Store-operated Ca(2+) Entry Blockers Research Articles

Store-operated calcium entry in the satellite glial cells of rat sympathetic ganglia.

Satellite glial cells (SGCs), a major type of glial cell in the autonomic ganglia, closely envelop the cell body and even the synaptic regions of a single neuron with a very narrow gap. This structurally unique organization suggests that autonomic neurons and SGCs may communicate reciprocally. Glial Ca2+ signaling is critical for controlling neural activity. Here, for the first time we identified the machinery of store-operated Ca2+ entry (SOCE) which is critical for cellular Ca2+ homeostasis in rat sympathetic ganglia under normal and pathological states. Quantitative realtime PCR and immunostaining analyses showed that Orai1 and stromal interaction molecules 1 (STIM1) proteins are the primary components of SOCE machinery in the sympathetic ganglia. When the internal Ca2+ stores were depleted in the absence of extracellular Ca2+, the number of plasmalemmal Orai1 puncta was increased in neurons and SGCs, suggesting activation of the Ca2+ entry channels. Intracellular Ca2+ imaging revealed that SOCE was present in SGCs and neurons; however, the magnitude of SOCE was much larger in the SGCs than in the neurons. The SOCE was significantly suppressed by GSK7975A, a selective Orai1 blocker, and Pyr6, a SOCE blocker. Lipopolysaccharide (LPS) upregulated the glial fibrillary acidic protein and Toll-like receptor 4 in the sympathetic ganglia. Importantly, LPS attenuated SOCE via downregulating Orai1 and STIM1 expression. In conclusion, sympathetic SGCs functionally express the SOCE machinery, which is indispensable for intracellular Ca2+ signaling. The SOCE is highly susceptible to inflammation, which may affect sympathetic neuronal activity and thereby autonomic output.

Excitatory cholinergic responses in mouse primary bronchial smooth muscle require both Ca2+ entry via l-type Ca2+ channels and store operated Ca2+ entry via Orai channels

Malfunctions in airway smooth muscle Ca2+-signalling leads to airway hyperresponsiveness in asthma and chronic obstructive pulmonary disease. Ca2+-release from intracellular stores is important in mediating agonist-induced contractions, but the role of influx via l-type Ca2+ channels is controversial. We re-examined roles of the sarcoplasmic reticulum Ca2+ store, refilling of this store via store-operated Ca2+ entry (SOCE) and l-type Ca2+ channel pathways on carbachol (CCh, 0.1–10 µM)-induced contractions of mouse bronchial rings and intracellular Ca2+ signals of mouse bronchial myocytes. In tension experiments, the ryanodine receptor (RyR) blocker dantrolene (100 µM) reduced CCh-responses at all concentrations, with greater effects on sustained rather than initial components of contraction. 2-Aminoethoxydiphenyl borate (2-APB, 100 μM), in the presence of dantrolene, abolished CCh-responses, suggesting the sarcoplasmic reticulum Ca2+ store is essential for contraction. The SOCE blocker GSK-7975A (10 µM) reduced CCh-contractions, with greater effects at higher (e.g. 3 and 10 µM) CCh concentrations. Nifedipine (1 µM), abolished remaining contractions in GSK-7975A (10 µM). A similar pattern was observed on intracellular Ca2+-responses to 0.3 µM CCh, where GSK-7975A (10 µM) substantially reduced Ca2+ transients induced by CCh, and nifedipine (1 µM) abolished remaining responses. When nifedipine (1 µM) was applied alone it had less effect, reducing tension responses at all CCh concentrations by 25% - 50%, with greater effects at lower (e.g. 0.1 and 0.3 µM) CCh concentrations. When nifedipine (1 µM) was examined on the intracellular Ca2+-response to 0.3 µM CCh, it only modestly reduced Ca2+ signals, while GSK-7975A (10 µM) abolished remaining responses. In conclusion, Ca2+-influx from both SOCE and l-type Ca2+ channels contribute to excitatory cholinergic responses in mouse bronchi. The contribution of l-type Ca2+ channels was especially pronounced at lower doses of CCh, or when SOCE was blocked. This suggests l-type Ca2+ channels might be a potential target for bronchoconstriction under certain circumstances.

Blocking Store-Operated Ca2+ Entry to Protect HL-1 Cardiomyocytes from Epirubicin-Induced Cardiotoxicity.

