Atherosclerosis remains a major cause of death in the developed world despite the success of therapies that lower cholesterol and BP. The intermediate-conductance calcium-activated potassium channel KCa3.1 is expressed in multiple cell types implicated in atherogenesis, and pharmacological blockade of this channel inhibits VSMC and lymphocyte activation in rats and mice. We found that coronary vessels from patients with coronary artery disease expressed elevated levels of KCa3.1. In Apoe–/– mice, a genetic model of atherosclerosis, KCa3.1 expression was elevated in the VSMCs, macrophages, and T lymphocytes that infiltrated atherosclerotic lesions. Selective pharmacological blockade and gene silencing of KCa3.1 suppressed proliferation, migration, and oxidative stress of human VSMCs. Furthermore, VSMC proliferation and macrophage activation were reduced in KCa3.1–/– mice. In vivo therapy with 2 KCa3.1 blockers, TRAM-34 and clotrimazole, significantly reduced the development of atherosclerosis in aortas of Apoe–/– mice by suppressing VSMC proliferation and migration into plaques, decreasing infiltration of plaques by macrophages and T lymphocytes, and reducing oxidative stress. Therapeutic concentrations of TRAM-34 in mice caused no discernible toxicity after repeated dosing and did not compromise the immune response to influenza virus. These data suggest that KCa3.1 blockers represent a promising therapeutic strategy for atherosclerosis.
The blood-brain tumor barrier (BTB) impedes the delivery of therapeutic agents to brain tumors. While adequate delivery of drugs occurs in systemic tumors, the BTB limits delivery of anti-tumor agents into brain metastases.
In this study, we examined the function and regulation of calcium-activated potassium (KCa) channels in a rat metastatic brain tumor model. We showed that intravenous infusion of NS1619, a KCa channel agonist, and bradykinin selectively enhanced BTB permeability in brain tumors, but not in normal brain. Iberiotoxin, a KCa channel antagonist, significantly attenuated NS1619-induced BTB permeability increase. We found KCa channels and bradykinin type 2 receptors (B2R) expressed in cultured human metastatic brain tumor cells (CRL-5904, non-small cell lung cancer, metastasized to brain), human brain microvessel endothelial cells (HBMEC) and human lung cancer brain metastasis tissues. Potentiometric assays demonstrated the activity of KCa channels in metastatic brain tumor cells and HBMEC. Furthermore, we detected higher expression of KCa channels in the metastatic brain tumor tissue and tumor capillary endothelia as compared to normal brain tissue. Co-culture of metastatic brain tumor cells and brain microvessel endothelial cells showed an upregulation of KCa channels, which may contribute to the overexpression of KCa channels in tumor microvessels and selectivity of BTB opening.
These findings suggest that KCa channels in metastatic brain tumors may serve as an effective target for biochemical modulation of BTB permeability to enhance selective delivery of chemotherapeutic drugs to metastatic brain tumors.
We previously reported in an ovalbumin-induced model of allergic asthma that Fms-like tyrosine kinase 3 ligand (Flt3-L) reversed airway hyperresponsiveness (AHR) and airway inflammation, and increased the number of regulatory CD11chighCD8αhighCD11blow dendritic cells in the lung. In this study, we investigated the effect of Flt3-L in a clinically relevant aeroallergen-induced asthma on the phenotypic expression of lung T cells. Balb/c mice were sensitized and challenged with cockroach antigen (CRA), and AHR to methacholine was established. These mice received three intraperitoneal injections of anti-CD25 antibody (PC61; 250 μg) and Flt3-L (3 μg) daily for 10 days. Cytokines and Ig levels in the serum were measured and differential bronchoalveolar lavage fluid (BALF) cell counts were examined. Flt3-L reversed AHR to methacholine to the control level. Flt3-L significantly decreased levels of BALF IL-5, IFN-γ, eosinophilia and substantially increased IL-10 and the number of CD4+CD25+ Forkhead winged helix transcription factor box P3 (Foxp3+) IL-10+ T cells in the lung. Administration of PC61 antibody blocked the effect of Flt3-L and substantially increased AHR, eosinophilia, and BALF IL-5 and IFN-γ levels, and decreased BALF IL-10 levels and the number of CD4+CD25+Foxp3+IL-10+ T cells. Flt3-L significantly decreased CD62-L, but increased inducible costimulatory molecule and Foxp3 mRNA expression in the CD4+CD25+ T cells isolated from lungs of Flt3-L–treated, CRA-sensitized mice compared to CRA-sensitized mice without Flt3-L treatment and PBS control group. Flt3-L significantly inhibited the effect of CRA sensitization and challenge to increase GATA3 expression in lung CD4+CD25+ T cells. Collectively, these data suggest that the therapeutic effect of Flt3-L is mediated by increased density of naturally occurring CD4+CD25+Foxp3+IL-10+ICOS+ T-regulatory cells in the lung. Flt3-L could be a therapeutic strategy for the management and prevention of allergic asthma.
