Sarcoplasmic reticulum Ca(2+) refilling is determined by L-type Ca(2+) and store operated Ca(2+) channels in guinea pig airway smooth muscle

17β-estradiol induces hyperresponsiveness in guinea pig airway smooth muscle by inhibiting the plasma membrane Ca2+-ATPase

High serum estrogen concentrations are associated with asthma development and severity, suggesting a link between estradiol and airway hyperresponsiveness (AHR). 17β-estradiol (E2) has non-genomic effects via Ca2+ regulatory mechanisms; however, its effect on the plasma membrane Ca2+-ATPases (PMCA1 and 4) and sarcoplasmic reticulum Ca2+-ATPase (SERCA) is unknown. Hence, in the present study, we aim to demonstrate if E2 favors AHR by increasing intracellular Ca2+ concentrations in guinea pig airway smooth muscle (ASM) through a mechanism involving Ca2+-ATPases. In guinea pig ASM, Ca2+ microfluorometry, muscle contraction, and Western blot were evaluated. Then, we performed molecular docking analysis between the estrogens and Ca2+ ATPases. In tracheal rings, E2 produced AHR to carbachol. In guinea pig myocytes, acute exposure to physiological levels of E2 modified the transient Ca2+ peak induced by caffeine to a Ca2+ plateau. The incubation with PMCA inhibitors (lanthanum and carboxyeosin, CE) partially reversed the E2-induced sustained plateau in the caffeine response. In contrast, cyclopiazonic acid (SERCA inhibitor), U-0126 (an inhibitor of ERK 1/2), and choline chloride did not modify the Ca2+ plateau produced by E2. The mitochondrial uniporter activity and the capacitative Ca2+ entry were unaffected by E2. In guinea pig ASM, Western blot analysis demonstrated PMCA1 and PMCA4 expression. The results from the docking modeling demonstrate that E2 binds to both plasma membrane ATPases. In guinea pig tracheal smooth muscle, inhibiting the PMCA with CE, induced hyperresponsiveness to carbachol. 17β-estradiol produces hyperresponsiveness by inhibiting the PMCA in the ASM and could be one of the mechanisms responsible for the increase in asthmatic crisis in women.

Chamaecyparis lawsoniana and Its Active Compound Quercetin as Ca2+ Inhibitors in the Contraction of Airway Smooth Muscle

The Cupressaceae family includes species considered to be medicinal. Their essential oil is used for headaches, colds, cough, and bronchitis. Cedar trees like Chamaecyparis lawsoniana (C. lawsoniana) are commonly found in urban areas. We investigated whether C. lawsoniana exerts some of its effects by modifying airway smooth muscle (ASM) contractility. The leaves of C. lawsoniana (363 g) were pulverized mechanically, and extracts were obtained by successive maceration 1:10 (w:w) with methanol/CHCl3. Guinea pig tracheal rings were contracted with KCl, tetraethylammonium (TEA), histamine (HIS), or carbachol (Cch) in organ baths. In the Cch experiments, tissues were pre-incubated with D-600, an antagonist of L-type voltage-dependent Ca2+ channels (L-VDCC) before the addition of C. lawsoniana. Interestingly, at different concentrations, C. lawsoniana diminished the tracheal contractions induced by KCl, TEA, HIS, and Cch. In ASM cells, C. lawsoniana significantly diminished L-type Ca2+ currents. ASM cells stimulated with Cch produced a transient Ca2+ peak followed by a sustained plateau maintained by L-VDCC and store-operated Ca2+ channels (SOCC). C. lawsoniana almost abolished this last response. These results show that C. lawsoniana, and its active metabolite quercetin, relax the ASM by inhibiting the L-VDCC and SOCC; further studies must be performed to obtain the complete set of metabolites of the extract and study at length their pharmacological properties.

Ca2+ dynamics in interstitial cells: foundational mechanisms for the motor patterns in the gastrointestinal tract

The gastrointestinal (GI) tract displays multiple motor patterns that move nutrients and wastes through the body. Smooth muscle cells (SMCs) provide the forces necessary for GI motility, but interstitial cells, electrically coupled to SMCs, tune SMC excitability, transduce inputs from enteric motor neurons, and generate pacemaker activity that underlies major motor patterns, such as peristalsis and segmentation. The interstitial cells regulating SMCs are interstitial cells of Cajal (ICC) and PDGF receptor (PDGFR)α+ cells. Together these cells form the SIP syncytium. ICC and PDGFRα+ cells express signature Ca2+-dependent conductances: ICC express Ca2+-activated Cl- channels, encoded by Ano1, that generate inward current, and PDGFRα+ cells express Ca2+-activated K+ channels, encoded by Kcnn3, that generate outward current. The open probabilities of interstitial cell conductances are controlled by Ca2+ release from the endoplasmic reticulum. The resulting Ca2+ transients occur spontaneously in a stochastic manner. Ca2+ transients in ICC induce spontaneous transient inward currents and spontaneous transient depolarizations (STDs). Neurotransmission increases or decreases Ca2+ transients, and the resulting depolarizing or hyperpolarizing responses conduct to other cells in the SIP syncytium. In pacemaker ICC, STDs activate voltage-dependent Ca2+ influx, which initiates a cluster of Ca2+ transients and sustains activation of ANO1 channels and depolarization during slow waves. Regulation of GI motility has traditionally been described as neurogenic and myogenic. Recent advances in understanding Ca2+ handling mechanisms in interstitial cells and how these mechanisms influence motor patterns of the GI tract suggest that the term "myogenic" should be replaced by the term "SIPgenic," as this review discusses.

