxaluric rats. In spectrophotometric crystallization assay system, l-arg supplemented rat THP showed inhibition in nucleation and aggregation phases, whereas EG-treated rat THP showed promotion of both calcium oxalate nucleation and aggregation phases. In calcium-(14)C-oxalate binding assay, THP derived from hyperoxaluric rats exhibited 2-fold increase (p<0.001) in the Ca*Ox binding when compared to control and l-arg supplemented animals.

CONCLUSIONS

l-Arg could act as a potent antilithic agent, by increasing the level of citrate in the hyperoxaluria-induced rats and decreasing calcium oxalate binding to the THP. l-Arg also effectively prevents the deposition of calcium oxalate crystals by curtailing the renal epithelial damage and protein oxidation as evidenced by the normal activities of urinary marker enzymes in l-arg supplemented hyperoxaluric rats.

SEA0400, a specific inhibitor of the Na+-Ca2+ exchanger, attenuates sodium nitroprusside-induced apoptosis in cultured rat microglia

1. Using SEA0400, a potent and selective inhibitor of the Na+-Ca2+ exchanger (NCX), we examined whether NCX is involved in nitric oxide (NO)-induced disturbance of endoplasmic reticulum (ER) Ca2+ homeostasis followed by apoptosis in cultured rat microglia. 2. Sodium nitroprusside (SNP), an NO donor, decreased cell viability in a dose- and time-dependent manner with apoptotic cell death in cultured microglia. 3. Treatment with SNP decreased the ER Ca2+ levels as evaluated by measuring the increase in cytosolic Ca2+ level induced by exposing cells to thapsigargin, an irreversible inhibitor of ER Ca2+-ATPase. 4. The treatment with SNP also increased mRNA expression of CHOP and GPR78, makers of ER stress. 5. SEA0400 at 0.3-1.0 microM protected microglia against SNP-induced apoptosis. 6. SEA0400 blocked not only the SNP-induced decrease in ER Ca2+ levels but also SNP-induced increase in CHOP and GRP78 mRNAs. 7. SEA0400 did not affect capacitative Ca2+ entry in the presence and absence of SNP. 8. SNP increased Na+-dependent 45Ca2+ uptake and this increase was blocked by SEA0400. 9. These results suggest that SNP induces apoptosis via the ER stress pathway and SEA0400 attenuates SNP-induced apoptosis via suppression of the ER stress in cultured microglia. Our findings imply that NCX plays a role in ER Ca2+ depletion under pathological conditions.

A potential role for extracellular nitric oxide generation in cGMP-independent inhibition of human platelet aggregation: biochemical and pharmacological considerations

1. Nitric oxide (NO) is a potent inhibitor of platelet activation, that inhibits the agonist-induced increase in cytosolic Ca2+ concentration through both cGMP-dependent and independent pathways. However, the NO-related (NOx) species responsible for cGMP-independent signalling in platelets is unclear. We tested the hypothesis that extracellular NO, but not NO+ or peroxynitrite, generated in the extracellular compartment is responsible for cGMP-independent inhibition of platelet activation via inhibition of Ca2+ signalling. 2. Concentration-response curves for diethylamine diazeniumdiolate (DEA/NO; a spontaneous NO generator), S-nitroso-N-valerylpenicillamine (SNVP; an S-nitrosothiol) and 3-morpholinosydnonomine (SIN-1; a peroxynitrite generator) were generated in platelet-rich plasma (PRP) and washed platelets (WP) in the presence and absence of a supramaximal concentration of the soluble guanylate cyclase inhibitor, ODQ (20 microM). All three NOx donors displayed cGMP-independent inhibition of platelet aggregation in PRP, but only DEA/NO exhibited cGMP-independent inhibition of aggregation in WP. 3. Analysis of NO generation using an isolated NO-electrode revealed that cGMP-independent effects coincided with the generation of substantial levels of extracellular NO (>40 nM) from the NOx donors. 4. Reconstitution of WP with plasma factors indicated that the copper-containing plasma protein, caeruloplasmin (CP), catalysed the release of NO from SNVP, while Cu/Zn superoxide dismutase (SOD) unmasked NO generated from SIN-1. The increased generation of extracellular NO correlated with a switch to cGMP-independent effects with both NOx donors. 5. Analysis of Fura-2 loaded WP revealed that only DEA/NO inhibited Ca2+ signalling in platelets via a cGMP-independent mechanism. However, preincubation of SNVP and SIN-1 with CP and SOD, respectively, induced cGMP-independent inhibition of intraplatelet Ca2+ trafficking by the NOx donors. 6. Taken together, our data suggest that extracellular NO (>40 nM) is required for cGMP-independent inhibition of platelet activation. Plasma constituents may play an important pharmacological role in activating cGMP-independent signalling by S-nitrosothiols or peroxynitrite generators.

