Activity of Ca -activated Cl channels contributes to regulating receptor- and store-operated Ca entry in human pulmonary artery smooth muscle cells

ANO1, CaV1.2, and IP3R form a localized unit of EC-coupling in mouse pulmonary arterial smooth muscle

Pulmonary arterial (PA) smooth muscle cells (PASMC) generate vascular tone in response to agonists coupled to Gq-protein receptor signaling. Such agonists stimulate oscillating calcium waves, the frequency of which drives the strength of contraction. These Ca2+ events are modulated by a variety of ion channels including voltage-gated calcium channels (CaV1.2), the Tmem16a or Anoctamin-1 (ANO1)-encoded calcium-activated chloride (CaCC) channel, and Ca2+ release from the sarcoplasmic reticulum through inositol-trisphosphate receptors (IP3R). Although these calcium events have been characterized, it is unclear how these calcium oscillations underly a sustained contraction in these muscle cells. We used smooth muscle-specific ablation of ANO1 and pharmacological tools to establish the role of ANO1, CaV1.2, and IP3R in the contractile and intracellular Ca2+ signaling properties of mouse PA smooth muscle expressing the Ca2+ biosensor GCaMP3 or GCaMP6. Pharmacological block or genetic ablation of ANO1 or inhibition of CaV1.2 or IP3R, or Ca2+ store depletion equally inhibited 5-HT-induced tone and intracellular Ca2+ waves. Coimmunoprecipitation experiments showed that an anti-ANO1 antibody was able to pull down both CaV1.2 and IP3R. Confocal and superresolution nanomicroscopy showed that ANO1 coassembles with both CaV1.2 and IP3R at or near the plasma membrane of PASMC from wild-type mice. We conclude that the stable 5-HT-induced PA contraction results from the integration of stochastic and localized Ca2+ events supported by a microenvironment comprising ANO1, CaV1.2, and IP3R. In this model, ANO1 and CaV1.2 would indirectly support cyclical Ca2+ release events from IP3R and propagation of intracellular Ca2+ waves.

Calcineurin Is a Universal Regulator of Vessel Function-Focus on Vascular Smooth Muscle Cells

Calcineurin, a serine/threonine phosphatase regulating transcription factors like NFaT and CREB, is well known for its immune modulatory effects and role in cardiac hypertrophy. Results from experiments with calcineurin knockout animals and calcineurin inhibitors indicate that calcineurin also plays a crucial role in vascular function, especially in vascular smooth muscle cells (VSMCs). In the aorta, calcineurin stimulates the proliferation and migration of VSMCs in response to vascular injury or angiotensin II administration, leading to pathological vessel wall thickening. In the heart, calcineurin mediates coronary artery formation and VSMC differentiation, which are crucial for proper heart development. In pulmonary VSMCs, calcineurin/NFaT signaling regulates the release of Ca2+, resulting in increased vascular tone followed by pulmonary arterial hypertension. In renal VSMCs, calcineurin regulates extracellular matrix secretion promoting fibrosis development. In the mesenteric and cerebral arteries, calcineurin mediates a phenotypic switch of VSMCs leading to altered cell function. Gaining deeper insights into the underlying mechanisms of calcineurin signaling will help researchers to understand developmental and pathogenetical aspects of the vasculature. In this review, we provide an overview of the physiological function and pathophysiology of calcineurin in the vascular system with a focus on vascular smooth muscle cells in different organs. Overall, there are indications that under certain pathological settings reduced calcineurin activity seems to be beneficial for cardiovascular health.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Translational potential of targeting Anoctamin-1-Encoded Calcium-Activated chloride channels in hypertension

Calcium-activated chloride channels (CaCC) provide a depolarizing stimulus to a variety of tissues through chloride efflux in response to a rise in internal Ca²⁺ and voltage. One of these channels, Anoctamin-1 (ANO1 or TMEM16A) is now recognized to play a central role in promoting smooth muscle tone in various types of blood vessels. Its role in hypertension, and thus the therapeutic promise of targeting ANO1, is less straightforward. This review gives an overview of our current knowledge about the potential role ANO1 may play in hypertension within the systemic, portal, and pulmonary vascular systems and the importance of this information when pursuing potential treatment strategies. While the role of ANO1 is well-established in several forms of pulmonary hypertension, its contributions to both the generation of vascular tone and its role in hypertension within the systemic and portal systems are much less clear. This, combined with ANO1's various roles throughout a multitude of tissues throughout the body, command caution when targeting ANO1 as a therapeutic target and may require tissue-selective strategies.

Upregulated ClC3 channels/transporters elicit swelling-activated Cl- currents and induce excessive cell proliferation in idiopathic pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by vascular remodeling of the pulmonary artery, which is mainly attributed to the excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs) comprising the medial layer of pulmonary arteries. The activity of ion channels associated with cytosolic Ca²⁺ signaling regulates the pathogenesis of PAH. Limited information is currently available on the role of Cl^- channels in PASMCs. Therefore, the functional expression of ClC3 channels/transporters was herein investigated in the PASMCs of normal subjects and patients with idiopathic pulmonary arterial hypertension (IPAH). Expression analyses revealed the upregulated expression of ClC3 channels/transporters at the mRNA and protein levels in IPAH-PASMCs. Hypoosmotic perfusion (230 mOsm) evoked swelling-activated Cl^- currents (I_Cl-swell) in normal-PASMCs, whereas 100 μM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) exerted the opposite effects. The siRNA knockdown of ClC3 did not affect I_Cl-swell. On the other hand, I_Cl-swell was larger in IPAH-PASMCs and inhibited by DIDS and the siRNA knockdown of ClC3. IPAH-PASMCs grew more than normal-PASMCs. The growth of IPAH-PASMCs was suppressed by niflumic acid and DIDS, but not by 9-anthracenecarboxylic acid or T16A_inh-A01. The siRNA knockdown of ClC3 also inhibited the proliferation of IPAH-PASMCs. Collectively, the present results indicate that upregulated ClC3 channels/transporters are involved in I_Cl-swell and the excessive proliferation of IPAH-PASMCs, thereby contributing to the pathogenesis of PAH. Therefore, ClC3 channels/transporters have potential as a target of therapeutic drugs for the treatment of PAH.