Estrogenic Modulation of Ionic Channels, Pumps and Exchangers in Airway Smooth Muscle

To preserve ionic homeostasis (primarily Ca²⁺, K⁺, Na⁺, and Cl^-), in the airway smooth muscle (ASM) numerous transporters (channels, exchangers, and pumps) regulate the influx and efflux of these ions. Many of intracellular processes depend on continuous ionic permeation, including exocytosis, contraction, metabolism, transcription, fecundation, proliferation, and apoptosis. These mechanisms are precisely regulated, for instance, through hormonal activity. The lipophilic nature of steroidal hormones allows their free transit into the cell where, in most cases, they occupy their cognate receptor to generate genomic actions. In the sense, estrogens can stimulate development, proliferation, migration, and survival of target cells, including in lung physiology. Non-genomic actions on the other hand do not imply estrogen's intracellular receptor occupation, nor do they initiate transcription and are mostly immediate to the stimulus. Among estrogen's non genomic responses regulation of calcium homeostasis and contraction and relaxation processes play paramount roles in ASM. On the other hand, disruption of calcium homeostasis has been closely associated with some ASM pathological mechanism. Thus, this paper intends to summarize the effects of estrogen on ionic handling proteins in ASM. The considerable diversity, range and power of estrogens regulates ionic homeostasis through genomic and non-genomic mechanisms.

Acute Cardiovascular and Cardiorespiratory Effects of JWH-018 in Awake and Freely Moving Mice: Mechanism of Action and Possible Antidotal Interventions?

JWH-018 is the most known compound among synthetic cannabinoids (SCs) used for their psychoactive effects. SCs-based products are responsible for several intoxications in humans. Cardiac toxicity is among the main side effects observed in emergency departments: SCs intake induces harmful effects such as hypertension, tachycardia, chest pain, arrhythmias, myocardial infarction, breathing impairment, and dyspnea. This study aims to investigate how cardio-respiratory and vascular JWH-018 (6 mg/kg) responses can be modulated by antidotes already in clinical use. The tested antidotes are amiodarone (5 mg/kg), atropine (5 mg/kg), nifedipine (1 mg/kg), and propranolol (2 mg/kg). The detection of heart rate, breath rate, arterial oxygen saturation (SpO2), and pulse distention are provided by a non-invasive apparatus (Mouse Ox Plus) in awake and freely moving CD-1 male mice. Tachyarrhythmia events are also evaluated. Results show that while all tested antidotes reduce tachycardia and tachyarrhythmic events and improve breathing functions, only atropine completely reverts the heart rate and pulse distension. These data may suggest that cardiorespiratory mechanisms of JWH-018-induced tachyarrhythmia involve sympathetic, cholinergic, and ion channel modulation. Current findings also provide valuable impetus to identify potential antidotal intervention to support physicians in the treatment of intoxicated patients in emergency clinical settings.

Aldosterone-Induced Sarco/Endoplasmic Reticulum Ca2+ Pump Upregulation Counterbalances Cav1.2-Mediated Ca2+ Influx in Mesenteric Arteries

In mesenteric arteries (MAs), aldosterone (ALDO) binds to the endogenous mineralocorticoid receptor (MR) and increases the expression of the voltage-gated L-type Ca_v1.2 channel, an essential ion channel for vascular contraction, sarcoplasmic reticulum (SR) Ca²⁺ store refilling, and Ca²⁺ spark generation. In mesenteric artery smooth muscle cells (MASMCs), Ca²⁺ influx through Ca_v1.2 is the indirect mechanism for triggering Ca²⁺ sparks. This process is facilitated by plasma membrane-sarcoplasmic reticulum (PM-SR) nanojunctions that drive Ca²⁺ from the extracellular space into the SR via Sarco/Endoplasmic Reticulum Ca²⁺ (SERCA) pump. Ca²⁺ sparks produced by clusters of Ryanodine receptors (RyRs) at PM-SR nanodomains, decrease contractility by activating large-conductance Ca²⁺-activated K⁺ channels (BK_Ca channels), which generate spontaneous transient outward currents (STOCs). Altogether, Ca_v1.2, SERCA pump, RyRs, and BK_Ca channels work as a functional unit at the PM-SR nanodomain, regulating intracellular Ca²⁺ and vascular function. However, the effect of the ALDO/MR signaling pathway on this functional unit has not been completely explored. Our results show that short-term exposure to ALDO (10 nM, 24 h) increased the expression of Ca_v1.2 in rat MAs. The depolarization-induced Ca²⁺ entry increased SR Ca²⁺ load, and the frequencies of both Ca²⁺ sparks and STOCs, while [Ca²⁺]_cyt and vasoconstriction remained unaltered in Aldo-treated MAs. ALDO treatment significantly increased the mRNA and protein expression levels of the SERCA pump, which counterbalanced the augmented Ca_v1.2-mediated Ca²⁺ influx at the PM-SR nanodomain, increasing SR Ca²⁺ content, Ca²⁺ spark and STOC frequencies, and opposing to hyperpolarization-induced vasoconstriction while enhancing Acetylcholine-mediated vasorelaxation. This work provides novel evidence for short-term ALDO-induced upregulation of the functional unit comprising Ca_v1.2, SERCA2 pump, RyRs, and BK_Ca channels; in which the SERCA pump buffers ALDO-induced upregulation of Ca²⁺ entry at the superficial SR-PM nanodomain of MASMCs, preventing ALDO-triggered depolarization-induced vasoconstriction and enhancing vasodilation. Pathological conditions that lead to SERCA pump downregulation, for instance, chronic exposure to ALDO, might favor the development of ALDO/MR-mediated augmented vasoconstriction of mesenteric arteries.

Could Lower Testosterone in Older Men Explain Higher COVID-19 Morbidity and Mortalities?