airway hyperresponsiveness; anti-CD25 antibody; Fms-like tyrosine kinase 3 ligand; Forkhead winged helix transcription factor box P3; naturally occurring CD4+CD25+ T-regulatory cells
Calcium-activated potassium (KCa) channels are present throughout the central nervous system as well as many peripheral tissues. Activation of KCa channels contribute to maintenance of the neuronal membrane potential and was shown to underlie the afterhyperpolarization (AHP) that regulates action potential firing and limits the firing frequency of repetitive action potentials. Different subtypes of KCa channels were anticipated on the basis of their physiological and pharmacological profiles, and cloning revealed two well defined but phylogenetic distantly related groups of channels. The group subject of this review includes both the small conductance KCa2 channels (KCa2.1, KCa2.2, and KCa2.3) and the intermediate-conductance (KCa3.1) channel. These channels are activated by submicromolar intracellular Ca2+ concentrations and are voltage independent. Of all KCa channels only the KCa2 channels can be potently but differentially blocked by the bee-venom apamin. In the past few years modulation of KCa channel activation revealed new roles for KCa2 channels in controlling dendritic excitability, synaptic functioning, and synaptic plasticity. Furthermore, KCa2 channels appeared to be involved in neurodegeneration, and learning and memory processes. In this review, we focus on the role of KCa2 and KCa3 channels in these latter mechanisms with emphasis on learning and memory, Alzheimer’s disease and on the interplay between neuroinflammation and different neurotransmitters/neuromodulators, their signaling components and KCa channel activation.
small conductance calcium-activated potassium channels; SK channels; learning and memory; neurodegeneration
Exacerbated activation of glutamate receptor-coupled calcium channels and subsequent increase in intracellular calcium ([Ca2+]i) are established hallmarks of neuronal cell death in acute and chronic neurological diseases. Here we show that pathological [Ca2+]i deregulation occurring after glutamate receptor stimulation is effectively modulated by small conductance calcium-activated potassium (KCa2) channels. We found that neuronal excitotoxicity was associated with a rapid downregulation of KCa2.2 channels within 3 h after the onset of glutamate exposure. Activation of KCa2 channels preserved KCa2 expression and significantly reduced pathological increases in [Ca2+]i providing robust neuroprotection in vitro and in vivo. These data suggest a critical role for KCa2 channels in excitotoxic neuronal cell death and propose their activation as potential therapeutic strategy for the treatment of acute and chronic neurodegenerative disorders.
calcium homeostasis; cerebral ischemia; KCa2 channels; glutamate excitotoxicity; neuroprotection
The molecular mechanisms underlying the effects of nitric oxide (NO) and carbon monoxide (CO), individually and collectively, on large-conductance calcium-activated K+ (KCa) channels were investigated in rat vascular smooth muscle cells (SMCs). Both NO and CO increased the activity of native KCa channels. Dehydrosoyasaponin-I, a specific agonist for β subunit of KCa channels, increased the open probability of native KCa channels only when it was delivered to the cytoplasmic surface of membrane. CO, but not NO, further increased the activity of native KCa channels that had been maximally stimulated by dehydrosoyasaponin-I. After treatment of SMCs with anti–KCa,β subunit antisense oligodeoxynucleotides, the stimulatory effect of NO, but not of CO, on KCa channels was nullified. CO, but not NO, enhanced the KCa current densities of heterologously expressed cloned KCa,α subunit, showing that the presence of KCa,β subunit is not a necessity for the effect of CO but essential for that of NO. Finally, pretreatment of SMCs with NO abolished the effects of subsequently applied CO or diethyl pyrocarbonate on KCa channels. In summary, the stimulatory effects of CO and NO on KCa channels rely on the specific interactions of these gases with KCa,α and KCa,β subunits.
In the present study we evaluated the expression of the intermediate conductance calcium-activated potassium (KCa3.1) channel in human glioblastoma stem-like cells (CSCs) and investigated its role in cell motility. While the KCa3.1 channel is not expressed in neuronal- and glial-derived tissues of healthy individuals, both the KCa3.1 mRNA and protein are present in the glioblastoma tumor population, and are significantly enhanced in CSCs derived from both established cell line U87MG and a primary cell line, FCN9. Consistent with these data, voltage-independent and TRAM-34 sensitive potassium currents imputable to the KCa3.1 channel were recorded in the murine GL261 cell line and several primary human glioblastoma cells lines. Moreover, a significantly higher KCa3.1 current was recorded in U87MG-CD133 positive cells as compared to the U87MG-CD133 negative subpopulation. Further, we found that the tumor cell motility is strongly associated with KCa3.1 channel expression. Blockade of the KCa3.1 channel with the specific inhibitor TRAM-34 has in fact a greater impact on the motility of CSCs (reduction of 75%), which express a high level of KCa3.1 channel, than on the FCN9 parental population (reduction of 32%), where the KCa3.1 channel is expressed at lower level. Similar results were also observed with the CSCs derived from U87MG. Because invasion of surrounding tissues is one of the main causes of treatment failure in glioblastoma, these findings can be relevant for future development of novel cancer therapeutic drugs.
