Stress-induced dissociations between intracellular calcium signaling and insulin secretion in pancreatic islets

In healthy pancreatic islets, glucose-stimulated changes in intracellular calcium ([Ca²⁺]_i) provide a reasonable reflection of the patterns and relative amounts of insulin secretion. We report that [Ca²⁺]_i in islets under stress, however, dissociates with insulin release in different ways for different stressors. Islets were exposed for 48 h to a variety of stressors: cytokines (low-grade inflammation), 28 mM glucose (28G, glucotoxicity), free fatty acids (FFAs, lipotoxicity), thapsigargin (ER stress), or rotenone (mitochondrial stress). We then measured [Ca²⁺]_i and insulin release in parallel studies. Islets exposed to all stressors except rotenone displayed significantly elevated [Ca²⁺]_i in low glucose, however, increased insulin secretion was only observed for 28G due to increased nifedipine-sensitive calcium-channel flux. Following 3–11 mM glucose stimulation, all stressors substantially reduced the peak glucose-stimulated [Ca²⁺]_i response (first phase). Thapsigargin and cytokines also substantially impacted aspects of calcium influx and ER calcium handling. Stressors did not significantly impact insulin secretion in 11 mM glucose for any stressor, although FFAs showed a borderline reduction, which contributed to a significant decrease in the stimulation index (11:3 mM glucose) observed for FFAs and also for 28G. We also clamped [Ca²⁺]_i using 30 mM KCl + 250 μM diazoxide to test the amplifying pathway. Only rotenone-treated islets showed a robust increase in 3–11 mM glucose-stimulated insulin secretion under clamped conditions, suggesting that low-level mitochondrial stress might activate the metabolic amplifying pathway. We conclude that different stressors dissociate [Ca²⁺]_i from insulin secretion differently: ER stressors (thapsigargin, cytokines) primarily affect [Ca²⁺]_i but not conventional insulin secretion and ‘metabolic’ stressors (FFAs, 28G, rotenone) impacted insulin secretion.     

Application of fluorescent indicators to analyse intracellular calcium and morphology in filamentous fungi

A novel staining and quantification method to investigate changes in intracellular calcium levels [Ca²⁺]_i and morphology in filamentous fungus is presented. Using a simple protocol, two fluorescent dyes, Fluo-4-AM and Cell trace calcein red-orange-AM were loaded into the filamentous fungus Penicillium chrysogenum. The present study investigates the applicability of using Ca²⁺-sensitive dye to quantify and image [Ca²⁺]_i in P. chrysogenum cultures chosen for its potential as an experimental system to study Ca²⁺ signalling in elicited cultures. The dye loading was optimised and investigated at different pH loading conditions. It was observed that the fluorophore was taken up throughout the hyphae, retaining cell membrane integrity and no dye compartmentalisation within organelles was observed. From the fluorescent plate-reader studies a significant rise (p < 0.001) in the relative fluorescence levels corresponding to [Ca²⁺]_i levels in the hyphae was observed when challenged with an elicitor (mannan oligosaccharide, 150 mg L^?1) which was dependent upon extracellular calcium. Concurrently a novel application of dye-loaded hyphae for morphological analysis was also examined using the imaging software Filament Tracer (Bitplane). Essential quantitative mycelial information including the length and diameter of the segments and number of branch points was obtained using this application based on the three-dimensional data.     

The mitochondrial calcium uniporter is involved in mitochondrial calcium cycle dysfunction: Underlying mechanism of hypertension associated with mitochondrial tRNAIle A4263G mutation