The health scourge imposed on humanity by the COVID-19 pandemic seems not to recede. This fact warrants refined and novel ideas analyzing different aspects of the illness. One such aspect is related to the observation that most COVID-19 casualties were older males, a tendency also noticed in the epidemics of SARS-CoV in 2003 and the Middle East respiratory syndrome in 2012. This gender-related difference in the COVID-19 death toll might be directly involved with testosterone (TEST) and its plasmatic concentration in men. TEST has been demonstrated to provide men with anti-inflammatory and immunological advantages. As the plasmatic concentration of this androgen decreases with age, the health benefit it confers also diminishes. Low plasmatic levels of TEST can be determinant in the infection’s outcome and might be related to a dysfunctional cell Ca²⁺ homeostasis. Not only does TEST modulate the activity of diverse proteins that regulate cellular calcium concentrations, but these proteins have also been proven to be necessary for the replication of many viruses. Therefore, we discuss herein how TEST regulates different Ca²⁺-handling proteins in healthy tissues and propose how low TEST concentrations might facilitate the replication of the SARS-CoV-2 virus through the lack of modulation of the mechanisms that regulate intracellular Ca²⁺ concentrations.

Inhibitors of L-Type Calcium Channels Show Therapeutic Potential for Treating SARS-CoV-2 Infections by Preventing Virus Entry and Spread

COVID-19 is caused by a novel coronavirus, the severe acute respiratory syndrome coronavirus (CoV)-2 (SARS-CoV-2). The virus is responsible for an ongoing pandemic and concomitant public health crisis around the world. While vaccine development is proving to be highly successful, parallel drug development approaches are also critical in the response to SARS-CoV-2 and other emerging viruses. Coronaviruses require Ca2+ ions for host cell entry, and we have previously shown that Ca2+ modulates the interaction of the viral fusion peptide with host cell membranes. In an attempt to accelerate drug repurposing, we tested a panel of L-type calcium channel blocker (CCB) drugs currently developed for other conditions to determine whether they would inhibit SARS-CoV-2 infection in cell culture. All the CCBs tested showed varying degrees of inhibition, with felodipine and nifedipine strongly limiting SARS-CoV-2 entry and infection in epithelial lung cells at concentrations where cell toxicity was minimal. Further studies with pseudotyped particles displaying the SARS-CoV-2 spike protein suggested that inhibition occurs at the level of virus entry. Overall, our data suggest that certain CCBs have the potential to treat SARS-CoV-2 infections and are worthy of further examination for possible treatment of COVID-19.

Possible Beneficial Actions of Caffeine in SARS-CoV-2

The COVID-19 pandemic has established an unparalleled necessity to rapidly find effective treatments for the illness; unfortunately, no specific treatment has been found yet. As this is a new emerging chaotic situation, already existing drugs have been suggested to ameliorate the infection of SARS-CoV-2. The consumption of caffeine has been suggested primarily because it improves exercise performance, reduces fatigue, and increases wakefulness and awareness. Caffeine has been proven to be an effective anti-inflammatory and immunomodulator. In airway smooth muscle, it has bronchodilator effects mainly due to its activity as a phosphodiesterase inhibitor and adenosine receptor antagonist. In addition, a recent published document has suggested the potential antiviral activity of this drug using in silico molecular dynamics and molecular docking; in this regard, caffeine might block the viral entrance into host cells by inhibiting the formation of a receptor-binding domain and the angiotensin-converting enzyme complex and, additionally, might reduce viral replication by the inhibition of the activity of 3-chymotrypsin-like proteases. Here, we discuss how caffeine through certain mechanisms of action could be beneficial in SARS-CoV-2. Nevertheless, further studies are required for validation through in vitro and in vivo models.

Acute cigarette smoke or extract exposure rapidly activates TRPA1-mediated calcium influx in primary human airway smooth muscle cells

Tobacco smoking is the largest risk factor for developing chronic obstructive pulmonary disease (COPD), and is associated with hyperresponsiveness of airway smooth muscle (ASM). Chronic exposure to cigarette smoke (CS) leads to airway inflammation and remodelling. However, the direct effect of gaseous CS or CS extract (CSE) on human airway smooth muscle cell (hASMC) function remains poorly understood. This study investigated the acute effect of CS/CSE on calcium homeostasis, a key regulator of ASM physiology and pathophysiology. Primary hASMC were isolated from non-smoking donor lungs, and subjected to Ca2+ imaging studies. We found that both CS, and CSE, rapidly elevated cytosolic Ca2+ in hASMC through stimulation of plasmalemmal Ca2+ influx, but excluded store-operated and L-type Ca2+ channels as mediators of this effect. Using a specific pharmacological inhibitor, or shRNA-driven knockdown, we established that both CS and CSE stimulated Ca2+ influx in hASMC through the neurogenic pain receptor channel, transient receptor potential ankyrin 1 (TRPA1). CS/CSE-dependent, TRPA1-mediated Ca2+ influx led to myosin light-chain phosphorylation, a key process regulating ASM contractility. We conclude that TRPA1 is likely an important link between CS/CSE exposure and airway hyperresponsiveness, and speculate that acute CS/CSE-induced Ca2+ influx could lead to exacerbated ASM contraction and potentially initiate further chronic pathological effects of tobacco smoke.