Human lung mast cells (HLMC) express the Ca2+-activated K+ channel KCa3.1, which opens following IgE-dependent activation. This hyperpolarises the cell membrane and potentiates both Ca2+ influx and degranulation. In addition, blockade of KCa3.1 profoundly inhibits HLMC migration to a variety of diverse chemotactic stimuli. KCa3.1 activation is attenuated by the β2adrenoceptor through a Gαs-coupled mechanism independent of cyclic AMP. Adenosine is an important mediator that both attenuates and enhances HLMC mediator release through the Gαs-coupled A2A and A2B adenosine receptors, respectively. We show that at concentrations that inhibit HLMC degranulation (10–5–10–3 M), adenosine closes KCa3.1 both dose-dependently and reversibly. KCa3.1 suppression by adenosine was reversed partially by the selective adenosine A2A receptor antagonist ZM241385 but not by the A2B receptor antagonist MRS1754, and the effects of adenosine were mimicked by the selective A2A receptor agonist CGS21680. Adenosine also opened a depolarising current carried by non-selective cations. As predicted from the role of KCa3.1 in HLMC migration, adenosine abolished HLMC chemotaxis to asthmatic airway smooth muscle-conditioned medium. In summary, the Gαs-coupled adenosine A2A receptor closes KCa3.1, providing a clearly defined mechanism by which adenosine inhibits HLMC migration and degranulation. A2A receptor agonists with channel-modulating function may be useful for the treatment of mast cell-mediated disease.
Adenosine; Chemotaxis; Ion channel; KCa3.1; Mast cell
The calcium-activated potassium channel KCa3.1 regulates membrane potential and calcium signaling in erythrocytes, activated T and B cells, macrophages, microglia, vascular endothelium, epithelia, and proliferating vascular smooth muscle cells and fibroblasts. KCa3.1 has therefore been suggested as a potential therapeutic target for diseases such as sickle cell anemia, asthma, coronary restenosis after angioplasty, atherosclerosis, kidney fibrosis and autoimmunity, where activation and excessive proliferation of one or more of these cell types is involved in the pathology. This article will review KCa3.1’s physiology and pharmacology and critically examine the available preclinical and clinical data validating KCa3.1 as a therapeutic target.
KCa3.1: intermediate-conductance calcium-activated K+ channels (also known as IK1, SK4 or KCNN4); Sickle-cell disease: is a life-long blood disorder characterized by red blood cells that assume an abnormal, rigid, sickle shape because of a mutation in the hemoglobin gene. “Sickling” decreases the flexibility of the erythrocytes and results in a risk of various complications such as baseline anemia, vaso-occlusive events and stroke.; ICA-17043: 4-fluoro-α-(4-fluorophenyl)-α-phenyl-benzeneacetamide, KCa3.1 blocker that entered clinical trials as Senicapoc®; TRAM-34: 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole, commonly used experimental KCa3.1 blocker; Atherosclerosis: is a disease of large and medium-sized muscular arteries and is characterized by endothelial dysfunction, vascular inflammation, and the buildup of lipids, cholesterol, calcium, and cellular debris within the intima of the vessel wall.; Restenosis: means the reoccurrence of stenosis, a narrowing of a blood vessel, leading to restricted blood flow. It typically occurs following angioplasty and is caused by the proliferation of intimal vascular smooth muscle cells (neointimal hyperplasia).; Fibrosis: is the formation or development of excess fibrous connective tissue in an organ or tissue.; Asthma: common chronic disorder of the airways characterized by variable and recurring symptoms, airflow obstruction, smooth muscle hypertrophy, bronchial hyperresponsiveness (bronchospasm), and an underlying inflammation.
The calmodulin/calcium-activated K+ channel KCa3.1 is expressed in red and white blood cells, epithelia and endothelia, and possibly central and peripheral neurons. However, our knowledge about its contribution to neurological functions and behavior is incomplete. Here, we investigated whether genetic deficiency or pharmacological activation of KCa3.1 change behavior and cerebral monoamine levels in mice.
