T-type calcium channels are involved in hypoxic pulmonary hypertension

Cav3.1 T-type calcium channel blocker NNC 55-0396 reduces atherosclerosis by increasing cholesterol efflux

Calcium channel blockers (CCBs) are commonly used as antihypertensive agents. While certain L-type CCBs exhibit antiatherogenic effects, the impact of Cav3.1 T-type CCBs on antiatherogenesis and lipid metabolism remains unexplored. NNC 55-0396 (NNC) is a highly selective blocker of T-type calcium channels (Cav3.1 channels). We investigated the effects of NNC on relevant molecules and molecular mechanisms in human THP-1 macrophages. Cholesterol efflux, an indicator of reverse cholesterol transport (RCT) efficiency, was assessed using [3H]-labeled cholesterol. In vivo, high cholesterol diet (HCD)-fed LDL receptor knockout (Ldlr-/-) mice, an atherosclerosis-prone model, underwent histochemical staining to analyze plaque burden. Treatment of THP-1 macrophages with NNC facilitated cholesterol efflux and reduced intracellular cholesterol accumulation. Pharmacological and genetic interventions demonstrated that NNC treatment or Cav3.1 knockdown significantly enhanced the protein expression of scavenger receptor B1 (SR-B1), ATP-binding cassette transporter A1 (ABCA1), ATP-binding cassette transporter G1 (ABCG1), and liver X receptor alpha (LXRα) transcription factor. Mechanistic analysis revealed that NNC activates p38 and c-Jun N-terminal kinase (JNK) phosphorylation, leading to increased expression of ABCA1, ABCG1, and LXRα-without involving the microRNA pathway. LXRα isrequired for NNC-induced ABCA1 and ABCG1 expression. Administering NNC diminished atherosclerotic lesion area and lipid deposition in HCD-fed Ldlr-/- mice. NNC's anti-atherosclerotic effects, achieved through enhanced cholesterol efflux and inhibition of lipid accumulation, suggest a promising therapeutic approach for hypertensive patients with atherosclerosis. This research highlights the potential of Cav3.1 T-type CCBs in addressing cardiovascular complications associated with hypertension.

Pulmonary Microcirculation in Experimental Model of Pulmonary Thromboembolism after Pretreatment with Chloroquine

Changes of pulmonary microcirculation in response to pulmonary artery embolization after pretreatment with chloroquine were studied on the model of isolated perfused rabbit lungs. The increase in the pulmonary vascular resistance and pre- and postcapillary resistance was less pronounced than after pulmonary thromboembolism after pretreatment with mibefradil (T-type Ca2+ channels blocker) or nifedipine (L-type Ca2+ channels blocker). The shifts of capillary filtration coefficient correlated with changes in the precapillary resistance. When modeling pulmonary thromboembolism after pretreatment with chloroquine combined with glibenclamide (KATP channels blocker), the studied hemodynamics parameters increased to the same extent as after pretreatment with nifedipine. The results indicate that chloroquine exhibits the properties of an L- and T-type Ca2+ channels blocker and an activator of KATP channels.

Acquired disorders of mitochondrial metabolism and dynamics in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an orphan disease of the cardiopulmonary unit that reflects an obstructive pulmonary vasculopathy and presents with hypertrophy, inflammation, fibrosis, and ultimately failure of the right ventricle (RVF). Despite treatment using pulmonary hypertension (PH)-targeted therapies, persistent functional impairment reduces the quality of life for people with PAH and death from RVF occurs in approximately 40% of patients within 5 years of diagnosis. PH-targeted therapeutics are primarily vasodilators and none, alone or in combination, are curative. This highlights a need to therapeutically explore molecular targets in other pathways that are involved in the pathogenesis of PAH. Several candidate pathways in PAH involve acquired mitochondrial dysfunction. These mitochondrial disorders include: 1) a shift in metabolism related to increased expression of pyruvate dehydrogenase kinase and pyruvate kinase, which together increase uncoupled glycolysis (Warburg metabolism); 2) disruption of oxygen-sensing related to increased expression of hypoxia-inducible factor 1α, resulting in a state of pseudohypoxia; 3) altered mitochondrial calcium homeostasis related to impaired function of the mitochondrial calcium uniporter complex, which elevates cytosolic calcium and reduces intramitochondrial calcium; and 4) abnormal mitochondrial dynamics related to increased expression of dynamin-related protein 1 and its binding partners, such as mitochondrial dynamics proteins of 49 kDa and 51 kDa, and depressed expression of mitofusin 2, resulting in increased mitotic fission. These acquired mitochondrial abnormalities increase proliferation and impair apoptosis in most pulmonary vascular cells (including endothelial cells, smooth muscle cells and fibroblasts). In the RV, Warburg metabolism and induction of glutaminolysis impairs bioenergetics and promotes hypokinesis, hypertrophy, and fibrosis. This review will explore our current knowledge of the causes and consequences of disordered mitochondrial function in PAH.