Role of Ion Channel Remodeling in Endothelial Dysfunction Induced by Pulmonary Arterial Hypertension

Endothelial dysfunction is a key player in advancing vascular pathology in pulmonary arterial hypertension (PAH), a disease essentially characterized by intense remodeling of the pulmonary vasculature, vasoconstriction, endothelial dysfunction, inflammation, oxidative stress, and thrombosis in situ. These vascular features culminate in an increase in pulmonary vascular resistance, subsequent right heart failure, and premature death. Over the past years, there has been a great development in our understanding of pulmonary endothelial biology related to the genetic and molecular mechanisms that modulate the endothelial response to direct or indirect injury and how their dysregulation can promote PAH pathogenesis. Ion channels are key regulators of vasoconstriction and proliferative/apoptotic phenotypes; however, they are poorly studied at the endothelial level. The current review will describe and categorize different expression, functions, regulation, and remodeling of endothelial ion channels (K+, Ca2+, Na+, and Cl− channels) in PAH. We will focus on the potential pathogenic role of ion channel deregulation in the onset and progression of endothelial dysfunction during the development of PAH and its potential therapeutic role.

The diverse roles of TMEM16A Ca2+-activated Cl- channels in inflammation

Background

Transmembrane protein 16A (TMEM16A) Ca²⁺-activated Cl^- channels have diverse physiological functions, such as epithelial secretion of Cl^- and fluid and sensation of pain. Recent studies have demonstrated that TMEM16A contributes to the pathogenesis of infectious and non-infectious inflammatory diseases. However, the role of TMEM16A in inflammation has not been clearly elucidated.

Aim of review

In this review, we aimed to provide comprehensive information regarding the roles of TMEM16A in inflammation by summarizing the mechanisms underlying TMEM16A expression and activation under inflammatory conditions, in addition to exploring the diverse inflammatory signaling pathways activated by TMEM16A. This review attempts to develop the idea that TMEM16A plays a diverse role in inflammatory processes and contributes to inflammatory diseases in a cellular environment-dependent manner.

Key scientific concepts of review

Multiple inflammatory mediators, including cytokines (e.g., interleukin (IL)-4, IL-13, IL-6), histamine, bradykinin, and ATP/UTP, as well as bacterial and viral infections, promote TMEM16A expression and/or activity under inflammatory conditions. In addition, TMEM16A activates diverse inflammatory signaling pathways, including the IP₃R-mediated Ca²⁺ signaling pathway, the NF-κB signaling pathway, and the ERK signaling pathway, and contributes to the pathogenesis of many inflammatory diseases. These diseases include airway inflammatory diseases, lipopolysaccharide-induced intestinal epithelial barrier dysfunction, acute pancreatitis, and steatohepatitis. TMEM16A also plays multiple roles in inflammatory processes by increasing vascular permeability and leukocyte adhesion, promoting inflammatory cytokine release, and sensing inflammation-induced pain. Furthermore, TMEM16A plays its diverse pathological roles in different inflammatory diseases depending on the disease severity, proliferating status of the cells, and its interacting partners. We herein propose cellular environment-dependent mechanisms that explain the diverse roles of TMEM16A in inflammation.

Halofuginone, a promising drug for treatment of pulmonary hypertension

BACKGROUND AND PURPOSE

Halofuginone is a febrifugine derivative originally isolated from Chinese traditional herb Chang Shan that exhibits anti-hypertrophic, anti-fibrotic and anti-proliferative effects. We sought to investigate whether halofuginone induced pulmonary vasodilation and attenuates chronic hypoxia-induced pulmonary hypertension (HPH).

EXPERIMENTAL APPROACH

Patch-clamp experiments were conducted to examine the activity of voltage-dependent Ca²⁺ channels (VDCCs) in pulmonary artery smooth muscle cells (PASMCs). Digital fluorescence microscopy was used to measure intracellular Ca²⁺ concentration in PASMCs. Isolated perfused and ventilated mouse lungs were used to measure pulmonary artery pressure (PAP). Mice exposed to hypoxia (10% O₂ ) for 4 weeks were used as model of HPH for in vivo experiments.

KEY RESULTS

Halofuginone increased voltage-gated K⁺ (K_v ) currents in PASMCs and K⁺ currents through KCNA5 channels in HEK cells transfected with KCNA5 gene. HF (0.03-1 μM) inhibited receptor-operated Ca²⁺ entry in HEK cells transfected with calcium-sensing receptor gene and attenuated store-operated Ca²⁺ entry in PASMCs. Acute (3-5 min) intrapulmonary application of halofuginone significantly and reversibly inhibited alveolar hypoxia-induced pulmonary vasoconstriction dose-dependently (0.1-10 μM). Intraperitoneal administration of halofuginone (0.3 mg·kg^-1 , for 2 weeks) partly reversed established PH in mice.

CONCLUSION AND IMPLICATIONS

Halofuginone is a potent pulmonary vasodilator by activating K_v channels and blocking VDCC and receptor-operated and store-operated Ca²⁺ channels in PASMCs. The therapeutic effect of halofuginone on experimental PH is probably due to combination of its vasodilator effects, via inhibition of excitation-contraction coupling and anti-proliferative effects, via inhibition of the PI3K/Akt/mTOR signalling pathway.

Chronic hypoxia promoted pulmonary arterial smooth muscle cells proliferation through upregulated calcium-sensing receptorcanonical transient receptor potential 1/6 pathway

OBJECTIVES

Although both calcium-sensing receptor (CaSR) and canonical transient receptor potential (TRPC) proteins contribute to chronic hypoxia (CH)-induced pulmonary arterial smooth muscle cells (PASMCs) proliferation, the relationship between CaSR and TRPC in hypoxic PASMCs proliferation remains poorly understood. The goal of this study was to identify that CH promotes PASMCs proliferation through CaSR-TRPC pathway.

METHODS

Rat PASMCs were isolated and treated with CH. Cell proliferation was assessed by cell counting, CCK-8 assay, and EdU incorporation. CaSR and TRPC expressions were determined by qPCR and Western blotting. Store-operated Ca²⁺ entry (SOCE) was assessed by extracellular Ca²⁺ restoration.

RESULTS

In PASMCs, CH enhanced the cell number, cell viability and DNA synthesis, which is accompanied by upregulated expression of CaSR, TRPC1 and TRPC6. Negative CaSR modulators (NPS2143, NPS2390) inhibited, whereas positive modulators (spermine, R568) enhanced, the CH-induced increases in cell number, cell viability and DNA synthesis in PASMCs. Knockdown of CaSR by siRNA inhibited the CH-induced upregulation of TRPC1 and TRPC6 and enhancement of SOCE and attenuated the CH-induced enhancements of cell number, cell viability and DNA synthesis in PASMCs. However, neither siTRPC1 nor siTRPC6 had an effect on the CH-induced CaSR upregulation, although both significantly attenuated the CH-induced enhancements of cell number, cell viability and DNA synthesis in PASMCs.

CONCLUSION

These results demonstrate that upregulated CaSR-TRPC1/6 pathway mediating PASMCs proliferation is an important pathogenic mechanism under hypoxic conditions.