Androgens are effective bronchodilators with anti-inflammatory properties: A potential alternative for asthma therapy

Changes in plasma androgen levels in asthmatic men may be linked to asthma severity, seemingly acting through nongenomic and genomic effects. Nongenomic effects include rapid relaxation of carbachol or antigenic challenge pre-contracted guinea pig airway smooth muscle (ASM) in vitro: testosterone (TES) blocks l-type voltage dependent Ca²⁺ channels, stored operated Ca²⁺ channels, inositol 1,4,5-trisphosphate receptors and promotes prostaglandin E₂ biosynthesis. In ASM at rest, TES lowers basal intracellular Ca²⁺ concentration and tension, maintaining a proper airway patency keeping steady smooth muscle tension and basal intracellular Ca²⁺ concentration at rest. Moreover, the bronchospasm in sensitized guinea-pigs was ablated by dehydroepiandrosterone (DHEA), a precursor of steroids, TES and its metabolites 5α- and 5β-dihydrotestosterone (DHT). On the other hand, genomic effects related to androgens' anti-inflammatory properties in asthma have been recently studied. Briefly, TES negatively regulates type 2 immune response sustained by CD4+ Th2 and group 2 innate lymphoid cells, diminishing allergic airway inflammation in males. Also, novel findings establish that TES decreases interleukin (IL)-17A protein expression produced by CD4+ Th17 cells and therefore neutrophilic airway inflammation. Clearly, DHEA, TES or its 5β-reduced metabolite that possesses minimal androgenic effect, might have potential therapeutic capacities in the treatment of severe asthma via mechanisms distinct from corticosteroid treatment.

Estrogen receptors differentially regulate intracellular calcium handling in human nonasthmatic and asthmatic airway smooth muscle cells

Asthma is defined as chronic inflammation of the airways and is characterized by airway remodeling, hyperresponsiveness, and acute bronchoconstriction of airway smooth muscle (ASM) cells. Clinical findings suggest a higher incidence and severity of asthma in adult women, indicating a concrete role of sex steroids in modulating the airway tone. Estrogen, a major female sex steroid mediates its role through estrogen receptors (ER) ERα and ERβ, which are shown to be expressed in human ASM, and their expression is upregulated in lung inflammation and asthma. Previous studies suggested rapid, nongenomic signaling of estrogen via ERs reduces intracellular calcium ([Ca²⁺]_i), thereby promoting relaxation of ASM. However, long-term ER activation on [Ca²⁺]_i regulation in human ASM during inflammation or in asthma is still not known. In Fura-2-loaded nonasthmatic and asthmatic human ASM cells, we found that prolonged (24 h) exposure to ERα agonist (PPT) increased [Ca²⁺]_i response to histamine, whereas ERβ activation (WAY) led to decreased [Ca²⁺] compared with vehicle. This was further confirmed by ER overexpression and knockdown studies using various bronchoconstrictor agents. Interestingly, ERβ activation was more effective than 17β-estradiol in reducing [Ca²⁺]_i responses in the presence of TNF-α or IL-13, while no observable changes were noticed with PPT in the presence of either cytokine. The [Ca²⁺]_i-reducing effects of ERβ were mediated partially via L-type calcium channel inhibition and increased Ca²⁺ sequestration by sarcoplasmic reticulum_. Overall, these data highlight the differential signaling of ERα and ERβ in ASM during inflammation. Specific ERβ activation reduces [Ca²⁺]_i in the inflamed ASM cells and is likely to play a crucial role in regulating ASM contractility, thereby relaxing airways.

Inflammatory cytokines tumour necrosis factor-α and interleukin-8 enhance airway smooth muscle contraction by increasing L-type Ca2+ channel expression

Inflammation elevates intracellular calcium concentrations ([Ca²⁺ ]_i ) in airway smooth muscle (ASM). The L-type Ca²⁺ channel (L-VDCC) plays an important role in regulating Ca²⁺ influx in ASM. However, the role of L-VDCC in the inflammatory cytokine-induced pathology of ASM remains unclear. In the present study, we used calcium imaging and isometric tension measurements to assess the role of L-VDCC in agonist-induced [Ca²⁺ ]_i rise and the associated contractions in mouse ASM, and we used immunoblotting to identify L-VDCC protein expression levels in mouse ASM after exposure to tumour necrosis factor alpha (TNF-α) or interleukin-8 (IL-8). Our results showed that high-K⁺ - or carbachol-induced contractions of mouse ASM were significantly greater after pretreatment with TNF-α or IL-8 for 24 hours. Both verapamil and nifedipine, L-VDCC inhibitors, abolished this increased contraction induced by TNF-α or IL-8 pretreatment. Moreover, TNF-α treatment enhanced carbachol-induced Ca²⁺ influx in ASM cells, and this effect was abrogated by verapamil. Additionally, immunoblotting results showed that preincubation of mouse ASM with TNF-α or IL-8 also enhanced L-VDCC protein expression. On the basis of these findings, we concluded that proinflammatory cytokines, such as TNF-α and IL-8, increase the expression level of L-VDCC, which in turn contributes to augmented agonist-induced ASM contractions. This effect of inflammation on L-VDCC expression in ASM may be associated with airway hyper-responsiveness and involved in the development of asthma.

Maintenance of intracellular Ca2+ basal concentration in airway smooth muscle (Review)