Piezo1 Channel Activation Reverses Pulmonary Artery Vasoconstriction in an Early Rat Model of Pulmonary Hypertension: The Role of Ca2+ Influx and Akt-eNOS Pathway

In intrapulmonary arteries (IPAs), mechanical forces due to blood flow control vessel tone, and these forces change during pulmonary hypertension (PH). Piezo1, a stretch-activated calcium channel, is a sensor of mechanical stress present in both endothelial cells (ECs) and smooth muscle cells (SMCs). The present study investigated the role of Piezo1 on IPA in the chronic hypoxia model of PH. Rats were raised in chronically hypoxic conditions for 1 (1W-CH, early stage) or 3 weeks (3W-CH, late-stage) of PH or in normoxic conditions (Nx). Immunofluorescence labeling and patch-clamping revealed the presence of Piezo1 in both ECs and SMCs. The Piezo1 agonist, Yoda1, induced an IPA contraction in Nx and 3W-CH. Conversely, Yoda1 induced an endothelial nitric oxide (eNOS) dependent relaxation in 1W-CH. In ECs, the Yoda1-mediated intracellular calcium concentration ([Ca²⁺]i) increase was greater in 1W-CH as compared to Nx. Yoda1 induced an EC hyperpolarization in 1W-CH. The eNOS levels were increased in 1W-CH IPA compared to Nx or 3W-CH PH and Yoda1 activated phosphorylation of Akt (Ser473) and eNOS (Ser1177). Thus, we demonstrated that endothelial Piezo1 contributes to intrapulmonary vascular relaxation by controlling endothelial [Ca²⁺]i, endothelial-dependent hyperpolarization, and Akt-eNOS pathway activation in the early stage of PH.

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 Action of 2-Aminoethyldiphenyl Borinate on the Pulmonary Arterial Hypertension and Remodeling of High-Altitude Hypoxemic Lambs

Calcium signaling is key for the contraction, differentiation, and proliferation of pulmonary arterial smooth muscle cells. Furthermore, calcium influx through store-operated channels (SOCs) is particularly important in the vasoconstrictor response to hypoxia. Previously, we found a decrease in pulmonary hypertension and remodeling in normoxic newborn lambs partially gestated under chronic hypoxia, when treated with 2-aminoethyldiphenyl borinate (2-APB), a non-specific SOC blocker. However, the effects of 2-APB are unknown in neonates completely gestated, born, and raised under environmental hypoxia. Accordingly, we studied the effects of 2-APB-treatment on the cardiopulmonary variables in lambs under chronic hypobaric hypoxia. Experiments were done in nine newborn lambs gestated, born, and raised in high altitude (3,600 m): five animals were treated with 2-APB [intravenous (i.v.) 10 mg kg^–1] for 10 days, while other four animals received vehicle. During the treatment, cardiopulmonary variables were measured daily, and these were also evaluated during an acute episode of superimposed hypoxia, 1 day after the end of the treatment. Furthermore, pulmonary vascular remodeling was assessed by histological analysis 2 days after the end of the treatment. Basal cardiac output and mean systemic arterial pressure (SAP) and resistance from 2-APB- and vehicle-treated lambs did not differ along with the treatment. Mean pulmonary arterial pressure (mPAP) decreased after the first day of 2-APB treatment and remained lower than the vehicle-treated group until the third day, and during the fifth, sixth, and ninth day of treatment. The net mPAP increase in response to acute hypoxia did not change, but the pressure area under the curve (AUC) during hypoxia was slightly lower in 2-APB-treated lambs than in vehicle-treated lambs. Moreover, the 2-APB treatment decreased the pulmonary arterial wall thickness and the α-actin immunoreactivity and increased the luminal area with no changes in the vascular density. Our findings show that 2-APB treatment partially reduced the contractile hypoxic response and reverted the pulmonary vascular remodeling, but this is not enough to normalize the pulmonary hemodynamics in chronically hypoxic newborn lambs.