Epirubicin (EPI) is one of the most widely used anthracycline chemotherapy drugs, yet its cardiotoxicity severely limits its clinical application. Altered intracellular Ca2+ homeostasis has been shown to contribute to EPI-induced cell death and hypertrophy in the heart. While store-operated Ca2+ entry (SOCE) has recently been linked with cardiac hypertrophy and heart failure, its role in EPI-induced cardiotoxicity remains unknown. Using a publicly available RNA-seq dataset of human iPSC-derived cardiomyocytes, gene analysis showed that cells treated with 2 µM EPI for 48 h had significantly reduced expression of SOCE machinery genes, e.g., Orai1, Orai3, TRPC3, TRPC4, Stim1, and Stim2. Using HL-1, a cardiomyocyte cell line derived from adult mouse atria, and Fura-2, a ratiometric Ca2+ fluorescent dye, this study confirmed that SOCE was indeed significantly reduced in HL-1 cells treated with EPI for 6 h or longer. However, HL-1 cells presented increased SOCE as well as increased reactive oxygen species (ROS) production at 30 min after EPI treatment. EPI-induced apoptosis was evidenced by disruption of F-actin and increased cleavage of caspase-3 protein. The HL-1 cells that survived to 24 h after EPI treatment demonstrated enlarged cell sizes, up-regulated expression of brain natriuretic peptide (a hypertrophy marker), and increased NFAT4 nuclear translocation. Treatment by BTP2, a known SOCE blocker, decreased the initial EPI-enhanced SOCE, rescued HL-1 cells from EPI-induced apoptosis, and reduced NFAT4 nuclear translocation and hypertrophy. This study suggests that EPI may affect SOCE in two phases: the initial enhancement phase and the following cell compensatory reduction phase. Administration of a SOCE blocker at the initial enhancement phase may protect cardiomyocytes from EPI-induced toxicity and hypertrophy.

Development of Store-Operated Calcium Entry-Targeted Compounds in Cancer.

Store-operated Ca2+ entry (SOCE) is the major pathway of Ca2+ entry in mammalian cells, and regulates a variety of cellular functions including proliferation, motility, apoptosis, and death. Accumulating evidence has indicated that augmented SOCE is related to the generation and development of cancer, including tumor formation, proliferation, angiogenesis, metastasis, and antitumor immunity. Therefore, the development of compounds targeting SOCE has been proposed as a potential and effective strategy for use in cancer therapy. In this review, we summarize the current research on SOCE inhibitors and blockers, discuss their effects and possible mechanisms of action in cancer therapy, and induce a new perspective on the treatment of cancer.

Blocking Store‐Operated Ca2+ Entry to Protect Cardiomyocytes from Epirubicin‐Induced Toxicity

Epirubicin (EPI) is one of widely used anthracycline chemotherapy drugs, yet its cardiotoxicity severely limits its clinical application. Altered intracellular Ca2+ homeostasis has been linked to epirubicin‐induced cell death and hypertrophy. While store‐operated Ca2+ entry (SOCE) recently has been linked with cardiac hypertrophy and heart failure, its role in epirubicin‐induced cardiotoxicity remains unknown.METHODHL‐1, a cardiomyocyte cell line derived from adult mouse atria, was used in this study. Intracellular ROS was measured by dihydroethidium(DHE) fluorescence and intracellular Ca2+ was monitored by ratiometric dye Fura‐2 on a spectrofluorometer (excitation λ = 350/385nm and emission λ = 510nm; Photon Technology International, NJ). Upon depletion of ER Ca2+ stores by 10μM thapsigargin (TG) in 0mM Ca2+ extracellular solution, SOCE was activated when extracellular solution was rapidly exchanged to 2mM Ca2+. Apoptosis assay was conducted by nuclei staining, F‐actin phalloidin staining and Western Blotting of caspase‐3. While cell size was compared in HL‐1 cells with different treatments using Image J, the mRNA of Orai1, Orai3, STIM1 and B‐type natriuretic peptide (BNP) were also compared using real time qPCR.RESULTSIncubation of 1uM EPI for 30min induced significant ROS production in cultured HL‐1 cells compared with vehicle control (10410±1492 vs. 2762±939, p<0.0001). EPI induced an enhanced SOCE (0.1214±0.0104 vs. 0.0682±0.0062, n=32, p=0.0008), likely through increased expression of SOCE components Orai1, Orai3, and STIM1 compared with control cells. Apoptosis was observed upon EPI treatment, indicated by the condensed and fragmented nuclei, degradation of F‐actin and increased cleavage of caspase‐3 protein. EPI treatment also resulted in larger cell size (3894±120 μm2) compared with non‐treated control cells (2452±57 μm2, n=581, p<0.0001). The hypertrophy marker BNP was up‐regulated upon EPI treatment as well. BTP‐2, a known SOCE blocker, could block this EPI‐induced SOCE and rescue HL‐1 cells from EPI‐induced apoptosis. BTP‐2 also prevented HL‐1 cells from EPI‐induced hypertrophy in terms of cell size (see Figure , 2548±69 μm2) and also reduction of BNP expression.CONCLUSIONEpirubicin upregulated SOCE, induced apoptosis and hypertrophy in HL‐1 cardiomyocytes. Blocking SOCE by BTP‐2 could at least partially rescue HL‐1 cells from epirubicin‐induced apoptosis and hypertrophy.Support or Funding Information(1) NIH S10 OD025230 to Dr. Zui Pan(2) University of Texas at Arlington Center for Research and Scholarship Pilot Grant for Trainee to Xian LiuFigure 1

