MaxiK channel and cell signalling

Kir6.1, a component of an ATP-sensitive potassium channel, regulates natural killer cell development

Involved in immunity and reproduction, natural killer (NK) cells offer opportunities to develop new immunotherapies to treat infections and cancer or to alleviate pregnancy complications. Most current strategies use cytokines or antibodies to enhance NK-cell function, but none use ion channel modulators, which are widely used in clinical practice to treat hypertension, diabetes, epilepsy, and other conditions. Little is known about ion channels in NK cells. We show that Kcnj8, which codes for the Kir6.1 subunit of a certain type of ATP-sensitive potassium (K ATP ) channel, is highly expressed in murine splenic and uterine NK cells compared to other K + channels previously identified in NK cells. Kcnj8 expression is highest in the most mature subset of splenic NK cells (CD27 - CD11b + ) and in NKG2A + or Ly49C/I + educated uterine NK cells. Using patch clamping, we show that a subset of NK cells expresses a current sensitive to the Kir6.1 blocker PNU-37883A. Kcnj8 does not participate in NK cell degranulation in response to tumor cells in vitro or rejection of tumor cells in vivo . Transcriptomics show that genes previously implicated in NK cell development are amongst those differentially expressed in CD27 - CD11b + NK cells deficient of Kcnj8 . Indeed, we found that mice with NK-cell specific Kcnj8 gene ablation have fewer CD11b + CD27 - and KLRG-1 + NK cells in the bone barrow and spleen. These results show that the K ATP subunit Kir6.1 has a key role in NK-cell development.

Transcriptional Up-Regulation of FBXW7 by KCa1.1 K+ Channel Inhibition through the Nrf2 Signaling Pathway in Human Prostate Cancer LNCaP Cell Spheroid Model

The tumor suppressor gene F-box and WD repeat domain-containing (FBXW) 7 reduces cancer stemness properties by promoting the protein degradation of pluripotent stem cell markers. We recently demonstrated the transcriptional repression of FBXW7 by the three-dimensional (3D) spheroid formation of several cancer cells. In the present study, we found that the transcriptional activity of FBXW7 was promoted by the inhibition of the Ca2+-activated K+ channel, KCa1.1, in a 3D spheroid model of human prostate cancer LNCaP cells through the Akt-Nrf2 signaling pathway. The transcriptional activity of FBXW7 was reduced by the siRNA-mediated inhibition of the CCAAT-enhancer-binding protein C/EBP δ (CEBPD) after the transfection of miR223 mimics in the LNCaP spheroid model, suggesting the transcriptional regulation of FBXW7 through the Akt-Nrf2-CEBPD-miR223 transcriptional axis in the LNCaP spheroid model. Furthermore, the KCa1.1 inhibition-induced activation of FBXW7 reduced (1) KCa1.1 activity and protein levels in the plasma membrane and (2) the protein level of the cancer stem cell (CSC) markers, c-Myc, which is a molecule degraded by FBXW7, in the LNCaP spheroid model, indicating that KCa1.1 inhibition-induced FBXW7 activation suppressed CSC conversion in KCa1.1-positive cancer cells.

The BKCa (slo) channel regulates the cardiac function of Drosophila

The large conductance, calcium, and voltage-active potassium channels (BKCa) were originally discovered in Drosophila melanogaster as slowpoke (slo). They are extensively characterized in fly models as ion channels for their roles in neurological and muscular function, as well as aging. BKCa is known to modulate cardiac rhythm and is localized to the mitochondria. Activation of mitochondrial BKCa causes cardioprotection from ischemia-reperfusion injury, possibly via modulating mitochondrial function in adult animal models. However, the role of BKCa in cardiac function is not well-characterized, partially due to its localization to the plasma membrane as well as intracellular membranes and the wide array of cells present in mammalian hearts. Here we demonstrate for the first time a direct role for BKCa in cardiac function and cardioprotection from IR injury using the Drosophila model system. We have also discovered that the BKCa channel plays a role in the functioning of aging hearts. Our study establishes the presence of BKCa in the fly heart and ascertains its role in aging heart function.

The BK Channel Limits the Pro-Inflammatory Activity of Macrophages

Macrophages play a crucial role in the innate immune response, serving as key effector cells in the defense against pathogens. Although the role of the large-conductance voltage and calcium-activated potassium channel, also known as the KCa1.1 or BK channel, in regulating neurotransmitter release and smooth muscle contraction is well known, its potential involvement in immune regulation remains unclear. We employed BK-knockout macrophages and noted that the absence of a BK channel promotes the polarization of macrophages towards a pro-inflammatory phenotype known as M1 macrophages. Specifically, the absence of the BK channel resulted in a significant increase in the secretion of the pro-inflammatory cytokine IL-6 and enhanced the activity of extracellular signal-regulated kinases 1 and 2 (Erk1/2 kinases), Ca2+/calmodulin-dependent protein kinase II (CaMKII), and the transcription factor ATF-1 within M1 macrophages. Additionally, the lack of the BK channel promoted the activation of the AIM2 inflammasome without affecting the activation of the NLRC4 and NLRP3 inflammasomes. To further investigate the role of the BK channel in regulating AIM2 inflammasome activation, we utilized BK channel inhibitors, such as paxilline and iberiotoxin, along with the BK channel activator NS-11021. Pharmacological inactivation of the BK channel increased, and its stimulation inhibited IL-1β production following AIM2 inflammasome activation in wild-type macrophages. Moreover, wild-type macrophages displayed increased calcium influx when activated with the AIM2 inflammasome, whereas BK-knockout macrophages did not due to the impaired extracellular calcium influx upon activation. Furthermore, under conditions of a calcium-free medium, IL-1β production following AIM2 inflammasome activation was increased in both wild-type and BK-knockout macrophages. This suggests that the BK channel is required for the influx of extracellular calcium in macrophages, thus limiting AIM2 inflammasome activation. In summary, our study reveals a regulatory role of the BK channel in macrophages under inflammatory conditions.

Exploring the Impact of BKCa Channel Function in Cellular Membranes on Cardiac Electrical Activity

This review paper delves into the current body of evidence, offering a thorough analysis of the impact of large-conductance Ca2+-activated K+ (BKCa or BK) channels on the electrical dynamics of the heart. Alterations in the activity of BKCa channels, responsible for the generation of the overall magnitude of Ca2+-activated K+ current at the whole-cell level, occur through allosteric mechanisms. The collaborative interplay between membrane depolarization and heightened intracellular Ca2+ ion concentrations collectively contribute to the activation of BKCa channels. Although fully developed mammalian cardiac cells do not exhibit functional expression of these ion channels, evidence suggests their presence in cardiac fibroblasts that surround and potentially establish close connections with neighboring cardiac cells. When cardiac cells form close associations with fibroblasts, the high single-ion conductance of these channels, approximately ranging from 150 to 250 pS, can result in the random depolarization of the adjacent cardiac cell membranes. While cardiac fibroblasts are typically electrically non-excitable, their prevalence within heart tissue increases, particularly in the context of aging myocardial infarction or atrial fibrillation. This augmented presence of BKCa channels' conductance holds the potential to amplify the excitability of cardiac cell membranes through effective electrical coupling between fibroblasts and cardiomyocytes. In this scenario, this heightened excitability may contribute to the onset of cardiac arrhythmias. Moreover, it is worth noting that the substances influencing the activity of these BKCa channels might influence cardiac electrical activity as well. Taken together, the BKCa channel activity residing in cardiac fibroblasts may contribute to cardiac electrical function occurring in vivo.

Novel insights into the role of ion channels in cellular DNA damage response

The DNA damage response (DDR) is a complex and highly regulated cellular process that detects and repairs DNA damage. The integrity of the DNA molecule is crucial for the proper functioning and survival of cells, as DNA damage can lead to mutations, genomic instability, and various diseases, including cancer. The DDR safeguards the genome by coordinating a series of signaling events and repair mechanisms to maintain genomic stability and prevent the propagation of damaged DNA to daughter cells. The study of an ion channels in the context of DDR is a promising avenue in biomedical research. Lately, it has been reported that the movement of ions through channels plays a crucial role in various physiological processes, including nerve signaling, muscle contraction, cell signaling, and maintaining cell membrane potential. Knowledge regarding the involvement of ion channels in the DDR could support refinement of our approach to several pathologies, mainly cancer, and perhaps lead to innovative therapies. In this review, we focused on the ion channel's possible role in the DDR. We present an analysis of the involvement of ion channels in DDR, their role in DNA repair mechanisms, and cellular outcomes. By addressing these areas, we aim to provide a comprehensive perspective on ion channels in the DDR and potentially guide future research in this field. It is worth noting that the interplay between ion channels and the cellular DDR is complex and multifaceted. More research is needed to fully understand the underlying mechanisms and potential therapeutic implications of these interactions.