Hypoestins A−D: highly modified fusicoccane diterpenoids with promising Cav3.1 calcium channel inhibitory activity from Hypoestes purpurea

Hypoestins A–D (1–4), four highly modified fusicoccane diterpenoids with two unreported carbon skeletons, and hypoestins E (5) and F (6), two prviously undescribed fusicoccane diterpenoids, were isolated from aerial parts...

Rhynchines A-E: Cav3.1 Calcium Channel Blockers from Uncaria rhynchophylla

Rhynchines A-E (1-5), five new indole alkaloids with an unprecedented skeleton, were isolated from Uncaria rhynchophylla. The new skeleton was characterized by an indole moiety and a 2-oxa-8-azatricyclo[6,5,01,5,01,8]tridecane core, forming a unique 6/5/7/5/5 ring system. Their structures were determined by nuclear magnetic resonance, high-resolution electrospray ionization mass spectrometry, infrared spectroscopy, and calculated electronic circular dichroism (ECD) and were confirmed by X-ray crystallography. Interestingly, 1 and 2 showed strong inhibitory activities against the Cav3.1 calcium channel with IC50 values of 6.86 and 10.41 μM.

Vasoconstrictor Mechanisms in Chronic Hypoxia-Induced Pulmonary Hypertension: Role of Oxidant Signaling

Elevated resistance of pulmonary circulation after chronic hypoxia exposure leads to pulmonary hypertension. Contributing to this pathological process is enhanced pulmonary vasoconstriction through both calcium-dependent and calcium sensitization mechanisms. Reactive oxygen species (ROS), as a result of increased enzymatic production and/or decreased scavenging, participate in augmentation of pulmonary arterial constriction by potentiating calcium influx as well as activation of myofilament sensitization, therefore mediating the development of pulmonary hypertension. Here, we review the effects of chronic hypoxia on sources of ROS within the pulmonary vasculature including NADPH oxidases, mitochondria, uncoupled endothelial nitric oxide synthase, xanthine oxidase, monoamine oxidases and dysfunctional superoxide dismutases. We also summarize the ROS-induced functional alterations of various Ca2+ and K+ channels involved in regulating Ca2+ influx, and of Rho kinase that is responsible for myofilament Ca2+ sensitivity. A variety of antioxidants have been shown to have beneficial therapeutic effects in animal models of pulmonary hypertension, supporting the role of ROS in the development of pulmonary hypertension. A better understanding of the mechanisms by which ROS enhance vasoconstriction will be useful in evaluating the efficacy of antioxidants for the treatment of pulmonary hypertension.

Revisiting the mechanism of hypoxic pulmonary vasoconstriction using isolated perfused/ventilated mouse lung

Hypoxic Pulmonary Vasoconstriction (HPV) is an important physiological mechanism of the lungs that matches perfusion to ventilation thus maximizing O2 saturation of the venous blood within the lungs. This study emphasizes on principal pathways in the initiation and modulation of hypoxic pulmonary vasoconstriction with a primary focus on the role of Ca2+ signaling and Ca2+ influx pathways in hypoxic pulmonary vasoconstriction. We used an ex vivo model, isolated perfused/ventilated mouse lung to evaluate hypoxic pulmonary vasoconstriction. Alveolar hypoxia (utilizing a mini ventilator) rapidly and reversibly increased pulmonary arterial pressure due to hypoxic pulmonary vasoconstriction in the isolated perfused/ventilated lung. By applying specific inhibitors for different membrane receptors and ion channels through intrapulmonary perfusion solution in isolated lung, we were able to define the targeted receptors and channels that regulate hypoxic pulmonary vasoconstriction. We show that extracellular Ca2+ or Ca2+ influx through various Ca2+-permeable channels in the plasma membrane is required for hypoxic pulmonary vasoconstriction. Removal of extracellular Ca2+ abolished hypoxic pulmonary vasoconstriction, while blockade of L-type voltage-dependent Ca2+ channels (with nifedipine), non-selective cation channels (with 30 µM SKF-96365), and TRPC6/TRPV1 channels (with 1 µM SAR-7334 and 30 µM capsazepine, respectively) significantly and reversibly inhibited hypoxic pulmonary vasoconstriction. Furthermore, blockers of Ca2+-sensing receptors (by 30 µM NPS2143, an allosteric Ca2+-sensing receptors inhibitor) and Notch (by 30 µM DAPT, a γ-secretase inhibitor) also attenuated hypoxic pulmonary vasoconstriction. These data indicate that Ca2+ influx in pulmonary arterial smooth muscle cells through voltage-dependent, receptor-operated, and store-operated Ca2+ entry pathways all contribute to initiation of hypoxic pulmonary vasoconstriction. The extracellular Ca2+-mediated activation of Ca2+-sensing receptors and the cell-cell interaction via Notch ligands and receptors contribute to the regulation of hypoxic pulmonary vasoconstriction.

