Molecular cloning and characterization of the intermediate-conductance Ca(2+)-activated K(+) channel in vascular smooth muscle: relationship between K(Ca) channel diversity and smooth muscle cell function

KCa2 and KCa3.1 Channels in the Airways: A New Therapeutic Target

K⁺ channels are involved in many critical functions in lung physiology. Recently, the family of Ca²⁺-activated K⁺ channels (K_Ca) has received more attention, and a massive amount of effort has been devoted to developing selective medications targeting these channels. Within the family of K_Ca channels, three small-conductance Ca²⁺-activated K⁺ (K_Ca2) channel subtypes, together with the intermediate-conductance K_Ca3.1 channel, are voltage-independent K⁺ channels, and they mediate Ca²⁺-induced membrane hyperpolarization. Many K_Ca2 channel members are involved in crucial roles in physiological and pathological systems throughout the body. In this article, different subtypes of K_Ca2 and K_Ca3.1 channels and their functions in respiratory diseases are discussed. Additionally, the pharmacology of the K_Ca2 and K_Ca3.1 channels and the link between these channels and respiratory ciliary regulations will be explained in more detail. In the future, specific modulators for small or intermediate Ca²⁺-activated K⁺ channels may offer a unique therapeutic opportunity to treat muco-obstructive lung diseases.

Molecular mechanism of HNTX-I activates the intermediate-conductance Ca2+-activated K+ (IK) channels

The IK channel, a potassium ion channel regulated by calcium ions and voltages in a bidirectional manner, has been implicated in a range of diseases. However, there are currently few compounds available that can target the IK channel with high potency and specificity. Hainantoxin-I (HNTX-I) is the first peptide activator of IK channel discovered so far, but its activity is not ideal, and the underlying mechanism interaction between HNTX-I toxin and IK channel remains unclear. Thus, our study aimed to enhance the potency of IK channel activating peptides derived from HNTX-I and elucidate the molecular mechanism underlying the interaction between HNTX-I and the IK channel. By employing virtual alanine scanning mutagenesis, we generated 11 HNTX-I mutants using site-directed mutagenesis to pinpoint specific residues crucial for the HNTX-I and IK channel interaction. Subsequently, we identified key residues on the IK channel that are involved in the interaction with HNTX-I. Additionally, molecular docking was employed to guide the molecular engineering process and clarify the binding interface between HNTX-I and the IK channel. Our results demonstrate that HNTX-I primarily acts on the IK channel via the N-terminal amino acid, and its interaction with the IK channel is mediated by electrostatic and hydrophobic interactions, specifically the amino acid residues at positions 1, 3, 5, and 7 on HNTX-I. This study provides valuable insights into the peptide toxins that may serve as potential templates for the development of activators with enhanced potency and selectivity for the IK channel.

Endothelial KCa channels: Novel targets to reduce atherosclerosis-driven vascular dysfunction

Elevated levels of cholesterol in the blood can induce endothelial dysfunction, a condition characterized by impaired nitric oxide production and decreased vasodilatory capacity. Endothelial dysfunction can promote vascular disease, such as atherosclerosis, where macrophages accumulate in the vascular intima and fatty plaques form that impair normal blood flow in conduit arteries. Current pharmacological strategies to treat atherosclerosis mostly focus on lipid lowering to prevent high levels of plasma cholesterol that induce endothelial dysfunction and atherosclerosis. While this approach is effective for most patients with atherosclerosis, for some, lipid lowering is not enough to reduce their cardiovascular risk factors associated with atherosclerosis (e.g., hypertension, cardiac dysfunction, stroke, etc.). For such patients, additional strategies targeted at reducing endothelial dysfunction may be beneficial. One novel strategy to restore endothelial function and mitigate atherosclerosis risk is to enhance the activity of Ca2+-activated K+ (KCa) channels in the endothelium with positive gating modulator drugs. Here, we review the mechanism of action of these small molecules and discuss their ability to improve endothelial function. We then explore how this strategy could mitigate endothelial dysfunction in the context of atherosclerosis by examining how KCa modulators can improve cardiovascular function in other settings, such as aging and type 2 diabetes. Finally, we consider questions that will need to be addressed to determine whether KCa channel activation could be used as a long-term add-on to lipid lowering to augment atherosclerosis treatment, particularly in patients where lipid-lowering is not adequate to improve their cardiovascular health.

Endothelial IK and SK channel activation decreases pulmonary arterial pressure and vascular remodeling in pulmonary hypertension

Endothelial cells (ECs) from small pulmonary arteries (PAs) release nitric oxide (NO) and prostacyclin, which lower pulmonary arterial pressure (PAP). In pulmonary hypertension (PH), the levels of endothelium-derived NO and prostacyclin are reduced, contributing to elevated PAP. Small-and intermediate-conductance Ca²⁺-activated K⁺ channels (IK and SK)-additional crucial endothelial mediators of vasodilation-are also present in small PAs, but their function has not been investigated in PH. We hypothesized that endothelial IK and SK channels can be targeted to lower PAP in PH. Whole-cell patch-clamp experiments showed functional IK and SK channels in ECs, but not smooth muscle cells, from small PAs. Using a SU5416 plus chronic hypoxia (Su + CH) mouse model of PH, we found that currents through EC IK and SK channels were unchanged compared with those from normal mice. Moreover, IK/SK channel-mediated dilation of small PAs was preserved in Su + CH mice. Consistent with previous reports, endothelial NO levels and NO-mediated dilation were reduced in small PAs from Su + CH mice. Notably, acute treatment with IK/SK channel activators decreased PAP in Su + CH mice but not in normal mice. Further, chronic activation of IK/SK channels decreased PA remodeling and right ventricular hypertrophy, which are pathological hallmarks of PH, in Su + CH mice. Collectively, our data provide the first evidence that, unlike endothelial NO release, IK/SK channel activity is not altered in PH. Our results also demonstrate proof of principle that IK/SK channel activation can be used as a strategy for lowering PAP in PH.

Ca2+-Activated K+ Channels and the Regulation of the Uteroplacental Circulation

Adequate uteroplacental blood supply is essential for the development and growth of the placenta and fetus during pregnancy. Aberrant uteroplacental perfusion is associated with pregnancy complications such as preeclampsia, fetal growth restriction (FGR), and gestational diabetes. The regulation of uteroplacental blood flow is thus vital to the well-being of the mother and fetus. Ca²⁺-activated K⁺ (K_Ca) channels of small, intermediate, and large conductance participate in setting and regulating the resting membrane potential of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) and play a critical role in controlling vascular tone and blood pressure. K_Ca channels are important mediators of estrogen/pregnancy-induced adaptive changes in the uteroplacental circulation. Activation of the channels hyperpolarizes uteroplacental VSMCs/ECs, leading to attenuated vascular tone, blunted vasopressor responses, and increased uteroplacental blood flow. However, the regulation of uteroplacental vascular function by K_Ca channels is compromised in pregnancy complications. This review intends to provide a comprehensive overview of roles of K_Ca channels in the regulation of the uteroplacental circulation under physiological and pathophysiological conditions.

Potassium Ion Channels in Malignant Central Nervous System Cancers

Malignant central nervous system (CNS) cancers are among the most difficult to treat, with low rates of survival and a high likelihood of recurrence. This is primarily due to their location within the CNS, hindering adequate drug delivery and tumour access via surgery. Furthermore, CNS cancer cells are highly plastic, an adaptive property that enables them to bypass targeted treatment strategies and develop drug resistance. Potassium ion channels have long been implicated in the progression of many cancers due to their integral role in several hallmarks of the disease. Here, we will explore this relationship further, with a focus on malignant CNS cancers, including high-grade glioma (HGG). HGG is the most lethal form of primary brain tumour in adults, with the majority of patient mortality attributed to drug-resistant secondary tumours. Hence, targeting proteins that are integral to cellular plasticity could reduce tumour recurrence, improving survival. This review summarises the role of potassium ion channels in malignant CNS cancers, specifically how they contribute to proliferation, invasion, metastasis, angiogenesis, and plasticity. We will also explore how specific modulation of these proteins may provide a novel way to overcome drug resistance and improve patient outcomes.

Ion channels in stem cells and their roles in stem cell biology and vascular diseases

Stem cell therapy may be a promising option for the treatment of vascular diseases. In recent years, significant progress has been made in stem cell research, especially in the mechanism of stem cell activation, homing and differentiation in vascular repair and reconstruction. Current research on stem cells focuses on protein expression and transcriptional networks. Ion channels are considered to be the basis for the generation of bioelectrical signals, which control the proliferation, differentiation and migration of various cell types. Although heterogeneity of multiple ion channels has been found in different types of stem cells, it is unclear whether the heterogeneous expression of ion channels is related to different cell subpopulations and/or different stages of the cell cycle. There is still a long way to go in clinical treatment by using the regulation of stem cell ion channels. In this review, we reviewed the main ion channels found on stem cells, their expression and function in stem cell proliferation, differentiation and migration, and the research status of stem cells' involvement in vascular diseases.