Recent studies have shown that the mitochondrial DNA mutations are involved in the pathogenesis of hypertension. Our previous study identified mitochondrial tRNA^Ile A4263G mutation in a large Chinese Han family with maternally-inherited hypertension. This mutation may contribute to mitochondrial Ca²⁺ cycling dysfuntion, but the mechanism is unclear. Lymphoblastoid cell lines were derived from hypertensive and normotensive individuals, either with or without tRNA^Ile A4263G mutation. The mitochondrial calcium ([Ca²⁺]_m) in cells from hypertensive subjects with the tRNA^Ile A4263G mutation, was lower than in cells from normotension or hypertension without mutation, or normotension with mutation (P < 0.05). Meanwhile, cytosolic calcium ([Ca²⁺]_c) in hypertensive with mutation cells was higher than another three groups. After exposure to caffeine, which could increase the [Ca²⁺]_c by activating ryanodine receptor on endoplasmic reticulum, [Ca²⁺]_c/[Ca²⁺]_m increased higher than in hypertensive with mutation cells from another three groups. Moreover, MCU expression was decreased in hypertensive with mutation cells compared with in another three groups (P < 0.05). [Ca²⁺]_c increased and [Ca²⁺]_m decreased after treatment with Ru360 (an inhibitor of MCU) or an siRNA against MCU. In this study we found decreased MCU expression in hypertensive with mutation cells contributed to dysregulated Ca²⁺ uptake into the mitochondria, and cytoplasmic Ca²⁺ overload. This abnormality might be involved in the underlying mechanisms of maternally inherited hypertension in subjects carrying the mitochondrial tRNA^Ile A4263G mutation.     

Effects of shear stress cultivation on cell membrane disruption and intracellular calcium concentration in sonoporation of endothelial cells

Microbubble facilitated ultrasound (US) application can enhance intracellular delivery of drugs and genes in endothelial cells cultured in static condition by transiently disrupting the cell membrane, or sonoporation. However, endothelial cells in vivo that are constantly exposed to blood flow may exhibit different sonoporation characteristics. This study investigates the effects of shear stress cultivation on sonoporation of endothelial cells in terms of membrane disruption and changes in the intracellular calcium concentration ([Ca²⁺]_i). Sonoporation experiments were conducted using murine brain microvascular endothelial (bEnd.3) cells and human umbilical vein endothelial cells (HUVECs) cultured under static or shear stress (5 dyne/cm² for 5 days) condition in a microchannel environment. The cells were exposed to a short US tone burst (1.25 MHz, 8 μs duration, 0.24 MPa) in the presence of Definity^TM microbubbles to facilitate sonoporation. Membrane disruption was assessed by propidium iodide (PI) and changes in [Ca²⁺]_i measured by fura-2AM. Results from this study show that shear stress cultivation significantly reduced the impact of ultrasound-driven microbubbles activities on endothelial cells. Cells cultured under shear stress condition exhibited much lower percentage with membrane disruption and changes in [Ca²⁺]_i compared to statically cultured cells. The maximum increases of PI uptake and [Ca²⁺]_i were also significantly lower in the shear stress cultured cells. In addition, the extent of [Ca²⁺]_i waves in shear cultured HUVECs was reduced compared to the statically cultured cells.     

Activation of alpha adrenergic and muscarinic receptors modifies early glucose suppression of cytoplasmic Ca2+ in pancreatic β-cells

Elevation of glucose induces transient inhibition of insulin release by lowering cytoplasmic Ca²⁺ ([Ca²⁺]_i) below baseline in pancreatic β-cells. The period of [Ca²⁺]_i decrease (phase 0) coincides with increased glucagon release and is therefore the starting point for antisynchronous pulses of insulin and glucagon. We now examine if activation of adrenergic α_2A and muscarinic M₃ receptors affects the initial [Ca²⁺]_i response to increase of glucose from 3 to 20 mM in β-cells situated in mouse islets. In the absence of receptor stimulation the elevation of glucose lowered [Ca²⁺]_i during 90–120 s followed by rise due to opening of voltage-dependent Ca²⁺ channels. The period of [Ca²⁺]_i decrease was prolonged by activation of the α_2A adrenergic receptors (1 μM epinephrine or 100 nM clonidine) and shortened by stimulation of the muscarinic M₃ receptors (0.1 μM acetylcholine). The latter effect was mimicked by the Na/K pump inhibitor ouabain (10–100 μM). The results indicate that prolonged initial decrease (phase 0) is followed by slow [Ca²⁺]_i rise and shorter decrease followed by fast rise. It is concluded that the period of initial decrease of [Ca²⁺]_i regulates the subsequent β-cell response to glucose.     