In the open field test, KCa3.1-deficiency increased horizontal activity, as KCa3.1−/− mice travelled longer distances (≈145% of KCa3.1+/+) and at higher speed (≈1.5-fold of KCa3.1+/+). Working memory in the Y-maze was reduced by KCa3.1-deficiency. Motor coordination on the rotarod and neuromuscular functions were unchanged. In KCa3.1−/− mice, HPLC analysis revealed that turn-over rates of serotonin were reduced in frontal cortex, striatum and brain stem, while noradrenalin turn-over rates were increased in the frontal cortex. Dopamine turn-over rates were unaltered. Plasma catecholamine and corticosterone levels were unaltered. Intraperitoneal injections of 10 mg/kg of the KCa3.1/KCa2-activator SKA-31 reduced rearing and turning behavior in KCa3.1+/+ but not in KCa3.1−/− mice, while 30 mg/kg SKA-31 caused strong sedation in 50% of the animals of either genotypes. KCa3.1−/− mice were hyperactive (≈+60%) in their home cage and SKA-31-administration reduced nocturnal physical activity in KCa3.1+/+ but not in KCa3.1−/− mice.
KCa3.1-deficiency causes locomotor hyperactivity and altered monoamine levels in selected brain regions, suggesting a so far unknown functional link of KCa3.1 channels to behavior and monoaminergic neurotransmission in mice. The tranquilizing effects of low-dose SKA-31 raise the possibility to use KCa3.1/KCa2 channels as novel pharmacological targets for the treatment of neuropsychiatric hyperactivity disorders.
During pulmonary mycobacterial infection, there is increased trafficking of dendritic cells from the lungs to the draining lymph nodes. We hypothesized that ongoing mycobacterial infection would modulate recruitment and activation of antigen-specific naive CD4+ T cells after airway antigen challenge. BALB/c mice were infected by aerosol with Mycobacterium bovis BCG. At peak bacterial burden in the lungs (4 to 6 weeks postinfection), carboxy-fluorescein diacetate succinimidyl ester-labeled naive ovalbumin-specific DO11.10 T cells were adoptively transferred into infected and uninfected mice. Recipient mice were challenged intranasally with soluble ovalbumin (OVA), and OVA-specific T-cell responses were measured in the lungs, draining mediastinal lymph nodes (MLN), and spleens. OVA challenge resulted in increased activation and proliferation of OVA-specific T cells in the draining MLN of both infected and uninfected mice. However, only BCG-infected mice had prominent OVA-specific T-cell activation, proliferation, and Th1 differentiation in the lungs. BCG infection caused greater distribution of airway OVA to pulmonary dendritic cells and enhanced presentation of OVA peptide by lung CD11c+ cells. Together, these data suggest that an existing pulmonary mycobacterial infection alters the phenotype of lung dendritic cells so that they can activate antigen-specific naive CD4+ T cells in the lungs in response to airway antigen challenge.
Mast cell recruitment and activation are critical for the initiation and progression of inflammation and fibrosis. Mast cells infiltrate specific structures in many diseased tissues such as the airway smooth muscle (ASM) in asthma. This microlocalisation of mast cells is likely to be key to disease pathogenesis. Human lung mast cells (HLMC) express the Ca2+ activated K+ channel KCa3.1 which modulates mediator release, and is proposed to facilitate the retraction of the cell body during migration of several cell types. A study was undertaken to test the hypothesis that blockade of KCa3.1 would attenuate HLMC proliferation and migration.
HLMC were isolated and purified from lung material resected for bronchial carcinoma. HLMC proliferation was assessed by cell counts at various time points following drug exposure. HLMC chemotaxis was assayed using standard Transwell chambers (8 μm pore size). Ion currents were measured using the single cell patch clamp technique.
KCa3.1 blockade with triarylmethane‐34 (TRAM‐34) did not inhibit HLMC proliferation and clotrimazole had cytotoxic effects. In contrast, HLMC migration towards the chemokine CXCL10, the chemoattractant stem cell factor, and the supernatants from tumour necrosis factor α stimulated asthmatic ASM was markedly inhibited with both the non‐selective KCa3.1 blocker charybdotoxin and the highly specific KCa3.1 blocker TRAM‐34 in a dose dependent manner. Although KCa3.1 blockade inhibits HLMC migration, KCa3.1 is not opened by the chemotactic stimulus, suggesting that it must be involved downstream of the initial receptor‐ligand interactions.
Since modulation of KCa3.1 can inhibit HLMC chemotaxis to diverse chemoattractants, the use of KCa3.1 blockers such as TRAM‐34 could provide new therapeutic strategies for mast cell mediated diseases such as asthma.
mast cell; migration; asthma; CXCL10; KCa3.1
Glioblastomas are characterized by altered expression of several ion channels that have important consequences in cell functions associated with their aggressiveness, such as cell survival, proliferation, and migration. Data on the altered expression and function of the intermediate-conductance calcium-activated K (KCa3.1) channels in glioblastoma cells have only recently become available. This paper aims to (i) illustrate the main structural, biophysical, pharmacological, and modulatory properties of the KCa3.1 channel, (ii) provide a detailed account of data on the expression of this channel in glioblastoma cells, as compared to normal brain tissue, and (iii) critically discuss its major functional roles. Available data suggest that KCa3.1 channels (i) are highly expressed in glioblastoma cells but only scantly in the normal brain parenchima, (ii) play an important role in the control of glioblastoma cell migration. Altogether, these data suggest KCa3.1 channels as potential candidates for a targeted therapy against this tumor.