The Molecular Basis for the Calcium-Dependent Slow Afterhyperpolarization in CA1 Hippocampal Pyramidal Neurons

Neuronal signal transmission depends on the frequency, pattern, and timing of spike output, each of which are shaped by spike afterhyperpolarizations (AHPs). There are classically three post-spike AHPs of increasing duration categorized as fast, medium and slow AHPs that hyperpolarize a cell over a range of 10 ms to 30 s. Intensive early work on CA1 hippocampal pyramidal cells revealed that all three AHPs incorporate activation of calcium-gated potassium channels. The ionic basis for a fAHP was rapidly attributed to the actions of big conductance (BK) and the mAHP to small conductance (SK) or Kv7 potassium channels. In stark contrast, the ionic basis for a prominent slow AHP of up to 30 s duration remained an enigma for over 30 years. Recent advances in pharmacological, molecular, and imaging tools have uncovered the expression of a calcium-gated intermediate conductance potassium channel (IK, KCa3.1) in central neurons that proves to contribute to the slow AHP in CA1 hippocampal pyramidal cells. Together the data show that the sAHP arises in part from a core tripartite complex between Cav1.3 (L-type) calcium channels, ryanodine receptors, and IK channels at endoplasmic reticulum-plasma membrane junctions. Work on the sAHP in CA1 pyramidal neurons has again quickened pace, with identified contributions by both IK channels and the Na-K pump providing answers to several mysteries in the pharmacological properties of the sAHP.

KCa3.1 Inhibition Decreases Size and Alters Composition of Atherosclerotic Lesions Induced by Low, Oscillatory Flow

Low, oscillatory flow/shear patterns are associated with atherosclerotic lesion development. Increased expression of K_Ca3.1 has been found in Vascular Smooth Muscle (VSM), macrophages and T-cells in lesions from humans and mice. Increased expression of K_Ca3.1, is also required for VSM cell proliferation and migration. Previously, we showed that the specific K_Ca3.1 inhibitor, TRAM-34, could inhibit coronary neointimal development following balloon injury in swine. Atherosclerosis develops in regions with a low, oscillatory (i.e. atheroprone) flow pattern. Therefore, we used the Partial Carotid Ligation (PCL) model in high-fat fed, Apoe^−/− mice to determine the role of K_Ca3.1 in atherosclerotic lesion composition and development. PCL was performed on 8–10 week old male Apoe^−/− mice and subsequently placed on a Western diet (TD.88137, Teklad) for 4 weeks. Mice received daily s.c. injections of TRAM-34 (120 mg/kg) or equal volumes of vehicle (peanut oil, PO). 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) treatment reduced lesion size ~50% (p < 0.05). In addition, lesions from TRAM-34 treated mice contained less collagen (6% ± 1% vs. 15% ± 2%; p < 0.05), fibronectin (14% ± 3% vs. 32% ± 3%; p < 0.05) and smooth muscle content (19% ± 2% vs. 29% ± 3%; p < 0.05). Conversely, TRAM-34 had no effect on total cholesterol (1455 vs. 1334 mg/dl, PO and TRAM, resp.) or body weight (29.1 vs. 28.8 g, PO and TRAM, resp.). Medial smooth muscle of atherosclerotic carotids showed diminished RE1-Silencing Transcription Factor (REST)/Neural Restrictive Silencing Factor (NRSF) expression, while REST overexpression in vitro inhibited smooth muscle migration. Together, these data support a downregulation of REST/NRSF and upregulation of K_Ca3.1 in determining smooth muscle and matrix content of atherosclerotic lesions.

The intermediate-conductance calcium-activated potassium channel KCa3.1 contributes to alkalinization-induced vascular calcification in vitro

OBJECTIVE

In order to find new strategies for the prevention of vascular calcification in uremic individuals especially treated by dialysis and develop novel therapeutic targets in vascular calcification, we explore the role of KCa3.1 in alkalinization-induced VSMCs calcification in vitro.

METHOD

Rat VSMCs calcification model was established by beta-glycerophosphate (β-GP, 10 mM) induction. The pH of Dulbecco's modified Eagle's medium (DMEM) was adjusted every 24 h with 10 mM HCl or 10 mM NaHCO3 . The mineralization was measured by Alizarin Red staining and O-cresolphthalein complex one method. mRNA and protein expression were detected by RT-PCR and Western blot or immunofluorescence. Ca2+ influx was measured by Elisa.

RESULT

The results indicated that alkalization induced an increase in Ca2+ influx to enhance VSMCs calcification. Furthermore, the increase of calcification was associated with the expression of KCa3.1 via advanced expression of osteoblastic differentiation markers alkaline phosphatase (ALP) and Runt-related transcription factor 2 (Runx2). Blocking KCa3.1 with TRAM-34 or shRNA vector can significantly lowered the effects of calcification in the activity of ALP and Runx2 expression.

CONCLUSION

Together all, our studies suggested that alkalinization can promote vascular calcification by upregulating KCa3.1 channel and enhancing osteogenic/chondrogenic differentiation by upregulating Runx2. The specific inhibitor TRAM-34 and KCa3.1-shRNA ameliorated VSMCs calcification by downregulating KCa3.1.

KCa channel activation normalizes endothelial function in Type 2 Diabetic resistance arteries by improving intracellular Ca2+ mobilization

BACKGROUND

Endothelial dysfunction is an early pathogenic event in the progression of cardiovascular disease in patients with Type 2 Diabetes (T2D). Endothelial KCa2.3 and KCa3.1 K⁺ channels are important regulators of arterial diameter, and we thus hypothesized that SKA-31, a small molecule activator of KCa2.3 and KCa3.1, would positively influence agonist-evoked dilation in myogenically active resistance arteries in T2D.

METHODOLOGY

Arterial pressure myography was utilized to investigate endothelium-dependent vasodilation in isolated cremaster skeletal muscle resistance arteries from 22 to 24 week old T2D Goto-Kakizaki rats, age-matched Wistar controls, and small human intra-thoracic resistance arteries from T2D subjects. Agonist stimulated changes in cytosolic free Ca²⁺ in acutely isolated, single endothelial cells from Wistar and T2D Goto-Kakizaki cremaster and cerebral arteries were examined using Fura-2 fluorescence imaging.

MAIN FINDINGS

Endothelium-dependent vasodilation in response to acetylcholine (ACh) or bradykinin (BK) was significantly impaired in isolated cremaster arteries from T2D Goto-Kakizaki rats compared with Wistar controls, and similar results were observed in human intra-thoracic arteries. In contrast, inhibition of myogenic tone by sodium nitroprusside, a direct smooth muscle relaxant, was unaltered in both rat and human T2D arteries. Treatment with a threshold concentration of SKA-31 (0.3 μM) significantly enhanced vasodilatory responses to ACh and BK in arteries from T2D Goto-Kakizaki rats and human subjects, whereas only modest effects were observed in non-diabetic arteries of both species. Mechanistically, SKA-31 enhancement of evoked dilation was independent of vascular NO synthase and COX activities. Remarkably, SKA-31 treatment improved agonist-stimulated Ca²⁺ elevation in acutely isolated endothelial cells from T2D Goto-Kakizaki cremaster and cerebral arteries, but not from Wistar control vessels. In contrast, SKA-31 treatment did not affect intracellular Ca²⁺ release by the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) inhibitor cyclopiazonic acid.

CONCLUSIONS

Collectively, our data demonstrate that KCa channel modulation can acutely restore endothelium-dependent vasodilatory responses in T2D resistance arteries from rats and humans, which appears to involve improved endothelial Ca²⁺ mobilization.

Ca2+ signalling in fibroblasts and the therapeutic potential of KCa3.1 channel blockers in fibrotic diseases

The role of Ca²⁺ signalling in fibroblasts is of great interest in fibrosis-related diseases. Intracellular free Ca²⁺ ([Ca²⁺ ]_i ) is a ubiquitous secondary messenger, regulating a number of cellular functions such as secretion, metabolism, differentiation, proliferation and contraction. The intermediate conductance Ca²⁺ -activated K⁺ channel K_Ca 3.1 is pivotal in Ca²⁺ signalling and plays a central role in fibroblast processes including cell activation, migration and proliferation through the regulation of cell membrane potential. Evidence from a number of approaches demonstrates that K_Ca 3.1 plays an important role in the development of many fibrotic diseases, including idiopathic pulmonary, renal tubulointerstitial fibrosis and cardiovascular disease. The K_Ca 3.1 selective blocker senicapoc was well tolerated in clinical trials for sickle cell disease, raising the possibility of rapid translation to the clinic for people suffering from pathological fibrosis. This review after analysing all the data, concludes that targeting K_Ca 3.1 should be a high priority for human fibrotic disease.