Experimental and Mathematical Modeling of Intracellular Calcium Dynamics for Anticancer Effects Evaluation in Esophageal Cancer

Targeting dysregulated Ca2+ signaling in cancer cells is an emerging chemotherapy approach. This group previously reported that store‐operated Ca2+ entry (SOCE) blocker, such as RP4010, could effectively inhibit intracellular Ca2+ oscillations and cell proliferation in esophageal cancer, a leading cancer worldwide with low 5‐year survival rate. While many current clinical chemotherapy drugs, such as tyrosine kinase inhibitors (TKIs) can induce intracellular Ca2+ release, it is not known whether combination of SOCE blockers and TKIs could achieve better chemotherapy effects. The present study employed both experimental and mathematical models to evaluate the effect of RP4010 and TKI (Afatinib) on intracellular Ca2+ oscillation periods in KYSE‐150 cells, an esophageal cancer cell line. The intracellular Ca2+ oscillation period in KYSE‐150 cells was measured as ~32.8 sec; both Afatinib and RP4010 could reduce intracellular Ca2+ and prolong the period in a dose‐dependent manner. Using a modified canonical model with variables of SOCE channel and IP3 receptor affected by RP4010 and Afatinib receptively, the intracellular Ca2+ oscillation dynamics were simulated. The theoretical data of the combined implementations of drugs also fitted well with experimental data. Both results demonstrated a synergetic effect of RP4010 and Afatinib on inhibiting intracellular Ca2+ oscillation period, which was further confirmed by cell proliferation analysis. This study suggests that experimental and mathematical modeling of intracellular Ca2+ dynamics could be used as a rapid and cost‐effective tool for evaluation of combined chemotherapy drugs.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

CaMKIIδ meditates phenylephrine induced cardiomyocyte hypertrophy through store-operated Ca2+ entry.

Evidence suggests that store-operated Ca2+ entry (SOCE) is involved in the hypertrophy of cardiomyocytes. The signaling mechanisms of SOCE contributing to cardiac hypertrophy following phenylephrine (PE) stimulation are not fully understood. Ca2+/calmodulin-dependent protein kinase II δ (CaMKIIδ) plays an important role in regulating intracellular Ca2+ hemostasis and function in the cardimyocytes. This study is aimed to determine the role of CaMKIIδ in regulating the PE-induced myocardial hypertrophy and the associated molecular signaling mechanisms. We used primary cultures of neonatal cardimyocytes isolated from the left ventricle of Sprague Dawley rats to investigate the effects of CaMKIIδ on myocardial hypertrophy and intracellular Ca2+ mobilization. We found that the expression of CaMKIIδ was enhanced in PE-induced hypertrophic cardiomyocytes. CaMKIIδ siRNA, CaMKII inhibitor KN93, and SOCE blocker BTP2 attenuated the increase in the expression of CaMKIIδ and normalized the hypertrophic markers, atrial natriuretic peptide and brain natriuretic peptide, and size of cardiomyocytes induced by PE stimulation. The protein level of stromal interaction molecule 1 and Orai1, the essential components of the SOCE, is also enhanced in hypertrophic cardiomyocytes, which were normalized by CaMKIIδ siRNA and KN93 treatment. Hypertrophic cardiomyocytes showed an increase in the peak of Ca2+ transient following store depletion, which was inhibited by SOCE blocker BTP2, CaMKIIδ siRNA, and KN93. The Ca2+ currents through Ca2+ release-activated Ca2+ channels were increased in PE-treated cardiomyocytes and were attenuated by CaMKIIδ siRNA and KN93. These data indicate that PE-induced myocardial hypertrophy requires a complex signaling pathway that involves activation of both CaMKIIδ and SOCE. In conclusion, these studies reveal that up-regulation of CaMKIIδ may contribute to the PE-induced myocardial hypertrophy through the activation of SOCE expressed in the cardiomyocytes.