The blockade of cyclopiazonic acid-induced store-operated Ca2+ entry pathway by YC-1 in neutrophils

In the presence of external Ca2+, pretreatment of neutrophils with 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) inhibited the cyclopiazonic acid (CPA)-induced [Ca2+](i) elevation in a concentration- but not a time-dependent manner, while YC-1 had no effect on the Ca2+ signals in a Ca2+-free medium. YC-1 failed to inhibit ATP- and interleukin-8 (IL-8)-induced [Ca2+](i) changes. Addition of YC-1 after cell activation strongly inhibited the CPA-induced [Ca2+](i) changes. In a classical Ca2+ readdition protocol, a similar extent inhibition of Ca2+ spike by YC-1 introduced either prior to or after CPA stimulation was obtained. In rat neutrophils, mRNA for endothelial differentiation gene (edg)1, edg5, edg6 and edg8, the putative targets for sphingosine 1-phosphate (S1P), could be detected. However, S1P was found to have little effect on Ca(2+) signals. YC-1 did not inhibit but enhanced the sphingosine-induced [Ca2+](i) changes. Inhibition by YC-1 of CPA-induced [Ca2+](i) changes was not prevented by 7-nitroindazole and N-(3-aminomethyl)benzylacetamidine (1400W), two nitric oxide synthase (NOS) inhibitors, by aristolochic acid, a phospholipase A(2) inhibitor, or by suspension in a Na(+)-deprived medium. YC-1 did not affect the mitochondrial membrane potential. Moreover, YC-1 did not alter [Ca2+](i) changes in response to ionomycin after CPA and formyl-Met-Leu-Phe (fMLP) stimulation in a Ca2+-free medium. YC-1 had no effect on the basal [Ca2+](i) level, the pharmacologically isolated plasma membrane Ca2+-ATPase activity, and Ba2+ entry into CPA-activated cells. YC-1 alone resulted in the accumulation of actin filaments in neutrophils, while significantly reduced the intensity of actin filament staining in the subsequent activation with CPA. These results indicate that YC-1 inhibited CPA-activated store-operated Ca2+ entry (SOCE) probably through the direct blockade of channel activation and/or the disruption of the integrity of the actin cytoskeleton necessary for supporting Ca2+ entry pathway in neutrophils.

Calcium channels, transporters and exchangers in placenta: a review

Calcium (Ca2+) entry in cells is crucial for development and physiology of virtually all cell types. It acts as an intracellular (second) messenger to regulate a diverse array of cellular functions, from cell division and differentiation to cell death. Among candidates for Ca2+ entry in cells are-voltage-dependant Ca2+ channels (VDCCs), transient receptor potential (TRP)-related Ca2+ channels and store-operated Ca2+ (SOC) channels. Plasma membrane Ca2+-ATPases (PMCA) and Na+/Ca2+ exchanger (NCX) are mainly responsible for Ca2+ extrusion. These different Ca2+channels/transporters and exchangers exhibit specific distribution and physiological properties. During pregnancy, the syncytiotrophoblast layer of the human placenta transfers as much as 30 g of Ca2+ from the mother to the fetus, especially in late gestation where Ca2+ transport through different channels must increase in response to the demands of accelerating bone mineralization of the fetus. The identification and characterization of the different Ca2+ channels/transporters and exchangers on the brush-border membrane (BBM) facing the maternal circulation, and the basal plasma membrane (BPM) facing the fetal circulation; placental membrane of the syncytiotrophoblasts have been the focus of numerous studies. This review discusses current views in this field regarding localization and functions during transcellular Ca2+ entry and extrusion from cells particularly in the placenta.