Kv channels and vascular smooth muscle cell proliferation

Kv channels are present in virtually all VSMCs and strongly influence contractile responses. However, they are also instrumental in the proliferative, migratory, and secretory functions of synthetic, dedifferentiated VSMCs upon PM. In fact, Kv channels not only contribute to all these processes but also are active players in the phenotypic switch itself. This review is focused on the role(s) of Kv channels in VSMC proliferation, which is one of the best characterized functions of dedifferentiated VSMCs. VSMC proliferation is a complex process requiring specific Kv channels at specific time and locations. Their identification is further complicated by their large diversity and the differences in expression across vascular beds. Of interest, both conserved changes in some Kv channels and vascular bed-specific regulation of others seem to coexist and participate in VSMC proliferation through complementary mechanisms. Such a system will add flexibility to the process while providing the required robustness to preserve this fundamental cellular response.

Colonic Potassium Absorption and Secretion in Health and Disease

The colon has large capacities for K⁺ absorption and K⁺ secretion, but its role in maintaining K⁺ homeostasis is often overlooked. For many years, passive diffusion and/or solvent drag were thought to be the primary mechanisms for K⁺ absorption in human and animal colon. However, it is now clear that apical H⁺ ,K⁺ -ATPase, in coordination with basolateral K⁺ -Cl^- cotransport and/or K⁺ and Cl^- channels operating in parallel, mediate electroneutral K⁺ absorption in animal colon. We now know that K⁺ absorption in rat colon reflects ouabain-sensitive and ouabain-insensitive apical H⁺ ,K⁺ -ATPase activities. Ouabain-insensitive and ouabain-sensitive H⁺ ,K⁺ -ATPases are localized in surface and crypt cells, respectively. Colonic H⁺ ,K⁺ -ATPase consists of α- (HKC_α ) and β- (HKC_β ) subunits which, when coexpressed, exhibit ouabain-insensitive H⁺ ,K⁺ -ATPase activity in HEK293 cells, while HKC_α coexpressed with the gastric β-subunit exhibits ouabain-sensitive H⁺ ,K⁺ -ATPase activity in Xenopus oocytes. Aldosterone enhances apical H⁺ ,K⁺ -ATPase activity, HKC_α specific mRNA and protein expression, and K⁺ absorption. Active K⁺ secretion, on the other hand, is mediated by apical K⁺ channels operating in a coordinated way with the basolateral Na⁺ -K⁺ -2Cl^- cotransporter. Both Ca²⁺ -activated intermediate conductance K⁺ (IK) and large conductance K⁺ (BK) channels are located in the apical membrane of colonic epithelia. IK channel-mediated K⁺ efflux provides the driving force for Cl^- secretion, while BK channels mediate active (e.g., cAMP-activated) K⁺ secretion. BK channel expression and activity are increased in patients with end-stage renal disease and ulcerative colitis. This review summarizes the role of apical H⁺ ,K⁺ -ATPase in K⁺ absorption, and apical BK channel function in K⁺ secretion in health and disease. © 2018 American Physiological Society. Compr Physiol 8:1513-1536, 2018.

SKA-31, an activator of endothelial Ca2+-activated K+ channels evokes robust vasodilation in rat mesenteric arteries

It is now well recognized that endothelial KCa2.3 and KCa3.1 channel activities contribute to dilation of resistance arteries via endothelium-mediated hyperpolarization and vascular smooth muscle relaxation. In this study, we have investigated the functional effect of the KCa channel activator SKA-31 in third order rat mesenteric arteries using arterial pressure myography. Isolated arteries were cannulated, pressurized intraluminally to 70 mmHg at 36 °C and then constricted with 1 μM phenylephrine. Acute bath exposure to SKA-31 evoked a robust and reversible inhibition of developed tone (IC₅₀ = 0.22 μM). The vasodilatory effects of SKA-31 and acetylcholine were blunted in the presence of KCa2.3 and KCa3.1 channel antagonists, and were largely prevented following endothelial denudation. Western blot and q-PCR analyses of isolated mesenteric arteries revealed KCa2.3 and KCa3.1 channel expression at the protein and mRNA levels, respectively. Penitrem-A, an inhibitor of KCa1.1 channels, decreased vasodilatory responses to acetylcholine, sodium nitroprusside and NS-1619, but had little effect on SKA-31. Similarly, bath exposure to the eNOS inhibitor L-NAME did not alter SKA-31 and acetylcholine-mediated vasodilation. Collectively, these data highlight the major cellular mechanisms by which the endothelial KCa channel activator SKA-31 inhibits agonist-evoked vasoconstriction in rat small mesenteric arteries.

Diabetes Mellitus and Ischemic Heart Disease: The Role of Ion Channels

Diabetes mellitus is one the strongest risk factors for cardiovascular disease and, in particular, for ischemic heart disease (IHD). The pathophysiology of myocardial ischemia in diabetic patients is complex and not fully understood: some diabetic patients have mainly coronary stenosis obstructing blood flow to the myocardium; others present with coronary microvascular disease with an absence of plaques in the epicardial vessels. Ion channels acting in the cross-talk between the myocardial energy state and coronary blood flow may play a role in the pathophysiology of IHD in diabetic patients. In particular, some genetic variants for ATP-dependent potassium channels seem to be involved in the determinism of IHD.

Exenatide Inhibits the KCa3.1 Channels of Aortic Vascular Smooth Muscle in Diabetic Rats

BACKGROUND

KCa3.1 ion channels play an important role during atherosclerosis. We aimed to investigate the effect of exenatide on KCa3.1 expression in aortic vascular smooth muscle cells (VSMCs) of diabetic rats.

METHODS

Sprague-Dawley rats were randomly divided into normal control (NC), diabetes model (DM), and exenatide treatment (ET) groups. Hematoxylin and eosin and α-actin immunohistochemical staining were used to detect changes in rat aortic vascular smooth muscle. Quantitative RT-PCR and Western blot analysis were used to detect changes in KCa3.1 mRNA and protein levels, respectively.

RESULTS

Aortic tissue staining in the DM group revealed an absence of smooth or integrated endothelium, increased smooth muscle cell proliferation in the media, smooth muscle hyperplasia, disorganized smooth muscle cells, and an increased number of collagen fibers, relative to the NC and ET groups. KCa3.1 mRNA expression was higher in the DM group than in the NC and ET groups. Similarly, the KCa3.1 protein level was higher in the DM group than in the NC and ET groups. The KCa3.1 protein level did not significantly differ between the ET and NC groups.

CONCLUSIONS

Exenatide could inhibit the expression of the KCa3.1 channel in VSMCs of diabetic rats.

Modulation of Retrograde Trafficking of KCa3.1 in a Polarized Epithelium

In epithelia, the intermediate conductance, Ca²⁺-activated K⁺ channel (KCa3.1) is targeted to the basolateral membrane (BLM) where this channel plays numerous roles in absorption and secretion. A growing body of research suggests that the membrane resident population of KCa3.1 may be critical in clinical manifestation of diseases. In this study, we investigated the key molecular components that regulate the degradation of KCa3.1 using a Fisher rat thyroid cell line stably expressing KCa3.1. Using immunoblot, Ussing chamber, and pharmacological approaches, we demonstrated that KCa3.1 is targeted exclusively to the BLM, provided a complete time course of degradation of KCa3.1 and degradation time courses of the channel in the presence of pharmacological inhibitors of ubiquitylation and deubiquitylation to advance our understanding of the retrograde trafficking of KCa3.1. We provide a complete degradation profile of KCa3.1 and that the degradation is via an ubiquitin-dependent pathway. Inhibition of E1 ubiquitin activating enzyme by UBEI-41 crippled the ability of the cells to internalize the channel, shown by the increased BLM surface expression resulting in an increased function of the channel as measured by a DCEBIO sensitive K⁺ current. Additionally, the involvement of deubiquitylases and degradation by the lysosome were also confirmed by treating the cells with PR-619 or leupeptin/pepstatin, respectively; which significantly decreased the degradation rate of membrane KCa3.1. Additionally, we provided the first evidence that KCa3.1 channels were not deubiquitylated at the BLM. These data further define the retrograde trafficking of KCa3.1, and may provide an avenue for therapeutic approach for treatment of disease.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Intermediate-Conductance-Ca2-Activated K Channel IKCa1 Is Upregulated and Promotes Cell Proliferation in Cervical Cancer