We previously reported that Fms-like tyrosine kinase 3 ligand (Flt3-L) reversed airway hyperresponsiveness (AHR) and airway inflammation, and increased the number of regulatory CD11chighCD8αhighCD11blow dendritic cells and CD4+CD25+ICOS+Foxp3+IL-10+ T-regulatory cells in the lung of allergen-sensitized and -challenged mice. In this study, we evaluated the effect of Flt3-L on Th17 cells and expression of suppressors of cytokine signaling (SOCS) proteins in the lungs of house dust mite (HDM)–sensitized and –challenged mice. BALB/c mice were sensitized and challenged with HDM, and AHR to methacholine was established. Mice were treated with Flt3-L (5 μg, intraperitoneal) daily for 10 days. Levels of IL-4, -5, -6, -8, and -13, and transforming growth factor (TGF)–β in the bronchoalveolar lavage fluid (BALF) were examined by ELISA. Flt3-L treatment reversed existing AHR to methacholine and substantially decreased eosinophils, neutrophils, IL-5, -6, -8, and IL-13, and TGF-β levels in the BALF. HDM-sensitized and -challenged mice showed a significant increase in lung CD4+IL-17+IL-23R+CD25− T cells with high expression of retinoic acid–related orphan receptor (ROR)–γt transcripts. However, administration of Flt3-L substantially decreased the number of lung CD4+IL-17+IL-23R+CD25− T cells, with significantly decreased expression of ROR-γt mRNA in these cells. HDM sensitization caused a significant increase in the expression of SOCS-1, -3, and -5 in the lung. Flt3-L treatment abolished the increase in SOCS-1 and SOCS-3 proteins, whereas SOCS-5 expression was significantly reduced. These data suggest that the therapeutic effect of Flt3-L in reversing the hallmarks of allergic asthma in a mouse model is mediated by decreasing IL-6 and TGF-β levels in the BALF, which, in turn, decrease CD4+IL-17+IL-23R+ROR-γt+CD25− T cells and the expression of SOCS-1 and SOCS-3 in the lung of HDM-sensitized and -challenged mice.
airway hyperresponsiveness; house dust mite; retinoic acid–related orphan receptor–γt; suppressors of cytokine signaling; T helper cell type 17
Ca2+-activated K+ (KCa)channels are a unique family of ion channels because they are capable of directly communicating calcium signals to changes in cell membrane potential required for cellular processes including but not limited to cellular proliferation and migration. It is now possible to distinguish three families of KCa channels based on differences in their biophysical and pharmacological properties as well as genomic sequence. Using a combination of biochemical, molecular, and biophysical approaches, we show that human tumor cells of astrocytic origin, i.e. glioma cells, express transcripts for all three family members of KCa channels including BK, IK, and all three SK channel types (SK1, SK2, and SK3). The use of selective pharmacological inhibitors shows prominent expression of currents that are inhibited by the BK channel specific inhibitors iberiotoxin and paxilline. However, despite the presence of transcripts for IK and SK, neither clotrimazole, an inhibitor of IK channels, nor apamin, known to block most SK channels inhibited any current. The exclusive expression of functional BK channels was further substantiated by shRNA knockdown experiments, which selectively reduced iberiotoxin sensitive currents. Western blotting of patient biopsies with antibodies specific for all three KCa channel types further substantiated the exclusive expression of BK type KCa channels in vivo. This finding is in sharp contrast to other cancers that express primarily IK channels.
BK channel; migration; astrocyte; glia
Human lung mast cells (HLMC) express the Ca2+-activated K+ channel KCa3.1, which plays a crucial role in their migration to a variety of diverse chemotactic stimuli. KCa3.1 activation is attenuated by the β2-adrenoceptor and the adenosine A2A receptor through a Gs-coupled mechanism independent of cyclic AMP. Prostaglandin E2 promotes degranulation and migration of mouse bone marrow-derived mast cells through the Gi-coupled EP3 prostanoid receptor, and induces LTC4 and cytokine secretion from human cord blood-derived mast cells. However, PGE2 binding to the Gs-coupled EP2 receptor on HLMC inhibits their degranulation. We show that EP2 receptor engagement closes KCa3.1 in HLMC. The EP2 receptor-specific agonist butaprost was more potent than PGE2 in this respect, and the effects of both agonists were reversed by the EP2 receptor antagonist AH6809. Butaprost markedly inhibited HLMC migration induced by chemokine-rich airway smooth muscle-conditioned media. Interestingly, PGE2 alone was chemotactic for HLMC at high concentrations (1 µM), but was a more potent chemoattractant for HLMC following EP2 receptor blockade. Therefore, the Gs-coupled EP2 receptor closes KCa3.1 in HLMC and attenuates both chemokine- and PGE2-dependent HLMC migration. EP2 receptor agonists with KCa3.1 modulating function may be useful for the treatment of mast cell-mediated disease.