In airway smooth muscle, the intracellular basal Ca²⁺ concentration [_b(Ca²⁺)_i] must be tightly regulated by several mechanisms in order to maintain a proper airway patency. The _b[Ca²⁺]_i is efficiently regulated by sarcoplasmic reticulum Ca²⁺-ATPase 2b, plasma membrane Ca²⁺-ATPase 1 or 4 and by the Na⁺/Ca²⁺ exchanger. Membranal Ca²⁺ channels, including the L-type voltage dependent Ca²⁺ channel (L-VDCC), T-type voltage dependent Ca²⁺ channel (T-VDCC) and transient receptor potential canonical 3 (TRPC3), appear to be constitutively active under basal conditions via the action of different signaling pathways, and are responsible for Ca²⁺ influx to maintain _b[Ca²⁺]_i. The two types of voltage-dependent Ca²⁺ channels (L- and T-type) are modulated by phosphorylation processes mediated by mitogen-activated protein kinase kinase (MEK) and extracellular-signal-regulated kinase 1 and 2 (ERK1/2). The MEK/ERK signaling pathway can be activated by G-protein-coupled receptors through the α_q subunit when the endogenous ligand (i.e., acetylcholine, histamine, leukotrienes, etc.) is present under basal conditions. It may also be stimulated when receptor tyrosine kinases are occupied by the appropriate ligand (cytokines, growth factors, etc.). ERK1/2 phosphorylates L-VDCC on Ser⁴⁹⁶ of the β₂ subunit and Ser¹⁹²⁸ of the α₁ subunit, decreasing or increasing the channel activity, respectively, and enabling it to switch between an open and closed state. T-VDCC is also probably phosphorylated by ERK1/2, although further research is required to identify the phosphorylation sites. TRPC3 is directly activated by diacylglycerol produced by phospholipase C (PLC_β or _γ). Constitutive inositol 1,4,5-trisphosphate production induces the release of Ca²⁺ from the sarcoplasmic reticulum through inositol triphosphate receptor 1. This ion induces Ca²⁺-induced Ca²⁺ release through the ryanodine receptor 2 (designated as Ca²⁺ ‘sparks’). Therefore, several Ca²⁺ handling mechanisms are finely tuned to regulate basal intracellular Ca²⁺ concentrations. It is conceivable that alterations in any of these processes may render airway smooth muscle susceptible to develop hyperresponsiveness that is observed in ailments such as asthma.

Testosterone induces hyporesponsiveness by interfering with IP3 receptors in guinea pig airway smooth muscle

Asthma symptoms have been associated with sex steroids. During childhood, this illness seems more frequent in boys than in girls and this tendency reverts in puberty when it is more severe in women. Testosterone (TES), at supraphysiological concentrations, relaxed pre-contracted airway smooth muscle, but its effects at physiological concentrations have not been thoroughly studied. We explored this possibility in guinea pig tracheal smooth muscle. In myocytes TES (10 nM) abolished carbachol (CCh)-induced intracellular Ca²⁺ concentration ([Ca²⁺]i) increment. Ca²⁺ responses to ATP were partially modified by TES while histamine's were not. These results indicate that inositol 1,4,5-trisphosphate (IP₃) signaling pathway might be involved. Photolysis of caged-IP₃ increased [Ca²⁺]i and TES abolished this effect. TES diminished reactivity of the smooth muscle to CCh and this effect was non-genomic since it was unchanged by flutamide. In tracheal smooth muscle, mRNA for each IP₃ receptor (ITPR) isoform was found and, by immunofluorescence, ITPR1 and ITPR3 seems to be the main isoforms observed while ITPR2 was less prominent. Comparing the amino acid sequence of ITPR1 and the sequence of the TES binding site on the androgen receptor, we found that they share a short sequence. This domain could be responsible for the TES binding to the ITPR1 and probably for its blocking effect. We conclude that TES modifies ITPR1 function in airway smooth muscle, turning this tissue less reactive to contractile agonists that act through PLCβ-IP₃ signaling cascade. These results might be related to the low asthma prevalence in males from puberty to adulthood.

Cellular Na+ handling mechanisms involved in airway smooth muscle contraction (Review)

A decrease in bronchial diameter is designated as bronchoconstriction (BC) and impedes the flow of air through the airway. Asthma is characterized by inflammation of the airways, reversible BC and nonspecific hyperreactivity. These last two symptoms are dependent on airway smooth muscle. Stimuli that trigger contraction can be characterized as chemical (neurotransmitters, cytokines and terpenoids) and physical (volume inspired, air pressure). Both stimuli activate signaling pathways by acting on membrane proteins and facilitating the passage of ions through the membrane, generating a voltage change and a subsequent depolarization. Na⁺ plays an important role in preserving the resting membrane potential; this ion is extracted from the cells by the Na⁺/K⁺ ATPase (NKA) or introduced into the cytoplasm by the Na⁺/Ca²⁺ exchanger (NCX). During depolarization, Na⁺ appears to accumulate in specific regions beneath the plasma membrane, generating local concentration gradients which determine the handling of Ca²⁺. At rest, the smooth muscle has a basal tone that is preserved by the continuous adjustment of intracytoplasmic concentrations of Ca²⁺ and Na⁺. At homeostasis, the Na⁺ concentration is primarily dependent on three structures: the NKA, the NCX and non-specific cation channels (NSCC). These three structures, their functions and the available evidence of the probable role of Na⁺ in asthma are described in the present review.

Prolactin-induced neuroprotection against glutamate excitotoxicity is mediated by the reduction of [Ca2+]i overload and NF-κB activation

Prolactin (PRL) is a peptidic hormone that displays pleiotropic functions in the organism including different actions in the brain. PRL exerts a neuroprotective effect against excitotoxicity produced by glutamate (Glu) or kainic acid in both in vitro and in vivo models. It is well known that Glu excitotoxicity causes cell death through apoptotic or necrotic pathways due to intracellular calcium ([Ca²⁺] i) overload. Therefore, the aim of the present study was to assess the molecular mechanisms by which PRL maintains cellular viability of primary cultures of rat hippocampal neurons exposed to Glu excitotoxicity. We determined cell viability by monitoring mitochondrial activity and using fluorescent markers for viable and dead cells. The intracellular calcium level was determined by a fluorometric assay and proteins involved in the apoptotic pathway were determined by immunoblot. Our results demonstrated that PRL afforded neuroprotection against Glu excitotoxicity, as evidenced by a decrease in propidium iodide staining and by the decrease of the LDH activity. In addition, the MTT assay shows that PRL maintains normal mitochondrial activity even in neurons exposed to Glu. Furthermore, the Glu-induced intracellular [Ca²⁺]i overload was attenuated by PRL. These data correlate with the reduction found in the level of active caspase-3 and the pro-apoptotic ratio (Bax/Bcl-2). Concomitantly, PRL elicited the nuclear translocation of the transcriptional factor NF-κB, which was detected by immunofluorescence and confocal microscopy. To our knowledge, this is the first report demonstrating that PRL prevents Glu excitotoxicity by a mechanism involving the restoration of the intracellular calcium homeostasis and mitochondrial activity, as well as an anti-apoptotic action possibly mediated by the activity of NF-κB. Overall, the current results suggest that PRL could be of potential therapeutic advantage in the treatment of neurodegenerative diseases.