BACKGROUND Accumulating data point to intermediate-conductance calcium-activated potassium channel (IKCa1) as a key player in controlling cell cycle progression and proliferation of human cancer cells. However, the role that IKCa1 plays in the growth of human cervical cancer cells is largely unexplored. MATERIAL AND METHODS In this study, Western blot analysis, immunohistochemical staining, and RT-PCR were first used for IKCa1protein and gene expression assays in cervical cancer tissues and HeLa cells. Then, IKCa1 channel blocker and siRNA were employed to inhibit the functionality of IKCa1 and downregulate gene expression in HeLa cells, respectively. After these treatments, we examined the level of cell proliferation by MTT method and measured IKCa1 currents by conventional whole-cell patch clamp technique. Cell apoptosis was assessed using the Annexin V-FITC/Propidium Iodide (PI) double-staining apoptosis detection kit. RESULTS We demonstrated that IKCa1 mRNA and protein are preferentially expressed in cervical cancer tissues and HeLa cells. We also showed that the IKCa1 channel blocker, clotrimazole, and IKCa1 channel siRNA can be used to suppress cervical cancer cell proliferation and decrease IKCa1 channel current. IKCa1 downregulation by specific siRNAs induced a significant increase in the proportion of apoptotic cells in HeLa cells. CONCLUSIONS IKCa1 is overexpressed in cervical cancer tissues, and IKCa1 upregulation in cervical cancer cell linea enhances cell proliferation, partly by reducing the proportion of apoptotic cells.

Vascular Tone Regulation Induced by C-Type Natriuretic Peptide: Differences in Endothelium-Dependent and -Independent Mechanisms Involved in Normotensive and Spontaneously Hypertensive Rats

Given that the role of C-type natriuretic peptide (CNP) in the regulation of vascular tone in hypertensive states is unclear, we hypothesized that impaired response of the nitric oxide system to CNP in spontaneously hypertensive rats (SHR) could affect vascular relaxation induced by the peptide in this model of hypertension, and that other endothelial systems or potassium channels opening could also be involved. We examined the effect of CNP on isolated SHR aortas, and the hindlimb vascular resistance (HVR) in response to CNP administration compared to normotensive rats. Aortas were mounted in an isometric organ bath and contracted with phenylephrine. CNP relaxed arteries in a concentration-dependent manner but was less potent in inducing relaxation in SHR. The action of CNP was diminished by removal of the endothelium, inhibition of nitric oxide synthase by N^ω-nitro-L-arginine methyl ester, and inhibition of soluble guanylyl cyclase by 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one in both groups. In contrast, blockade of cyclooxygenase or subtype 2 bradykinin receptor increased CNP potency only in SHR. In both Wistar and SHR, CNP relaxation was blunted by tetraethylammonium and partially inhibited by BaCl₂ and iberiotoxin, indicating that it was due to opening of the Kir and BKCa channels. However, SHR seem to be more sensitive to Kir channel blockade and less sensitive to BKCa channel blockade than normotensive rats. In addition, CNP decreases HVR in Wistar and SHR, but the effect of CNP increasing blood flow was more marked in SHR. We conclude that CNP induces aorta relaxation by activation of the nitric oxide system and opening of potassium channels, but the response to the peptide is impaired in conductance vessel of hypertensive rats.

Inhibition of SK4 Potassium Channels Suppresses Cell Proliferation, Migration and the Epithelial-Mesenchymal Transition in Triple-Negative Breast Cancer Cells

Treatments for triple-negative breast cancer (TNBC) are limited; intermediate-conductance calcium-activated potassium (SK4) channels are closely involved in tumor progression, but little is known about these channels in TNBC. We aimed to investigate whether SK4 channels affect TNBC. First, by immunohistochemistry (IHC) and western blotting (WB), increased SK4 protein expression in breast tumor tissues was detected relative to that in non-tumor breast tissues, but there was no apparent expression difference between various subtypes of breast cancer (p>0.05). Next, functional SK4 channels were detected in the TNBC cell line MDA-MB-231 using WB, real-time PCR, immunofluorescence and patch-clamp recording. By employing SK4 specific siRNAs and blockers, including TRAM-34 and clotrimazole, in combination with an MTT assay, a colony-formation assay, flow cytometry and a cell motility assay, we found that the suppression of SK4 channels significantly inhibited cell proliferation and migration and promoted apoptosis in MDA-MB-231 cells (p<0.05). Further investigation revealed that treatment with epidermal growth factor (EGF)/basic fibroblast growth factor (bFGF) caused MDA-MB-231 cells to undergo the epithelial-mesenchymal transition (EMT) and to show increased SK4 mRNA expression. In addition, the down-regulation of SK4 expression inhibited the EMT markers Vimentin and Snail1. Collectively, our findings suggest that SK4 channels are expressed in TNBC and are involved in the proliferation, apoptosis, migration and EMT processes of TNBC cells.

Calcium-Activated Potassium Channels: Potential Target for Cardiovascular Diseases

Ca(2+)-activated K(+) channels (KCa) are classified into three subtypes: big conductance (BKCa), intermediate conductance (IKCa), and small conductance (SKCa) KCa channels. The three types of KCa channels have distinct physiological or pathological functions in cardiovascular system. BKCa channels are mainly expressed in vascular smooth muscle cells (VSMCs) and inner mitochondrial membrane of cardiomyocytes, activation of BKCa channels in these locations results in vasodilation and cardioprotection against cardiac ischemia. IKCa channels are expressed in VSMCs, endothelial cells, and cardiac fibroblasts and involved in vascular smooth muscle proliferation, migration, vessel dilation, and cardiac fibrosis. SKCa channels are widely expressed in nervous and cardiovascular system, and activation of SKCa channels mainly contributes membrane hyperpolarization. In this chapter, we summarize the physiological and pathological roles of the three types of KCa channels in cardiovascular system and put forward the possibility of KCa channels as potential target for cardiovascular diseases.

Smooth Muscle-Like Cells Generated from Human Mesenchymal Stromal Cells Display Marker Gene Expression and Electrophysiological Competence Comparable to Bladder Smooth Muscle Cells

The use of mesenchymal stromal cells (MSCs) differentiated toward a smooth muscle cell (SMC) phenotype may provide an alternative for investigators interested in regenerating urinary tract organs such as the bladder where autologous smooth muscle cells cannot be used or are unavailable. In this study we measured the effects of good manufacturing practice (GMP)-compliant expansion followed by myogenic differentiation of human MSCs on the expression of a range of contractile (from early to late) myogenic markers in relation to the electrophysiological parameters to assess the functional role of the differentiated MSCs and found that differentiation of MSCs associated with electrophysiological competence comparable to bladder SMCs. Within 1-2 weeks of myogenic differentiation, differentiating MSCs significantly expressed alpha smooth muscle actin (αSMA; ACTA2), transgelin (TAGLN), calponin (CNN1), and smooth muscle myosin heavy chain (SM-MHC; MYH11) according to qRT-PCR and/or immunofluorescence and Western blot. Voltage-gated Na+ current levels also increased within the same time period following myogenic differentiation. In contrast to undifferentiated MSCs, differentiated MSCs and bladder SMCs exhibited elevated cytosolic Ca2+ transients in response to K+-induced depolarization and contracted in response to K+ indicating functional maturation of differentiated MSCs. Depolarization was suppressed by Cd2+, an inhibitor of voltage-gated Ca2+-channels. The expression of Na+-channels was pharmacologically identified as the Nav1.4 subtype, while the K+ and Ca2+ ion channels were identified by gene expression of KCNMA1, CACNA1C and CACNA1H which encode for the large conductance Ca2+-activated K+ channel BKCa channels, Cav1.2 L-type Ca2+ channels and Cav3.2 T-type Ca2+ channels, respectively. This protocol may be used to differentiate adult MSCs into smooth muscle-like cells with an intermediate-to-late SMC contractile phenotype exhibiting voltage-gated ion channel activity comparable to bladder SMCs which may be important for urological regenerative medicine applications.

KCa3.1-Dependent Hyperpolarization Enhances Intracellular Ca2+ Signaling Induced by fMLF in Differentiated U937 Cells

Formylated peptides are chemotactic agents generated by pathogens. The most relevant peptide is fMLF (formyl-Met-Leu-Phe) which participates in several immune functions, such as chemotaxis, phagocytosis, cytokine release and generation of reactive oxygen species. In macrophages fMLF-dependent responses are dependent on both, an increase in intracellular calcium concentration and on a hyperpolarization of the membrane potential. However, the molecular entity underlying this hyperpolarization remains unknown and it is not clear whether changes in membrane potential are linked to the increase in intracellular Ca²⁺. In this study, differentiated U937 cells, as a macrophage-like cell model, was used to characterize the fMLF response using electrophysiological and Ca²⁺ imaging techniques. We demonstrate by means of pharmacological and molecular biology tools that fMLF induces a Ca²⁺-dependent hyperpolarization via activation of the K⁺ channel K_Ca3.1 and thus, enhancing fMLF-induced intracellular Ca²⁺ increase through an amplification of the driving force for Ca²⁺ entry. Consequently, enhanced Ca²⁺ influx would in turn lengthen the hyperpolarization, operating as a positive feedback mechanism for fMLF-induced Ca²⁺ signaling.