Stretch-activated Piezo1 Channel in Endothelial Cells Relaxes Mouse Intrapulmonary Arteries

In intrapulmonary arteries (IPA), endothelial cells (EC) respond to mechanical stimuli by releasing vasoactive factors to set the vascular tone. Piezo1, a stretch-activated, calcium-permeable channel, is a sensor of mechanical stress in EC. The present study was undertaken to investigate the implication of Piezo1 in the endothelium-dependent regulation of IPA tone and potential involvement of Piezo1 in pulmonary hypertension, the main disease of this circulation. IPA tone was quantified by means of a myograph in control Piezo1^+/+ mice and in mice lacking endothelial Piezo1 (EC-Piezo1^-/-). Endothelial intracellular calcium concentration ([Ca²⁺]_i) and nitric oxide (NO) production were measured, in mouse or human EC, with Fluo-4 or DAF-FM probe, respectively. Immunofluorescent labeling and patch-clamp experiments revealed the presence of Piezo1 channels in EC. Yoda1, a Piezo1 agonist, induced an endothelium-dependent relaxation that was significantly reduced in pulmonary arteries in EC-Piezo1^-/- compared with Piezo1^+/+ mice. Yoda1 as well as mechanical stimulation (by osmotic stress) increased [Ca²⁺]_i in mouse or human EC. Consequently, both stimuli increased the production of NO. NO and [Ca²⁺]_i increases were reduced in EC from Piezo1^-/- mice or in the presence of Piezo1 inhibitors. Furthermore, deletion of Piezo1 increased α-adrenergic agonist-mediated contraction. Finally, in chronically hypoxic mice, a model of pulmonary hypertension, Piezo1 still mediated arterial relaxation, and deletion of this channel did not impair the development of the disease. The present study thus demonstrates that endothelial Piezo1 contributes to intrapulmonary vascular relaxation by controlling endothelial [Ca²⁺]_i and NO production and that this effect is still present in pulmonary hypertension.

miR-137 and its target T-type CaV 3.1 channel modulate dedifferentiation and proliferation of cerebrovascular smooth muscle cells in simulated microgravity rats by regulating calcineurin/NFAT pathway

Objectives

Postflight orthostatic intolerance has been regarded as a major adverse effect after microgravity exposure, in which cerebrovascular adaptation plays a critical role. Our previous finding suggested that dedifferentiation of vascular smooth muscle cells (VSMCs) might be one of the key contributors to cerebrovascular adaptation under simulated microgravity. This study was aimed to confirm this concept and elucidate the underlying mechanisms.

Materials and Methods

Sprague Dawley rats were subjected to 28‐day hindlimb‐unloading to simulate microgravity exposure. VSMC dedifferentiation was evaluated by ultrastructural analysis and contractile/synthetic maker detection. The role of T‐type Ca_V3.1 channel was revealed by assessing its blocking effects. MiR‐137 was identified as the upstream of Ca_V3.1 channel by luciferase assay and investigated by gain/loss‐of‐function approaches. Calcineurin/nuclear factor of activated T lymphocytes (NFAT) pathway, the downstream of Ca_V3.1 channel, was investigated by detecting calcineurin activity and NFAT nuclear translocation.

Results

Simulated microgravity induced the dedifferentiation and proliferation in rat cerebral VSMCs. T‐type Ca_V3.1 channel promoted the dedifferentiation and proliferation of VSMC. MiR‐137 and calcineurin/NFATc3 pathway were the upstream and downstream signalling of T‐type Ca_V3.1 channel in modulating the dedifferentiation and proliferation of VSMCs, respectively.

Conclusions

The present work demonstrated that miR‐137 and its target T‐type Ca_V3.1 channel modulate the dedifferentiation and proliferation of rat cerebral VSMCs under simulated microgravity by regulating calcineurin/NFATc3 pathway.