Foeniculum vulgare Mill. increases cytosolic Ca2+ concentration and inhibits store-operated Ca2+ entry in vascular endothelial cells.

This study assessed the effects of essential oil of Foeniculum vulgare Mill. (fennel oil) and of trans-anethole, the main component of fennel oil, on extracellular Ca2+-induced store-operated Ca2+ entry (SOCE) into vascular endothelial (EA) cells and their mechanisms of action. Components of fennel oil were analyzed by gas chromatography-mass spectrometry. Cytosolic Ca2+ concentration ([Ca2+]c) in EA cells was determined using Fura-2 fluorescence. In the presence of extracellular Ca2+, fennel oil significantly increased [Ca2+]c in EA cells; this increase was significantly inhibited by the Ca2+ channel blockers La3+ and nifedipine. In contrast, fennel oil induced [Ca2+]c was significantly lower in Ca2+-free solution, suggesting that fennel oil increases [Ca2+]c mainly by enhancing Ca2+ influx into EA cells. [Ca2+]c mobilization by trans-anethole was similar to that of fennel oil. Moreover, SOCE was suppressed by fennel oil and trans-anethole. SOCE was also attenuated by lanthanum (La3+), a non-selective cation channel (NSC) blocker; 2-aminoethoxydiphenyl borane (2-APB), an inositol 1,4,5-triphosphate (IP3) receptor inhibitor and SOCE blocker; and U73122, an inhibitor of phospholipase C (PLC). Further, SOCE was more strongly inhibited by La3+ plus fennel oil or trans-anethole than by La3+ alone. These findings suggest that fennel oil and trans-anethole significantly inhibit SOCE-induced [Ca2+]c increase in vascular endothelial cells and that these reactions may be mediated by NSC, IP3-dependent Ca2+ mobilization, and PLC activation.

Retinoic Acid Regulates Calcium Signaling to Promote Mouse Ovarian Granulosa Cell Proliferation.

Normal development of ovarian follicles is critical for female reproduction and endocrine function. We have identified retinoic acid (RA) and the RA-degrading enzyme CYP26B1 as regulators of ovarian follicle development and showed that RA and a CYP26 inhibitor stimulated ovarian granulosa cell proliferation. The mechanism underpinning RA-dependent proliferation, however, is not known. The current study was designed to examine the role of intracellular calcium (Ca2+) signaling in mediating the effects of RA on primary mouse granulosa cell proliferation. In single-cell Ca2+ imaging experiments, treatment of cultured granulosa cells with RA increased the steady-state Ca2+ content of the endoplasmic reticulum (ER) stores. This correlated with increased store-operated Ca2+ entry (SOCE) and enhanced inositol 1,4,5-trisphosphate receptor (IP3R)-dependent Ca2+ release. In proliferation assays, RA treatment or Cyp26b1 knockdown stimulated proliferation, whereas Cyp26b1 overexpression inhibited proliferation. When RA was given together with 2-aminoethoxydiphenylborane (2-APB), a blocker of IP3R-dependent ER Ca2+ release and SOCE, with xestospongin C, a selective IP3R- receptor antagonist, or with 3,5-bis (trifluoromethyl)pyrazole (BTP-2), a specific SOCE blocker, the stimulatory effect of RA on cell proliferation was abolished. Further investigation showed that treatment with 2-APB or BTP-2 inhibited RA induction of RA response element (RARE) activation in granulosa cells, confirming an important role for Ca2+ signaling in mediating RA actions. Overall, these data support a model in which RA regulates ovarian follicle development by stimulating granulosa cell proliferation and that this stimulatory effect is at least in part driven by the modulation of Ca2+ signaling.

Stromal interaction molecule 2 regulates C2C12 myoblast differentiation

BackgroundEnhanced intracellular Ca2+ signaling by stromal interaction molecule 1 (STIM1)-mediated store-operated Ca2+ entry (SOCE) is required for skeletal muscle differentiation. However, the contribution of STIM2, STIM1's analogue protein, on muscle cell differentiation has not been clearly elucidated. The present study aimed to explore the contribution of STIM2-mediated SOCE on C2C12 myoblast differentiation. MethodsChanges in STIM2 expression level (reverse transcription-polymerase chain reaction and Western blotting) and SOCE activity ([Ca2+]i measurement) were measured during 3 days of in vitro differentiation of C2C12 skeletal myoblast. Transcriptional regulation of STIM2 by nuclear factor of activated T cells, cytoplasmic (NFATc) overexpression was observed, and the effect of STIM2 knockdown on NFAT transcriptional activity (luciferase assay) and myoblast differentiation was quantified. ResultsIncrease of STIM2 protein level and enhanced SOCE activity were observed in differentiating myoblasts. Treatment with a SOCE blocker (2-APB) inhibited the differentiation. Overexpression of NFATc1 increased STIM2 expression and SOCE activity. Knockdown of STIM2 decreased NFAT transcriptional activity, SOCE activity, and differentiation of C2C12 myoblast. ConclusionIt is suggested that STIM2-activated SOCE controls C2C12 myoblast differentiation.