Design, synthesis, and biological evaluation of a novel series of 1,2,4-oxadiazole inhibitors of SLACK potassium channels: Identification of in vitro tool VU0935685

Malignant migrating partial seizure of infancy (MMPSI) is a devastating and pharmacoresistant form of infantile epilepsy. MMPSI has been linked to multiple gain-of-function (GOF) mutations in the KCNT1 gene, which encodes for a potassium channel often referred to as SLACK. SLACK channels are sodium-activated potassium channels distributed throughout the central nervous system (CNS) and the periphery. The investigation described here aims to discover SLACK channel inhibitor tool compounds and profile their pharmacokinetic and pharmacodynamic properties. A SLACK channel inhibitor VU0531245 (VU245) was identified via a high-throughput screen (HTS) campaign. Structure-activity relationship (SAR) studies were conducted in five distinct regions of the hit VU245. VU245 analogs were evaluated for their ability to affect SLACK channel activity using a thallium flux assay in HEK-293 cells stably expressing wild-type (WT) human SLACK. Selected analogs were tested for metabolic stability in mouse liver microsomes and plasma-protein binding in mouse plasma. The same set of analogs was tested via thallium flux for activity versus human A934T SLACK and other structurally related potassium channels, including SLICK and Maxi-K. In addition, potencies for selected VU245 analogs were obtained using whole-cell electrophysiology (EP) assays in CHO cells stably expressing WT human SLACK through an automated patch clamp system. Results revealed that this scaffold tolerates structural changes in some regions, with some analogs demonstrating improved SLACK inhibitory activity, good selectivity against the other channels tested, and modest improvements in metabolic clearance. Analog VU0935685 represents a new, structurally distinct small-molecule inhibitor of SLACK channels that can serve as an in vitro tool for studying this target.

Effects of Walnut-Rich Diet on Cation-Handling Proteins in the Heart of Healthy and Metabolically Compromised Male Rats

The transport of cations in the cardiomyocytes, crucial for the functioning of the heart, can be affected by walnut diet due to the high content of polyunsaturated fatty acids. Healthy and metabolically compromised rats (drinking 10% fructose solution) were subjected to a diet supplemented with 2.4 g of walnuts for 6 weeks to investigate the effect on proteins involved in cation transport in the heart cells. Fructose increased the level of the α1 subunit of Na+/K+-ATPase and the phosphorylation of extracellular signal-regulated kinase 1/2 in the heart of control and walnut-eating rats, while elevated L-type calcium channel α (LTCCα), sodium-calcium exchanger 1 (NCX1), and Maxi Kα level were observed only in rats that did not consume walnuts. However, walnuts significantly increased the cardiac content of LTCC, NCX1, and Maxi Kα, as well as Kir6.1 and SUR2B subunits of KATP channel, but only in fructose-naive rats. In animals that drank fructose, a significant increasing effect of walnuts was observed only in Akt kinase phosphorylation, which may be a part of the antiarrhythmic mechanism of decreasing cation currents in cardiomyocytes. The walnut diet-induced increase in LTCC and NCX1 expression in healthy rats may indicate intense cardiac calcium turnover, whereas the effect on Kir6.1 and SUR2B subunits suggests stimulation of KATP channel transport in the cardiac vasculature. The effects of walnuts on the cation-handling proteins in the heart, mostly limited to healthy animals, suggest the possible use of a walnut-supplemented diet in the prevention rather than the treatment of cardiological channelopathies.

Sex differences in pituitary corticotroph excitability

Stress-related illness represents a major burden on health and society. Sex differences in stress-related disorders are well documented, with women having twice the lifetime rate of depression compared to men and most anxiety disorders. Anterior pituitary corticotrophs are central components of the hypothalamic-pituitary-adrenal (HPA) axis, receiving input from hypothalamic neuropeptides corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP), while regulating glucocorticoid output from the adrenal cortex. The dynamic control of electrical excitability by CRH/AVP and glucocorticoids is critical for corticotroph function; however, whether corticotrophs contribute to sexually differential responses of the HPA axis, which might underlie differences in stress-related disorders, is very poorly understood. Using perforated patch clamp electrophysiology in corticotrophs from mice expressing green fluorescent protein under the control of the Pomc promoter, we characterized basal and secretagogue-evoked excitability. Both male and female corticotrophs show predominantly single-spike action potentials under basal conditions; however, males predominantly display spikes with small-amplitude (<20 mV) afterhyperpolarizations (B-type), whereas females displayed a mixture of B-type spikes and spikes with a large-amplitude (>25 mV) afterhyperpolarization (A-type). In response to CRH, or CRH/AVP, male cells almost exclusively transition to a predominantly pseudo-plateau bursting, whereas only female B-type cells display bursting in response to CRH±AVP. Treatment of male or female corticotrophs with 1 nM estradiol (E2) for 24-72 h has no effect on the proportion of cells with A- or B-type spikes in either sex. However, E2 results in the cessation of CRH-induced bursting in both male and female corticotrophs, which can be partially reversed by adding a BK current using a dynamic clamp. RNA-seq analysis of purified corticotrophs reveals extensive differential gene expression at the transcriptional level, including more than 71 mRNAs encoding ion channel subunits. Interestingly, there is a two-fold lower level (p < 0.01) of BK channel pore-forming subunit (Kcnma1) expression in females compared to males, which may partially explain the decrease in CRH-induced bursting. This study identified sex differences at the level of the anterior pituitary corticotroph ion channel landscape and control of both spontaneous and CRH-evoked excitability. Determining the mechanisms of sex differences of corticotroph and HPA activity at the cellular level could be an important step for better understanding, diagnosing, and treating stress-related disorders.

Specificities of Protein Homology Modeling for Allosteric Drug Design

The allosteric binding sites are usually located in the flexible areas of proteins, which are hardly visible in the crystal structures. However, there are notable exceptions like allosteric sites in receptors in class B and C of GPCRs, which are located within a well-defined bundle of transmembrane helices. Class B and C evolved from class A and even after swapping of orthosteric and allosteric sites the central binding site persisted and it can be used for easy design of allosteric drugs. However, studying the ligand binding to the allosteric sites in the most populated class A of GPCRs is still a challenge, since they are located mostly in unresolved parts of the receptor's structure, and especially N-terminus. This chapter provides an example of cannabinoid CB1 receptor N-terminal homology modeling, ligand-guided modeling of the allosteric site in GABA receptor, as well as C-linker modeling in the potassium ion channels where the allosteric phospholipid ligand PIP2 is bound.

KCa-Related Neurological Disorders: Phenotypic Spectrum and Therapeutic Indications

Although potassium channelopathies have been linked to a wide range of neurological conditions, the underlying pathogenic mechanism is not always clear, and a systematic summary of clinical manifestation is absent. Several neurological disorders have been associated with alterations of calcium-activated potassium channels (KCa channels), such as loss- or gain-of-function mutations, post-transcriptional modification, etc. Here, we outlined the current understanding of the molecular and cellular properties of three subtypes of KCa channels, including big conductance KCa channels (BK), small conductance KCa channels (SK), and the intermediate conductance KCa channels (IK). Next, we comprehensively reviewed the loss- or gain-of-function mutations of each KCa channel and described the corresponding mutation sites in specific diseases to broaden the phenotypic-genotypic spectrum of KCa-related neurological disorders. Moreover, we reviewed the current pharmaceutical strategies targeting KCa channels in KCa-related neurological disorders to provide new directions for drug discovery in anti-seizure medication.