Cav3.2 T-type calcium channels shape electrical firing in mouse Lamina II neurons

The T-type calcium channel, Cav3.2, is necessary for acute pain perception, as well as mechanical and cold allodynia in mice. Being found throughout sensory pathways, from excitatory primary afferent neurons up to pain matrix structures, it is a promising target for analgesics. In our study, Cav3.2 was detected in ~60% of the lamina II (LII) neurons of the spinal cord, a site for integration of sensory processing. It was co-expressed with Tlx3 and Pax2, markers of excitatory and inhibitory interneurons, as well as nNOS, calretinin, calbindin, PKCγ and not parvalbumin. Non-selective T-type channel blockers slowed the inhibitory but not the excitatory transmission in LII neurons. Furthermore, T-type channel blockers modified the intrinsic properties of LII neurons, abolishing low-threshold activated currents, rebound depolarizations, and blunting excitability. The recording of Cav3.2-positive LII neurons, after intraspinal injection of AAV-DJ-Cav3.2-mcherry, showed that their intrinsic properties resembled those of the global population. However, Cav3.2 ablation in the dorsal horn of Cav3.2^GFP-Flox KI mice after intraspinal injection of AAV-DJ-Cav3.2-Cre-IRES-mcherry, had drastic effects. Indeed, it (1) blunted the likelihood of transient firing patterns; (2) blunted the likelihood and the amplitude of rebound depolarizations, (3) eliminated action potential pairing, and (4) remodeled the kinetics of the action potentials. In contrast, the properties of Cav3.2-positive neurons were only marginally modified in Cav3.1 knockout mice. Overall, in addition to their previously established roles in the superficial spinal cord and in primary afferent neurons, Cav3.2 channel appear to be necessary for specific, significant and multiple controls of LII neuron excitability.

Ion Channels in Pulmonary Hypertension: A Therapeutic Interest?

Pulmonary arterial hypertension (PAH) is a multifactorial and severe disease without curative therapies. PAH pathobiology involves altered pulmonary arterial tone, endothelial dysfunction, distal pulmonary vessel remodeling, and inflammation, which could all depend on ion channel activities (K⁺, Ca²⁺, Na⁺ and Cl^-). This review focuses on ion channels in the pulmonary vasculature and discusses their pathophysiological contribution to PAH as well as their therapeutic potential in PAH.

Moderate hypothermia and responses to calcium channel blockers - Role of the nitric oxide

Moderate hypothermia (25-31 °C) may have a significant influence on vascular tone. At present, very little is known about the role of endothelial nitric oxide on the hypothermia-induced responses. In this study, we investigated the effect of hypothermia (to 28 °C) on the vasodilatation induced by verapamil, a phenylalkylamine calcium channel blocker (10^-9-3 × 10^-4 M) and dihydropyridines, amlodipine (10^-9-3 × 10^-4 M), and benidipine (10^-9-10^-3 M) on 5-hydroxytryptamine (5-HT or serotonin) precontracted calf cardiac veins. Furthermore, the role of nitric oxide in the hypothermia-induced responses was analyzed. Ring preparations of veins obtained from calf hearts were suspended in organ baths containing 15 ml of Krebs-Henseleit solution, maintained at 37 °C, and continuously gassed with 95% O₂-5% CO₂. After a resting period, verapamil, amlodipine, and benidipine were applied cumulatively on serotonin (10^-6 M) precontracted calf cardiac vein rings and induced concentration-dependent relaxations. In another part of the study, the medium temperature was decreased to 28 °C after the preparations were contracted with 5-HT, then cumulative concentrations of verapamil, amlodipine, or benidipine were added. During hypothermia, the pIC₅₀ value, but not the maximal response, to all blockers were significantly higher than at 37 °C. Hypothermia in the presence of N^G-nitro-l-arginine methyl ester (L-NAME, 10^-4 M) decreased the pIC₅₀ and E_max values to verapamil, amlodipine, and benidipine. Only one blocker was tested in each preparation. These results suggest that nitric oxide may play a role in the hypothermia-induced changes in vasodilation caused by verapamil, amlodipine, and benidipine in calf cardiac vein, but further research is needed to explain the complete mechanism.