Chemotaxis; Ion channel; KCa3.1; Mast cell; Prostaglandin E2
Mitochondria regulate intracellular calcium (Ca2+) signals in smooth muscle cells, but mechanisms mediating these effects, and the functional relevance, are poorly understood. Similarly, antihypertensive ATP-sensitive potassium (KATP) channel openers (KCOs) activate plasma membrane KATP channels and depolarize mitochondria in several cell types, but the contribution of each of these mechanisms to vasodilation is unclear. Here, we show that cerebral artery smooth muscle cell mitochondria are most effectively depolarized by diazoxide (−15%, tetramethylrhodamine [TMRM]), less so by levcromakalim, and not depolarized by pinacidil. KCO-induced mitochondrial depolarization increased the generation of mitochondria-derived reactive oxygen species (ROS) that stimulated Ca2+ sparks and large-conductance Ca2+-activated potassium (KCa) channels, leading to transient KCa current activation. KCO-induced mitochondrial depolarization and transient KCa current activation were attenuated by 5-HD and glibenclamide, KATP channel blockers. MnTMPyP, an antioxidant, and Ca2+ spark and KCa channel blockers reduced diazoxide-induced vasodilations by >60%, but did not alter dilations induced by pinacidil, which did not elevate ROS. Data suggest diazoxide drives ROS generation by inducing a small mitochondrial depolarization, because nanomolar CCCP, a protonophore, similarly depolarized mitochondria, elevated ROS, and activated transient KCa currents. In contrast, micromolar CCCP, or rotenone, an electron transport chain blocker, induced a large mitochondrial depolarization (−84%, TMRM), reduced ROS, and inhibited transient KCa currents. In summary, data demonstrate that mitochondria-derived ROS dilate cerebral arteries by activating Ca2+ sparks, that some antihypertensive KCOs dilate by stimulating this pathway, and that small and large mitochondrial depolarizations lead to differential regulation of ROS and Ca2+ sparks.
vascular smooth muscle; ryanodine receptor; vasodilation; redox
L-type, voltage-dependent calcium (Ca2+) channels,
ryanodine-sensitive Ca2+ release (RyR) channels, and
large-conductance Ca2+-activated potassium (KCa) channels
comprise a functional unit that regulates smooth muscle contractility. Here, we
investigated whether genetic ablation of caveolin-1 (cav-1), a caveolae protein,
alters Ca2+ spark to KCa channel coupling and
Ca2+ spark regulation by voltage-dependent Ca2+ channels
in murine cerebral artery smooth muscle cells. Caveolae were abundant in the
sarcolemma of control (cav-+/+) cells but were not observed in
cav-1-deficient (cav-1−/−) cells.
Ca2+ spark and transient KCa current frequency were
approximately twofold higher in cav-1−/− than
in cav-1+/+ cells. Although voltage-dependent Ca2+ current
density was similar in cav-1+/+ and
cav-1−/− cells, diltiazem and
Cd2+, voltage-dependent Ca2+ channel blockers, reduced
transient KCa current frequency to ∼55% of control in
cav-1+/+ cells but did not alter transient KCa current
frequency in cav-1−/− cells. Furthermore,
although KCa channel density was elevated in
cav-1−/− cells, transient KCa
current amplitude was similar to that in cav-1+/+ cells. Higher
Ca2+ spark frequency in cav-1−/−
cells was not due to elevated intracellular Ca2+ concentration,
sarcoplasmic reticulum Ca2+ load, or nitric oxide synthase activity.
Similarly, Ca2+ spark amplitude and spread, the percentage of
Ca2+ sparks that activated a transient KCa current,
the amplitude relationship between sparks and transient KCa currents,
and KCa channel conductance and apparent Ca2+ sensitivity
were similar in cav-1+/+ and
cav-1−/− cells. In summary, cav-1 ablation
elevates Ca2+ spark and transient KCa current frequency,
attenuates the coupling relationship between voltage-dependent Ca2+
channels and RyR channels that generate Ca2+ sparks, and elevates
KCa channel density but does not alter transient KCa
current activation by Ca2+ sparks. These findings indicate that cav-1
is required for physiological Ca2+ spark and transient KCa
current regulation in cerebral artery smooth muscle cells.