Synthesis and insecticidal evaluation of novel N-pyridylpyrazolecarboxamides containing cyano substituent in the ortho-position

In an attempt to search for potent insecticides targeting the ryanodine receptor (RyR), a series of novel N-pyridylpyrazolecarboxamides containing cyano substituent in the ortho-position were designed and synthesized. Their insecticidal activities of target compounds against oriental armyworm (Mythimna separata) and diamondback moth (Plutella xylostella) indicated that most of the compounds showed moderate to high activities at the tested concentrations. In particular, compound 6l and 6o showed 86% larvicidal activities against Plutella xylostella at the concentration of 0.1 mg/L, while the activity of compound 6h against Mythimna separate was 80% at 1 mg/L. The calcium imaging technique was applied to investigate the effects of some title compounds on the intracellular calcium ion concentration ([Ca²⁺]_i), experimental results demonstrated that compound 6h stimulates a transient elevation in [Ca²⁺]_i in the absence of external calcium after the central neurons dye loading with fluo-3 AM. However, when the central neurons were dyed with fluo-5 N and incubated with 2-APB, [Ca²⁺]i decreased transiently by treated of compound 6h. All of the calcium imaging technique experiments demonstrated that these novel compounds deliver calcium from endoplasmic reticulum to cytoplasm, which proved that the title compounds were the possible activators of insect RyR.     

Action of ANP on the nongenomic dose-dependent biphasic effect of aldosterone on NHE1 in proximal S3 segment

The rapid (2 min) nongenomic effects of aldosterone (ALDO) and/or spironolactone (MR antagonist), RU 486 (GR antagonist), atrial natriuretic peptide (ANP) and dimethyl-BAPTA (BAPTA) on the intracellular pH recovery rate (pHirr) via NHE1 (basolateral Na⁺/H⁺ exchanger isoform), after the acid load induced by NH₄Cl, and on the cytosolic free calcium concentration ([Ca²⁺]_i) were investigated in the proximal S3 segment isolated from rats, by the probes BCECF-AM and FLUO-4-AM, respectively. The basal pHi was 7.15 ± 0.008 and the basal pHirr was 0.195 ± 0.012 pH units/min (number of tubules/number of tubular areas = 16/96). Our results confirmed the rapid biphasic effect of ALDO on NHE1: ALDO (10^?12 M) increases the pHirr to approximately 59% of control value, and ALDO (10^?6 M) decreases it to approximately 49%. Spironolactone did not change these effects, but RU 486 inhibited the stimulatory effect and maintained the inhibitory effect. ANP (10^?6 M) or BAPTA (5 × 10^?5 M) alone had no significant effect on NHE1 but prevented both effects of ALDO on this exchanger. The basal [Ca²⁺]_i was 104 ± 3 nM (15), and ALDO (10^?12 or 10^?6 M) increased the basal [Ca²⁺]_i to approximately 50% or 124%, respectively. RU 486, ANP and BAPTA decreased the [Ca²⁺]_i and inhibited the stimulatory effect of both doses of ALDO. The results suggest the involvement of GR on the nongenomic effects of ALDO and indicate a pHirr-regulating role for [Ca²⁺]_i that is mediated by NHE1, stimulated/impaired by ALDO, and affected by ANP or BAPTA with ALDO. The observed nongenomic hormonal interaction in the S3 segment may represent a rapid and physiologically relevant regulatory mechanism in the intact animal under conditions of volume alterations.     

Increased mechanosensitivity of cells cultured on nanotopographies

Enhancing cellular mechanosensitivity is recognized as a novel tool for successful musculoskeletal tissue engineering. We examined the hypothesis that mechanosensitivity of human mesenchymal stem cells (hMSCs) is enhanced on nanotopographic substrates relative to flat surfaces. hMSCs were cultured on polymer-demixed, randomly distributed nanoisland surfaces with varying island heights and changes in intracellular calcium concentration, [Ca²⁺]_i, in response to fluid flow induced shear stress were quantifide. Stem cells cultured on specific scale nanotopographies displayed greater intracellular calcium responses to fluid flow. hMSCs cultured on 10–20 nm high nanoislands displayed a greater percentage of cells responding in calcium relative to cells cultured on flat control, and showed greater average [Ca²⁺]_i increase relative to cells cultured on other nanoislands (45–80 nm high nanoislands). As [Ca²⁺]_i is an important regulator of downstream signaling, as well as proliferation and differentiation of hMSCs, this observation suggests that specific scale nanotopographies provide an optimal milieu for promoting stem cell mechanotransduction activity. That mechanical signals and substrate nanotopography may synergistically regulate cell behavior is of significant interest in the development of regenerative medicine protocols.     