Deletion of large-conductance calcium-activated potassium channels promotes vascular remodelling through the CTRP7-mediated PI3K/Akt signaling pathway

The large-conductance calcium-activated potassium (BK) channel is a critical regulator and potential therapeutic target of vascular tone and architecture, and abnormal expression or dysfunction of this channel is linked to many vascular diseases. Vascular remodelling is the early pathological basis of severe vascular diseases. Delaying the progression of vascular remodelling can reduce cardiovascular events, but the pathogenesis remains unclear. To clarify the role of BK channels in vascular remodelling, we use rats with BK channel α subunit knockout (BK α ^‒/‒). The results show that BK α ^‒/‒ rats have smaller inner and outer diameters, thickened aortic walls, increased fibrosis, and disordered elastic fibers of the aortas compared with WT rats. When the expression and function of BK α are inhibited in human umbilical arterial smooth muscle cells (HUASMCs), the expressions of matrix metalloproteinase 2 (MMP2), MMP9, and interleukin-6 are enhanced, while the expressions of smooth muscle cell contractile phenotype proteins are reduced. RNA sequencing, bioinformatics analysis and qPCR verification show that C1q/tumor necrosis factor-related protein 7 ( CTRP7) is the downstream target gene. Furthermore, except for that of MMPs, a similar pattern of IL-6, smooth muscle cell contractile phenotype proteins expression trend is observed after CTRP7 knockdown. Moreover, knockdown of both BK α and CTRP7 in HUASMCs activates PI3K/Akt signaling. Additionally, CTRP7 is expressed in vascular smooth muscle cells (VSMCs), and BK α deficiency activates the PI3K/Akt pathway by reducing CTRP7 level. Therefore, we first show that BK channel deficiency leads to vascular remodelling. The BK channel and CTRP7 may serve as potential targets for the treatment of cardiovascular diseases.

Contributions of SGK3 to transporter-related diseases

Serum- and glucocorticoid-induced kinase 3 (SGK3), which is ubiquitously expressed in mammals, is regulated by estrogens and androgens. SGK3 is activated by insulin and growth factors through signaling pathways involving phosphatidylinositol-3-kinase (PI3K), 3-phosphoinositide-dependent kinase-1 (PDK-1), and mammalian target of rapamycin complex 2 (mTORC2). Activated SGK3 can activate ion channels (TRPV5/6, SOC, Kv1.3, Kv1.5, Kv7.1, BKCa, Kir2.1, Kir2.2, ENaC, Nav1.5, ClC-2, and ClC Ka), carriers and receptors (Npt2a, Npt2b, NHE3, GluR1, GluR6, SN1, EAAT1, EAAT2, EAAT4, EAAT5, SGLT1, SLC1A5, SLC6A19, SLC6A8, and NaDC1), and Na+/K+-ATPase, promoting the transportation of calcium, phosphorus, sodium, glucose, and neutral amino acids in the kidney and intestine, the absorption of potassium and neutral amino acids in the renal tubules, the transportation of glutamate and glutamine in the nervous system, and the transportation of creatine. SGK3-sensitive transporters contribute to a variety of physiological and pathophysiological processes, such as maintaining calcium and phosphorus homeostasis, hydro-salinity balance and acid-base balance, cell proliferation, muscle action potential, cardiac and neural electrophysiological disturbances, bone density, intestinal nutrition absorption, immune function, and multiple substance metabolism. These processes are related to kidney stones, hypophosphorous rickets, multiple syndromes, arrhythmia, hypertension, heart failure, epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, glaucoma, ataxia idiopathic deafness, and other diseases.

K+ channels in the coronary microvasculature of the ischemic heart

Ischemic heart disease is the leading cause of death and a major public health and economic burden worldwide with expectations of predicted growth in the foreseeable future. It is now recognized clinically that flow-limiting stenosis of the large coronary conduit arteries as well as microvascular dysfunction in the absence of severe stenosis can each contribute to the etiology of ischemic heart disease. The primary site of coronary vascular resistance, and control of subsequent coronary blood flow, is found in the coronary microvasculature, where small changes in radius can have profound impacts on myocardial perfusion. Basal active tone and responses to vasodilators and vasoconstrictors are paramount in the regulation of coronary blood flow and adaptations in signaling associated with ion channels are a major factor in determining alterations in vascular resistance and thereby myocardial blood flow. K+ channels are of particular importance as contributors to all aspects of the regulation of arteriole resistance and control of perfusion into the myocardium because these channels dictate membrane potential, the resultant activity of voltage-gated calcium channels, and thereby, the contractile state of smooth muscle. Evidence also suggests that K+ channels play a significant role in adaptations with cardiovascular disease states. In this review, we highlight our research examining the role of K+ channels in ischemic heart disease and adaptations with exercise training as treatment, as well as how our findings have contributed to this area of study.

Reciprocal Relationship between Ca2+ Signaling and Ca2+-Gated Ion Channels as a Potential Target for Drug Discovery

Cellular Ca²⁺ signaling functions as one of the most common second messengers of various signal transduction pathways in cells and mediates a number of physiological roles in a cell-type dependent manner. Ca²⁺ signaling also regulates more general and fundamental cellular activities, including cell proliferation and apoptosis. Among ion channels, Ca²⁺-permeable channels in the plasma membrane as well as endo- and sarcoplasmic reticulum membranes play important roles in Ca²⁺ signaling by directly contributing to the influx of Ca²⁺ from extracellular spaces or its release from storage sites, respectively. Furthermore, Ca²⁺-gated ion channels in the plasma membrane often crosstalk reciprocally with Ca²⁺ signals and are central to the regulation of cellular functions. This review focuses on the physiological and pharmacological impact of i) Ca²⁺-gated ion channels as an apparatus for the conversion of cellular Ca²⁺ signals to intercellularly propagative electrical signals and ii) the opposite feedback regulation of Ca²⁺ signaling by Ca²⁺-gated ion channel activities in excitable and non-excitable cells.

The Effect of MaxiK Channel on Regulating the Activation of NLRP3 Inflammasome in Rats of Blast-induced Traumatic Brain Injury

Abundant findings including our previous work proved that the NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome exerts a key role in the process of neuroinflammation following blast-induced traumatic brain injury (bTBI). The opening of potassium channels leads to low K⁺ environment in cells, which appears to be an essential requirement for NLRP3 inflammasome activation. Notably, MaxiK (BK) channel is significant for K⁺ transport. The present study is aim to investigate the potential role of MaxiK in the activation of NLRP3 and to evaluate whether MaxiK channel blocker paxilline could confer beneficial effects on attenuating the severity of bTBI in rats. Rats were randomly assigned into five groups (n = 8). MaxiK channel expression was measured in bTBI rats. The effect of paxilline on the expression of NLRP3 inflammasome, the level of inflammatory cytokines, brain injury biomarkers in serum and brain edema were also evaluated in bTBI rats. The results showed that the expression of MaxiK was elevated significantly in the cerebral cortex of bTBI rats. The treatment of MaxiK channel blocker paxilline suppressed the NLRP3 inflammasome expression substantially. In addition, paxilline could also decrease the level of pro-inflammatory cytokines and the biomarkers of brain injury and alleviate brain edema of bTBI rats. Our findings have revealed that MaxiK channel might be involved in the process of neuroinflammation of bTBI. Paxilline could depress neuro-inflammation response and alleviate brain injury by blocking MaxiK channel and subsequently inhibition of NLRP3 inflammasome activation.