ryanodine-sensitive Ca2+ release channel; large-conductance Ca2+-activated potassium channel; caveolae; voltage-dependent Ca2+ channel
Turtle auditory-hair cells are frequency-tuned by the activity of calcium-activated potassium (KCa) channels, a cell's characteristic frequency being determined by the KCa channel density and kinetics which both vary systematically along the cochlea. As a first step towards identifying the source of KCa channel variation, we have isolated, by reverse-transcription polymerase chain reaction on dissociated hair cells, the main cDNAs homologous to the slo gene which encodes the channel's alpha-subunit. A total of six alternatively spliced variants were identified, the smallest of which is 94% identical to a mouse Slo sequence. Variation occurs by insertion of exons at only two splice sites, two of these exons encoding novel 31- and 61-amino acid sequences. As we were unable to detect splicing at other potential sites, we infer that the six variants correspond to naturally occurring combinations. The spatial distribution of the variants, defined by isolating hair cells from different regions of the cochlea, indicated that some isoforms were non-uniformly distributed. Those containing large inserts in the first splice site were notably absent from the highest-frequency region. We suggest that alternative splicing of the slo gene may contribute to variation in KCa channel properties.
Calcium-sensitive potassium (KCa) channels have been shown to modulate the diameter of cerebral pial arteries; however, little is known regarding their roles in controlling cerebral parenchymal arterioles (PAs). We explored the function and cellular distribution of small-conductance (SKCa) and intermediate-conductance (IKCa) KCa channels and large-conductance KCa (BKCa) channels in endothelial cells (ECs) and smooth muscle cells (SMCs) of PAs. Both SKCa and IKCa channels conducted the outward current in isolated PA ECs (current densities, ∼20 pA/pF and ∼28 pA/pF at +40 mV, respectively), but these currents were not detected in PA SMCs. In contrast, BKCa currents were prominent in PA SMCs (∼154 pA/pF), but were undetectable in PA ECs. Pressurized PAs constricted to inhibition of SKCa (∼16%) and IKCa (∼16%) channels, but were only modestly affected by inhibition of BKCa channels (∼5%). Blockade of SKCa and IKCa channels decreased resting cortical cerebral blood flow (CBF) by ∼15%. NS309 (6,7-dichloro-1H-indole-2,3-dione3-oxime), a SKCa/IKCa channel opener, hyperpolarized PA SMCs by ∼27 mV, maximally dilated pressurized PAs, and increased CBF by ∼40%. In conclusion, these data show that SKCa and IKCa channels in ECs profoundly modulate PA tone and CBF, whereas BKCa channels in SMCs only modestly influence PA diameter.
BKCa; calcium-activated potassium channel; IKCa; parenchymal arterioles; SKCa
The voltage-gated Kv1.3 and the calcium-activated KCa3.1 potassium channel modulate many calcium-dependent cellular processes in immune cells, including T-cell activation and proliferation, and have therefore been proposed as novel therapeutic targets for immunomodulation. Kv1.3 is highly expressed in CCR7− effector memory T cells and is emerging as a target for T-cell mediated diseases like multiple sclerosis, rheumatoid arthritis, type-1 diabetes mellitus, allergic contact dermatitis, and psoriasis. KCa3.1 in contrast is expressed in CCR7+ naïve and central memory T cells, as well as in mast cells, macrophages, dedifferentiated vascular smooth muscle cells, fibroblasts, vascular endothelium, and airway epithelium. Given this expression pattern, KCa3.1 is a potential therapeutic target for conditions ranging from inflammatory bowel disease, multiple sclerosis, arthritis, and asthma to cardiovascular diseases like atherosclerosis and post-angioplasty restenosis. Results from animal studies have been supportive of the therapeutic potential of both Kv1.3 and KCa3.1 blockers and have also not shown any toxicities associated with pharmacological Kv1.3 and KCa3.1 blockade. To date, two compounds targeting Kv1.3 are in preclinical development but, so far, no Kv1.3 blocker has advanced into clinical trials. KCa3.1 blockers, on the other hand, have been evaluated in clinical trials for sickle cell anemia and exercise-induced asthma, but have so far not shown efficacy. However, the trial results support KCa3.1 as a safe therapeutic target, and will hopefully help enable clinical trials for other medical conditions that might benefit from KCa3.1 blockade.
immunosuppression; potassium channel; Kv1.3; KCa3.1; TRAM-34; PAP-1
New concepts on potassium channel function in neuroinflammation suggest that they regulate mechanisms of microglial activation, including intracellular calcium homeostasis, morphological alterations, pro-inflammatory cytokine release, antigen presentation, and phagocytosis. Although little is known about voltage independent potassium channels in microglia, special attention emerges on small (SK/KCNN1-3/KCa2) and intermediate (IK/KCNN4/KCa3.1)-conductance calcium-activated potassium channels as regulators of microglial activation in the field of research on neuroinflammation and neurodegeneration. In particular, recent findings suggested that SK/KCa2 channels, by regulating calcium homeostasis, may elicit a dual mechanism of action with protective properties in neurons and inhibition of inflammatory responses in microglia. Thus, modulating SK/KCa2 channels and calcium signaling may provide novel therapeutic strategies in neurological disorders, where neuronal cell death and inflammatory responses concomitantly contribute to disease progression. Here, we review the particular role of SK/KCa2 channels for [Ca2+]i regulation in microglia and neurons, and we discuss the potential impact for further experimental approaches addressing novel therapeutic strategies in neurological diseases, where neuronal cell death and neuroinflammatory processes are prominent.