BAPTA-AM,an intracellular calcium chelator,inhibits RANKL-induced bone marrow macrophages differentiation through MEK/ERK,p38 MAPK and Akt,but not JNK pathways

To examine the roles of intracellular calcium in RANKL-induced bone marrow macrophages (BMMs) differentiation, the effects of intracellular calcium chelator BAPTA-AM on RANKL-induced BMMs differentiation, and the activation of its relating signal proteins (MAPKs, and the PI3K/Akt) were studied. BMMs were cultured with various concentrations of BAPTA-AM in the presence of M-CSF (25 ng/ml) and RANKL (25 ng/ml) for 7 days, osteoclastogenic ability, cytosolic free Ca²⁺ concentration, osteoclast survival and the expression of phosphorylated ERK1/2, SAPK/JNK, Akt and p38 MAPK were measured by TRAP staining, spectrofluorometer and Western blotting. BAPTA-AM inhibited osteoclastogenesis and osteoclast survival of BMMs by RANKL induction. In osteoclasts without the pretreatment of BAPTA-AM, the increased response of [Ca²⁺]_i was observed within 15 min and the maximum was about 1.2 times that of control. This response was sustained for 30 min and returned to the control level at 1 h after RANKL-inducing, and the increased response of [Ca²⁺]_i was completely abolished and sustained to at least 8 h by BAPTA-AM. Although immunoblotting data revealed that RANKL could activate the phosphorylation of ERK1/2, SAPK/JNK, Akt and p38 MAPK, the expression of ERK1/2, Akt and p38 MAPK phosphorylation was inhibited by BAPTA-AM dose-dependently. These results revealed that BAPTA-AM inhibit osteoclastogenic ability of BMMs via suppressing the increase of [Ca²⁺]_i which lead to inhibit RANKL-induced the phosphorylation of ERK, Akt and p38 MAPK, but not JNK. This finding may be useful in the development of an osteoclastic inhibitor that targets intracellular signaling factors.     

p11 modulates calcium handling through 5-HT4R pathway in rat ventricular cardiomyocytes

BackgroundThe role of the serotonin receptor 4 (5-HT₄R) pathway in cardiac excitation-contraction coupling (ECC) remains unclear. In the brain, induction of the calcium (Ca²⁺)-binding protein p11 enhances 5-HT₄R translocation and signaling and could therefore be considered as a modulator of the 5-HT₄R pathway in the myocardium. p11 expression is increased by brain-derived neurotrophic factor (BDNF) or antidepressant drugs (imipramine). Thus, we investigated whether p11 regulates the 5-HT₄R pathway in the heart in physiological conditions or under pharmacological induction and the effects on calcium handling.Methods and resultsp11 expression was induced in vivo in healthy Wistar rats by imipramine (10 mg/kg/21 days) and in vitro in left ventricular cardiomyocytes exposed to BDNF (50 ng/ml/8 h). Cell shortening and real-time Ca²⁺ measurements were processed on field-stimulated intact cardiomyocytes with the selective 5-HT₄R agonist, prucalopride (1 μM). Both imipramine and BDNF-induced cardiomyocyte p11 expression unmasked a strong response to prucalopride characterized by an increase of both cell shortening and Ca²⁺ transient amplitude compared to basal prucalopride associated with a high propensity to trigger diastolic Ca²⁺ events. Healthy rats treated with BDNF (180 ng/day/14 days) exhibited a sustained elevated heart rate following a single injection of prucalopride (0.1 mg/kg) which was not observed prior to treatment.ConclusionsWe have identified a novel role for p11 in 5-HT₄R signaling in healthy rat ventricular cardiomyocytes. Increased p11 expression by BDNF and imipramine unraveled a 5-HT₄R-mediated modulation of cardiac Ca²⁺ handling and ECC associated with deleterious Ca²⁺ flux disturbances. Such mechanism could partly explain some cardiac adverse effects induced by antidepressant treatments.     