Role of transient receptor potential vanilloid 1 in the modulation of airway smooth muscle tone and calcium handling

Asthma is a common disorder characterized, in part, by airway smooth muscle (ASM) hyperresponsiveness. Transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel expressed on airway nerve fibers that modulates afferent signals, resulting in cough, and potentially bronchoconstriction. In the present study, the TRPV1 transcript was detected by RT-PCR in primary cultured human ASM cells, and the TRPV1 protein was detected in ASM of human trachea by immunohistochemistry. Proximity ligation assays suggest that TRPV1 is expressed in the sarcoplasmic reticulum membrane of human ASM cells in close association with sarco/endoplasmic reticulum Ca²⁺-ATPase-2. In guinea pig tracheal ring organ bath experiments, the TRPV1 agonist capsaicin led to ASM contraction, but this contraction was significantly attenuated by the sodium channel inhibitor bupivacaine (n = 4, P < 0.05) and the neurokinin-2 receptor antagonist GR-159897 (n = 4, P < 0.05), suggesting that this contraction is neutrally mediated. However, pretreatment of guinea pig and human ASM in organ bath experiments with the TRPV1 antagonist capsazepine inhibited the maintenance phase of an acetylcholine-induced contraction (n = 4, P < 0.01 for both species). Similarly, capsazepine inhibited methacholine-induced contraction of peripheral airways in mouse precision-cut lung slice (PCLS) experiments (n = 4-5, P < 0.05). Although capsazepine did not inhibit store-operated calcium entry in mouse ASM cells in PCLS (n = 4-7, P = nonsignificant), it did inhibit calcium oscillations (n = 3, P < 0.001). These studies suggest that TRPV1 is expressed on ASM, including the SR, but that ASM TRPV1 activation does not play a significant role in initiation of ASM contraction. However, capsazepine does inhibit maintenance of contraction, likely by inhibiting calcium oscillations.

Sex steroids effects on guinea pig airway smooth muscle tone and intracellular Ca2+ basal levels

Testosterone (TES), other androgens and female sex steroids induce non-genomic rapid relaxing effects in airway smooth muscle (ASM). In guinea pig ASM, basal tension was relaxed by dehydroepiandrosterone (DHEA) and TES; 17β-estradiol (E2) had a small effect. Blockers of L-type voltage dependent Ca²⁺ channel (L-VDCC, D-600) and store operated Ca²⁺ channel (SOC, 2-APB) also relaxed the basal tone. In tracheal myocytes, DHEA and TES diminished intracellular basal Ca²⁺ concentrations (_b[Ca²⁺]_i) as D-600+2-APB but to a higher extend. TES after D-600+2APB or Pyr3, a blocker of canonical transient receptor potential 3 (TRPC3), further decreased _b[Ca²⁺]_i rendering this response equal to TES alone. With indomethacin, the _b[Ca²⁺]_i decrease induced by the blockade of L-VDCC and TRPC3 was not changed by the addition of TES. PGE₂ or forskolin addition after D600+2-APB, decreased _b[Ca²⁺]_i resembling TES response. An adenylate cyclase inhibitor followed by D-600+2-APB lowered _b[Ca²⁺]_i, TES showed no further effect. Carbachol-induced [Ca²⁺]i increment was reduced by TES or DHEA. 17β-estradiol diminished KCl-induced contraction and, in tracheal myocytes, the voltage-dependent inward Ca²⁺ current.

CONCLUSION

DHEA and TES diminish ASM tone and _b[Ca²⁺]i by blocking L-VDCC and probably a constitutively active TRPC3, and by PGE₂ synthesis. E2 lowers ASM basal tone by blocking only L-VDCC.

The effects of nifedipine on respiratory mechanics investigated by theend-inflation occlusion method in the rat

CONTEXT

Calcium channel blockers may theoretically exhibit relaxing effects not only on vascular smooth muscle but also on airway smooth muscle.

OBJECTIVE

To investigate possible effects of nifedipine on respiratory mechanics in the rat.

METHODS

Respiratory system mechanical parameters were measured by the end-inflation occlusion method in the rat in vivo before and after the intraperitoneal administration of nifedipine.

RESULTS

We found that nifedipine affects respiratory mechanics, inducing a reduction of airway resistance and of respiratory system elastance, probably because of a relaxing action on airway and parenchimal smooth muscle cells.

CONCLUSION

Should these results be further confirmed by human investigations, a possible role of nifedipine in pharmacological respiratory system's diseases treatment may be suggested.

Potential L-Type Voltage-Operated Calcium Channel Blocking Effect of Drotaverine on Functional Models

