The Ca2+-activated K+ channel of intermediate conductance:a possible target for immune suppression

Access to chiral dihydrophenanthridines via a palladium(0)-catalyzed Suzuki coupling and C-H arylation cascade reaction using new chiral-bridged biphenyl bifunctional ligands

A class of chiral-bridged biphenyl phosphine-carboxylate bifunctional ligands CB-Phos has been developed and successfully applied to Pd(0)-catalyzed single enantioselective C-H arylation and a one pot cascade reaction involving Suzuki cross-coupling and C-H arylation. The catalytic system provides a new and convenient way for the synthesis of versatile chiral dihydrophenanthridines with rich structures and broad functional group tolerance. Good to excellent yields with high enantioselectivities were generally achieved. The reaction mechanism of the cascade reaction was also preliminarily discussed.

Efficacy of combined tumor irradiation and KCa3.1-targeting with TRAM-34 in a syngeneic glioma mouse model

The intermediate-conductance calcium-activated potassium channel KCa3.1 has been proposed to be a new potential target for glioblastoma treatment. This study analyzed the effect of combined irradiation and KCa3.1-targeting with TRAM-34 in the syngeneic, immune-competent orthotopic SMA-560/VM/Dk glioma mouse model. Whereas neither irradiation nor TRAM-34 treatment alone meaningfully prolonged the survival of the animals, the combination significantly prolonged the survival of the mice. We found an irradiation-induced hyperinvasion of glioma cells into the brain, which was inhibited by concomitant TRAM-34 treatment. Interestingly, TRAM-34 did neither radiosensitize nor impair SMA-560's intrinsic migratory capacities in vitro. Exploratory findings hint at increased TGF-β1 signaling after irradiation. On top, we found a marginal upregulation of MMP9 mRNA, which was inhibited by TRAM-34. Last, infiltration of CD3+, CD8+ or FoxP3+ T cells was not impacted by either irradiation or KCa3.1 targeting and we found no evidence of adverse events of the combined treatment. We conclude that concomitant irradiation and TRAM-34 treatment is efficacious in this preclinical glioma model.

Stereochemistry of N-Acyl-5H-dibenzo[b,d]azepin-7(6H)-ones

The stereochemical properties of N-acyl-5H-dibenzo[b,d]azepin-7(6H)-ones (2a-c), which inhibit potassium channels in T cells, were examined by freezing their conformational change due to 4-methyl substitution. N-Acyl-5H-dibenzo[b,d]azepin-7(6H)-ones exist as pairs of enantiomers [(a¹R, a²R), (a¹S, a²S)], and each atropisomer is separable at room temperature. An alternate procedure for preparing 5H-dibenzo[b,d]azepin-7(6H)-ones involves the intramolecular Friedel-Crafts cyclization of N-benzyloxycarbonylated biaryl amino acids. Consequently, the N-benzyloxy group was removed during the cyclization reaction to produce 5H-dibenzo[b,d]azepin-7(6H)-ones suitable for the subsequent N-acylation reaction.

Role of organellar Ca2+-activated K+ channels in disease development

The organellar Ca2+-activated K+ channels share a similar ability to transfer the alteration of Ca2+ concentration to membrane conductance of potassium. Multiple effects of Ca2+-activated K+ channels on cell metabolism and complex signaling pathways during organ development have been explored. The organellar Ca2+-activated K+ channels are able to control the ionic equilibrium and are always associated with oxidative stress in different organelles and the whole cells. Some drugs targeting Ca2+-activated K+ channels have been tested for various diseases in clinical trials. In this review, the known roles of organellar Ca2+-activated K+ channels were described, and their effects on different diseases, particularly on diabetes, cardiovascular diseases, and neurological diseases were discussed. It was attempted to summarize the currently known operational modes with the involvement of organellar Ca2+-activated K+ channels. This review may assist scholars to more comprehensively understand organellar Ca2+-activated K+ channels and related diseases.

Regulatory role of KCa3.1 in immune cell function and its emerging association with rheumatoid arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease characterized by chronic inflammation. Immune dysfunction is an essential mechanism in the pathogenesis of RA and directly linked to synovial inflammation and cartilage/bone destruction. Intermediate conductance Ca²⁺-activated K⁺ channel (KCa3.1) is considered a significant regulator of proliferation, differentiation, and migration of immune cells by mediating Ca²⁺ signal transduction. Earlier studies have demonstrated abnormal activation of KCa3.1 in the peripheral blood and articular synovium of RA patients. Moreover, knockout of KCa3.1 reduced the severity of synovial inflammation and cartilage damage to a significant extent in a mouse collagen antibody-induced arthritis (CAIA) model. Accumulating evidence implicates KCa3.1 as a potential therapeutic target for RA. Here, we provide an overview of the KCa3.1 channel and its pharmacological properties, discuss the significance of KCa3.1 in immune cells and feasibility as a drug target for modulating the immune balance, and highlight its emerging role in pathological progression of RA.