calcium regulation; KCa2/SK channels; KCa3/IK channels; microglia; neuroprotection
Activation of muscarinic acetylcholine receptors (mAChR) facilitates the induction of synaptic plasticity and enhances cognitive function. In the hippocampus, M1 mAChR on CA1 pyramidal cells inhibit both small conductance Ca2+-activated KCa2 potassium channels and voltage-activated Kv7 potassium channels. Inhibition of KCa2 channels facilitates long-term potentiation (LTP) by enhancing Ca2+calcium influx through postsynaptic NMDA receptors (NMDAR). Inhibition of Kv7 channels is also reported to facilitate LTP but the mechanism of action is unclear. Here, we show that inhibition of Kv7 channels with XE-991 facilitated LTP induced by theta burst pairing at Schaffer collateral commissural synapses in rat hippocampal slices. Similarly, negating Kv7 channel conductance using dynamic clamp methodologies also facilitated LTP. Negation of Kv7 channels by XE-991 or dynamic clamp did not enhance synaptic NMDAR activation in response to theta burst synaptic stimulation. Instead, Kv7 channel inhibition increased the amplitude and duration of the after-depolarisation following a burst of action potentials. Furthermore, the effects of XE-991 were reversed by re-introducing a Kv7-like conductance with dynamic clamp. These data reveal that Kv7 channel inhibition promotes NMDAR opening during LTP induction by enhancing depolarisation during and after bursts of postsynaptic action potentials. Thus, during the induction of LTP M1 mAChRs enhance NMDAR opening by two distinct mechanisms namely inhibition of KCa2 and Kv7 channels.
Episodic ataxia type-2 (EA2) is an inherited movement disorder caused by mutations in the gene encoding the Cav2.1α1 subunit of the P/Q-type voltage-gated calcium channel that result in an overall reduction in the P/Q-type calcium current. A consequence of these mutations is loss of precision of pacemaking in cerebellar Purkinje cells. This diminished precision reduces the information encoded by Purkinje cells and is thought to contribute to symptoms associated with this disorder. The loss of the precision of pacemaking in EA2 is the consequence of reduced activation of calcium-dependant potassium channels (KCa) by the smaller calcium current and in vitro can be pharmacologically restored by KCa activators.
We used a well-established mouse model of EA2, the tottering (tg/tg) mouse, to examine the potential therapeutic utility of one such FDA-approved compound, chlorzoxazone (CHZ). Compared to wild-type Purkinje cells, we found the firing rate of tg/tg Purkinje cells in acutely prepared cerebellar slices to be very irregular. Bath application of CHZ successfully restored the precision of pacemaking in a dose-dependent manner. Oral administration of CHZ to tg/tg mice improved their baseline motor performance and reduced the severity, frequency and duration of episodes of dyskinesia without producing any adverse effects. We propose the use of CHZ, which is currently FDA-approved as a muscle relaxant, as a safe and novel treatment of EA2.
We investigated the role of calcium-activated potassium (KCa) channel activity in human skeletal muscle microvascular function in the setting of cardiopulmonary bypass (CPB).
Methods and Results
Human skeletal muscle arterioles (80- to 180 μm in diameter) were dissected from tissue harvested before and after CPB. In vitro relaxation responses of precontracted arterioles in a pressurized no-flow state were examined in the presence of KCa channel activators/blockers and several other vasodilators. Post-CPB responses to the activator of intermediate (IKCa) and small conductance (SKCa) KCa channels, NS309, to the endothelium-dependent vasodilator adenosine 5′-diphosphate (ADP), and to substance P were reduced compared with pre-CPB responses (P < .05), respectively, whereas responses to the activator of large conductance (BKCa) KCa channels, NS1619, and to the endothelium-independent vasodilator, sodium nitroprusside (SNP) were unchanged. Endothelial denudation decreased NS309-induced relaxation and abolished that induced by ADP or substance P (P< .05), but had no effect on relaxation induced by either NS1619 or SNP. Polypeptide levels of BKCa, IKCa, and SK3Ca were not altered post-CPB.
IK/SK-mediated relaxation is predominantly endothelium dependent, whereas BK-mediated relaxation seems to be largely independent of endothelial function in human skeletal muscle microvasculature. CPB-associated microvascular dysfunction likely arises in part from impaired function of endothelial SK and IK channels in the peripheral microvasculature.