Electrophysiological Properties of Endogenous Single Ca2+ Activated Cl- Channels Induced by Local Ca2+ Entry in HEK293

Microdomains formed by proteins of endoplasmic reticulum and plasma membrane play a key role in store-operated Ca2+ entry (SOCE). Ca2+ release through inositol 1,4,5-trisphosphate receptor (IP3R) and subsequent Ca2+ store depletion activate STIM (stromal interaction molecules) proteins, sensors of intraluminal Ca2+, which, in turn, open the Orai channels in plasma membrane. Downstream to this process could be activated TRPC (transient receptor potential-canonical) calcium permeable channels. Using single channel patch-clamp technique we found that a local Ca2+ entry through TRPC1 channels activated endogenous Ca2+-activated chloride channels (CaCCs) with properties similar to Anoctamin6 (TMEM16F). Our data suggest that their outward rectification is based on the dependence from membrane potential of both the channel conductance and the channel activity: (1) The conductance of active CaCCs highly depends on the transmembrane potential (from 3 pS at negative potentials till 60 pS at positive potentials); (2) their activity (NPo) is enhanced with increasing Ca2+ concentration and/or transmembrane potential, conversely lowering of intracellular Ca2+ concentration reduced the open state dwell time; (3) CaCC amplitude is only slightly increased by intracellular Ca2+ concentration. Experiments with Ca2+ buffering by EGTA or BAPTA suggest close local arrangement of functional CaCCs and TRPC1 channels. It is supposed that Ca2+-activated chloride channels are involved in Ca2+ entry microdomains.

The Prognostic Value and Mechanisms of TMEM16A in Human Cancer

As a calcium ion-dependent chloride channel transmembrane protein 16A (TMEM16A) locates on the cell membrane. Numerous research results have shown that TMEM16A is abnormally expressed in many cancers. Mechanically, TMEM16A participates in cancer proliferation and migration by affecting the MAPK and CAMK signaling pathways. Additionally, it is well documented that TMEM16A exerts a regulative impact on the hyperplasia of cancer cells by interacting with EGFR in head and neck squamous cell carcinoma (HNSCC), an epithelial growth factor receptor in head and neck squamous cell carcinoma respectively. Meanwhile, as an EGFR activator, TMEM16A is considered as an oncogene or a tumor-promoting factor. More and more experimental data showed that down-regulation of TMEM16A or gene targeted therapy may be an effective treatment for cancer. This review summarized its role in various cancers and research advances related to its clinical application included treatment and diagnosis.

Notch enhances Ca2+ entry by activating calcium-sensing receptors and inhibiting voltage-gated K+ channels

The increase in cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) and upregulation of calcium-sensing receptor (CaSR) and stromal interaction molecule 2 (STIM2) along with inhibition of voltage-gated K⁺ (K_V) channels in pulmonary arterial smooth muscle cells (PASMC) have been implicated in the development of pulmonary arterial hypertension; however, the precise upstream mechanisms remain elusive. Activation of CaSR, a G protein-coupled receptor (GPCR), results in Ca²⁺ release from the endoplasmic/sarcoplasmic reticulum (ER/SR) and Ca²⁺ influx through receptor-operated and store-operated Ca²⁺ channels (SOC). Upon Ca²⁺ depletion from the SR, STIM forms clusters to mediate store-operated Ca²⁺ entry. Activity of K_V channels, like KCNA5/K_V1.5 and KCNA2/K_V1.2, contributes to regulating membrane potential, and inhibition of K_V channels results in membrane depolarization that increases [Ca²⁺]_cyt by opening voltage-dependent Ca²⁺ channels. In this study, we show that activation of Notch by its ligand Jag-1 promotes the clustering of STIM2, and clustered STIM2 subsequently enhances the CaSR-induced Ca²⁺ influx through SOC channels. Extracellular Ca²⁺-mediated activation of CaSR increases [Ca²⁺]_cyt in CASR-transfected HEK293 cells. Treatment of CASR-transfected cells with Jag-1 further enhances CaSR-mediated increase in [Ca²⁺]_cyt. Moreover, CaSR-mediated increase in [Ca²⁺]_cyt was significantly augmented in cells co-transfected with CASR and STIM2. CaSR activation results in STIM2 clustering in CASR/STIM2-cotransfected cells. Notch activation also induces significant clustering of STIM2. Furthermore, activation of Notch attenuates whole cell K⁺ currents in KCNA5- and KCNA2-transfected cells. Together, these results suggest that Notch activation enhances CaSR-mediated increases in [Ca²⁺]_cyt by enhancing store-operated Ca²⁺ entry and inhibits KCNA5/K_V1.5 and KCNA2/K_V1.2, ultimately leading to voltage-activated Ca²⁺ entry.

Targeting TMEM16A to reverse vasoconstriction and remodelling in idiopathic pulmonary arterial hypertension

Our systematic analysis of anion channels and transporters in idiopathic pulmonary arterial hypertension (IPAH) showed marked upregulation of the Cl^- channel TMEM16A gene. We hypothesised that TMEM16A overexpression might represent a novel vicious circle in the molecular pathways causing pulmonary arterial hypertension (PAH).We investigated healthy donor lungs (n=40) and recipient lungs with IPAH (n=38) for the expression of anion channel and transporter genes in small pulmonary arteries and pulmonary artery smooth muscle cells (PASMCs).In IPAH, TMEM16A was strongly upregulated and patch-clamp recordings confirmed an increased Cl^- current in PASMCs (n=9-10). These cells were depolarised and could be repolarised by TMEM16A inhibitors or knock-down experiments (n=6-10). Inhibition/knock-down of TMEM16A reduced the proliferation of IPAH-PASMCs (n=6). Conversely, overexpression of TMEM16A in healthy donor PASMCs produced an IPAH-like phenotype. Chronic application of benzbromarone in two independent animal models significantly decreased right ventricular pressure and reversed remodelling of established pulmonary hypertension.Our findings suggest that increased TMEM16A expression and activity comprise an important pathologic mechanism underlying the vasoconstriction and remodelling of pulmonary arteries in PAH. Inhibition of TMEM16A represents a novel therapeutic approach to reverse remodelling in PAH.