Stimulation of cellular free Ca2+ elevation and inhibition of store-operated Ca2+ entry by kazinol B in neutrophils

Kazinol B, a natural isoprenylated flavan, stimulated the [Ca(2+)](i) elevation in the presence or absence of Ca(2+) in the medium. Treatment with chymotrypsin or phorbol 12-myristate 13-acetate to shedding of L: -selectin had no effect on subsequent kazinol B-induced Ca(2+) response. Upon initial cyclopiazonic acid (CPA) treatment in the absence of external Ca(2+), the subsequent [Ca(2+)](i) rise followed by challenge with kazinol B was greatly diminished. The ryanodine receptor blockers, 8-bromo-cyclic ADP-ribose and ruthenium red did not affect kazinol B-evoked Ca(2+) release from internal stores. However, the inhibitors of sphingosine kinase, dimethylsphingosine, but not dihydrosphingosine, inhibited kazinol B-induced Ca(2+) release. Kazinol B-induced [Ca(2+)](i) rise was not affected by two nitric oxidase inhibitors, N-(3-aminomethyl)benzylacetamidine (1400W) and 7-nitroindazole, cytochalasin B and Na(+)-deprivation. This response was slightly attenuated by 2-aminoethyldiphenyl borate (2-APB), a D: -myo-inositol 1,4,5-trisphosphate (IP(3)) receptor blocker, and by genistein, a general tyrosine kinase inhibitor. However, the Ca(2+) response was greatly diminished by two actin filament reorganizers, calyculin A and jasplakinolide, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY 294002), an inhibitor of phosphoinositide 3-kinase, N-(3-aminomethyl)benzylacetamidine (SB 203580), the p38 mitogen-activated protein kinase inhibitor, 1-[6-[17beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U-73122), the inhibitor of phospholipase C-coupled processes, and by 0.3 mM La(3+) or Ni(2+). Kazinol B did not evoke any appreciable Ba(2+) and Sr(2+) entry into cells. The Ca(2+) entry blockers, 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole (SKF-96365), but not cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL-12,330A), inhibited a kazinol B-induced [Ca(2+)](i) rise. Kazinol B had no effect on the pharmacologically isolated plasma membrane Ca(2+)-ATPase activity. In a Ca(2+)-free medium, kazinol B inhibited the subsequent Ca(2+) addition, resulting in robust entry in CPA- and formyl peptide-activated cells. Kazinol B produced a concentration-dependent reduction in the mitochondrial membrane potential. These results indicate that kazinol B stimulates Ca(2+) release from internal Ca(2+) store, probably through the sphingosine 1-phosphate and IP(3) signaling, and activates external Ca(2+) influx mainly through a non-store-operated Ca(2+) entry (non-SOCE) pathway. Inhibition of SOCE by kazinol B is probably attributable to a break in the Ca(2+) driven force of mitochondria.

2-Benzyloxybenzaldehyde inhibits formyl peptide-stimulated increase in intracellular Ca2+ in neutrophils mainly by blocking Ca2+ entry

2-Benzyloxybenzaldehyde (CCY1a) inhibited the formyl-Met-Leu-Phe (fMLP)-induced elevation of cytosolic [Ca(2+)]() ([Ca(2+)](i)) in rat neutrophils. The late plateau phase, but not the initial Ca(2+) spike, of the fMLP-induced [Ca(2+)](i) change was inhibited by CCY1a. In the absence of external Ca(2+), CCY1a had no appreciable effect on either the fMLP- or cyclopiazonic acid (CPA)-induced [Ca(2+)](i) elevation. CCY1a failed to inhibit [Ca(2+)](i) changes induced by N-ethylmaleimide, GEA3162, ionomycin or sphingosine, but slightly inhibited the Ca(2+) signals elicited by ATP or interleukin-8 (IL-8). In a classical Ca(2+) readdition protocol, addition of CCY1a after cell activation strongly inhibited the [Ca(2+)](i) response to fMLP, whilst that to CPA was only slightly reduced. CCY1a nearly abrogated the fMLP-stimulated Mn(2+) influx but was less effective on the CPA-induced response. CCY1a attenuated the levels of tyrosine-phosphorylated bands in the 70-85 kDa molecular mass range. CCY1a had no effect on the basal [Ca(2+)](i) level, the pharmacologically isolated plasma membrane Ca(2+)-ATPase activity or on the mitochondrial membrane potential. Thus, CCY1a blocks fMLP-induced Ca(2+) entry into neutrophils probably by blocking the relevant Ca(2+) channel directly or, alternatively, indirectly through the attenuation of tyrosine phosphorylation of some cellular proteins.