Drotaverine is considered an inhibitor of cyclic-3',5'-nucleotide-phophodiesterase (PDE) enzymes; however, published receptor binding data also support the potential L-type voltage- operated calcium channel (L-VOCC) blocking effect of drotaverine. Hence, in this work, we focus on the potential L-VOCC blocking effect of drotaverine by using L-VOCC-associated functional in vitro models. Accordingly, drotaverine and reference agents were tested on KCl-induced guinea pig tracheal contraction. Drotaverine, like the L-VOCC blockers nifedipine or diltiazem, inhibited the KCl-induced inward Ca²⁺- induced contraction in a concentration- dependent fashion. The PDE inhibitor theophylline had no effect on the KCl-evoked contractions, indicating its lack of inhibition on inward Ca²⁺ flow. Drotaverine was also tested on the L-VOCC-mediated resting Ca²⁺ refill model. In this model, the extracellular Ca²⁺ enters the cells to replenish the emptied intracellular Ca²⁺ stores. Drotaverine and L-VOCC blocker reference molecules inhibited Ca²⁺ replenishment of Ca²⁺-depleted preparations detected by agonist-induced contractions in post-Ca²⁺ replenishment Ca²⁺-free medium. Theophylline did not modify the Ca²⁺ store replenishment after contraction. It seems that drotaverine, but not theophylline, inhibits inward Ca²⁺ flux. The addition of CaCl₂ to Ca²⁺-free medium containing the agonist induced inward Ca²⁺ flow and subsequent contraction of Ca²⁺-depleted tracheal preparations. Drotaverine, similar to the L-VOCC blockers, inhibited inward Ca²⁺ flow and blunted the slope of CaCl₂-induced contraction in agonist containing Ca²⁺-free medium with Ca²⁺-depleted tracheal preparations. These results show that drotaverine behaves like L-VOCC blockers but, unlike PDE inhibitors using L-VOCC associated in vitro experimental models.

Store-operated calcium entry is required for sustained contraction and Ca2+ oscillations of airway smooth muscle

KEY POINTS

Airway hyper-responsiveness in asthma is driven by excessive contraction of airway smooth muscle cells (ASMCs). Agonist-induced Ca²⁺ oscillations underlie this contraction of ASMCs and the magnitude of this contraction is proportional to the Ca²⁺ oscillation frequency. Sustained contraction and Ca²⁺ oscillations require an influx of extracellular Ca²⁺ , although the mechanisms and pathways mediating this Ca²⁺ influx during agonist-induced ASMC contraction are not well defined. By inhibiting store-operated calcium entry (SOCE) or voltage-gated Ca²⁺ channels (VGCCs), we show that SOCE, rather than Ca²⁺ influx via VGCCs, provides the major Ca²⁺ entry pathway into ASMCs to sustain ASMCs contraction and Ca²⁺ oscillations. SOCE may therefore serve as a potential target for new bronchodilators to reduce airway hyper-responsiveness in asthma.

ABSTRACT

Asthma is characterized by airway hyper-responsiveness: the excessive contraction of airway smooth muscle. The extent of this airway contraction is proportional to the frequency of Ca²⁺ oscillations within airway smooth muscle cells (ASMCs). Sustained Ca²⁺ oscillations require a Ca²⁺ influx to replenish Ca²⁺ losses across the plasma membrane. Our previous studies implied store-operated calcium entry (SOCE) as the major pathway for this Ca²⁺ influx. In the present study, we explore this hypothesis, by examining the effects of SOCE inhibitors (GSK7975A and GSK5498A) as well as L-type voltage-gated Ca²⁺ channel inhibitors (nifedipine and nimodipine) on airway contraction and Ca²⁺ oscillations and SOCE-mediated Ca²⁺ influx in ASMCs within mouse precision-cut lung slices. We found that both GSK7975A and GSK5498A were able to fully relax methacholine-induced airway contraction by abolishing the Ca²⁺ oscillations, in a manner similar to that observed in zero extracellular Ca²⁺ ([Ca²⁺ ]_e ). In addition, GSK7975A and GSK5498A inhibited increases in intracellular Ca²⁺ ([Ca²⁺ ]_i ) in ASMCs with depleted Ca²⁺ -stores in response to increased [Ca²⁺ ]_e , demonstrating a response consistent with the inhibition of SOCE. However, GSK7975A and GSK5498A did not reduce Ca²⁺ release via IP₃ receptors stimulated with IP₃ released from caged-IP₃ . By contrast, nifedipine and nimodipine only partially reduced airway contraction, Ca²⁺ oscillation frequency and SOCE-mediated Ca²⁺ influx. These data suggest that SOCE is the major Ca²⁺ influx pathway for ASMCs with respect to sustaining agonist-induced airway contraction and the underlying Ca²⁺ oscillations. The mechanisms of SOCE may therefore form novel targets for new bronchodilators.

Tumor Necrosis Factor Alpha Inhibits L-Type Ca(2+) Channels in Sensitized Guinea Pig Airway Smooth Muscle through ERK 1/2 Pathway

Tumor necrosis factor alpha (TNF-α) is a potent proinflammatory cytokine that plays a significant role in the pathogenesis of asthma by inducing hyperresponsiveness and airway remodeling. TNF-α diminishes the L-type voltage dependent Ca²⁺ channel (L-VDCC) current in cardiac myocytes, an observation that seems paradoxical. In guinea pig sensitized tracheas KCl responses were lower than in control tissues. Serum from sensitized animals (Ser-S) induced the same phenomenon. In tracheal myocytes from nonsensitized (NS) and sensitized (S) guinea pigs, an L-VDCC current (ICa) was observed and diminished by Ser-S. The same decrease was detected in NS myocytes incubated with TNF-α, pointing out that this cytokine might be present in Ser-S. We observed that a small-molecule inhibitor of TNF-α (SMI-TNF) and a TNF-α receptor 1 (TNFR1) antagonist (WP9QY) reversed ICa decrease induced by Ser-S in NS myocytes, confirming the former hypothesis. U0126 (a blocker of ERK 1/2 kinase) also reverted the decrease in ICa. Neither cycloheximide (a protein synthesis inhibitor) nor actinomycin D (a transcription inhibitor) showed any effect on the TNF-α-induced ICa reduction. We found that Ca_V1.2 and Ca_V1.3 mRNA and proteins were expressed in tracheal myocytes and that sensitization did not modify them. In cardiac myocytes, ERK 1/2 phosphorylates two sites of the L-VDCC, augmenting or decreasing ICa; we postulate that, in guinea pig tracheal smooth muscle, TNF-α diminishes ICa probably by phosphorylating the L-VDCC site that reduces its activity through the ERK1/2 MAP kinase pathway.