STIM2 (Stromal Interaction Molecule 2)-Mediated Increase in Resting Cytosolic Free Ca2+ Concentration Stimulates PASMC Proliferation in Pulmonary Arterial Hypertension

An increase in cytosolic free Ca²⁺ concentration ([Ca²⁺]_cyt) in pulmonary artery smooth muscle cells (PASMCs) triggers pulmonary vasoconstriction and stimulates PASMC proliferation leading to vascular wall thickening. Here, we report that STIM2 (stromal interaction molecule 2), a Ca²⁺ sensor in the sarcoplasmic reticulum membrane, is required for raising the resting [Ca²⁺]_cyt in PASMCs from patients with pulmonary arterial hypertension (PAH) and activating signaling cascades that stimulate PASMC proliferation and inhibit PASMC apoptosis. Downregulation of STIM2 in PAH-PASMCs reduces the resting [Ca²⁺]_cyt, whereas overexpression of STIM2 in normal PASMCs increases the resting [Ca²⁺]_cyt The increased resting [Ca²⁺]_cyt in PAH-PASMCs is associated with enhanced phosphorylation (p) of CREB (cAMP response element-binding protein), STAT3 (signal transducer and activator of transcription 3), and AKT, increased NFAT (nuclear factor of activated T-cell) nuclear translocation, and elevated level of Ki67 (a marker of cell proliferation). Furthermore, the STIM2-associated increase in the resting [Ca²⁺]_cyt also upregulates the antiapoptotic protein Bcl-2 in PAH-PASMCs. Downregulation of STIM2 in PAH-PASMCs with siRNA (1) decreases the level of pCREB, pSTAT3, and pAKT and inhibits NFAT nuclear translocation, thereby attenuating proliferation, and (2) decreases Bcl-2, which leads to an increase of apoptosis. In summary, these data indicate that upregulated STIM2 in PAH-PASMCs, by raising the resting [Ca²⁺]_cyt, contributes to enhancing PASMC proliferation by activating the CREB, STAT3, AKT, and NFAT signaling pathways and stimulating PASMC proliferation. The STIM2-associated increase in the resting [Ca²⁺]_cyt is also involved in upregulating Bcl-2 that makes PAH-PASMCs resistant to apoptosis, and thus plays an important role in sustained pulmonary vasoconstriction and excessive pulmonary vascular remodeling in patients with PAH.

Inhibition of phosphodiesterase-5 suppresses calcineurin/NFAT- mediated TRPC6 expression in pulmonary artery smooth muscle cells

The up-regulation of transient receptor potential channel 6 (TRPC6) has been found to contribute to the proliferation of pulmonary artery smooth muscle cells (PASMCs), and inhibition of phosphodiesterase-5 (PDE5) has been shown to suppress TRPC6 expression in PASMCs. However, the molecular mechanisms underlying the up-regulation of TRPC6 expression and PDE5 modulation of TRPC6 expression in PASMCs remain largely unclear. The aim of this study is to address these issues. Endothelin-1 (ET-1) dose and time-dependently up-regulated TRPC6 expression in primary cultured rat PASMCs, and this was accompanied with the activation of calcineurin and subsequent translocation of NFATc4 to the nucleus. Further study indicated that inhibition of calcineurin by cyclosporine A or knockdown of NFATc4 using small interfering RNA suppressed ET-1-induced TRPC6 up-regulation. In addition, luciferase reporter assay showed that NFATc4 directly regulated the expression of TRPC6 in PASMCs. Inhibition of PDE5 by sildenafil suppressed ET-1-induced activation of calcineurin/NFATc4 signaling pathway and consequent TRPC6 up-regulation in PASMCs, while these inhibitory effects of sildenafil were abolished by PKG inhibitor Rp-8Br-cGMPs. Taken together, our study indicates that ET-1 stimulates TRPC6 expression by activation of calcineurin/NFATc4 signaling pathway, and inhibition of PDE5 suppresses calcineurin/NFATc4- mediated TRPC6 expression in PASMCs in a cGMP-PKG-dependent manner.

IL-4 and serum amyloid P inversely regulate fibrocyte differentiation by targeting store-operated Ca2+ channels

BACKGROUND

Circulating fibrocytes (CFs) have been shown to participate in subepithelial fibrosis of asthma with chronic airflow limitation by acting as an important source of fibroblasts deposited beneath airway epithelia. Serum amyloid P (SAP) is an innate inhibitor of fibrocytes differentiation. Store-operated Ca²⁺ entry (SOCE) is the major Ca²⁺ influx of non-excitable cells. In this study, the role of SOCE in the regulation of fibrocytes differentiation and the effects of Th2 cytokine IL-4 and SAP on SOCE of fibrocytes were investigated.

METHODS

Peripheral blood mononuclear cells or monocytes were cultured in serum-free medium for 7days to differentiate into fibrocytes; the expression of SOC channels was determined with PCR, SOCE was measured with Ca²⁺ fluorescence imaging.

RESULTS

IL-4 significantly promoted monocyte derived fibrocytes differentiation in vitro. It also increased both SOCE which was induced by thapsigargin or UTP and molecules STIM1 and Orai1 which were related to expression of SOC channels in fibrocytes. Fibrocytes differentiation induced by IL-4 and SOC channels activity could be inhibited by SOC channel blocker SKF-96365. As expected, SAP significantly inhibited IL-4-induced differentiation of fibrocytes, the activity of SOCE and the expression of STIM1 and Orai1 in IL-4-treated fibrocytes.

CONCLUSION

IL-4 and SAP reversely regulates cultured fibrocytes differentiation in vitro by respectively promoting or inhibiting the expression and activity of SOC channels in fibrocytes.

Altered expression of PPAR‑γ and TRPC in neonatal rats with persistent pulmonary hypertension

Persistent pulmonary hypertension of the newborn (PPHN) is a life-threatening disease that is commonly observed in the neonatal intensive care unit. PPHN is pathologically characterized by pulmonary vascular remodeling and, in particular, pulmonary artery smooth muscle cell (PASMC) proliferation. Decreased expression levels of peroxisome proliferator-activated receptor γ (PPAR-γ), which is a member of the nuclear receptor hormone superfamily, in combination with elevated expressions of transient receptor potential cation channel, subfamily C, member 1 (TRPC1) and TRPC6 contributes to the PASMC proliferation and excessive pulmonary vascular remodeling in adult pulmonary hypertension (PH). Whether PPAR-γ, TRPC1 and TRPC6 affect the development of vascular remodeling in PPHN model rats remains unknown. The aim of the present study was to investigate the roles of PPAR-γ, TRPC1 and TRP6 on the pathogenesis of PPHN in rats. The rat model of PPHN was established by exposure to hypoxic conditions and indomethacin treatment. Lung tissues, hearts and blood from PPHN model and Control rats were collected and examined. Parameters, including the percentage of medial wall thickness (WT %), the percentage of medial wall area (WA %), right ventricular hypertrophy (RVH) and the plasma concentration of B-type natriuretic peptide (BNP) were used to estimate the development of PPHN. The expression levels of PPAR-γ, TRPC1 and TRPC6 in lung tissues were detected by immunohistochemistry, western blotting and reverse transcription-quantitative polymerase chain reaction. Significant increases were observed in the WT %, WA %, RVH and plasma BNP in the PPHN group compare with the Control group (P<0.01). In addition, the mRNA and protein expression levels of PPAR-γ were markedly downregulated (P<0.05 vs. Control). In the PPHN group, the protein expression levels of TRPC1 and TRPC6 were higher compared to the control group; however, there was no difference in the mRNA expression levels (P>0.05). In conclusion, the present study successfully established a PPHN rat model, and the altered expressions of PPAR-γ, TRPC1 and TRPC6 in the pulmonary artery located in the lungs of newborn rats with PPHN suggested that these proteins may be important mediators of PPHN.