KCa channel blockers increase effectiveness of the EGF receptor TK inhibitor erlotinib in non-small cell lung cancer cells (A549)

Non-small cell lung cancer (NSCLC) has a poor prognosis with a 5 year survival rate of only ~ 10%. Important driver mutations underlying NSCLC affect the epidermal growth factor receptor (EGFR) causing the constitutive activation of its tyrosine kinase domain. There are efficient EGFR tyrosine kinase inhibitors (TKIs), but patients develop inevitably a resistance against these drugs. On the other hand, K_Ca3.1 channels contribute to NSCLC progression so that elevated K_Ca3.1 expression is a strong predictor of poor NSCLC patient prognosis. The present study tests whether blocking K_Ca3.1 channels increases the sensitivity of NSCLC cells towards the EGFR TKI erlotinib and overcomes drug resistance. mRNA expression of K_Ca3.1 channels in erlotinib-sensitive and -resistant NSCLC cells was analysed in datasets from Gene expression omnibus (GEO) and ArrayExpress. We assessed proliferation and migration of NSCLC cells. These (live cell-imaging) experiments were complemented by patch clamp experiments and Western blot analyses. We identified three out of four datasets comparing erlotinib-sensitive and -resistant NSCLC cells which revealed an altered expression of K_Ca3.1 mRNA in erlotinib-resistant NSCLC cells. Therefore, we evaluated the combined effect of erlotinib and the K_Ca3.1 channel inhibition with sencapoc. Erlotinib elicits a dose-dependent inhibition of migration and proliferation of NSCLC cells. The simultaneous application of the K_Ca3.1 channel blocker senicapoc increases the sensitivity towards a low dose of erlotinib (300 nmol/L) which by itself has no effect on migration and proliferation. Partial erlotinib resistance can be overcome by K_Ca3.1 channel blockade. The sensitivity towards erlotinib as well as the potentiating effect of K_Ca3.1 blockade is further increased by mimicking hypoxia. Our results suggest that K_Ca3.1 channel blockade may constitute a therapeutic concept for treating NSCLC and overcome EGFR TKI resistance. We propose that this is due to complementary mechanisms of action of both blockers.

Expression and functional characterization of the large-conductance calcium and voltage-activated potassium channel Kca 1.1 in megakaryocytes and platelets

BACKGROUND

Ion channels are transmembrane proteins that play important roles in cell function regulation modulating ionic cell permeability. In megakaryocytes and platelets, regulated ion flows have been demonstrated to modulate platelet production and function. However, a relatively limited characterization of ion channel expression and function is available in the human megakaryocyte-platelet lineage.

OBJECTIVE

We analyzed the expression and function of the large-conductance calcium and voltage-activated potassium channel Kca 1.1 (also known as Maxi-K, BK, slo1) in human megakaryocytes and platelets.

METHODS

To investigate the functionality of Kca 1.1, we exploited different agonists (BMS-191011, NS1619, NS11021, epoxyeicosatrienoic acid isoforms) and inhibitors (iberiotoxin, penitrem A) of the channel.

RESULTS

In megakaryocytes, Kca 1.1 agonists determined a decreased proplatelet formation and altered interaction with the extracellular matrix. Analysis of the actin cytoskeleton demonstrated a significant decrease in megakaryocyte spreading and adhesion to collagen. In platelets, the opening of the channel Kca 1.1 led to a reduced sensitivity to agonists with blunted aggregation in response to ADP, with an inhibitory capacity additive to that of aspirin. The Kca 1.1 agonists, but not the inhibitors, determined a reduction of platelet adhesion and aggregation onto immobilized collagen underflow to an extent similar to that of aspirin and ticagrelor. The opening of the Kca 1.1 resulted in cell hyperpolarization impairing free intracellular calcium in ADP-stimulated platelets and megakaryocytes.

CONCLUSIONS

The present study reveals new mechanisms in platelet formation and activation, suggesting that targeting Kca 1.1 channels might be of potential pharmacological interest in hemostasis and thrombosis.

Selective expression of KCNA5 and KCNB1 genes in gastric and colorectal carcinoma

Background

Gastric and colorectal cancers are the most common malignant tumours, leading to a significant number of cancer-related deaths worldwide. Recently, increasing evidence has demonstrated that cancer cells exhibit a differential expression of potassium channels and this can contribute to cancer progression. However, their expression and localisation at the somatic level remains uncertain. In this study, we have investigated the expression levels of KCNB1 and KCNA5 genes encoding ubiquitous Kv2.1 and Kv1.5 potassium channels in gastric and colorectal tumours.

Methods

Gastric and colorectal tumoral and peritumoral tissues were collected to evaluate the expression of KCNB1 and KCNA5 mRNA by quantitative PCR. Moreover, the immunohistochemical staining profile of Kv2.1 and Kv1.5 was assessed on 40 Formalin-Fixed and Paraffin-Embedded (FFPE) gastric carcinoma tissues. Differences in gene expression between tumoral and peritumoral tissues were compared statistically with the Mann-Whitney U test. The association between the clinicopathological features of the GC patients and the expression of both Kv proteins was investigated with χ2 and Fisher’s exact tests.

Results

The mRNA fold expression of KCNB1 and KCNA5 genes showed a lower mean in the tumoral tissues (0.06 ± 0.17, 0.006 ± 0.009) compared to peritumoral tissues (0.08 ± 0.16, 0.16 ± 0.48, respectively) without reaching the significance rate (p = 0.861, p = 0.152, respectively). Interestingly, Kv2.1 and Kv1.5 immunostaining was detectable and characterised by a large distribution in peritumoral and tumoral epithelial cells. More interestingly, inflammatory cells were also stained. Surprisingly, Kv2.1 and Kv1.5 staining was undoubtedly and predominantly detected in the cytoplasm compartment of tumour cells. Indeed, the expression of Kv2.1 in tumour cells revealed a significant association with the early gastric cancer clinical stage (p = 0.026).

Conclusion

The data highlight, for the first time, the potential role of Kv1.5 and Kv2.1 in gastrointestinal-related cancers and suggests they may be promising prognostic markers for these tumours.

Hydrogen Sulfide Relaxes Human Uterine Artery via Activating Smooth Muscle BKCa Channels

Opening of large conductance calcium-activated and voltage-dependent potassium (BK_Ca) channels hyperpolarizes plasma membranes of smooth muscle (SM) to cause vasodilation, underling a key mechanism for mediating uterine artery (UA) dilation in pregnancy. Hydrogen sulfide (H₂S) has been recently identified as a new UA vasodilator, yet the mechanism underlying H₂S-induced UA dilation is unknown. Here, we tested whether H₂S activated BK_Ca channels in human UA smooth muscle cells (hUASMC) to mediate UA relaxation. Multiple BK_Ca subunits were found in human UA in vitro and hUASMC in vitro, and high β1 and γ1 proteins were localized in SM cells in human UA. Baseline outward currents, recorded by whole-cell and single-channel patch clamps, were significantly inhibited by specific BK_Ca blockers iberiotoxin (IBTX) or tetraethylammonium, showing specific BK_Ca activity in hUASMC. H₂S dose (NaHS, 1–1000 µM)-dependently potentiated BK_Ca currents and open probability. Co-incubation with a Ca²⁺ blocker nifedipine (5 µM) or a chelator (ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), 5 mM) did not alter H₂S-potentiated BK_Ca currents and open probability. NaHS also dose-dependently relaxed phenylephrine pre-constricted freshly prepared human UA rings, which was inhibited by IBTX. Thus, H₂S stimulated human UA relaxation at least partially via activating SM BK_Ca channels independent of extracellular Ca²⁺.

The action of a BK channel opener

Rockman et al. in this issue of JGP describe how NS11021 opens BK channels, which make the compound a better tool to probe physiological roles and gating mechanisms of BK channels.

BKCa Channels as Targets for Cardioprotection

The large-conductance calcium- and voltage-activated K⁺ channel (BK_Ca) are encoded by the Kcnma1 gene. They are ubiquitously expressed in neuronal, smooth muscle, astrocytes, and neuroendocrine cells where they are known to play an important role in physiological and pathological processes. They are usually localized to the plasma membrane of the majority of the cells with an exception of adult cardiomyocytes, where BK_Ca is known to localize to mitochondria. BK_Ca channels couple calcium and voltage responses in the cell, which places them as unique targets for a rapid physiological response. The expression and activity of BK_Ca have been linked to several cardiovascular, muscular, and neurological defects, making them a key therapeutic target. Specifically in the heart muscle, pharmacological and genetic activation of BK_Ca channels protect the heart from ischemia-reperfusion injury and also facilitate cardioprotection rendered by ischemic preconditioning. The mechanism involved in cardioprotection is assigned to the modulation of mitochondrial functions, such as regulation of mitochondrial calcium, reactive oxygen species, and membrane potential. Here, we review the progress made on BK_Ca channels and cardioprotection and explore their potential roles as therapeutic targets for preventing acute myocardial infarction.