STIM1 elevation in the heart results in aberrant Ca2 + handling and cardiomyopathy

Stromal interaction molecule 1 (STIM1) is a Ca2+ sensor that partners with Orai1 to elicit Ca2+ entry in response to endoplasmic reticulum (ER) Ca2+ store depletion. While store-operated Ca2+ entry (SOCE) is important for maintaining ER Ca2+ homeostasis in non-excitable cells, it is unclear what role it plays in the heart, although STIM1 is expressed in the heart and upregulated during disease. Here we analyzed transgenic mice with STIM1 overexpression in the heart to model the known increase of this protein in response to disease. As expected, STIM1 transgenic myocytes showed enhanced Ca2+ entry following store depletion and partial co-localization with the type 2 ryanodine receptor (RyR2) within the sarcoplasmic reticulum (SR), as well as enrichment around the sarcolemma. STIM1 transgenic mice exhibited sudden cardiac death as early as 6weeks of age, while mice surviving past 12weeks of age developed heart failure with hypertrophy, induction of the fetal gene program, histopathology and mitochondrial structural alterations, loss of ventricular functional performance and pulmonary edema. Younger, pre-symptomatic STIM1 transgenic mice exhibited enhanced pathology following pressure overload stimulation or neurohumoral agonist infusion, compared to controls. Mechanistically, cardiac myocytes isolated from STIM1 transgenic mice displayed spontaneous Ca2+ transients that were prevented by the SOCE blocker SKF-96365, increased L-type Ca2+ channel (LTCC) current, and enhanced Ca2+ spark frequency. Moreover, adult cardiac myocytes from STIM1 transgenic mice showed both increased diastolic Ca2+ and maximal transient amplitude but no increase in total SR Ca2+ load. Associated with this enhanced Ca2+ profile was an increase in cardiac nuclear factor of activated T-cells (NFAT) and Ca2+/calmodulin-dependent kinase II (CaMKII) activity. We conclude that STIM1 has an unexpected function in the heart where it alters communication between the sarcolemma and SR resulting in greater Ca2+ flux and a leaky SR compartment.

Abstract 186: Increased STIM1 Expression Results in Altered Calcium Handling and Heart Failure

Stromal interaction molecule 1 (STIM1) is a Ca2+ sensor that partners with Orai1, resulting in store-operated Ca2+ entry (SOCE) that is important for maintaining endoplasmic reticulum (ER) Ca2+ homeostasis. STIM1 is expressed in the heart and upregulated during disease, but its role in disease progression is unclear. In this study we used transgenic mice with STIM1 overexpression in the heart to model the known increase of this protein in response to cardiac disease. We found that STIM1 transgenic myocytes showed elevated Ca2+ entry following store depletion and STIM1 co-localized with the type 2 ryanodine receptor (RyR2) in the sarcoplasmic reticulum (SR). In addition, STIM1 transgenic mice exhibited sudden cardiac death as early as 6 weeks of age, while mice that survived past 12 weeks developed cardiac hypertrophy that progressed to heart failure, pulmonary edema, activation of the fetal gene program, alterations in mitochondrial structure, and reduced ventricular functional performance. When pre-symptomatic STIM1 transgenic mice were subjected to disease stimuli including pressure overload stimulation or neurohumoral agonist infusion, they showed greater pathology compared to control mice. STIM1 elevation also disrupted normal Ca2+ handling in cardiac myocytes, which showed spontaneous Ca2+ transients that could be inhibited by the SOCE blocker SKF-96265, as well as increased diastolic Ca2+ levels and elevated Ca2+ spark frequency. In keeping with this increase in Ca2+ cycling we also found that STIM1 elevation resulted in an increased baseline activity of cardiac nuclear factor of activated T-cells (NFAT) and Ca2+/calmodulin-dependent protein kinase II (CaMKII). This increased CaMKII activity did not, however, translate into additional RyR2 phosphorylation, suggesting that the augmented Ca2+ spark frequency observed was likely due to an elevation in SR Ca2+ load. Our results suggest that increased STIM1 expression elicits augmented Ca2+ entry, SR Ca2+ load and Ca2+ spark frequency, that leads to mitochondrial pathology and the induction of Ca2+ sensitive hypertrophic signaling pathways that contribute to cardiac disease.