Notch activation of Ca2+-sensing receptor mediates hypoxia-induced pulmonary hypertension

A recent study from our group demonstrated that the Ca²⁺-sensing receptor (CaSR) was upregulated and that the extracellular Ca²⁺-induced increase in the cytosolic Ca²⁺ concentration [Ca²⁺]_cyt was enhanced in pulmonary arterial smooth muscle cells (PASMCs) from patients with idiopathic pulmonary arterial hypertension. Here, we examined whether hypoxia-induced activation of Notch signaling leads to the activation and upregulation of CaSR in hypoxia-induced pulmonary hypertension (HPH). The activation of Notch signaling with Jag-1, a Notch ligand, can activate the function and increase the expression of CaSR in acute and chronic hypoxic PASMCs. Downregulation of Notch3 with a siRNA attenuates the extracellular Ca²⁺-induced increase in [Ca²⁺]_cyt and the increase in hypoxia-induced PASMC proliferation in acute hypoxic rat PASMCs. Furthermore, we tested the prevention and rescue effects of a γ-secretase inhibitor (DAPT) in HPH rats. For the Jag-1-treated group, right ventricular systolic pressure (RVSP), right heart hypertrophy (RV/LV+S ratio), and the level of right ventricular myocardial fibrosis were higher than the hypoxia alone group. Meanwhile, DAPT treatment prevented and rescued pulmonary hypertension in HPH rats. The Notch activation of CaSR mediates hypoxia-induced pulmonary hypertension. Understanding the new molecular mechanisms that regulate [Ca²⁺]_cyt and PASMC proliferation is critical to elucidating the pathogenesis of HPH and the development of novel therapies for pulmonary hypertension.

Pathogenic role of calcium-sensing receptors in the development and progression of pulmonary hypertension

An increase in cytosolic free Ca(2+) concentration ([Ca(2+)]cyt) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and a critical stimulation for PASMC proliferation and migration. Previously, we demonstrated that expression and function of calcium sensing receptors (CaSR) in PASMC from patients with idiopathic pulmonary arterial hypertension (IPAH) and animals with experimental pulmonary hypertension (PH) were greater than in PASMC from normal subjects and control animals. However, the mechanisms by which CaSR triggers Ca(2+) influx in PASMC and the implication of CaSR in the development of PH remain elusive. Here, we report that CaSR functionally interacts with TRPC6 to regulate [Ca(2+)]cyt in PASMC. Downregulation of CaSR or TRPC6 with siRNA inhibited Ca(2+)-induced [Ca(2+)]cyt increase in IPAH-PASMC (in which CaSR is upregulated), whereas overexpression of CaSR or TRPC6 enhanced Ca(2+)-induced [Ca(2+)]cyt increase in normal PASMC (in which CaSR expression level is low). The upregulated CaSR in IPAH-PASMC was also associated with enhanced Akt phosphorylation, whereas blockade of CaSR in IPAH-PASMC attenuated cell proliferation. In in vivo experiments, deletion of the CaSR gene in mice (casr(-/-)) significantly inhibited the development and progression of experimental PH and markedly attenuated acute hypoxia-induced pulmonary vasoconstriction. These data indicate that functional interaction of upregulated CaSR and upregulated TRPC6 in PASMC from IPAH patients and animals with experimental PH may play an important role in the development and progression of sustained pulmonary vasoconstriction and pulmonary vascular remodeling. Blockade or downregulation of CaSR and/or TRPC6 with siRNA or miRNA may be a novel therapeutic strategy to develop new drugs for patients with pulmonary arterial hypertension.

Modulating Ca²⁺ signals: a common theme for TMEM16, Ist2, and TMC

Since the discovery of TMEM16A (anoctamin 1, ANO1) as Ca(2+)-activated Cl(-) channel, the protein was found to serve different physiological functions, depending on the type of tissue. Subsequent reports on other members of the anoctamin family demonstrated a broad range of yet poorly understood properties. Compromised anoctamin function is causing a wide range of diseases, such as hearing loss (ANO2), bleeding disorder (ANO6), ataxia and dystonia (ANO3, 10), persistent borrelia and mycobacteria infection (ANO10), skeletal syndromes like gnathodiaphyseal dysplasia and limb girdle muscle dystrophy (ANO5), and cancer (ANO1, 6, 7). Animal models demonstrate CF-like airway disease, asthma, and intestinal hyposecretion (ANO1). Although present data indicate that ANO1 is a Ca(2+)-activated Cl(-) channel, it remains unclear whether all anoctamins form plasma membrane-localized or intracellular chloride channels. We find Ca(2+)-activated Cl(-) currents appearing by expression of most anoctamin paralogs, including the Nectria haematococca homologue nhTMEM16 and the yeast homologue Ist2. As recent studies show a role of anoctamins, Ist2, and the related transmembrane channel-like (TMC) proteins for intracellular Ca(2+) signaling, we will discuss the role of these proteins in generating compartmentalized Ca(2+) signals, which may give a hint as to the broad range of cellular functions of anoctamins.

ATP promotes cell survival via regulation of cytosolic [Ca2+] and Bcl-2/Bax ratio in lung cancer cells

Adenosine triphosphate (ATP) is a ubiquitous extracellular messenger elevated in the tumor microenvironment. ATP regulates cell functions by acting on purinergic receptors (P2X and P2Y) and activating a series of intracellular signaling pathways. We examined ATP-induced Ca(2+) signaling and its effects on antiapoptotic (Bcl-2) and proapoptotic (Bax) proteins in normal human airway epithelial cells and lung cancer cells. Lung cancer cells exhibited two phases (transient and plateau phases) of increase in cytosolic [Ca(2+)] ([Ca(2+)]cyt) caused by ATP, while only the transient phase was observed in normal cells. Removal of extracellular Ca(2+) eliminated the plateau phase increase of [Ca(2+)]cyt in lung cancer cells, indicating that the plateau phase of [Ca(2+)]cyt increase is due to Ca(2+) influx. The distribution of P2X (P2X1-7) and P2Y (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11) receptors was different between lung cancer cells and normal cells. Proapoptotic P2X7 was nearly undetectable in lung cancer cells, which may explain why lung cancer cells showed decreased cytotoxicity when treated with high concentration of ATP. The Bcl-2/Bax ratio was increased in lung cancer cells following treatment with ATP; however, the antiapoptotic protein Bcl-2 demonstrated more sensitivity to ATP than proapoptotic protein Bax. Decreasing extracellular Ca(2+) or chelating intracellular Ca(2+) with BAPTA-AM significantly inhibited ATP-induced increase in Bcl-2/Bax ratio, indicating that a rise in [Ca(2+)]cyt through Ca(2+) influx is the critical mediator for ATP-mediated increase in Bcl-2/Bax ratio. Therefore, despite high ATP levels in the tumor microenvironment, which would induce cell apoptosis in normal cells, the decreased P2X7 and elevated Bcl-2/Bax ratio in lung cancer cells may enable tumor cells to survive. Increasing the Bcl-2/Bax ratio by exposure to high extracellular ATP may, therefore, be an important selective pressure promoting transformation and cancer progression.