Signalling pathways in the nitric oxide donor-induced dopamine release in the striatum of freely moving rats: evidence that exogenous nitric oxide promotes Ca2+ entry through store-operated channels

We showed previously, using in vitro microdialysis, that the activation of the soluble guanylate cyclase (sGC)/cyclic GMP pathway was the underlying mechanism of the extracellular Ca(2+)-dependent effects of exogenous NO on dopamine (DA) secretion from PC12 cells. In this study, the co-infusion of the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3] quinoxalin-1-one (ODQ) failed to affect the NO donor 3-morpholinosydnonimine (SIN-1, 5.0 mM)-induced DA increase (sevenfold baseline) in dialysates from the striatum of freely moving rats. Ca(2+) omission from the perfusion fluid abolished baseline DA release but did not affect SIN-1-induced DA increases. The reintroduction of Ca(2+) in the perfusion fluid restored the baseline dialysate DA; however, when Ca(2+) reintroduction was associated with the infusion of either SIN-1 or the NO-donor S-nitrosoglutathione (SNOG), a sustained DA overflow was observed. DA overflow was selectively inhibited by the co-infusion of the store-operated channel blocker 2-aminoethoxydiphenyl borate. The chelation of intracellular Ca(2+) by co-infusing 1,2-bis (o-amino-phenoxy)ethane-N,N,N',N'-tetraacetic acid tetra (acetoxymethyl) ester (BAPTA-AM, 0.2 mM) greatly potentiated both SIN-1- and SNOG-induced increases in dialysate DA. BAPTA-AM-induced potentiation was inhibited by Ca(2+) omission. We conclude that the sGC/cyclic GMP pathway is not involved in the extracellular Ca(2+)-independent exogenous NO-induced striatal DA release; however, when intracellular Ca(2+) is either depleted (by Ca(2+) omission) or chelated (by BAPTA-AM co-infusion), exogenous NO does promote Ca(2+) entry, most likely through store-operated channels, with a consequent further increase in DA release.

Anandamide initiates Ca(2+) signaling via CB2 receptor linked to phospholipase C in calf pulmonary endothelial cells

The endocannabinoid anandamide has been reported to affect neuronal cells, immune cells and smooth muscle cells via either CB1 or CB2 receptors. In endothelial cells, the receptors involved in activating signal transduction are still unclear, despite the fact that anandamide is produced in this cell type. The present study was designed to explore in detail the effect of this endocannabinoid on Ca2+ signaling in single cells of a calf pulmonary endothelial cell line. Anandamide initiated a transient Ca2+ elevation that was prevented by the CB2 receptor antagonist SR144528, but not by the CB1 antagonist SR141716A. These data were confirmed by molecular identification of the bovine CB2 receptor in these endothelial cells by partial sequencing. The phospholipase C inhibitor 1-[6-[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5dione and the inositol 1,4,5-trisphosphate receptor antagonist 2-aminoethoxydiphenylborate prevented Ca2+ signaling in response to anandamide. Using an improved cameleon probe targeted to the endoplasmic reticulum (ER), fura-2 and ratiometric-pericam, which is targeted to the mitochondria, anandamide was found to induce Ca2+ depletion of the ER accompanied by the activation of capacitative Ca2+ entry (CCE) and a transient elevation of mitochondrial Ca2+. These data demonstrate that anandamide stimulates the endothelial cells used in this study via CB2 receptor-mediated activation of phospholipase C, formation of inositol 1,4,5-trisphosphate, Ca2+ release from the ER and subsequent activation of CCE. Moreover, the cytosolic Ca2+ elevation was accompanied by a transient Ca2+ increase in the mitochondria. Thus, in addition to its actions on smooth muscle cells, anandamide also acts as a powerful stimulus for endothelial cells.