Flufenamic acid is a tool for investigating TRPC6-mediated calcium signalling in human conditionally immortalised podocytes and HEK293 cells

Mutations in the cation channel TRPC6 result in a renal-specific phenotype of familial nephrotic syndrome, affecting intracellular calcium ([Ca²⁺]_i) signalling in the glomerular podocyte. Tools to study native TRPC6 activity are scarce, although there has been recent success with flufenamic acid (FFA). We confirm the specificity of FFA for TRPC6 both in an artificial expression system and in a human conditionally immortalised podocyte cell line (ciPod).Cells were loaded with fura-2AM and changes in intracellular calcium ([Ca²⁺]_i) were calculated. 200 μM FFA induced an increase in [Ca²⁺]_i in HEK293 cells with native TRPC6 expression, which was enhanced by overexpression of TRPC6 and completely blocked in the absence of extracellular calcium. Expressed TRPC7 did not significantly affect the response to FFA whereas expressed TRPC3 reduced it. FFA also induced an increase ciPod in [Ca²⁺]_i, which was inhibited using SKF96365 and 2-APB, but not indomethacin. In ciPod, adenovirus (Ad-v) wild type (WT) TRPC6 increased [Ca²⁺]_i activity to FFA compared to native TRPC6, whereas activity was significantly reduced with Ad-v dominant negative (DN) TRPC6. The niflumic acid (NFA) induced increase in [Ca²⁺]_i in ciPod was not affected by Ad-v TRPC6 DN, and in HEK293 cells was not affected by WT TRPC6.In conclusion, FFA activates TRPC6 [Ca²⁺]_i signalling in both ciPod and HEK293 cells independently of TRPC3 and TRPC7, and independently of properties of the fenamate family.     

Redox-sensitive stimulation of type-1 ryanodine receptors by the scorpion toxin maurocalcine

The scorpion toxin maurocalcine acts as a high affinity agonist of the type-1 ryanodine receptor expressed in skeletal muscle. Here, we investigated the effects of the reducing agent dithiothreitol or the oxidizing reagent thimerosal on type-1 ryanodine receptor stimulation by maurocalcine. Maurocalcine addition to sarcoplasmic reticulum vesicles actively loaded with calcium elicited Ca²⁺ release from native vesicles and from vesicles pre-incubated with dithiothreitol; thimerosal addition to native vesicles after Ca²⁺ uptake completion prevented this response. Maurocalcine enhanced equilibrium [³H]-ryanodine binding to native and to dithiothreitol-treated reticulum vesicles, and increased 5-fold the apparent K_i for Mg²⁺ inhibition of [³H]-ryanodine binding to native vesicles. Single calcium release channels incorporated in planar lipid bilayers displayed a long-lived open sub-conductance state after maurocalcine addition. The fractional time spent in this sub-conductance state decreased when lowering cytoplasmic [Ca²⁺] from 10 μM to 0.1 μM or at cytoplasmic [Mg²⁺] ≥ 30 μM. At 0.1 μM [Ca²⁺], only channels that displayed poor activation by Ca²⁺ were readily activated by 5 nM maurocalcine; subsequent incubation with thimerosal abolished the sub-conductance state induced by maurocalcine. We interpret these results as an indication that maurocalcine acts as a more effective type-1 ryanodine receptor channel agonist under reducing conditions.     

Shear stress-induced Ca2+ mobilization in MDCK cells is ATP dependent,no matter the primary cilium

Primary cilium has emerged as mechanosensor to subtle flow variations in epithelial cells, but its role in shear stress detection remains controversial. To probe the function of this non-motile organelle in shear stress detection by cells, we compared calcium signalling responses induced by shear stress in ciliated and unciliated MDCK cells. Cytosolic free Ca²⁺ ([Ca²⁺]_i) was measured using Fura-PE3 video imaging fluorescence microscopy in response to shear stress due to laminar flow (385 μl s^?1). Our results show that both unciliated and ciliated MDCK cells are shear stress sensitive via ATP release and autocrine feedback through purinergic receptors. However, purinergic calcium signals differed in response intensity and receptor subtypes. In unciliated cells, shear stress-induced elevation in [Ca²⁺]_i was predominantly mediated through P2X receptors (P2XR). In contrast, calcium mobilization in ciliated MDCK cells resulted from P2YRs and store-operated Ca²⁺-permeable channels besides P2XRs. These findings lend support to the hypothesis that ATP release in response to shear stress is independent of the primary cilium and that transduction of mechanical strain into a specific biochemical responses stems on the mobilization of different sets of purinergic receptors.     