Inhibition of Excessive Cell Proliferation by Calcilytics in Idiopathic Pulmonary Arterial Hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a rare and progressive disease of unknown pathogenesis. Vascular remodeling due to excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs) is a critical pathogenic event that leads to early morbidity and mortality. The excessive cell proliferation is closely linked to the augmented Ca2+ signaling in PASMCs. More recently, we have shown by an siRNA knockdown method that the Ca2+-sensing receptor (CaSR) is upregulated in PASMCs from IPAH patients, involved in the enhanced Ca2+ response and subsequent excessive cell proliferation. In this study, we examined whether pharmacological blockade of CaSR attenuated the excessive proliferation of PASMCs from IPAH patients by MTT assay. The proliferation rate of PASMCs from IPAH patients was much higher (~1.5-fold) than that of PASMCs from normal subjects and patients with chronic thromboembolic pulmonary hypertension (CTEPH). Treatment with NPS2143, an antagonist of CaSR or calcilytic, clearly suppressed the cell proliferation in a concentration-dependent manner (IC50 = 2.64 μM) in IPAH-PASMCs, but not in normal and CTEPH PASMCs. Another calcilytic, Calhex 231, which is structurally unrelated to NPS2143, also concentration-dependently inhibited the excessive proliferation of IPAH-PASMCs (IC50 = 1.89 μM). In contrast, R568, an activator of CaSR or calcimimetic, significantly facilitated the proliferation of IPAH-PASMCs (EC50 = 0.33 μM). Similar results were obtained by BrdU incorporation assay. These results reveal that the excessive PASMC proliferation was modulated by pharmacological tools of CaSR, showing us that calcilytics are useful for a novel therapeutic approach for pulmonary arterial hypertension.

Molecular and functional significance of Ca(2+)-activated Cl(-) channels in pulmonary arterial smooth muscle

Increased peripheral resistance of small distal pulmonary arteries is a hallmark signature of pulmonary hypertension (PH) and is believed to be the consequence of enhanced vasoconstriction to agonists, thickening of the arterial wall due to remodeling, and increased thrombosis. The elevation in arterial tone in PH is attributable, at least in part, to smooth muscle cells of PH patients being more depolarized and displaying higher intracellular Ca(2+) levels than cells from normal subjects. It is now clear that downregulation of voltage-dependent K(+) channels (e.g., Kv1.5) and increased expression and activity of voltage-dependent (Cav1.2) and voltage-independent (e.g., canonical and vanilloid transient receptor potential [TRPC and TRPV]) Ca(2+) channels play an important role in the functional remodeling of pulmonary arteries in PH. This review focuses on an anion-permeable channel that is now considered a novel excitatory mechanism in the systemic and pulmonary circulations. It is permeable to Cl(-) and is activated by a rise in intracellular Ca(2+) concentration (Ca(2+)-activated Cl(-) channel, or CaCC). The first section outlines the biophysical and pharmacological properties of the channel and ends with a description of the molecular candidate genes postulated to encode for CaCCs, with particular emphasis on the bestrophin and the newly discovered TMEM16 and anoctamin families of genes. The second section provides a review of the various sources of Ca(2+) activating CaCCs, which include stimulation by mobilization from intracellular Ca(2+) stores and Ca(2+) entry through voltage-dependent and voltage-independent Ca(2+) channels. The third and final section summarizes recent findings that suggest a potentially important role for CaCCs and the gene TMEM16A in PH.

Pathological function of Ca2+-sensing receptor in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is defined as an intractable disease characterized by a progressive elevation of pulmonary vascular resistance (PVR) and pulmonary arterial pressure (PAP), leading to right heart failure and premature death. The five-year survival rate after diagnosis is approximately 57%. Although extensive research has identified some factors associated with the cause of PAH, the etiology and pathogenesis remain unclear. In addition to Ca²⁺ channel blockers (nifedipine, diltiazem), three categories of drug have been developed for the treatment of PAH based on the pathological mechanisms: prostacyclin and its analogues (epoprostenol, treprostinil, iloprost), endothelin receptor antagonists (bosentan, ambrisentan), and phosphodiesterase type 5 inhibitors (sildenafil, tadalafil). However, screening of novel types of drug acting on the signal pathway associated with the pathological mechanism underlying PAH is ongoing. We recently found that the extracellular Ca²⁺-sensing receptor (CaSR), which belongs to family C of the G protein-coupled receptor (GPCR) superfamily, is upregulated in pulmonary arterial smooth muscle cells (PASMCs) from patients with idiopathic PAH (IPAH). The upregulated CaSR is necessary for the enhanced Ca²⁺ signaling and the augmented cell proliferation in PASMCs from IPAH patients. Most importantly, blockage of CaSR with an antagonist, NPS2143, prevents the development of pulmonary hypertension and right ventricular hypertrophy in animal models of pulmonary hypertension. The use of calcilytics, antagonists of CaSR, may be a novel therapeutic approach for PAH patients.

Antenatal hypoxia and pulmonary vascular function and remodeling

This review provides evidence that antenatal hypoxia, which represents a significant and worldwide problem, causes prenatal programming of the lung. A general overview of lung development is provided along with some background regarding transcriptional and signaling systems of the lung. The review illustrates that antenatal hypoxic stress can induce a continuum of responses depending on the species examined. Fetuses and newborns of certain species and specific human populations are well acclimated to antenatal hypoxia. However, antenatal hypoxia causes pulmonary vascular disease in fetuses and newborns of most mammalian species and humans. Disease can range from mild pulmonary hypertension, to severe vascular remodeling and dangerous elevations in pressure. The timing, length, and magnitude of the intrauterine hypoxic stress are important to disease development, however there is also a genetic-environmental relationship that is not yet completely understood. Determining the origins of pulmonary vascular remodeling and pulmonary hypertension and their associated effects is a challenging task, but is necessary in order to develop targeted therapies for pulmonary hypertension in the newborn due to antenatal hypoxia that can both treat the symptoms and curtail or reverse disease progression.