The Blockage of KCa3.1 Channel Inhibited Proliferation, Migration and Promoted Apoptosis of Human Hepatocellular Carcinoma Cells

The intermediate conductance calcium-activated potassium channel KCa3.1 plays an important role in regulating cell proliferation and migration. However, the role of KCa3.1 channel in human hepatocellular carcinoma remained unknown. This study was therefore performed to investigate the effects of KCa3.1 potassium channel blocker on the proliferation, apoptosis and migration of human hepatocellular cancer cells HepG2. KCa3.1 mRNA and protein were detected in HepG2. Furthermore, KCa3.1 potassium channel blocker TRAM-34 was capable to inhibit the proliferation and induce the apoptosis of HepG2 cells, which can be partially attenuated by 1-EBIO, an activator of KCa3.1 channel. Moreover, the migration of HepG2 was obviously inhibited by TRAM-34. Consistently, knockdown of KCa3.1 channel using its siRNA was also able to induce apoptosis and suppress proliferation and migration of HepG2. Meanwhile, intracellular ROS level was found augmented in HepG2 treated with TRAM-34. More importantly, p53 protein was found translocation from the cytoplasm into the nuclei of HepG2. Collectively, inhibition of KCa3.1 channel suppressed the growth and migration, and promoted the apoptosis of human hepatocellular carcinoma cells by regulating intracellular ROS level and promoting p53 activation. This data suggests TRAM-34 as a promising anti-tumor drug for liver cancer.

K⁺-channel inhibition reduces portal perfusion pressure in fibrotic rats and fibrosis associated characteristics of hepatic stellate cells

BACKGROUND & AIMS

In liver fibrosis, activated hepatic stellate cells (HSC) secrete excess extracellular matrix, thus, represent key targets for antifibrotic treatment strategies. Intermediate-conductance Ca(2) (+) -activated K(+) -channels (KCa3.1) are expressed in non-excitable tissues affecting proliferation, migration and vascular resistance rendering KCa3.1 potential targets in liver fibrosis. So far, no information about KCa3.1 expression and their role in HSC exists. Aim was to quantify the KCa3.1 expression in HSC depending on HSC activation and investigation of antifibrotic properties of the specific KCa3.1 inhibitor TRAM-34 in vitro and in vivo.

METHODS

KCa3.1 expression and functionality were studied in TGF-β1-activated HSC by quantitative real time PCR, western-blot and patch-clamp analysis respectively. Effects of TRAM-34 on HSC proliferation, cell cycle and fibrosis-related gene expression were assessed by [(3) H]-thymidine incorporation, FACS-analysis and RT-PCR respectively. In vivo, vascular resistance and KCa3.1 gene and protein expression were determined in bile duct ligated rats by in situ liver perfusion, Taqman PCR and immunohistochemistry respectively.

RESULTS

Fibrotic tissues and TGF-β1-activated HSC exhibited higher KCa3.1-expressions than normal tissue and untreated cells. KCa3.1 inhibition with TRAM-34 reduced HSC proliferation by induction of cell cycle arrest and reduced TGF-β1-induced gene expression of collagen I, alpha-smooth muscle actin and TGF-β1 itself. Furthermore, TRAM-34 blocked TGF-β1-induced activation of TGF-β signalling in HSC. In vivo, TRAM-34 reduced the thromboxane agonist-induced portal perfusion pressure.

CONCLUSION

Inhibition of KCa3.1 with TRAM-34 downregulates fibrosis-associated gene expression in vitro, and reduces portal perfusion pressure in vivo. Thus, KCa3.1 may represent novel targets for the treatment of liver fibrosis.

Modulation of K(Ca)3.1 channels by eicosanoids, omega-3 fatty acids, and molecular determinants

BACKGROUND

Cytochrome P450- and ω-hydrolase products (epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraeonic acid (20-HETE)), natural omega-3 fatty acids (ω3), and pentacyclic triterpenes have been proposed to contribute to a wide range of vaso-protective and anti-fibrotic/anti-cancer signaling pathways including the modulation of membrane ion channels. Here we studied the modulation of intermediate-conductance Ca(2+)/calmodulin-regulated K(+) channels (K(Ca)3.1) by EETs, 20-HETE, ω3, and pentacyclic triterpenes and the structural requirements of these fatty acids to exert channel blockade.

METHODOLOGY/PRINCIPAL FINDINGS

We studied modulation of cloned human hK(Ca)3.1 and the mutant hK(Ca)3.1(V275A) in HEK-293 cells, of rK(Ca)3.1 in aortic endothelial cells, and of mK(Ca)3.1 in 3T3-fibroblasts by inside-out and whole-cell patch-clamp experiments, respectively. In inside-out patches, Ca(2+)-activated hK(Ca)3.1 were inhibited by the ω3, DHA and α-LA, and the ω6, AA, in the lower µmolar range and with similar potencies. 5,6-EET, 8,9-EET, 5,6-DiHETE, and saturated arachidic acid, had no appreciable effects. In contrast, 14,15-EET, its stable derivative, 14,15-EEZE, and 20-HETE produced channel inhibition. 11,12-EET displayed less inhibitory activity. The K(Ca)3.1(V275A) mutant channel was insensitive to any of the blocking EETs. Non-blocking 5,6-EET antagonized the inhibition caused by AA and augmented cloned hK(Ca)3.1 and rK(Ca)3.1 whole-cell currents. Pentacyclic triterpenes did not modulate K(Ca)3.1 currents.

CONCLUSIONS/SIGNIFICANCE

Inhibition of K(Ca)3.1 by EETs (14,15-EET), 20-HETE, and ω3 critically depended on the presence of electron double bonds and hydrophobicity within the 10 carbons preceding the carboxyl-head of the molecules. From the physiological perspective, metabolism of AA to non-blocking 5,6,- and 8,9-EET may cause AA-de-blockade and contribute to cellular signal transduction processes influenced by these fatty acids.

Immunosuppressive/anti-inflammatory cytokines directly and indirectly inhibit endothelial dysfunction--a novel mechanism for maintaining vascular function

Endothelial dysfunction is a pathological status of the vascular system, which can be broadly defined as an imbalance between endothelium-dependent vasoconstriction and vasodilation. Endothelial dysfunction is a key event in the progression of many pathological processes including atherosclerosis, type II diabetes and hypertension. Previous reports have demonstrated that pro-inflammatory/immunoeffector cytokines significantly promote endothelial dysfunction while numerous novel anti-inflammatory/immunosuppressive cytokines have recently been identified such as interleukin (IL)-35. However, the effects of anti-inflammatory cytokines on endothelial dysfunction have received much less attention. In this analytical review, we focus on the recent progress attained in characterizing the direct and indirect effects of anti-inflammatory/immunosuppressive cytokines in the inhibition of endothelial dysfunction. Our analyses are not only limited to the importance of endothelial dysfunction in cardiovascular disease progression, but also expand into the molecular mechanisms and pathways underlying the inhibition of endothelial dysfunction by anti-inflammatory/immunosuppressive cytokines. Our review suggests that anti-inflammatory/immunosuppressive cytokines serve as novel therapeutic targets for inhibiting endothelial dysfunction, vascular inflammation and cardio- and cerebro-vascular diseases.

Pulmonary hypertension in wild type mice and animals with genetic deficit in KCa2.3 and KCa3.1 channels

Objective

In vascular biology, endothelial K_Ca2.3 and K_Ca3.1 channels contribute to arterial blood pressure regulation by producing membrane hyperpolarization and smooth muscle relaxation. The role of K_Ca2.3 and K_Ca3.1 channels in the pulmonary circulation is not fully established. Using mice with genetically encoded deficit of K_Ca2.3 and K_Ca3.1 channels, this study investigated the effect of loss of the channels in hypoxia-induced pulmonary hypertension.