Fluid shear stress induces calcium transients in osteoblasts through depolarization of osteoblastic membrane

Intracellular calcium transient ([Ca²⁺]_i transient) induced by fluid shear stress (FSS) plays an important role in osteoblastic mechanotransduction. Changes of membrane potential usually affect [Ca²⁺]_i level. Here, we sought to determine whether there was a relationship between membrane potential and FSS-induced [Ca²⁺]_i transient in osteoblasts. Fluorescent dyes DiBAC₄(3) and fura-2 AM were respectively used to detect membrane potential and [Ca²⁺]_i. Our results showed that FSS firstly induced depolarization of membrane potential and then a transient rising of [Ca²⁺]_i in osteoblasts. There was a same threshold for FSS to induce depolarization of membrane potential and [Ca²⁺]_i transients. Replacing extracellular Na⁺ with tetraethylammonium or blocking stretch-activated channels (SACs) with gadolinium both effectively inhibited FSS-induced membrane depolarization and [Ca²⁺]_i transients. However, voltage-activated K⁺ channel inhibitor, 4-Aminopyridine, did not affect these responses. Removing extracellular Ca²⁺ or blocking of L-type voltage-sensitive Ca²⁺ channels (L-VSCCs) with nifedipine inhibited FSS-induced [Ca²⁺]_i transients in osteoblasts too. Quantifying membrane potential with patch clamp showed that the resting potential of osteoblasts was −43.3 mV and the depolarization induced by FSS was about 44 mV. Voltage clamp indicated that this depolarization was enough to activated L-VSCCs in osteoblasts. These results suggested a time line of Ca²⁺ mobilization wherein FSS activated SACs to promote Na⁺ entry to depolarize membrane that, in turn, activated L-VSCCs and Ca²⁺ influx though L-VSCCs switched on [Ca²⁺]_i response in osteoblasts.     

Increase of intracellular Ca2+ by adenine and uracil nucleotides in human midbrain-derived neuronal progenitor cells

Nucleotides play an important role in brain development and may exert their action via ligand-gated cationic channels or G protein-coupled receptors. Patch-clamp measurements indicated that in contrast to AMPA, ATP did not induce membrane currents in human midbrain derived neuronal progenitor cells (hmNPCs). Various nucleotide agonists concentration-dependently increased [Ca²⁺]_i as measured by the Fura-2 method, with the rank order of potency ATP > ADP > UTP > UDP. A Ca²⁺-free external medium moderately decreased, whereas a depletion of the intracellular Ca²⁺ storage sites by cyclopiazonic acid markedly depressed the [Ca²⁺]_i transients induced by either ATP or UTP. Further, the P2Y₁ receptor antagonistic PPADS and MRS 2179, as well as the nucleotide catalyzing enzyme apyrase, allmost abolished the effects of these two nucleotides. However, the P2Y_1,2,12 antagonistic suramin only slightly blocked the action of ATP, but strongly inhibited that of UTP. In agreement with this finding, UTP evoked the release of ATP from hmNPCs in a suramin-, but not PPADS-sensitive manner. Immunocytochemistry indicated the co-localization of P2Y_1,2,4-immunoreactivities (IR) with nestin-IR at these cells. In conclusion, UTP may induce the release of ATP from hmNPCs via P2Y₂ receptor-activation and thereby causes [Ca²⁺]_i transients by stimulating a P2Y₁-like receptor.     

Carvacrol-induced [Ca2+]i rise and apoptosis in human glioblastoma cells

AimsThis study examined whether the essential oil component carvacrol altered cytosolic free Ca²⁺ level ([Ca²⁺]_i) and viability in human glioblastoma cells.Main methodsThe Ca²⁺-sensitive fluorescent dye fura-2 was applied to measure [Ca²⁺]_i. Cell viability was measured by detecting reagent WST-1. Apoptosis and reactive oxygen species (ROS) were detected by flow cytometry.Key findingsCarvacrol at concentrations of 400–1000 μM induced a [Ca²⁺]_i rise in a concentration-dependent fashion. The response was decreased partially by removal of extracellular Ca²⁺. Carvacrol-induced Ca²⁺ signal was not altered by nifedipine, econazole, SK&;F96365, and protein kinase C activator phorbol myristate acetate (PMA), but was inhibited by the protein kinase C inhibitor GF109203X. When extracellular Ca²⁺ was removed, incubation with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ) abolished carvacrol-induced [Ca²⁺]_i rise. Incubation with carvacrol also abolished thapsigargin or BHQ-induced [Ca²⁺]_i rise. Inhibition of phospholipase C with U73122 abolished carvacrol-induced [Ca²⁺]_i rise. At concentrations of 200–800 μM, carvacrol killed cells in a concentration-dependent manner. This cytotoxic effect was not changed by chelating cytosolic Ca²⁺ with 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N–-tetraacetic acid/acetoxy methyl (BAPTA/AM). Annexin V/propidium iodide staining data suggest that carvacrol (200, 400 and 600 μM) induced apoptosis in a concentration-dependent manner. At concentrations of 200, 400 and 600 μM, carvacrol induced production of ROS.SignificanceIn human glioblastoma cells, carvacrol induced a [Ca²⁺]_i rise by inducing phospholipase C-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ entry via protein kinase C-sensitive, non store-operated Ca²⁺ channels. Carvacrol induced cell death that might involve ROS-mediated apoptosis.     