Activation of BK Channels Prevents Hepatic Stellate Cell Activation and Liver Fibrosis Through the Suppression of TGFβ1/SMAD3 and JAK/STAT3 Profibrotic Signaling Pathways

Large-conductance and Ca²⁺-activated K⁺ (BK) channels are expressed in human hepatic stellate cells (HSCs), where they have roles in normal hepatic microcirculation, as well as in portal hypertension in liver cirrhosis through the regulation of contractility in activated HSCs. Nevertheless, whether BK channel activity exerts protective effects against aberrant HSC activation and hepatic fibrosis is unknown. Here, we report that BK channels are expressed in activated primary rat HSCs as well as in a human HSC line. Moreover, whole-cell K⁺ currents recorded from activated HSCs were markedly increased by exposure to rottlerin, a BK channel-specific activator, but were inhibited by treatment with the BK channel-specific inhibitor, paxilline, suggesting that BK channels are functional in activated HSCs. Overexpression but not downregulation of the BK channel pore-forming alpha subunit, KCNMA1, led to reduced migration and collagen expression in activated HSCs. Consistently, rottlerin treatment suppressed the fibrogenic cell function both in vitro and in CCl₄-induced liver fibrosis in vivo. Microarray and pathway analysis, combined with a luciferase reporter assay and western blotting, further showed that rottlerin treatment led to a significant downregulation of the profibrotic TGFβ1/SMAD3 and JAK/STAT3 signaling pathways, both in vitro and in vivo. Our findings not only link BK channel function to profibrotic signaling pathways, but also provide evidence that BK channel activation represents a promising therapeutic strategy for the treatment of liver fibrosis.

Intracellular Chloride Channels: Novel Biomarkers in Diseases

Ion channels are integral membrane proteins present on the plasma membrane as well as intracellular membranes. In the human genome, there are more than 400 known genes encoding ion channel proteins. Ion channels are known to regulate several cellular, organellar, and physiological processes. Any mutation or disruption in their function can result in pathological disorders, both common or rare. Ion channels present on the plasma membrane are widely acknowledged for their role in various biological processes, but in recent years, several studies have pointed out the importance of ion channels located in intracellular organelles. However, ion channels located in intracellular organelles are not well-understood in the context of physiological conditions, such as the generation of cellular excitability and ionic homeostasis. Due to the lack of information regarding their molecular identity and technical limitations of studying them, intracellular organelle ion channels have thus far been overlooked as potential therapeutic targets. In this review, we focus on a novel class of intracellular organelle ion channels, Chloride Intracellular Ion Channels (CLICs), mainly documented for their role in cardiovascular, neurophysiology, and tumor biology. CLICs have a single transmembrane domain, and in cells, they exist in cytosolic as well as membranous forms. They are predominantly present in intracellular organelles and have recently been shown to be localized to cardiomyocyte mitochondria as well as exosomes. In fact, a member of this family, CLIC5, is the first mitochondrial chloride channel to be identified on the molecular level in the inner mitochondrial membrane, while another member, CLIC4, is located predominantly in the outer mitochondrial membrane. In this review, we discuss this unique class of intracellular chloride channels, their role in pathologies, such as cardiovascular, cancer, and neurodegenerative diseases, and the recent developments concerning their usage as theraputic targets.

BKCa (Slo) Channel Regulates Mitochondrial Function and Lifespan in Drosophila melanogaster

BK_Ca channels, originally discovered in Drosophila melanogaster as slowpoke (slo), are recognized for their roles in cellular and organ physiology. Pharmacological approaches implicated BK_Ca channels in cellular and organ protection possibly for their ability to modulate mitochondrial function. However, the direct role of BK_Ca channels in regulating mitochondrial structure and function is not deciphered. Here, we demonstrate that BK_Ca channels are present in fly mitochondria, and slo mutants show structural and functional defects in mitochondria. slo mutants display an increase in reactive oxygen species and the modulation of ROS affected their survival. We also found that the absence of BK_Ca channels reduced the lifespan of Drosophila, and overexpression of human BK_Ca channels in flies extends life span in males. Our study establishes the presence of BK_Ca channels in mitochondria of Drosophila and ascertains its novel physiological role in regulating mitochondrial structural and functional integrity, and lifespan.

Involvement of sex hormonal regulation of K+ channels in electrophysiological and contractile functions of muscle tissues

Sex hormones, such as testosterone, progesterone, and 17β-estradiol, control various physiological functions. This review focuses on the sex hormonal regulation of K⁺ channels and the effects of such regulation on electrophysiological and contractile functions of muscles. In the cardiac tissue, testosterone and progesterone shorten action potential, and estrogen lengthens QT interval, a marker of increased risk of ventricular tachyarrhythmias. We have shown that testosterone and progesterone in physiological concentration activate KCNQ1 channels via membrane-delimited sex hormone receptor/eNOS pathways to shorten the action potential duration. Mitochondrial K⁺ channels are also involved in the protection of cardiac muscle. Testosterone and 17β-estradiol directly activate mitochondrial inner membrane K⁺ channels (Ca²⁺ activated K⁺ channel (K_Ca channel) and ATP-sensitive K⁺ channel (K_ATP channel)) that are involved in ischemic preconditioning and cardiac protection. During pregnancy, uterine blood flow increases to support fetal growth and development. It has been reported that 17β-estradiol directly activates large-conductance Ca²⁺-activated K⁺ channel (BK_Ca channel) attenuating arterial contraction. Furthermore, 17β-estradiol increases expression of BK_Ca channel β1 subunit which enhances BK_Ca channel activity by DNA demethylation. These findings are useful for understanding the mechanisms of sex or generation-dependent differences in the physiological and pathological functions of muscles, and the mechanisms of drug actions.

Expression and Activation of BKCa Channels in Mice Protects Against Ischemia-Reperfusion Injury of Isolated Hearts by Modulating Mitochondrial Function

Aims: Activation and expression of large conductance calcium and voltage-activated potassium channel (BK_Ca) by pharmacological agents have been implicated in cardioprotection from ischemia-reperfusion (IR) injury possibly by regulating mitochondrial function. Given the non-specific effects of pharmacological agents, it is not clear whether activation of BK_Ca is critical to cardioprotection. In this study, we aimed to decipher the mechanistic role of BK_Ca in cardioprotection from IR injury by genetically activating BK_Ca channels. Methods and Results: Hearts from adult (3 months old) wild-type mice (C57/BL6) and mice expressing genetically activated BK_Ca (Tg-BK_Ca ^R207Q, referred as Tg-BK_Ca) along with wild-type BK_Ca were subjected to 20 min of ischemia and 30 min of reperfusion with or without ischemic preconditioning (IPC, 2 times for 2.5 min interval each). Left ventricular developed pressure (LVDP) was recorded using Millar's Mikrotip® catheter connected to ADInstrument data acquisition system. Myocardial infarction was quantified by 2,3,5-triphenyl tetrazolium chloride (TTC) staining. Our results demonstrated that Tg-BK_Ca mice are protected from IR injury, and BK_Ca also contributes to IPC-mediated cardioprotection. Cardiac function parameters were also measured by echocardiography and no differences were observed in left ventricular ejection fraction, fractional shortening and aortic velocities. Amplex Red® was used to assess reactive oxygen species (ROS) production in isolated mitochondria by spectrofluorometry. We found that genetic activation of BK_Ca reduces ROS after IR stress. Adult cardiomyocytes and mitochondria from Tg-BK_Ca mice were isolated and labeled with Anti-BK_Ca antibodies. Images acquired via confocal microscopy revealed localization of cardiac BK_Ca in the mitochondria. Conclusions: Activation of BK_Ca is essential for recovery of cardiac function after IR injury and is likely a factor in IPC mediated cardioprotection. Genetic activation of BK_Ca reduces ROS produced by complex I and complex II/III in Tg-BK_Ca mice after IR, and IPC further decreases it. These results implicate BK_Ca-mediated cardioprotection, in part, by reducing mitochondrial ROS production. Localization of Tg-BK_Ca in adult cardiomyocytes of transgenic mice was similar to BK_Ca in wild-type mice.