Approach and Result

Male wild type and K_Ca3.1^−/−/K_Ca2.3^T/T(+DOX) mice were exposed to chronic hypoxia for four weeks to induce pulmonary hypertension. The degree of pulmonary hypertension was evaluated by right ventricular pressure and assessment of right ventricular hypertrophy. Segments of pulmonary arteries were mounted in a wire myograph for functional studies and morphometric studies were performed on lung sections. Chronic hypoxia induced pulmonary hypertension, right ventricular hypertrophy, increased lung weight, and increased hematocrit levels in either genotype. The K_Ca3.1^−/−/K_Ca2.3^T/T(+DOX) mice developed structural alterations in the heart with increased right ventricular wall thickness as well as in pulmonary vessels with increased lumen size in partially- and fully-muscularized vessels and decreased wall area, not seen in wild type mice. Exposure to chronic hypoxia up-regulated the gene expression of the K_Ca2.3 channel by twofold in wild type mice and increased by 2.5-fold the relaxation evoked by the K_Ca2.3 and K_Ca3.1 channel activator NS309, whereas the acetylcholine-induced relaxation - sensitive to the combination of K_Ca2.3 and K_Ca3.1 channel blockers, apamin and charybdotoxin - was reduced by 2.5-fold in chronic hypoxic mice of either genotype.

Conclusion

Despite the deficits of the K_Ca2.3 and K_Ca3.1 channels failed to change hypoxia-induced pulmonary hypertension, the up-regulation of K_Ca2.3-gene expression and increased NS309-induced relaxation in wild-type mice point to a novel mechanism to counteract pulmonary hypertension and to a potential therapeutic utility of K_Ca2.3/K_Ca3.1 activators for the treatment of pulmonary hypertension.

Intermediate conductance Ca2+-activated K+ channels modulate human placental trophoblast syncytialization

Regulation of human placental syncytiotrophoblast renewal by cytotrophoblast migration, aggregation/fusion and differentiation is essential for successful pregnancy. In several tissues, these events are regulated by intermediate conductance Ca²⁺-activated K⁺ channels (IK_Ca), in part through their ability to regulate cell volume. We used cytotrophoblasts in primary culture to test the hypotheses that IK_Ca participate in the formation of multinucleated syncytiotrophoblast and in syncytiotrophoblast volume homeostasis. Cytotrophoblasts were isolated from normal term placentas and cultured for 66 h. This preparation recreates syncytiotrophoblast formation in vivo, as mononucleate cells (15 h) fuse into multinucleate syncytia (66 h) concomitant with elevated secretion of human chorionic gonadotropin (hCG). Cells were treated with the IK_Ca inhibitor TRAM-34 (10 µM) or activator DCEBIO (100 µM). Culture medium was collected to measure hCG secretion and cells fixed for immunofluorescence with anti-IK_Ca and anti-desmoplakin antibodies to assess IK_Ca expression and multinucleation respectively. K⁺ channel activity was assessed by measuring ⁸⁶Rb efflux at 66 h. IK_Ca immunostaining was evident in nucleus, cytoplasm and surface of mono- and multinucleate cells. DCEBIO increased ⁸⁶Rb efflux 8.3-fold above control and this was inhibited by TRAM-34 (85%; p<0.0001). Cytotrophoblast multinucleation increased 12-fold (p<0.05) and hCG secretion 20-fold (p<0.05), between 15 and 66 h. Compared to controls, DCEBIO reduced multinucleation by 42% (p<0.05) and hCG secretion by 80% (p<0.05). TRAM-34 alone did not affect cytotrophoblast multinucleation or hCG secretion. Hyposmotic solution increased ⁸⁶Rb efflux 3.8-fold (p<0.0001). This effect was dependent on extracellular Ca²⁺, inhibited by TRAM-34 and 100 nM charybdotoxin (85% (p<0.0001) and 43% respectively) but unaffected by 100 nM apamin. In conclusion, IK_Ca are expressed in cytotrophoblasts and their activation inhibits the formation of multinucleated cells in vitro. IK_Ca are stimulated by syncytiotrophoblast swelling implicating a role in syncytiotrophoblast volume homeostasis. Inappropriate activation of IK_Ca in pathophysiological conditions could compromise syncytiotrophoblast turnover and volume homeostasis in pregnancy disease.

The Ca²⁺-activated K⁺ channel KCa3.1 as a potential new target for the prevention of allograft vasculopathy

Allograft vasculopathy (AV) remains one of the major challenges to the long-term functioning of solid organ transplants. Although its exact pathogenesis remains unclear, AV is characterized by both fibromuscular proliferation and infiltration of CD4⁺ memory T cells. We here tested whether two experimental immunosuppressants targeting K⁺ channels might be useful for preventing AV. PAP-1 inhibits the voltage-gated Kv1.3 channel, which is overexpressed on CCR7⁻ memory T cells and we therefore hypothesize that it should suppress the memory T cell component of AV. Based on its previous efficacy in restenosis and kidney fibrosis we expected that the KCa3.1 blocker TRAM-34 would primarily affect smooth muscle and fibroblast proliferation and thus reduce intimal hyperplasia. Using immunohistochemistry we demonstrated the presence of Kv1.3 on infiltrating T cells and of KCa3.1 on lymphocytes as well as on proliferating neointimal smooth muscle cells in human vasculopathy samples and in a rat aorta transplant model developing chronic AV. Treatment of PVG rats receiving orthotopically transplanted aortas from ACI rats with TRAM-34 dose-dependently reduced aortic luminal occlusion, intimal hyperplasia, mononuclear cell infiltration and collagen deposition 120 days after transplantation. The Kv1.3 blocker PAP-1 in contrast did not reduce intima hyperplasia despite drastically reducing plasma IFN-γ levels and inhibiting lymphocyte infiltration. Our findings suggest that KCa3.1 channels play an important role in the pathogenesis of chronic AV and constitute an attractive target for the prevention of arteriopathy.

Protein kinase A and C regulate leak potassium currents in freshly isolated vascular myocytes from the aorta

We tested the hypothesis that protein kinase A (PKA) inhibits K2P currents activated by protein kinase C (PKC) in freshly isolated aortic myocytes. PDBu, the PKC agonist, applied extracellularly, increased the amplitude of the K2P currents in the presence of the “cocktail” of K⁺ channel blockers. Gö 6976 significantly reduced the increase of the K2P currents by PDBu suggesting the involvement of either α or β isoenzymes of PKC. We found that forskolin, or membrane permeable cAMP, did not inhibit K2P currents activated by the PKC. However, when PKA agonists were added prior to PDBu, they produced a strong decrease in the K2P current amplitudes activated by PKC. Inhibition of PDBu-elicited K2P currents by cAMP agonists was not prevented by the treatment of vascular smooth muscle cells with PKA antagonists (H-89 and Rp-cAMPs). Zn²⁺ and Hg²⁺ inhibited K2P currents in one population of cells, produced biphasic responses in another population, and increased the amplitude of the PDBu-elicited K⁺ currents in a third population of myocytes, suggesting expression of several K2P channel types. We found that cAMP agonists inhibited biphasic responses and increase of amplitude of the PDBu-elicited K2P currents produced by Zn²⁺ and Hg². 6-Bnz-cAMp produced a significantly altered pH sensitivity of PDBu-elicited K2P-currents, suggesting the inhibition of alkaline-activated K2P-currents. These results indicate that 6-Bnz-cAMP and other cAMP analogs may inhibit K2P currents through a PKA-independent mechanism. cAMP analogs may interact with unidentified proteins involved in K2P channel regulation. This novel cellular mechanism could provide insights into the interplay between PKC and PKA pathways that regulate vascular tone.

The intermediate conductance calcium-activated potassium channel KCa3.1 regulates vascular smooth muscle cell proliferation via controlling calcium-dependent signaling

The intermediate conductance calcium-activated potassium channel KCa3.1 contributes to a variety of cell activation processes in pathologies such as inflammation, carcinogenesis, and vascular remodeling. We examined the electrophysiological and transcriptional mechanisms by which KCa3.1 regulates vascular smooth muscle cell (VSMC) proliferation. Platelet-derived growth factor-BB (PDGF)-induced proliferation of human coronary artery VSMCs was attenuated by lowering intracellular Ca(2+) concentration ([Ca(2+)]i) and was enhanced by elevating [Ca(2+)]i. KCa3.1 blockade or knockdown inhibited proliferation by suppressing the rise in [Ca(2+)]i and attenuating the expression of phosphorylated cAMP-response element-binding protein (CREB), c-Fos, and neuron-derived orphan receptor-1 (NOR-1). This antiproliferative effect was abolished by elevating [Ca(2+)]i. KCa3.1 overexpression induced VSMC proliferation, and potentiated PDGF-induced proliferation, by inducing CREB phosphorylation, c-Fos, and NOR-1. Pharmacological stimulation of KCa3.1 unexpectedly suppressed proliferation by abolishing the expression and activity of KCa3.1 and PDGF β-receptors and inhibiting the rise in [Ca(2+)]i. The stimulation also attenuated the levels of phosphorylated CREB, c-Fos, and cyclin expression. After KCa3.1 blockade, the characteristic round shape of VSMCs expressing high l-caldesmon and low calponin-1 (dedifferentiation state) was maintained, whereas KCa3.1 stimulation induced a spindle-shaped cellular appearance, with low l-caldesmon and high calponin-1. In conclusion, KCa3.1 plays an important role in VSMC proliferation via controlling Ca(2+)-dependent signaling pathways, and its modulation may therefore constitute a new therapeutic target for cell proliferative diseases such as atherosclerosis.