Activation of Notch signaling by short-term treatment with Jagged-1 enhances store-operated Ca(2+) entry in human pulmonary arterial smooth muscle cells

Notch signaling plays a critical role in controlling proliferation and differentiation of pulmonary arterial smooth muscle cells (PASMC). Upregulated Notch ligands and Notch3 receptors in PASMC have been reported to promote the development of pulmonary vascular remodeling in patients with pulmonary arterial hypertension (PAH) and in animals with experimental pulmonary hypertension. Activation of Notch receptors by their ligands leads to the cleavage of the Notch intracellular domain (NICD) to the cytosol by γ-secretase; NICD then translocates into the nucleus to regulate gene transcription. In this study, we examined whether short-term activation of Notch functionally regulates store-operated Ca(2+) entry (SOCE) in human PASMC. Treatment of PASMC with the active fragment of human Jagged-1 protein (Jag-1) for 15-60 min significantly increased the amplitude of SOCE induced by passive deletion of Ca(2+) from the intracellular stores, the sarcoplasmic reticulum (SR). The Jag-1-induced enhancement of SOCE was time dependent: the amplitude was maximized at 30 min of treatment with Jag-1, which was closely correlated with the time course of Jag-1-mediated increase in NICD protein level. The scrambled peptide of Jag-1 active fragment had no effect on SOCE. Inhibition of γ-secretase by N-[N-(3,5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester (DAPT) significantly attenuated the Jag-1-induced augmentation of SOCE. In addition to the short-term effect, prolonged treatment of PASMC with Jag-1 for 48 h also markedly enhanced the amplitude of SOCE. These data demonstrate that short-term activation of Notch signaling enhances SOCE in PASMC; the NICD-mediated functional interaction with store-operated Ca(2+) channels (SOC) may be involved in the Jag-1-mediated enhancement of SOCE in human PASMC.

Inhibition of the Ca(2+)-sensing receptor rescues pulmonary hypertension in rats and mice

A recent study from our group demonstrated that the Ca(2+)-sensing receptor (CaSR) was upregulated, and the extracellular Ca(2+)-induced increase in cytosolic Ca(2+) concentration ([Ca(2+)]cyt) was enhanced in pulmonary arterial smooth muscle cells from patients with idiopathic pulmonary arterial hypertension and animals with experimental pulmonary hypertension (PH). However, it is unclear whether CaSR antagonists (for example, NPS2143) rescue the development of experimental PH. We tested the rescue effects of NPS2143 in rats with monocrotaline (MCT)-induced PH and mice with chronic hypoxia-induced PH. For the NPS2143 treatment group, rats and mice were i.p. injected with NPS2143 once per day from days 14 to 24. Four weeks after MCT injection or exposure to normobaric hypoxia, the right ventricular (RV) systolic pressure, right heart hypertrophy (RV/LV+S ratio) and RV myocardial fibrosis were rescued or nearly restored to normal levels by NPS2143 treatment. The rescue effects of NPS2143 on experimental PH further support a critical role for the CaSR in the PH mechanism. Therefore, NPS2143 may be a promising potential treatment for pulmonary arterial hypertension.

Flufenamic acid as an ion channel modulator

Flufenamic acid has been known since the 1960s to have anti-inflammatory properties attributable to the reduction of prostaglandin synthesis. Thirty years later, flufenamic acid appeared to be an ion channel modulator. Thus, while its use in medicine diminished, its use in ionic channel research expanded. Flufenamic acid commonly not only affects non-selective cation channels and chloride channels, but also modulates potassium, calcium and sodium channels with effective concentrations ranging from 10(-6)M in TRPM4 channel inhibition to 10(-3)M in two-pore outwardly rectifying potassium channel activation. Because flufenamic acid effects develop and reverse rapidly, it is a convenient and widely used tool. However, given the broad spectrum of its targets, experimental results have to be interpreted cautiously. Here we provide an overview of ion channels targeted by flufenamic acid to aid in interpreting its effects at the molecular, cellular, and system levels. If it is used with good practices, flufenamic acid remains a useful tool for ion channel research. Understanding the targets of FFA may help reevaluate its physiological impacts and revive interest in its therapeutic potential.

Dihydropyridine Ca(2+) channel blockers increase cytosolic [Ca(2+)] by activating Ca(2+)-sensing receptors in pulmonary arterial smooth muscle cells

RATIONALE

An increase in cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and an important stimulus for PASMC proliferation and pulmonary vascular remodeling. The dihydropyridine Ca(2+) channel blockers, such as nifedipine, have been used for treatment of idiopathic pulmonary arterial hypertension (IPAH).

OBJECTIVE

Our previous study demonstrated that the Ca(2+)-sensing receptor (CaSR) was upregulated and the extracellular Ca(2+)-induced increase in [Ca(2+)](cyt) was enhanced in PASMC from patients with IPAH and animals with experimental pulmonary hypertension. Here, we report that the dihydropyridines (eg, nifedipine) increase [Ca(2+)](cyt) by activating CaSR in PASMC from IPAH patients (in which CaSR is upregulated), but not in normal PASMC.

METHODS AND RESULTS

The nifedipine-mediated increase in [Ca(2+)](cyt) in IPAH-PASMC was concentration dependent with a half maximal effective concentration of 0.20 µmol/L. Knockdown of CaSR with siRNA in IPAH-PASMC significantly inhibited the nifedipine-induced increase in [Ca(2+)](cyt), whereas overexpression of CaSR in normal PASMC conferred the nifedipine-induced rise in [Ca(2+)](cyt). Other dihydropyridines, nicardipine and Bay K8644, had similar augmenting effects on the CaSR-mediated increase in [Ca(2+)](cyt) in IPAH-PASMC; however, the nondihydropyridine blockers, such as diltiazem and verapamil, had no effect on the CaSR-mediated rise in [Ca(2+)](cyt).

CONCLUSIONS

The dihydropyridine derivatives increase [Ca(2+)](cyt) by potentiating the activity of CaSR in PASMC independently of their blocking (or activating) effect on Ca(2+) channels; therefore, it is possible that the use of dihydropyridine Ca(2+) channel blockers (eg, nifedipine) to treat IPAH patients with upregulated CaSR in PASMC may exacerbate pulmonary hypertension.