STIM1, STIM2, and Orai1 regulate store-operated calcium entry and purinergic activation of microglia.

Activation of microglia is the first and main immune response to brain injury. Release of the nucleotides ATP, ADP, and UDP from damaged cells regulate microglial migration and phagocytosis via purinergic P2Y receptors. We hypothesized that store-operated Ca(2+) entry (SOCE), the prevalent Ca(2+) influx mechanism in non-excitable cells, is a potent mediator of microglial responses to extracellular nucleotides. Expression analyses of STIM Ca(2+) sensors and Orai Ca(2+) channel subunits, that comprise the molecular machinery of SOCE, showed relevant levels of STIM1, STIM2, and Orai1 in cultured mouse microglia. STIM1 expression and SOCE were down-regulated by treatment of microglia with lipopolysaccharide, suggesting that inflammation limits SOCE by lower STIM1 abundance. Ca(2+) entry induced by cyclopiazonic acid, ATP, the P2Y6 receptor agonist UDP, or the P2Y12 receptor agonist 2-methylthio-ADP (2-MeSADP) was clearly affected in microglia from Stim1(-/-) , Stim2(-/-) , and Orai1(-/-) mice. SOCE blockers or ablation of STIM1, STIM2, or Orai1 severely impaired nucleotide-induced migration and phagocytosis in microglia. Thus, this study assigns SOCE, regulated by STIM1, STIM2, and Orai1 an essential role in purinergic signaling and activation of microglia.

Abstract 161: TRPC6 Activator Hyperforin Facilitates Arrhythmias Via Activating Store-operated Calcium Entry

Hyperforin, a major antidepressant constituent of St. John’s wort ( Hypericum perforatum ), exhibits high selectivity in activating the canonical transient potential channel 6 (TRPC6). Our previous studies have shown that TRPC6 may modulate Ca 2+ handling via store-operated Ca 2+ entry (SOCE) in adult ventricular myocytes. In the present study, we aim to test whether hyperforin is arrhythmogenic by facilitating Ca 2+ waves. Intracellular Ca 2+ fluorescence (F/F 0 ) was imaged in Fluo-4-AM loaded ventricular myocytes isolated from adult mice (2-4 month old). SOCE was evaluated by increasing the external Ca 2+ concentration ([Ca 2+ ] o ) from 0 to 1 mM after caffeine (10 mM) and thapsigargin (10 µM) were used to completely deplete SR Ca 2+ . Hyperforin (0.1-10 µM) perfusion increased SOCE up to 3.7 folds (F/F 0 = 3.73 ± 0.42, n = 7, compared to the control F/F 0 = 1.69 ± 0.37, n = 9, p < 0.05), in a concentration dependent fashion. Whole-cell currents were recorded using ramp pulses from -110 mV to +50 mV, while K + , Na + , L-type Ca 2+ , and Na + -Ca 2+ exchange currents were pre-blocked. Hyperforin at a lower concentration (0.1 µM) induced a significant increase of inward current (from -1.44 ± 0.23 pA/pF to -2.56 ± 0.36 pA/pF, n = 8, p < 0.05), which was then inhibited by the SOCE blocker Gd 3+ (1 mM) (-0.43 ± 0.22 pA/pF, n = 8, p < 0.05). Hyperforin promotes spontaneous CaWs ([Ca 2+ ] o 4 mM) by increasing the frequency to 180± 14 % (n = 11. p < 0.05), which can be attenuated by Gd 3+ (1 mM), or SKF-96265 (10 μM). In addition, both the amplitudes of Ca 2+ transients (F/F 0 =1.92 ± 0.09 to 2.09 ± 0.10, n = 12, p < 0.05) and calcium content (control: F/F 0 = 2.03 ± 0.11, n=16 to 2.12 ± 0.13, n = 11, p < 0.05) were enhanced by acute hyperforin perfusion (0.1 µM), when the cells were paced at a pacing cycle length of 2 seconds. The proarrhythmic effect of hyperforin was also confirmed in Langendorff-perfused hearts, from which optical membrane voltage mapping and EKG were simultaneously recorded. In conclusion, the TRPC6 activator hyperforin exhibits an arrhythmogenic effect in the heart. Its action is likely to be mediated by generating an inward current and increasing the calcium load in cardiac myocytes through the SOCE pathway. Caution should be taken when prescribing this drug to patients with heart disease.