Rock Tea extract (Jasonia glutinosa) relaxes rat aortic smooth muscle by inhibition of L-type Ca(2+) channels

In traditional herbal medicine, Rock Tea (Jasonia glutinosa) is known for its prophylactic and therapeutic value in various disorders including arterial hypertension. However, the mechanism by which Rock Tea exerts blood pressure-lowering actions has not been elucidated yet. Our aim was to demonstrate vasorelaxing effects of Rock Tea extract and to reveal its possible action mechanism. Isometric myography was conducted on high-K+-precontracted rings from rat thoracic aorta and tested extracts at concentrations of 0.5-5 mg/ml. Whole-cell patch-clamp experiments were performed in rat aortic vascular smooth muscle cells (line A7r5) to determine blocking effects on L-type Ca(2+) channels. Rock Tea extract relaxed the aorta contracted by high [K+] concentration dependently with an EC50 of ≈2.4 mg/ml and produced ≈75 % relaxation at the highest concentration tested. The L-type Ca(2+) channel blocker, verapamil (10(-6) M), had similar effects. Rock Tea extract had no effect in nominally Ca(2+)-free high-K(+) buffer but significantly inhibited contractions to re-addition of Ca(2+). Rock Tea extract inhibited the contractions induced by the L-type Ca(2+) channel activator Bay K 8644 (10(-5) M) and by phenylephrine (10(-6) M). Rock Tea extract and Y-27632 (10(-6) M), Rho-kinase inhibitor, had similar effects and the respective effects were not additive. Patch-clamp experiments demonstrated that Rock Tea extract (2.5 mg/ml) virtually abolished L-type Ca(2+) currents in A7r5. We conclude that Rock Tea extract produced vasorelaxation of rat aorta and that this relaxant effect is mediated by inhibition of L-type Ca(2+) channels. Rock Tea extracts may be of phytomedicinal value for prevention and adjuvant treatment of hypertension and other cardiovascular diseases.

Androgens are bronchoactive drugs that act by relaxing airway smooth muscle and preventing bronchospasm

Changes in the androgen levels in asthmatic men may be associated with the severity of asthma. Androgens induce a nongenomic relaxation in airway smooth muscle, but the underlying mechanisms remain unclear. The aim of this study was to investigate the potential bronchorelaxing action of testosterone (TES) and its metabolites (5α- and 5β-dihydrotestosterone (DHT). A preventive effect on ovalbumin (OVA)-induced bronchospasm was observed in sensitized guinea pigs for each androgen. Androgens were studied in response to bronchoconstrictors: carbachol (CCh) and KCl in isolated trachea rings with and without epithelium from non-sensitized and sensitized animals as well as on OVA-induced contraction. Androgens concentration-dependently abolished the contraction in response to CCh, KCl, and OVA. There were significant differences in the sensitivity to the relaxation induced by each androgen. 5β-DHT was more potent for relaxing KCl-induced contraction, while TES and 5α-DHT were more potent for CCh- and OVA-induced contraction. No differences were found in preparations with and without epithelium or in the presence of a nitric oxide (NO) synthase inhibitor or an inhibitor of K(+) channels. These data indicate the absence of involvement of the epithelium-, NO- and K(+) channels-dependent pathway in androgen-induced relaxation. However, in dissociated tracheal myocytes loaded with the calcium-binding fluorescent dye Fura -2, physiological concentrations of androgens decreased the KCl-induced [Ca(2+)]i increment. 5β-DHT was the most potent at decreasing KCl-induced [Ca(2+)]i increment and preventing bronchospasm. We suggest that androgen-induced brochorelaxation was mediated via decreased Ca(2+) influx through L-type Ca(2+)channels but additional Ca(2+) entry blockade may be involved. Molecular changes in androgen structure may determine its preferential site of action.

Testosterone-induced relaxation involves L-type and store-operated Ca2+ channels blockade, and PGE 2 in guinea pig airway smooth muscle

In vascular smooth muscle, it has been described that testosterone (TES) produces relaxation by blocking L-type Ca(2+) channels. Recently, we found that L-type Ca(2+) and store-operated Ca(2+) (SOC) channels are the main membranal structures that provide extracellular Ca(2+) for carbachol (CCh)-induced contraction in airway smooth muscle (ASM). We studied the possible interactions between L-type and SOC channels in TES-induced relaxation in guinea pig ASM. TES (10, 32, 100, and 178 μM) induced a complete relaxation of CCh-precontracted tracheal smooth muscle, and indomethacin partially inhibited this response. In single myocytes, the KCl-induced intracellular Ca(2+) increase ([Ca(2+)]i) was decreased by 32 and completely blocked by 100 nM TES. This androgen (32 and 100 μM) significantly diminished (~25 and 49 %, respectively) the capacitative Ca(2+) entry. Myocytes stimulated with CCh produced a transient Ca(2+) peak followed by a sustained plateau. D-600 was added during the plateau phase, and a partial diminution (~35 %) was observed. A greater decrease (~78 %) was seen when 2-aminoethyl diphenylborinate (2-APB, SOC antagonist) was used. The combination of both drugs completely abolished the Ca(2+) plateau induced by CCh. TES (100 μM) also completely abolished the CCh-induced Ca(2+) plateau. Indomethacin significantly diminished this effect of TES. PGE2 and butaprost proportionally decreased the Ca(2+) plateau as indomethacin blocked it. Sarcoplasmic reticulum refilling was partially, dependently, and significantly diminished by TES. We concluded that TES-induced relaxation involves blockade of L-type Ca(2+) channels at nanomolar and SOC channels at micromolar concentration and PGE2 seems to be also involved in this phenomenon.