Inhibition of BKCa negatively alters cardiovascular function

Large conductance calcium and voltage-activated potassium channels (BKCa ) are transmembrane proteins, ubiquitously expressed in the majority of organs, and play an active role in regulating cellular physiology. In the heart, BKCa channels are known to play a role in regulating the heart rate and protect it from ischemia-reperfusion injury. In vascular smooth muscle cells, the opening of BKCa channels results in membrane hyperpolarization which eventually results in vasodilation mediated by a reduction in Ca2+ influx due to the closure of voltage-dependent Ca2+ channels. Ex vivo studies have shown that BKCa channels play an active role in the regulation of the function of the majority of blood vessels. However, in vivo role of BKCa channels in cardiovascular function is not completely deciphered. Here, we have evaluated the rapid in vivo role of BKCa channels in regulating the cardiovascular function by using two well-established, rapid-acting, potent blockers, paxilline and iberiotoxin. Our results show that BKCa channels are actively involved in regulating the heart rate, the function of the left and right heart as well as major vessels. We also found that the effect on BKCa channels by blockers is completely reversible, and hence, BKCa channels can be exploited as potential targets for clinical applications for modulating heart rate and cardiac contractility.

The Maxi-K (BK) Channel Antagonist Penitrem A as a Novel Breast Cancer-Targeted Therapeutic

Breast cancer (BC) is a heterogeneous disease with different molecular subtypes. The high conductance calcium-activated potassium channels (BK, Maxi-K channels) play an important role in the survival of some BC phenotypes, via membrane hyperpolarization and regulation of cell cycle. BK channels have been implicated in BC cell proliferation and invasion. Penitrems are indole diterpene alkaloids produced by various terrestrial and marine Penicillium species. Penitrem A (1) is a selective BK channel antagonist with reported antiproliferative and anti-invasive activities against multiple malignancies, including BC. This study reports the high expression of BK channel in different BC subtypes. In silico BK channel binding affinity correlates with the antiproliferative activities of selected penitrem analogs. 1 showed the best binding fitting at multiple BK channel crystal structures, targeting the calcium-sensing aspartic acid moieties at the calcium bowel and calcium binding sites. Further, 1 reduced the levels of BK channel expression and increased expression of TNF-&alpha; in different BC cell types. Penitrem A (1) induced G1 cell cycle arrest of BC cells, and induced upregulation of the arrest protein p27. Combination treatment of 1 with targeted anti-HER drugs resulted in synergistic antiproliferative activity, which was associated with reduced EGFR and HER2 receptor activation, as well as reduced active forms of AKT and STAT3. Collectively, the BK channel antagonists represented by penitrem A can be novel sensitizing, chemotherapeutics synergizing, and therapeutic agents for targeted BC therapy.

Drosophila Voltage-Gated Calcium Channel α1-Subunits Regulate Cardiac Function in the Aging Heart

Ion channels maintain numerous physiological functions and regulate signaling pathways. They are the key targets for cellular reactive oxygen species (ROS), acting as signaling switches between ROS and ionic homeostasis. We have carried out a paraquat (PQ) screen in Drosophila to identify ion channels regulating the ROS handling and survival in Drosophila melanogaster. Our screen has revealed that α1-subunits (D-type, T-type, and cacophony) of voltage-gated calcium channels (VGCCs) handle PQ-mediated ROS stress differentially in a gender-based manner. Since ROS are also involved in determining the lifespan, we discovered that the absence of T-type and cacophony decreased the lifespan while the absence of D-type maintained a similar lifespan to that of the wild-type strain. VGCCs are also responsible for electrical signaling in cardiac cells. The cardiac function of each mutant was evaluated through optical coherence tomography (OCT), which revealed that α1-subunits of VGCCs are essential in maintaining cardiac rhythmicity and cardiac function in an age-dependent manner. Our results establish specific roles of α1-subunits of VGCCs in the functioning of the aging heart.

Long-term hypoxia uncouples Ca2+ and eNOS in bradykinin-mediated pulmonary arterial relaxation

Bradykinin-induced activation of the pulmonary endothelium triggers a rise in intracellular Ca²⁺ that activates nitric oxide (NO)-dependent vasorelaxation. Chronic hypoxia is commonly associated with increased pulmonary vascular tone, which can cause pulmonary hypertension in responsive individuals. In the present study, we tested the hypothesis that long-term high-altitude hypoxia (LTH) diminishes bradykinin-induced Ca²⁺ signals and inhibits endothelial nitric oxide synthase (eNOS), prostacyclin (PGI₂), and large-conductance K⁺ (BK_Ca) channels in sheep, which are moderately responsive to LTH, resulting in decreased pulmonary arterial vasorelaxation. Pulmonary arteries were isolated from ewes kept near sea level (720 m) or at high altitude (3,801 m) for >100 days. Vessel force was measured with wire myography and endothelial intracellular Ca²⁺ with confocal microscopy. eNOS was inhibited with 100 μM N^G-nitro-l-arginine methyl ester (l-NAME), PGI₂ production was inhibited with 10 µM indomethacin that inhibits cyclooxygenase, and BK_Ca channels were blocked with 1 mM tetraethylammonium. Bradykinin-induced endothelial Ca²⁺ signals increased following LTH, but bradykinin relaxation decreased. Furthermore, some vessels contracted in response to bradykinin after LTH. l-NAME sensitivity decreased, suggesting that eNOS dysfunction played a role in uncoupling Ca²⁺ signals and bradykinin relaxation. The Ca²⁺ ionophore A-23187 (10 µM) elicited an enhanced Ca²⁺ response following LTH while relaxation was unchanged although l-NAME sensitivity increased. Additionally, BK_Ca function decreased during bradykinin relaxation following LTH. Western analysis showed that BK_Ca α-subunit expression was increased by LTH while that for the β₁ subunit was unchanged. Overall, these results suggest that those even moderately responsive to LTH can have impaired endothelial function.

The role of BKCa in endometrial cancer HEC-1-B cell proliferation and migration

BKCa is a large conductance calcium activated potassium channel ubiquitously expressed in various cell types. Accumulating evidence demonstrates that BKCa is aberrantly expressed in many malignancies, involving in cancerous behaviors such as cell proliferation and migration. In this study, we investigated the functional role of BKCa in endometrial cancer HEC-1-B cells. Overexpression of BKCa by plasmid transfection enhanced endometrial cancer cell proliferation and migration. Conversely, silence of BKCa by lentivirus mediated RNAi system not only inhibited proliferation and migration but also impaired tumor growth in vivo. Patch clamp assay identified the BKCa currents in HEC-1-B cells, which was supported by the observation of channel activation or inhibition in response to the specific opener (NS1619) or blocker (IBTX) of BKCa. Moreover, NS1619 significantly increased cell proliferation and migration while IBTX exhibited the opposite effects. In summary, these data suggested an important role of BKCa in proliferation and migration of endometrial cancer HEC-1-B cells. Thus, BKCa may be established as a potential therapeutic target in endometrial cancer.

Reactive Oxygen Species Mediate the Suppression of Arterial Smooth Muscle T-type Ca2+ Channels by Angiotensin II

Vascular T-type Ca²⁺ channels (Ca_V3.1 and Ca_V3.2) play a key role in arterial tone development. This study investigated whether this conductance is a regulatory target of angiotensin II (Ang II), a vasoactive peptide that circulates and which is locally produced within the arterial wall. Patch clamp electrophysiology performed on rat cerebral arterial smooth muscle cells reveals that Ang II (100 nM) inhibited T-type currents through AT₁ receptor activation. Blocking protein kinase C failed to eliminate channel suppression, a finding consistent with unique signaling proteins enabling this response. In this regard, inhibiting NADPH oxidase (Nox) with apocynin or ML171 (Nox1 selective) abolished channel suppression highlighting a role for reactive oxygen species (ROS). In the presence of Ni²⁺ (50 µM), Ang II failed to modulate the residual T-type current, an observation consistent with this peptide targeting Ca_V3.2. Selective channel suppression by Ang II impaired the ability of Ca_V3.2 to alter spontaneous transient outward currents or vessel diameter. Proximity ligation assay confirmed Nox1 colocalization with Ca_V3.2. In closing, Ang II targets Ca_V3.2 channels via a signaling pathway involving Nox1 and the generation of ROS. This unique regulatory mechanism alters BK_Ca mediated feedback giving rise to a “constrictive” phenotype often observed with cerebrovascular disease.