Antithrombotic Potential of Blockers of Store-Operated Calcium Channels in Platelets

Platelet Orai1 channels mediate store-operated Ca(2+) entry (SOCE), which is required for procoagulant activity and arterial thrombus formation. Pharmacological blockage of these channels may provide a novel way of antithrombotic therapy. Therefore, the thromboprotective effect of SOCE blockers directed against platelet Orai1 is determined. Candidate inhibitors were screened for their effects on SOCE in washed human platelets. Tested antagonists included the known compounds, SKF96365, 2-aminoethyl diphenylborate, and MRS1845 and the novel compounds, Synta66 and GSK-7975A. The potency of SOCE inhibition was in the order of Synta66>2-aminoethyl diphenylborate>GSK-7975A>SKF96365>MRS1845. The specificity of the first 3 compounds was verified with platelets from Orai1-deficient mice. Inhibitory activity on procoagulant activity and high-shear thrombus formation was assessed in plasma and whole blood. In the presence of plasma, all 3 compounds suppressed platelet responses and restrained thrombus formation under flow. Using a murine stroke model, arterial thrombus formation was provoked in vivo by transient middle cerebral artery occlusion. Postoperative administration of 2-aminoethyl diphenylborate markedly diminished brain infarct size. Plasma-soluble SOCE blockers such as 2-aminoethyl diphenylborate suppress platelet-dependent coagulation and thrombus formation. The platelet Orai1 channel is a novel target for preventing thrombotic events causing brain infarction.

Contribution of Store-Operated Ca2+ Entry to Beat-to-Beat Ca2+ Transient in Early Fetal Mouse Heart

Introduction: Store-operated Ca2+ entry (SOCE) is triggered by ER/SR Ca2+ depletion to maintain intracellular Ca2+ concentration. In adult myocytes, SOCE contributes to cell growth or hypertrophy. However, in fetus, little is known about the role of SOCE. We hypothesize that SOCE may contribute to fetal cardiac contraction. Method: The whole hearts in embryonic day(ED) 9.5/12.5/15.5 and neonate were stained by Fluo-3 AM. Fluorescence signals in beating hearts stimulated electrically were recorded using a photomultiplier, then analyzed as Ca2+ transient(CaT) in each age. 1) SOCE was induced by changing the solutions from zero to 1.8mM Ca2+. With inhibiting voltage-dependent Ca2+ channels(VDCC), we tested whether SOCE was suppressed by 0.2mM Gd3+ application, as SOCE blocker. 2) We tested whether beat-to-beat CaT was suppressed by 0.2mM Gd3+ application. Results: 1) In fetal heart, SOCE was suppressed significantly by Gd3+ application (ED9.5; 46% decreased, p=0.011, n=5. ED12.5; 82% decreased, p<0.0001, n=6). 2) In ED 9.5, CaT was depressed significantly by Gd3+ application (49.2+/-7.6% vs. 2.0+/-2.0%), but after ED 12.5, CaT was not depressed. Conclusion: SOCE would contribute to beat-to-beat CaT in early fetal mouse myocytes.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Enhanced store-operated Ca2+ entry and TRPC channel expression in pulmonary arteries of monocrotaline-induced pulmonary hypertensive rats

Pulmonary hypertension (PH) is associated with profound vascular remodeling and alterations in Ca(2+) homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Previous studies show that canonical transient receptor potential (TRPC) genes are upregulated and store-operated Ca(2+) entry (SOCE) is augmented in PASMCs of chronic hypoxic rats and patients of pulmonary arterial hypertension (PAH). Here we further examine the involvement of TRPC and SOCE in PH with a widely used rat model of monocrotaline (MCT)-induced PAH. Rats developed severe PAH, right ventricular hypertrophy, and significant increase in store-operated TRPC1 and TRPC4 mRNA and protein in endothelium-denuded pulmonary arteries (PAs) 3 wk after MCT injection. Contraction of PA and Ca(2+) influx in PASMC evoked by store depletion using cyclopiazonic acid (CPA) were enhanced dramatically, consistent with augmented SOCE in the MCT-treated group. The time course of increase in CPA-induced contraction corresponded to that of TRPC1 expression. Endothelin-1 (ET-1)-induced vasoconstriction was also potentiated in PAs of MCT-treated rats. The response was partially inhibited by SOCE blockers, including Gd(3+), La(3+), and SKF-96365, as well as the general TRPC inhibitor BTP-2, suggesting that TRPC-dependent SOCE was involved. Moreover, the ET-1-induced contraction and Ca(2+) response in the MCT group were more susceptible to the inhibition caused by the various SOCE blockers. Hence, our study shows that MCT-induced PAH is associated with increased TRPC expression and SOCE, which are involved in the enhanced vascular reactivity to ET-1, and support the hypothesis that TRPC-dependent SOCE is an important pathway for the development of PH.