SKCa Channels Blockage Increases the Expression of Adenosine A2A Receptor in Jurkat Human T Cells

Adenosine is a nucleoside displaying various biological effects via stimulation of four G-protein-coupled receptors, A1, A2A, A2B, and A3. Adenosine also modulates voltage-gated (Kv) and small conductance calcium-activated (SKCa) potassium channels. The effect of these potassium channels on the expression of adenosine receptors is poorly understood. We evaluated the action of BgK (a natural Kv channel blocker) and Lei-Dab7 (a synthetic SKCa channel blocker) on the expression of adenosine A2A receptors (A2AR) in Jurkat human T cells. We found that Lei-Dab7, but not BgK, increased the maximal binding value of the tritiated ligand ZM241385 to A2AR in a dose-dependent manner (+45% at 5 nM; +70% at 50 nM as compared to control). These results were further confirmed by Western blotting using a specific monoclonal antibody to human A2AR. The ligand affinity-related dissociation constant and A2AR mRNA amount were not significantly modified by either drug. We suggest that modulation of SKCa channels can influence membrane expression of A2AR and thus has a therapeutic potential.

Novel phenolic inhibitors of small/intermediate-conductance Ca²⁺-activated K⁺ channels, KCa3.1 and KCa2.3

Background

KCa3.1 channels are calcium/calmodulin-regulated voltage-independent K⁺ channels that produce membrane hyperpolarization and shape Ca²⁺-signaling and thereby physiological functions in epithelia, blood vessels, and white and red blood cells. Up-regulation of KCa3.1 is evident in fibrotic and inflamed tissues and some tumors rendering the channel a potential drug target. In the present study, we searched for novel potent small molecule inhibitors of KCa3.1 by testing a series of 20 selected natural and synthetic (poly)phenols, synthetic benzoic acids, and non-steroidal anti-inflammatory drugs (NSAIDs), with known cytoprotective, anti-inflammatory, and/or cytostatic activities.

Methodology/Principal Findings

In electrophysiological experiments, we identified the natural phenols, caffeic acid (EC50 1.3 µM) and resveratrol (EC50 10 µM) as KCa3.1 inhibitors with moderate potency. The phenols, vanillic acid, gallic acid, and hydroxytyrosol had weak or no blocking effects. Out of the NSAIDs, flufenamic acid was moderately potent (EC50 1.6 µM), followed by mesalamine (EC50≥10 µM). The synthetic fluoro-trivanillic ester, 13b ([3,5-bis[(3-fluoro-4-hydroxy-benzoyl)oxymethyl]phenyl]methyl 3-fluoro-4-hydroxy-benzoate), was identified as a potent mixed KCa2/3 channel inhibitor with an EC50 of 19 nM for KCa3.1 and 360 pM for KCa2.3, which affected KCa1.1 and Kv channels only at micromolar concentrations. The KCa3.1/KCa2-activator SKA-31 antagonized the 13b-blockade. In proliferation assays, 13b was not cytotoxic and reduced proliferation of 3T3 fibroblasts as well as caffeic acid. In isometric vessel myography, 13b increased contractions of porcine coronary arteries to serotonin and antagonized endothelium-derived hyperpolarization-mediated vasorelaxation to pharmacological KCa3.1/KCa2.3 activation.

Conclusions/Significance

We identified the natural phenols, caffeic acid and resveratrol, the NSAID, flufenamic acid, and the polyphenol 13b as novel KCa3.1 inhibitors. The high potency of 13b with pan-activity on KCa3.1/KCa2 channels makes 13b a new pharmacological tool to manipulate inflammation and cancer growth through KCa3.1/KCa2 blockade and a promising template for new drug design.

Blockade of the intermediate-conductance Ca(2+)-activated K+ channel inhibits the angiogenesis induced by epidermal growth factor in the treatment of corneal alkali burn

Epidermal growth factor (EGF) is used to treat alkali-burned corneas. However, EGF-induced corneal angiogenesis, which is currently untreatable, is a side effect of this therapy. We therefore explored the role of the intermediate-conductance Ca(2+)-activated K(+) channel (KCa3.1) in EGF-induced angiogenesis and tested whether KCa3.1 blockade can suppress EGF-induced corneal angiogenesis. The proliferation, migration and tube formation of HUVECs (human umbilical vein endothelial cells) in response to EGF, the MEK inhibitor PD98059 and the KCa3.1 inhibitor TRAM-34 were analyzed in vitro via MTT, cell counting, scratch and tube formation assays. The protein and mRNA levels of KCa3.1, phosphorylated-ERK (P-ERK), total-ERK (T-ERK), cyclin-dependent kinase 4 (CDK4), vimentin and MMP-2 were assessed via western blotting and RT-PCR. KCa3.1 and vimentin expression were also detected through immunofluorescence staining. Flow cytometry was performed to examine the cell cycle. Further, an in vivo murine alkali-burned cornea model was developed and treated with EGF and TRAM-34 eye drops to analyze the effect of these treatments on corneal healing and angiogenesis. The corneas were also analyzed by histological staining. The in vitro results showed that EGF induces the upregulation of KCa3.1 and P-ERK in HUVECs and that this upregulation is suppressed by PD98059. EGF stimulates proliferation, migration and tube formation in HUVECs, and this effect can be suppressed by TRAM-34. TRAM-34 also arrests HUVECs in the G1 phase of the cell cycle and downregulates CDK4, vimentin and MMP-2 in these cells. The in vivo results indicated that TRAM-34 suppresses EGF-induced corneal angiogenesis without affecting EGF-induced corneal wound healing. In summary, the upregulation of KCa3.1 may be crucial for EGF-induced angiogenesis through the MAPK/ERK signaling pathway. Thus, KCa3.1 may be a potential target for the treatment of EGF-induced corneal angiogenesis.

Characterisation of K+ channels in human fetoplacental vascular smooth muscle cells

Adequate blood flow through placental chorionic plate resistance arteries (CPAs) is necessary for oxygen and nutrient transfer to the fetus and a successful pregnancy. In non-placental vascular smooth muscle cells (SMCs), K(+) channels regulate contraction, vascular tone and blood flow. Previous studies showed that K(+) channel modulators alter CPA tone, but did not distinguish between effects on K(+) channels in endothelial cells and SMCs. In this study, we developed a preparation of freshly isolated CPASMCs of normal pregnancy and investigated K(+) channel expression and function. CPASMCs were isolated from normal human term placentas using enzymatic digestion. Purity and phenotype was confirmed with immunocytochemistry. Whole-cell patch clamp was used to assess K(+) channel currents, and mRNA and protein expression was determined in intact CPAs and isolated SMCs with RT-PCR and immunostaining. Isolated SMCs expressed α-actin but not CD31, a marker of endothelial cells. CPASMCs and intact CPAs expressed h-caldesmon and non-muscle myosin heavy chain-2; phenotypic markers of contractile and synthetic SMCs respectively. Whole-cell currents were inhibited by 4-AP, TEA, charybdotoxin and iberiotoxin implicating functional K(v) and BK(Ca) channels. 1-EBIO enhanced whole cell currents which were abolished by TRAM-34 and reduced by apamin indicating activation of IK(Ca) and SK(Ca) respectively. BK(Ca), IK(Ca) and SK(Ca)3 mRNA and/or protein were expressed in CPASMCs and intact CPAs. This study provides the first direct evidence for functional K(v), BK(Ca,) IK(Ca) and SK(Ca) channels in CPASMCs. These cells display a mixed phenotype implicating a dual role for CPASMCs in controlling both fetoplacental vascular resistance and vasculogenesis.

Role of gap junction involved with endothelium-derived hyperpolarizing factor for the quercetin-induced vasodilatation in rat mesenteric artery

AIMS

Modulation of vasodilating actions by quercetin, a kind of flavonoid, was investigated using rat mesenteric arterial ring strips.

MAIN METHODS

Ring strips (1mm) of rat mesenteric artery were used. The specimens were kept at 36.5 °C in Krebs-Henseleit solution oxygenated with 95% O(2) and 5% CO(2).