BKCa promotes growth and metastasis of prostate cancer through facilitating the coupling between αvβ3 integrin and FAK

BKCa is a large conductance calcium activated potassium channel promoting prostate cancer cell proliferation, although the mechanism is not fully elucidated. In addition, whether BKCa is involved in metastasis of prostate cancer remains to be explored. Here, we report that BKCa is overexpressed in prostate cancer. BKCa expression positively correlates with Ki67 index and gleason score of prostate cancer. Upregulation of BKCa promoted proliferation, migration and invasion of prostate cancer cells. On the contrary, downregulation of BKCa inhibited growth and metastasis of prostate cancer cells both in vitro and in vivo. Moreover, the ion-conducting function of BKCa contributed moderately to prostate cancer proliferation and migration, although, this was not the primary mechanism. BKCa action was mainly mediated through forming a functional complex with αvβ3 integrin. The BKCa/αvβ3 integrin complex promoted FAK phosphorylation independent of the channel activity. Overexpression of BKCa enhanced its association with αvβ3 integrin and FAK which increased FAK phosphorylation. Conversely, disrupting the complex by downregulation of BKCa reduced FAK phosphorylation. Finally, blocking of αvβ3 integrin or p-FAK activity using LM609 or Y15 markedly abrogated BKCa-enhanced cell proliferation and migration. Taken together, these results suggest that targeting BKCa/αvβ3/FAK may inaugurate innovative approaches to inhibit prostate cancer growth and metastasis.

Urothelial MaxiK-activity regulates mucosal and detrusor metabolism

There is increasing evidence for a role of MaxiK potassium channel-activity in regulating the metabolism and intracellular signaling of non-contractile bladder mucosal tissues. At present however no studies have determined the impact of urothelial MaxiK-activity on overall bladder metabolism. To address this we have investigated the effect of bladder lumen instillation of the MaxiK inhibitor, iberiotoxin (IBTX), on mucosal and detrusor metabolism using metabolomics. Since IBTX does not cross plasma membranes, when instilled into the bladder lumen it would only effect urothelially expressed MaxiK-activity. Surprisingly IBTX treatment caused more effect on the metabolome of the detrusor than mucosa (the levels of 17% of detected detrusor metabolites were changed in comparison to 6% of metabolites in mucosal tissue following IBTX treatment). In mucosal tissues, the major effects can be linked to mitochondrial-associated metabolism whereas in detrusor there were additional changes in energy generating pathways (such as glycolysis and the TCA cycle). In the detrusor, changes in metabolism are potentially a result of IBTX effecting MaxiK-linked signaling pathways between the mucosa and detrusor, secondary to changes in physiological activity or a combination of both. Overall we demonstrate that urothelial MaxiK-activity plays a significant role in determining mitochondrially-associated metabolism in mucosal tissues, which effects the metabolism of detrusor tissue. Our work adds further evidence that the urothelium plays a major role in determining overall bladder physiology. Since decreased MaxiK-activity is associated with several bladder pathophysiology's, the changes in mucosal metabolism reported here may represent novel downstream targets for therapeutic interventions.

Functional BKCa channel in human resident cardiac stem cells expressing W8B2

Recently, a new population of resident cardiac stem cells (CSCs) positive for the W8B2 marker has been identified. These CSCs are considered to be an ideal cellular source to repair myocardial damage after infarction. However, the electrophysiological profile of these cells has not been characterized yet. We first establish the conditions of isolation and expansion of W8B2⁺ CSCs from human heart biopsies using a magnetic sorting system followed by flow cytometry cell sorting. These cells display a spindle-shaped morphology, are highly proliferative, and possess self-renewal capacity demonstrated by their ability to form colonies. Besides, W8B2⁺ CSCs are positive for mesenchymal markers but negative for hematopoietic and endothelial ones. RT-qPCR and immunostaining experiments show that W8B2⁺ CSCs express some early cardiac-specific transcription factors but lack the expression of cardiac-specific structural genes. Using patch clamp in the whole-cell configuration, we show for the first time the electrophysiological signature of BKCa current in these cells. Accordingly, RT-PCR and western blotting analysis confirmed the presence of BKCa at both mRNA and protein levels in W8B2⁺ CSCs. Interestingly, BKCa channel inhibition by paxilline decreased cell proliferation in a concentration-dependent manner and halted cell cycle progression at the G0/G1 phase. The inhibition of BKCa also decreased the self-renewal capacity but did not affect migration of W8B2⁺ CSCs. Taken together, our results are consistent with an important role of BKCa channels in cell cycle progression and self-renewal in human cardiac stem cells.

Tagging of Endogenous BK Channels with a Fluorogen-Activating Peptide Reveals β4-Mediated Control of Channel Clustering in Cerebellum

BK channels are critical regulators of neuronal activity, controlling firing, neurotransmitter release, cerebellar function, and BK channel mutations have been linked to seizure disorders. Modulation of BK channel gating is well characterized, regulated by accessory subunit interactions, intracellular signaling pathways, and membrane potential. In contrast, the role of intracellular trafficking mechanisms in controlling BK channel function, especially in live cells, has been less studied. Fluorogen-activating peptides (FAPs) are well-suited for trafficking and physiological studies due to the binding of malachite green (MG)-based dyes with sub-nanomolar affinity to the FAP, resulting in bright, photostable, far-red fluorescence. Cell-excluded MG dyes enable the selective tagging of surface protein and tracking through endocytic pathways. We used CRISPR to insert the FAP at the extracellular N-terminus of BKα in the first exon of its native locus, enabling regulation by the native promoter elements and tag incorporation into multiple splice isoforms. Motor coordination was found to be normal; however, BK channel expression seems to be reduced in some locations. Alternate start site selection or post-translational proteolytic processing resulted in incomplete FAP tagging of the BKα proteins in brain tissues. In Purkinje cell somata, FAP revealed BK channel clustering previously only observed by electron microscopy. Measurement of these clusters in β4^+/- and β4^-/- mice showed that puncta number and cluster fluorescence intensity on the soma are reduced in β4^-/- knockout animals. This novel mouse line provides a versatile fluorescent platform for studying endogenous BK channels in living and fixed tissues. Future studies could apply this line to ex vivo neuronal cultures to study live-cell channel trafficking.

Regulation of Ca2+-Sensitive K+ Channels by Cholesterol and Bile Acids via Distinct Channel Subunits and Sites

Cholesterol (CLR) conversion into bile acids (BAs) in the liver constitutes the major pathway for CLR elimination from the body. Moreover, these steroids regulate each other's metabolism. While the roles of CLR and BAs in regulating metabolism and tissue function are well known, research of the last two decades revealed the existence of specific protein receptors for CLR or BAs in tissues with minor contribution to lipid metabolism, raising the possibility that these lipids serve as signaling molecules throughout the body. Among other lipids, CLR and BAs regulate ionic current mediated by the activity of voltage- and Ca²⁺-gated, K⁺ channels of large conductance (BK channels) and, thus, modulate cell physiology and participate in tissue pathophysiology. Initial work attributed modification of BK channel function by CLR or BAs to the capability of these steroids to directly interact with bilayer lipids and thus alter the physicochemical properties of the bilayer with eventual modification of BK channel function. Based on our own work and that of others, we now review evidence that supports direct interactions between CLR or BA and specific BK protein subunits, and the consequence of such interactions on channel activity and organ function, with a particular emphasis on arterial smooth muscle. For each steroid type, we will also briefly discuss several mechanisms that may underlie modification of channel steady-state activity. Finally, we will present novel computational data that provide a chemical basis for differential recognition of CLR vs lithocholic acid by distinct BK channel subunits and recognition sites.