A Role of Canonical Transient Receptor Potential 5 Channel in Neuronal Differentiation from A2B5 Neural Progenitor Cells

Store-operated Ca2+ entry (SOCE) channels are the main pathway of Ca2+ entry in non-excitable cells such as neural progenitor cells (NPCs). However, the role of SOCE channels has not been defined in the neuronal differentiation from NPCs. Here, we show that canonical transient receptor potential channel (TRPC) as SOCE channel influences the induction of the neuronal differentiation of A2B5+ NPCs isolated from postnatal-12-day rat cerebrums. The amplitudes of SOCE were significantly higher in neural cells differentiated from proliferating A2B5+ NPCs and applications of SOCE blockers, 2-aminoethoxy-diphenylborane (2-APB), and ruthenium red (RR), inhibited their rise of SOCE. Among TRPC subtypes (TRPC1-7), marked expression of TRPC5 and TRPC6 with turned-off TRPC1 expression was observed in neuronal cells differentiated from proliferating A2B5+ NPCs. TRPC5 small interfering RNA (siRNA) blocked the neuronal differentiation from A2B5+ NPCs and reduced the rise of SOCE. In contrast, TRPC6 siRNA had no significant effect on the neuronal differentiation from A2B5+ NPCs. These results indicate that calcium regulation by TRPC5 would play a key role as a switch between proliferation and neuronal differentiation from NPCs.

Reversible translocation of EYFP-tagged STIM1 is coupled to calcium influx in insulin secreting β-cells

Calcium (Ca2+) signaling regulates insulin secretion in pancreatic β-cells. STIM1 has been proposed to function as an endoplasmic reticulum (ER) Ca2+ sensor regulating store-operated Ca2+ entry (SOCE). Here we studied the translocation of EYFP-STIM1 in response to ER calcium depletion in mouse insulinoma MIN6 cells by fluorescent microscopy. While in resting cells EYFP-STIM1 is co-localized with an ER marker, in thapsigargin (Tg)-stimulated cells it occupied highly defined areas of the peri-PM space in punctae adjacent to, but not entirely coincident with the ER. Co-staining with fluorescent phalloidin revealed that EYFP-STIM1 punctae was located in actin-poor areas. Use of the SOCE blocker in MIN6 cells, 2-aminoethoxy diphenylborate (2-APB), prevented store depletion-dependent translocation of EYFP-STIM1 to the PM in a concentration-dependent (3.75–100μM) and reversible manner. TIRF microscopy revealed that 2-APB treatment led to the reversible disappearance of peri-PM EYFP-STIM1 punctae, while the ER structure in this compartment remained grossly unaffected. We conclude from this data that in these cells EYFP-STIM1 is delivered to a peri-PM location from the ER upon store depletion and this trafficking is reversibly blocked by 2-APB.

Store-operated Ca 2+ channels formed by TRPC1, TRPC6 and Orai1 and non-store-operated channels formed by TRPC3 are involved in the regulation of NADPH oxidase in HL-60 granulocytes

Ca(2+) influx has been shown to be essential for NADPH oxidase activity which is involved in the inflammatory process. Ca(2+) conditions underlying the oxidative response are clearly delineated. Here, we show that store-operated Ca(2+) entry (SOCE) is required at the beginning of NADPH oxidase activation in response to fMLF (N-formyl-L-methionyl-L-leucyl-L-phenylalanine) in neutrophil-like HL-60 cells. When extracellular Ca(2+) is initially removed, early addition of Ca(2+) after stimulation causes a complete restoration of Ca(2+) entry and H(2)O(2) production. Both Ca(2+) entry and H(2)O(2) production are decreased by purported SOCE blockers, 2-aminoethoxydiphenyl borane (2-APB) and SK&F 96365. Endogenously expressed TRPC (transient receptor potential canonical) homologues and Orai1 were investigated for their role in supporting store-operated Ca(2+) channels activity. TRPC1, TRPC6 and Orai1 knock-out by siRNA resulted in the inhibition of Ca(2+) influx and H(2)O(2) production in response to fMLF and thapsigargin while suppression of TRPC3 had no effect on thapsigargin induced-SOCE. 2-APB and SK&F 96365 were able to amplify the reduction of fMLF-stimulated Ca(2+) entry and H(2)O(2) production observed in cells transfected by TRPC3 siRNA. In summary, Ca(2+) influx in HL-60 cells relies on different membrane TRPC channels and Orai1 for allowing NADPH oxidase activation. TRPC3 primarily mediates SOCE-independent pathways and TRPC1, TRPC6 and Orai1 exclusively contribute to SOCE.