KEY FINDINGS

Quercetin (0.1 to 100 μM) dilated the contraction induced by norepinephrine (1 μM) in a concentration-dependent manner. The quercetin-induced vasodilatation was almost resistant to both 100 μM L-N(G)-nitro arginine methyl ester (L-NAME) and 100 μM indomethacin. At 1mM tetraethylammonium (a KCa channel inhibitor) decreased the quercetin-induced vasodilatation, which was resistant to L-NAME and indomethacin, but not significantly. L-NAME- and indomethacin-resistant quercetin-induced vasodilatation was significantly attenuated by 100 μM 18α- and 50 μM 18β-glycyrrhetinic acids (gap junction inhibitors). Endothelium removal as well significantly attenuated the vasodilatation to the same extent.

SIGNIFICANCE

These results indicate that quercetin dilates the mesenteric artery via endothelium-dependent mechanisms, and the dilatation is mainly mediated by gap junctions closely involved with endothelium-derived hyperpolarizing factor (EDHF).

KCa3.1 channels mediate the increase of cell migration and proliferation by advanced glycation endproducts in cultured rat vascular smooth muscle cells

The mechanisms underlying the involvement of advanced glycation endproducts (AGEs) in diabetic atherosclerosis are not fully understood. The present study was designed to investigate whether intermediate-conductance Ca(2+)-activated K(+) channels (K(Ca)3.1 channels) are involved in migration and proliferation induced by AGEs in cultured rat vascular smooth muscle cells (VSMCs) using approaches of whole-cell patch voltage-clamp, cell proliferation and migration assay, and western blot analysis. It was found that the current density and protein level of K(Ca)3.1 channels were enhanced in cells incubated with AGE-BSA (bovine serum albumin), and the effects were reversed by co-incubation of AGE-BSA with anti-RAGE (anti-receptors of AGEs) antibody. The ERK1/2 inhibitors PD98059 and U0126, the P38-MAPK inhibitors SB203580 and SB202190, or the PI3K inhibitors LY294002 and wortmannin countered the K(Ca)3.1 channel expression by AGE-BSA. In addition, AGE-BAS increased cell migration and proliferation, and the effects were fully reversed with anti-RAGE antibody, the K(Ca)3.1 channel blocker TRAM-34, or K(Ca)3.1 small interfering RNA. These results demonstrate for the first time that AGEs-induced increase of migration and proliferation is related to the upregulation of K(Ca)3.1 channels in rat VMSCs, and the intracellular signals ERK1/2, P38-MAPK and PI3K are involved in the regulation of K(Ca)3.1 channel expression.

SKA-31, a novel activator of SK(Ca) and IK(Ca) channels, increases coronary flow in male and female rat hearts

AIMS

Endothelial SK(Ca) and IK(Ca) channels play an important role in the regulation of vascular function and systemic blood pressure. Based on our previous findings that small molecule activators of SK(Ca) and IK(Ca) channels (i.e. NS309 and SKA-31) can inhibit myogenic tone in isolated resistance arteries, we hypothesized that this class of compounds may induce effective vasodilation in an intact vascular bed, such as the coronary circulation.

METHODS AND RESULTS

In a Langendorff-perfused, beating rat heart preparation, acute bolus administrations of SKA-31 (0.01-5 µg) dose-dependently increased total coronary flow (25-30%) in both male and female hearts; these responses were associated with modest, secondary increases in left ventricular (LV) systolic pressure and heart rate. SKA-31 evoked responses in coronary flow, LV pressure, and heart rate were qualitatively comparable to acute responses evoked by bradykinin (1 µg) and adenosine (10 µg). In the presence of apamin and TRAM-34, selective blockers of SK(Ca) and IK(Ca) channels, respectively, SKA-31 and bradykinin-induced responses were largely inhibited, whereas the adenosine-induced changes were blocked by ∼40%; TRAM-34 alone produced less inhibition. Sodium nitroprusside (SNP, 0.2 μg bolus dose) evoked changes in coronary flow, LV pressure, and heart rate were similar to those induced by SKA-31, but were unaffected by apamin + TRAM-34. The NOS inhibitor L-NNA reduced bradykinin- and adenosine-evoked changes, but did not affect responses to either SKA-31 or SNP.

CONCLUSION

Our study demonstrates that SKA-31 can rapidly and reversibly induce dilation of the coronary circulation in intact functioning hearts under basal flow and contractility conditions.

Airway smooth muscle STIM1 and Orai1 are upregulated in asthmatic mice and mediate PDGF-activated SOCE, CRAC currents, proliferation, and migration

Airway smooth muscle cell (ASMC) remodeling contributes to the structural changes in the airways that are central to the clinical manifestations of asthma. Ca(2+) signals play an important role in ASMC remodeling through control of ASMC migration and hypertrophy/proliferation. Upregulation of STIM1 and Orai1 proteins, the molecular components of the store-operated Ca(2+) entry (SOCE) pathway, has recently emerged as an important mediator of vascular remodeling. However, the potential upregulation of STIM1 and Orai1 in asthmatic airways remains unknown. An important smooth muscle migratory agonist with major contributions to ASMC remodeling is the platelet-derived growth factor (PDGF). Nevertheless, the Ca(2+) entry route activated by PDGF in ASMC remains elusive. Here, we show that STIM1 and Orai1 protein levels are greatly upregulated in ASMC isolated from ovalbumin-challenged asthmatic mice, compared to control mice. Furthermore, we show that PDGF activates a Ca(2+) entry pathway in rat primary ASMC that is pharmacologically reminiscent of SOCE. Molecular knockdown of STIM1 and Orai1 proteins inhibited PDGF-activated Ca(2+) entry in these cells. Whole-cell patch clamp recordings revealed the activation of Ca(2+) release-activated Ca(2+) (CRAC) current by PDGF in ASMC. These CRAC currents were abrogated upon either STIM1 or Orai1 knockdown. We show that either STIM1 or Orai1 knockdown significantly inhibited ASMC proliferation and chemotactic migration in response to PDGF. These results implicate STIM1 and Orai1 in PDGF-induced ASMC proliferation and migration and suggest the potential use of STIM1 and Orai1 as targets for ASMC remodeling during asthma.

The Ca(v)3.1 T-type calcium channel is required for neointimal formation in response to vascular injury in mice

AIMS

Restenosis is an undesirable consequence following percutaneous vascular interventions. However, the current strategy for preventing restenosis is inadequate. The aim of this study was to investigate the role of low-voltage gated T-type calcium channels in regulating vascular smooth muscle cell (VSMC) proliferation during neointimal formation.

METHODS AND RESULTS

Wire injury of mice carotid arteries resulted in neointimal formation in the wild-type and Ca(v)3.2(-/-) but not Ca(v)3.1(-/-) mice, indicating a critical role of Ca(v)3.1 in neointimal formation. In addition, we found a significant increase of Ca(v)3.1 mRNA and protein in injured arteries. Ca(v)3.1 knockout or knockdown (shCa(v)3.1) reduced VSMC proliferation. Since T-channels are expressed predominantly in the G(1) and S phases in VSMCs, we examined whether an abnormal G(1)/S transition was the cause of the reduced cell proliferation in shCa(v)3.1 VSMCs. We found a disrupted expression of cyclin E in shCa(v)3.1 VSMCs, and calmodulin agonist CALP1 partially rescued the defective cell proliferation. Furthermore, we demonstrated that infusion of NNC55-0396, a selective T-channel blocker, inhibited neointimal formation in wild-type mice.

CONCLUSION

Ca(v)3.1 is required for VSMC proliferation during neointimal formation, and blocking of Ca(v)3.1 may be beneficial for preventing restenosis.

Calcium-activated potassium channels in vasculature in response to ischemia-reperfusion

Based on the genetic relationship, single-channel conductance, and gating mechanisms, calcium-activated potassium (KCa) channels identified in vasculature can be divided into 3 groups including large-conductance KCa, small, and intermediate conductance KCa. KCa channels in smooth muscle and endothelial cells are essential for the regulation of vascular tone. Vascular dysfunction under ischemia-reperfusion (I-R) or hypoxia-reoxygenation (H-R) conditions is associated with modulations of KCa channels that are attributable to multiple mechanisms. Most studies in this regard relied on the change of relaxation components sensitive to certain channel blockers to indicate the alteration of KCa channels under I-R conditions, which however provided conflicting results for the effect of I-R. The possible mechanisms involved in KCa channel modulation under I-R/H-R include overproduction of reactive oxygen species such as superoxide anion, hydrogen peroxide, and peroxynitrite, increase of intracellular H ion, and lactate accumulation, etc. However, more studies are necessary to further understand the discrepancies in the sensitivity of KCa channels to I-R injury in different vascular beds.