Gaseous Signaling Molecules in Cardiovascular Function: From Mechanisms to Clinical Translation

Carbon monoxide (CO), hydrogen sulfide (H₂S), and nitric oxide (NO) constitute endogenous gaseous molecules produced by specific enzymes. These gases are chemically simple, but exert multiple effects and act through shared molecular targets to control both physiology and pathophysiology in the cardiovascular system (CVS). The gases act via direct and/or indirect interactions with each other in proteins such as heme-containing enzymes, the mitochondrial respiratory complex, and ion channels, among others. Studies of the major impacts of CO, H₂S, and NO on the CVS have revealed their involvement in controlling blood pressure and in reducing cardiac reperfusion injuries, although their functional roles are not limited to these conditions. In this review, the basic aspects of CO, H₂S, and NO, including their production and effects on enzymes, mitochondrial respiration and biogenesis, and ion channels are briefly addressed to provide insight into their biology with respect to the CVS. Finally, potential therapeutic applications of CO, H₂S, and NO with the CVS are addressed, based on the use of exogenous donors and different types of delivery systems.

T-type Ca2+ channels elicit pro-proliferative and anti-apoptotic responses through impaired PP2A/Akt1 signaling in PASMCs from patients with pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (iPAH) is characterized by obstructive hyperproliferation and apoptosis resistance of distal pulmonary artery smooth muscle cells (PASMCs). T-type Ca²⁺ channel blockers have been shown to reduce experimental pulmonary hypertension, although the impact of T-type channel inhibition remains unexplored in PASMCs from iPAH patients. Here we show that T-type channels Cav3.1 and Cav3.2 are present in the lung and PASMCs from iPAH patients and control subjects. The blockade of T-type channels by the specific blocker, TTA-A2, prevents cell cycle progression and PASMCs growth. In iPAH cells, T-type channel signaling fails to activate phosphatase PP2A, leading to an increase in ERK1/2, P38 activation. Moreover, T-type channel signaling is redirected towards the activation of the kinase Akt1, leading to increased expression of the anti-apoptotic protein survivin, and a decrease in the pro-apoptotic mediator FoxO3A. Finally, in iPAH cells, Akt1 is no longer able to regulate caspase 9 activation, whereas T-type channel overexpression reverses PP2A defect in iPAH cells but reinforces the deleterious effects of Akt1 activation. Altogether, these data highlight T-type channel signaling as a strong trigger of the pathological phenotype of PASMCs from iPAH patients (hyper-proliferation/cells survival and apoptosis resistance), suggesting that both T-type channels and PP2A may be promising therapeutic targets for pulmonary hypertension.

T-type voltage gated calcium channels are involved in endothelium-dependent relaxation of mice pulmonary artery

In pulmonary arterial endothelial cells, Ca²⁺ channels and intracellular Ca²⁺ concentration ([Ca²⁺]_i) control the release of vasorelaxant factors such as nitric oxide and are involved in the regulation of pulmonary arterial blood pressure. The present study was undertaken to investigate the implication of T-type voltage-gated Ca²⁺ channels (T-VGCCs, Ca_v3.1 channel) in the endothelium-dependent relaxation of intrapulmonary arteries. Relaxation was quantified by means of a myograph in wild type and Ca_v3.1^-/- mice. Endothelial [Ca²⁺]_i and NO production were measured, on whole vessels, with the fluo-4 and DAF-fm probes. Acetylcholine (ACh) induced a nitric oxide- and endothelium-dependent relaxation that was significantly reduced in pulmonary arteries from Ca_v3.1^-/- compared to wild type mice as well as in the presence of T-VGCC inhibitors (NNC 55-0396 or mibefradil). ACh also increased endothelial [Ca²⁺]_i and NO production that were both reduced in Ca_v3.1^-/- compared to wild type mice or in the presence of T-VGCC inhibitors. Immunofluorescence labeling revealed the presence of Ca_v3.1 channels in endothelial cells that co-localized with endothelial nitric oxide synthase in arteries from wild type mice. TRPV4-, beta2 adrenergic- and nitric oxide donors (SNP)-mediated relaxation were not altered in Ca_v3.1^-/- compared to wild type mice. Finally, in chronically hypoxic mice, a model of pulmonary hypertension, ACh relaxation was reduced but still depended on Ca_v3.1 channels activity. The present study thus demonstrates that T-VGCCs, mainly Ca_v3.1 channel, contribute to intrapulmonary vascular reactivity in mice by controlling endothelial [Ca²⁺]_i and ACh-mediated relaxation.