Sustained Ca2+ transfer across mitochondria is Essential for mitochondrial Ca2+ buffering, sore-operated Ca2+ entry, and Ca2+ store refilling

Mitochondria have been found to sequester and release Ca2+ during cell stimulation with inositol 1,4,5-triphosphate-generating agonists, thereby generating subplasmalemmal microdomains of low Ca2+ that sustain activity of capacitative Ca2+ entry (CCE). Procedures that prevent mitochondrial Ca2+ uptake inhibit local Ca2+ buffering and CCE, but it is not clear whether Ca2+ has to transit through or remains trapped in the mitochondria. Thus, we analyzed the contribution of mitochondrial Ca2+ efflux on the ability of mitochondria to buffer subplasmalemmal Ca2+, to maintain CCE, and to facilitate endoplasmic reticulum (ER) refilling in endothelial cells. Upon the addition of histamine, the initial mitochondrial Ca2+ transient, monitored with ratio-metric-pericam-mitochondria, was largely independent of extracellular Ca2+. However, subsequent removal of extracellular Ca2+ produced a reversible decrease in [Ca2+]mito, indicating that Ca2+ was continuously taken up and released by mitochondria, although [Ca2+]mito had returned to basal levels. Accordingly, inhibition of the mitochondrial Na+/Ca2+ exchanger with CGP 37157 increased [Ca2+]mito and abolished the ability of mitochondria to buffer subplasmalemmal Ca2+, resulting in an increased activity of BKCa channels and a decrease in CCE. Hence, CGP 37157 also reversibly inhibited ER refilling during cell stimulation. These effects of CGP 37157 were mimicked if mitochondrial Ca2+ uptake was prevented with oligomycin/antimycin A. Thus, during cell stimulation a continuous Ca2+ flux through mitochondria underlies the ability of mitochondria to generate subplasmalemmal microdomains of low Ca2+, to facilitate CCE, and to relay Ca2+ from the plasma membrane to the ER.

Mitochondria efficiently buffer subplasmalemmal Ca2+ elevation during agonist stimulation

In endothelial cells, local Ca(2+) release from superficial endoplasmic reticulum (ER) activates BK(Ca) channels. The resulting hyperpolarization promotes capacitative Ca(2+) entry (CCE), which, unlike BK(Ca) channels, is inhibited by high Ca(2+). To understand how the coordinated activation of plasma membrane ion channels with opposite Ca(2+) sensitivity is orchestrated, the individual contribution of mitochondria and ER in regulation of subplasmalemmal Ca(2+) concentration ([Ca(2+)](pm)) was investigated. For organelle visualization, cells were transfected with DsRed and yellow cameleon targeted to mitochondria and ER. The patch pipette was placed far from any organelle (L1), close to ER (L3), or mitochondria (L2) and activity of BK(Ca) channels was used to estimate local [Ca(2+)](pm). Under standard patch conditions (130 mm K(+) in the bath), histamine increased [Ca(2+)](pm) at L1 and L3 to approximately 1.6 microm, whereas close to mitochondria [Ca(2+)](pm) remained unchanged. If mitochondria moved apart from the pipette or in the presence of carbonyl cyanide-4-trifluoromethoxyphenylhyrazone, [Ca(2+)](pm) at L2 increased in response to histamine. Under standard patch conditions Ca(2+) entry was negligible due to cell depolarization. Using a physiological patch approach (5.6 mm K(+) in the bath), changes in [Ca(2+)](pm) to histamine could be monitored without cell depolarization and, thus, in conditions where Ca(2+) entry occurred. Here, histamine induced an initial transient Ca(2+) elevation to > or =3.5 microm followed by a long lasting plateau at approximately 1.2 microm in L1 and L3, whereas mitochondria kept neighboring [Ca(2+)](pm) low during stimulation. Thus, superficial mitochondria and ER generate local domains of low and high Ca(2+) allowing simultaneous activation of BK(Ca) and CCE, despite their opposite Ca(2+) sensitivity.