Self-cleavage of human CLCA1 protein by a novel internal metalloprotease domain controls calcium-activated chloride channel activation

The chloride channel calcium-activated (CLCA) family are secreted proteins that regulate both chloride transport and mucin expression, thus controlling the production of mucus in respiratory and other systems. Accordingly, human CLCA1 is a critical mediator of hypersecretory lung diseases, such as asthma, chronic obstructive pulmonary disease, and cystic fibrosis, that manifest mucus obstruction. Despite relevance to homeostasis and disease, the mechanism of CLCA1 function remains largely undefined. We address this void by showing that CLCA proteins contain a consensus proteolytic cleavage site recognized by a novel zincin metalloprotease domain located within the N terminus of CLCA itself. CLCA1 mutations that inhibit self-cleavage prevent activation of calcium-activated chloride channel (CaCC)-mediated chloride transport. CaCC activation requires cleavage to unmask the N-terminal fragment of CLCA1, which can independently gate CaCCs. Gating of CaCCs mediated by CLCA1 does not appear to involve proteolytic cleavage of the channel because a mutant N-terminal fragment deficient in proteolytic activity is able to induce currents comparable with that of the native fragment. These data provide both a mechanistic basis for CLCA1 self-cleavage and a novel mechanism for regulation of chloride channel activity specific to the mucosal interface.

Increased TMEM16A-encoded calcium-activated chloride channel activity is associated with pulmonary hypertension

Pulmonary artery smooth muscle cells (PASMCs) are more depolarized and display higher Ca(2+) levels in pulmonary hypertension (PH). Whether the functional properties and expression of Ca(2+)-activated Cl- channels (Cl(Ca)), an important excitatory mechanism in PASMCs, are altered in PH is unknown. The potential role of Cl(Ca) channels in PH was investigated using the monocrotaline (MCT)-induced PH model in the rat. Three weeks postinjection with a single dose of MCT (50 mg/kg ip), the animals developed right ventricular hypertrophy (heart weight measurements) and changes in pulmonary arterial flow (pulse-waved Doppler imaging) that were consistent with increased pulmonary arterial pressure and PH. Whole cell patch experiments revealed an increase in niflumic acid (NFA)-sensitive Ca(2+)-activated Cl(-) current [I(Cl(Ca))] density in PASMCs from large conduit and small intralobar pulmonary arteries of MCT-treated rats vs. aged-matched saline-injected controls. Quantitative RT-PCR and Western blot analysis revealed that the alterations in I(Cl(Ca)) were accompanied by parallel changes in the expression of TMEM16A, a gene recently shown to encode for Cl(Ca) channels. The contraction to serotonin of conduit and intralobar pulmonary arteries from MCT-treated rats exhibited greater sensitivity to nifedipine (1 μM), an l-type Ca(2+) channel blocker, and NFA (30 or 100 μM, with or without 10 μM indomethacin to inhibit cyclooxygenases) or T16A(Inh)-A01 (10 μM), TMEM16A/Cl(Ca) channel inhibitors, than that of control animals. In conclusion, augmented Cl(Ca)/TMEM16A channel activity is a major contributor to the changes in electromechanical coupling of PA in this model of PH. TMEM16A-encoded channels may therefore represent a novel therapeutic target in this disease.

Activation of Ca2+-activated Cl- channels by store-operated Ca2+ entry in arterial smooth muscle cells does not require reverse-mode Na+/Ca2+ exchange

The main purpose of this study was to characterize the stimulation of Ca(2+)-activated Cl(-) (Cl(Ca)) by store-operated Ca(2+) entry (SOCE) channels in rabbit pulmonary arterial smooth muscle cells (PASMCs) and determine if this process requires reverse-mode Na(+)/Ca(2+) exchange (NCX). In whole-cell voltage clamped PASMCs incubated with 1 μmol/L nifedipine (Nif) to inhibit Ca(2+) channels, 30 μmol/L cyclopiazonic acid (CPA), a SERCA pump inhibitor, activated a nonselective cation conductance permeable to Na(+) (I(SOC)) during an initial 1-3 s step, ranging from-120 to +60 mV, and Ca(2+)-activated Cl(-) current (I(Cl(Ca))) during a second step to +90 mV that increased with the level of the preceding hyperpolarizing step. Niflumic acid (100 μmol/L), a Cl(Ca) channel blocker, abolished I(Cl(Ca)) but had no effect on I(SOC), whereas the I(SOC) blocker SKF-96365 (50 μmol/L) suppressed both currents. Dual patch clamp and Fluo-4 fluorescence measurements revealed the appearance of CPA-induced Ca(2+) transients of increasing magnitude with increasing hyperpolarizing steps, which correlated with I(Cl(Ca)) amplitude. The absence of Ca(2+) transients at positive potentials following a hyperpolarizing step combined with the observation that SOCE-stimulated I(Cl(Ca)) was unaffected by the NCX blocker KB-R7943 (1 μmol/L) suggest that the SOCE/Cl(Ca) interaction does not require reverse-mode NCX in our conditions.

Enhanced Ca(2+)-sensing receptor function in idiopathic pulmonary arterial hypertension

RATIONALE

A rise in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) in pulmonary arterial smooth muscle cells (PASMC) is an important stimulus for pulmonary vasoconstriction and vascular remodeling. Increased resting [Ca(2+)](cyt) and enhanced Ca(2+) influx have been implicated in PASMC from patients with idiopathic pulmonary arterial hypertension (IPAH).

OBJECTIVE

We examined whether the extracellular Ca(2+)-sensing receptor (CaSR) is involved in the enhanced Ca(2+) influx and proliferation in IPAH-PASMC and whether blockade of CaSR inhibits experimental pulmonary hypertension.

METHODS AND RESULTS

In normal PASMC superfused with Ca(2+)-free solution, addition of 2.2 mmol/L Ca(2+) to the perfusate had little effect on [Ca(2+)](cyt). In IPAH-PASMC, however, restoration of extracellular Ca(2+) induced a significant increase in [Ca(2+)](cyt). Extracellular application of spermine also markedly raised [Ca(2+)](cyt) in IPAH-PASMC but not in normal PASMC. The calcimimetic R568 enhanced, whereas the calcilytic NPS 2143 attenuated, the extracellular Ca(2+)-induced [Ca(2+)](cyt) rise in IPAH-PASMC. Furthermore, the protein expression level of CaSR in IPAH-PASMC was greater than in normal PASMC; knockdown of CaSR in IPAH-PASMC with siRNA attenuated the extracellular Ca(2+)-mediated [Ca(2+)](cyt) increase and inhibited IPAH-PASMC proliferation. Using animal models of pulmonary hypertension, our data showed that CaSR expression and function were both enhanced in PASMC, whereas intraperitoneal injection of the calcilytic NPS 2143 prevented the development of pulmonary hypertension and right ventricular hypertrophy in rats injected with monocrotaline and mice exposed to hypoxia.

CONCLUSIONS

The extracellular Ca(2+)-induced increase in [Ca(2+)](cyt) due to upregulated CaSR is a novel pathogenic mechanism contributing to the augmented Ca(2+) influx and excessive PASMC proliferation in patients and animals with pulmonary arterial hypertension.