Caveolae are involved in mechanotransduction during pulmonary hypertension

Caveolae are stiff plasma membrane microdomains implicated in various cell response mechanisms like Ca(2+) signaling and mechanotransduction. Pulmonary arterial smooth muscle cells (PASMC) transduce mechanical stimuli into Ca(2+) increase via plasma membrane stretch-activated channels (SAC). This mechanotransduction process is modified in pulmonary hypertension (PH) during which stretch forces are increased by the increase in arterial blood pressure. We propose to investigate how caveolae are involved in the pathophysiology of PH and particularly in mechanotransduction. PASMC were freshly isolated from control rats (Ctrl rats) and rats suffering from PH induced by 3 wk of chronic hypoxia (CH rats). Using a caveolae disrupter (methyl-β-cyclodextrin), we showed that SAC activity measured by patch-clamp, stretch-induced Ca(2+) increase measured with indo-1 probe and pulmonary arterial ring contraction to osmotic shock are enhanced in Ctrl rats when caveolae are disrupted. In CH rats, SAC activity, Ca(2+), and contraction responses to stretch are all higher compared with Ctrl rats. However, in contrast to Ctrl rats, caveolae disruption in CH-PASMC, reduces SAC activity, Ca(2+) responses to stretch and arterial contractions. Furthermore, by means of immunostainings and transmission electron microscopy, we observed that caveolae and caveolin-1 are expressed in PASMC from both Ctrl and CH rats and localize close to subplasmalemmal sarcoplasmic reticulum (ryanodine receptors) and mitochondria, thus facilitating Ca(2+) exchanges, particularly in CH. In conclusion, caveolae are implicated in mechanotransduction in Ctrl PASMC by buffering mechanical forces. In PH-PASMC, caveolae form a distinct Ca(2+) store facilitating Ca(2+) coupling between SAC and sarcoplasmic reticulum.

Regulation of the T-type Ca(2+) channel Cav3.2 by hydrogen sulfide: emerging controversies concerning the role of H2 S in nociception

Ion channels represent a large and growing family of target proteins regulated by gasotransmitters such as nitric oxide, carbon monoxide and, as described more recently, hydrogen sulfide. Indeed, many of the biological actions of these gases can be accounted for by their ability to modulate ion channel activity. Here, we report recent evidence that H2 S is a modulator of low voltage-activated T-type Ca(2+) channels, and discriminates between the different subtypes of T-type Ca(2+) channel in that it selectively modulates Cav3.2, whilst Cav3.1 and Cav3.3 are unaffected. At high concentrations, H2 S augments Cav3.2 currents, an observation which has led to the suggestion that H2 S exerts its pro-nociceptive effects via this channel, since Cav3.2 plays a central role in sensory nerve excitability. However, at more physiological concentrations, H2 S is seen to inhibit Cav3.2. This inhibitory action requires the presence of the redox-sensitive, extracellular region of the channel which is responsible for tonic metal ion binding and which particularly distinguishes this channel isoform from Cav3.1 and 3.3. Further studies indicate that H2 S may act in a novel manner to alter channel activity by potentiating the zinc sensitivity/affinity of this binding site. This review discusses the different reports of H2 S modulation of T-type Ca(2+) channels, and how such varying effects may impact on nociception given the role of this channel in sensory activity. This subject remains controversial, and future studies are required before the impact of T-type Ca(2+) channel modulation by H2 S might be exploited as a novel approach to pain management.

Hypoxic pulmonary hypertension in chronic lung diseases: novel vasoconstrictor pathways

Pulmonary hypertension is a well recognised complication of chronic hypoxic lung diseases, which are among the most common causes of death and disability worldwide. Development of pulmonary hypertension independently predicts reduced life expectancy. In chronic obstructive pulmonary disease, long-term oxygen therapy ameliorates pulmonary hypertension and greatly improves survival, although the correction of alveolar hypoxia and pulmonary hypertension is only partial. Advances in understanding of the regulation of vascular smooth muscle tone show that chronic vasoconstriction plays a more important part in the pathogenesis of hypoxic pulmonary hypertension than previously thought, and that structural vascular changes contribute less. Trials of existing vasodilators show that pulmonary hypertension can be ameliorated and systemic oxygen delivery improved in carefully selected patients, although systemic hypotensive effects limit the doses used. Vasoconstrictor pathways that are selective for the pulmonary circulation can be blocked to reduce hypoxic pulmonary hypertension without causing systemic hypotension, and thus provide potential targets for novel therapeutic strategies.