Preconditioning with the BKCa channel activator NS-1619 prevents ischemia-reperfusion-induced inflammation and mucosal barrier dysfunction: roles for ROS and heme oxygenase-1

Activation of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels evokes cell survival programs that mitigate intestinal ischemia and reperfusion (I/R) inflammation and injury 24 h later. The goal of the present study was to determine the roles of reactive oxygen species (ROS) and heme oxygenase (HO)-1 in delayed acquisition of tolerance to I/R induced by pretreatment with the BK_Ca channel opener NS-1619. Superior mesentery arteries were occluded for 45 min followed by reperfusion for 70 min in wild-type (WT) or HO-1-null (HO-1^-/-) mice that were pretreated with NS-1619 or saline vehicle 24 h earlier. Intravital microscopy was used to quantify the numbers of rolling and adherent leukocytes. Mucosal permeability, tumor necrosis factor-α (TNF-α) levels, and HO-1 activity and expression in jejunum were also determined. I/R induced leukocyte rolling and adhesion, increased intestinal TNF-α levels, and enhanced mucosal permeability in WT mice, effects that were largely abolished by pretreatment with NS-1619. The anti-inflammatory and mucosal permeability-sparing effects of NS-1619 were prevented by coincident treatment with the HO-1 inhibitor tin protoporphyrin-IX or a cell-permeant SOD mimetic, Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), in WT mice. NS-1619 also increased jejunal HO-1 activity in WT animals, an effect that was attenuated by treatment with the BK_Ca channel antagonist paxilline or MnTBAP. I/R also increased postischemic leukocyte rolling and adhesion and intestinal TNF-α levels in HO-1^-/- mice to levels comparable to those noted in WT animals. However, NS-1619 was ineffective in preventing these effects in HO-1-deficient mice. In summary, our data indicate that NS-1619 induces the development of an anti-inflammatory phenotype and mitigates postischemic mucosal barrier disruption in the small intestine by a mechanism that may involve ROS-dependent HO-1 activity.NEW & NOTEWORTHY Antecedent treatment with the large-conductance Ca²⁺-activated K⁺ channel opener NS-1619 24 h before ischemia-reperfusion limits postischemic tissue injury by an oxidant-dependent mechanism. The present study shows that NS-1619-induced oxidant production prevents ischemia-reperfusion-induced inflammation and mucosal barrier disruption in the small intestine by provoking increases in heme oxygenase-1 activity.

The Slo(w) path to identifying the mitochondrial channels responsible for ischemic protection

Mitochondria play an important role in tissue ischemia and reperfusion (IR) injury, with energetic failure and the opening of the mitochondrial permeability transition pore being the major causes of IR-induced cell death. Thus, mitochondria are an appropriate focus for strategies to protect against IR injury. Two widely studied paradigms of IR protection, particularly in the field of cardiac IR, are ischemic preconditioning (IPC) and volatile anesthetic preconditioning (APC). While the molecular mechanisms recruited by these protective paradigms are not fully elucidated, a commonality is the involvement of mitochondrial K⁺ channel opening. In the case of IPC, research has focused on a mitochondrial ATP-sensitive K⁺ channel (mitoK_ATP), but, despite recent progress, the molecular identity of this channel remains a subject of contention. In the case of APC, early research suggested the existence of a mitochondrial large-conductance K⁺ (BK, big conductance of potassium) channel encoded by the Kcnma1 gene, although more recent work has shown that the channel that underlies APC is in fact encoded by Kcnt2 In this review, we discuss both the pharmacologic and genetic evidence for the existence and identity of mitochondrial K⁺ channels, and the role of these channels both in IR protection and in regulating normal mitochondrial function.

Anion Channels of Mitochondria

Mitochondria are the "power house" of a cell continuously generating ATP to ensure its proper functioning. The constant production of ATP via oxidative phosphorylation demands a large electrochemical force that drives protons across the highly selective and low-permeable mitochondrial inner membrane. Besides the conventional role of generating ATP, mitochondria also play an active role in calcium signaling, generation of reactive oxygen species (ROS), stress responses, and regulation of cell-death pathways. Deficiencies in these functions result in several pathological disorders like aging, cancer, diabetes, neurodegenerative and cardiovascular diseases. A plethora of ion channels and transporters are present in the mitochondrial inner and outer membranes which work in concert to preserve the ionic equilibrium of a cell for the maintenance of cell integrity, in physiological as well as pathophysiological conditions. For, e.g., mitochondrial cation channels KATP and BKCa play a significant role in cardioprotection from ischemia-reperfusion injury. In addition to the cation channels, mitochondrial anion channels are equally essential, as they aid in maintaining electro-neutrality by regulating the cell volume and pH. This chapter focusses on the information on molecular identity, structure, function, and physiological relevance of mitochondrial chloride channels such as voltage dependent anion channels (VDACs), uncharacterized mitochondrial inner membrane anion channels (IMACs), chloride intracellular channels (CLIC) and the aspects of forthcoming chloride channels.

The mitochondrial BKCa channel cardiac interactome reveals BKCa association with the mitochondrial import receptor subunit Tom22, and the adenine nucleotide translocator

Mitochondrial BK_Ca channel, mitoBK_Ca, regulates mitochondria function in the heart but information on its protein partnerships in cardiac mitochondria is missing. A directed proteomic approach discovered the novel interaction of BK_Ca with Tom22, a component of the mitochondrion outer membrane import system, and the adenine nucleotide translocator (ANT). The expressed protein partners co-immunoprecipitated and co-segregated into mitochondrial fractions in HEK293T cells. The BK_Ca 50 amino acid splice insert, DEC, facilitated BK_Ca interaction with ANT. Further, BK_Ca transmembrane domain was required for the association with both Tom22 and ANT. The results serve as a working framework to understand mitoBK_Ca import and functional relationships.

Modulation of BK Channels by Small Endogenous Molecules and Pharmaceutical Channel Openers

Voltage- and Ca(2+)-activated K(+) channels of big conductance (BK channels) are abundantly found in various organs and their relevance for smooth muscle tone and neuronal signaling is well documented. Dysfunction of BK channels is implicated in an array of human diseases involving many organs including the nervous, pulmonary, cardiovascular, renal, and urinary systems. In humans a single gene (KCNMA1) encodes the pore-forming α subunit (Slo1) of BK channels, but the channel properties are variable because of alternative splicing, tissue- and subcellular-specific auxiliary subunits (β, γ), posttranslational modifications, and a multitude of endogenous signaling molecules directly affecting the channel function. Initiatives to develop drugs capable of activating BK channels (channel openers) therefore need to consider the tissue-specific variability of BK channel structure and the potential interference with endogenously produced regulatory factors. The atomic structural basis of BK channel function is only beginning to be revealed. However, building on detailed knowledge of BK channel function, including its single-channel characteristics, voltage- and Ca(2+) dependence of channel gating, and modulation by diffusible messengers, a multi-tier allosteric model of BK channel gating (Horrigan and Aldrich (HA) model) has become a valuable tool in studying modulation of the channel. Using the conceptual framework of the HA model, we here review the functional impact of endogenous modulatory factors and select small synthetic compounds that regulate BK channel activity. Furthermore, we devise experimental approaches for studying BK channel-drug interactions with the aim to classify BK-modulating substances according to their molecular mode of action.

Ion channel-transporter interactions

All living cells require membrane proteins that act as conduits for the regulated transport of ions, solutes and other small molecules across the cell membrane. Ion channels provide a pore that permits often rapid, highly selective and tightly regulated movement of ions down their electrochemical gradient. In contrast, active transporters can move moieties up their electrochemical gradient. The secondary active transporters (such as SLC superfamily solute transporters) achieve this by coupling uphill movement of the substrate to downhill movement of another ion, such as sodium. The primary active transporters (including H(+)/K(+)-ATPases and Na(+)/K(+)-ATPases) utilize ATP hydrolysis as an energy source to power uphill transport. It is well known that proteins in each of these classes work in concert with members of the other classes to ensure, for example, ion homeostasis, ion secretion and restoration of ion balance following action potentials. More recently, evidence is emerging of direct physical interaction between true ion channels, and some primary or secondary active transporters. Here, we review the first known members of this new class of macromolecular complexes that we term "chansporters", explore their biological roles and discuss the pathophysiological consequences of their disruption. We compare functional and/or physical interactions between the ubiquitous KCNQ1 potassium channel and various active transporters, and examine other newly discovered chansporter complexes that suggest we may be seeing the tip of the iceberg in a newly emerging signaling modality.