Nickel induces intracellular calcium mobilization and pathophysiological responses in human cultured airway epithelial cells

Environmental exposure to nickel is associated to respiratory disorders and potential toxicity in the lung but molecular mechanisms remain incompletely explored. The extracellular Ca²⁺-sensing receptor (CaSR) is widely distributed and may be activated by divalent cations. In this study, we investigated the presence of CaSR in human cultured airway epithelial cells and its activation by nickel. Nickel transiently increased intracellular calcium (?log EC₅₀ = 4.67 ± 0.06) in A549 and human bronchial epithelial cells as measured by epifluorescence microscopy. Nickel (20 μM)-induced calcium responses were reduced after thapsigargin or ryanodine exposure but not by Ca²⁺-free medium. Inhibition of phospholipase-C or inositol trisphosphate release reduced intracellular calcium responses to nickel indicating activation of G_q-signaling. CaSR mRNA and protein expression in epithelial cells was demonstrated by RT-PCR, western blot and immunofluorescence. Transfection of specific siRNA inhibited CaSR expression and suppressed nickel-induced intracellular calcium responses in A549 cells thus confirming nickel-CaSR activation. NPS2390, a CaSR antagonist, abolished the calcium response to nickel. Nickel-induced contraction, proliferation, α₁(I)collagen production and inflammatory cytokines mRNA expression by epithelial cells as measured by traction microscopy, BrdU assay and RT-PCR, respectively. These responses were blocked by NPS2390. In conclusion, micromolar nickel concentrations, relevant to nickel found in the lung tissue of humans exposed to high environmental nickel, trigger intracellular Ca²⁺ mobilization in human airway epithelial cells through the activation of CaSR which translates into pathophysiological outputs potentially related to pulmonary disease.     

Involvement of Intracellular or Extracellular Calcium in Activation of Tyrosine Hydroxylase Gene Expression in PC12 Cells

Abstract: The relationship between elevations in intracellular free Ca²⁺ concentration ([Ca²⁺]_i) by different mechanisms and tyrosine hydroxylase (TH) gene expression was examined. Depolarization by an elevated K⁺ concentration triggered rapid and sustained increases in [Ca²⁺]_i from a basal level of ～50 to 110–150 nM and three- to fourfold elevations in TH mRNA levels, requiring extracellular calcium but not inositol 1,4,5-trisphosphate (IP₃). On the other hand, bradykinin or thapsigargin, both of which induce release of intracellular calcium stores via IP₃ or inhibition of Ca²⁺-ATPase, rapidly elevated [Ca²⁺]_i to >200 nM and increased TH gene expression (three-to fivefold). Confocal imaging showed that the elevations in [Ca²⁺]_i in each case occurred throughout the cyto- and nucleoplasm. The initial rise in [Ca²⁺]_i due to either bradykinin or thapsigargin, which did not require extracellular calcium, was sufficient to initiate the events leading to increased TH expression. Consistent with this, the effects of bradykinin on TH expression were inhibited by 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid or 3,4,5-trimethoxybenzoic acid 8-(diethylamino)-octyl ester which chelates or inhibits the release of intracellular calcium, respectively. Bradykinin required a rise in [Ca²⁺]_i for <10 min, as opposed to 10–30 min for depolarization to increase TH mRNA levels. These results demonstrate that although each of these treatments increased TH gene expression by raising [Ca²⁺]_i, there are important differences among them in terms of the magnitude of elevated [Ca²⁺]_i, requirements for extracellular calcium or release of intracellular calcium stores, and duration of elevated [Ca²⁺]_i, indicating the involvement of different calcium signaling pathways leading to regulation of TH gene expression.