Bibliometrics analysis on the research status and trends of adult-onset Still’s disease: 1921-2021

Objectives

The aim of this research is to discuss the research status, hotspots, frontiers and development trends in the field of adult-onset Still’s disease (AOSD) based on bibliometrics and visual analysis by CiteSpace software.

Methods

The relevant research articles on AOSD from 1921 to 2021 were retrieved from the Scopus database. CiteSpace software was used to form a visual knowledge map and conduct analysis for the countries/regions, journals, authors, keywords, clusters, research hotspots and frontiers of the included articles.

Results

There were 2,373 articles included, and the number of articles published during 1921-2021 is increasing. The country with the highest number of articles published was Japan (355, 14.96%), followed by the United States (329, 13.86%) and France (215, 9.06%). The author with the highest number of publications is Ansell, Barbara M. (30, 1.26%), and the author with the highest co-citation frequency is Yamaguchi, Masaya (703). Clinical Rheumatology is the journal with the highest publication frequency. The top five cluster groups were “joint”, “differential diagnosis”, “prednisolone”, “methotrexate” and “macrophage activation syndrome”. The diagnosis, treatment and pathogenesis of AOSD form the main research fields, and prognosis and complications are the research hotspots and trends.

Conclusions

The global research field in AOSD has expanded in the past 100 years. The complications and new pathogenesis of AOSD are hotspots in this field and need further study in the future.

Explanation of Structure and Function of kv1.3 Potent Blocker From Mesobuthus eupeus Venom Gland: A New Promise in Drug Development

Background: Scorpions and other venomous animals are sought with great concern because venom is a source of novel peptides with exciting features. Some toxins of scorpion venom are effectors of potassium channels. Previous studies strongly support the importance of potassium channel toxins for use as pharmacological tools or potential drugs. Objectives: Here, a three-dimensional (3-D) structure and function of a potent acidic blocker of the human voltage-gated potassium ion channel, Kv1.3, previously identified in the scorpion Mesobuthus eupeus venom gland, were interpreted. Methods: The 3-D structure of meuK2-2 was generated using homology modeling. The interaction of meuK2-2 with the Kv1.3 channel was evaluated using a computational protocol employing peptide-protein docking experiments, pose clustering, and 100 ns molecular dynamic simulations to make the 3-D models of the meuK2-2/Kv1.3 complex trustworthy. Results: A CSα/β (cysteine-stabilized α-helical and β-sheet) fold was found for the 3-D structure of meuK2-2. In a different mechanism from what was identified so far, meuK2-2 binds to both turret and pore loop of Kv1.3 through two key residues (Ala28 and Ser11) and H-bonds. The binding of meuK2-2 induces some conformational changes to Kv1.3. Eventually, the side chain of a positively charged amino acid (His9) occupies the channel's pore. All together blocks the ion permeation pathway. Conclusions: MeuK2-2 could block Kv1.3 by a new mechanism. So, it could be a unique target for further investigations to develop a pharmacological tool and potential drug.

Atropisomeric Properties of N-Acyl/N-Sulfonyl 5H-Dibenzo[b,d]azepin-7(6H)-ones

The stereochemistry of N-acyl/N-sulfonyl 5H-dibenzo[b,d]azepin-7(6H)-ones (I, II) was examined in detail by freezing the conformation with a methyl group at the C-4 of dibenzoazepine. Because the two axes (axis 1, axis 2) move together concertedly, I and II exist only as a pair of enantiomers [(a¹R, a²R) and (a¹S, a²S)], which was confirmed by X-ray analysis of IIBc. It was elucidated that the amide derivatives I exist in equilibrium with the E/Z-amide (100:2–100:34), which means that the exocyclic bond (axis 3) is not in concert with the endocyclic axes (axis 1, axis 2). For the preparation of 5H-dibenzo[b,d]azepin-7(6H)-one, the intramolecular Friedel–Crafts acylation of N-(1,1′)-biphenyl-2-yl-glycine derivatives was revisited. It was revealed that the electron-withdrawing property of the amino-protective group was a key to the success of seven-membered cyclization.

Role of potassium channels in female reproductive system

Potassium channels are widely expressed in most types of cells in living organisms and regulate the functions of a variety of organs, including kidneys, neurons, cardiovascular organs, and pancreas among others. However, the functional roles of potassium channels in the reproductive system is less understood. This mini-review provides information about the localization and functions of potassium channels in the female reproductive system. Five types of potassium channels, which include inward-rectifying (Kir), voltage-gated (Kv), calcium-activated (K_Ca), 2-pore domain (K_2P), and rapidly-gating sodium-activated (Slo) potassium channels are expressed in the hypothalamus, ovaries, and uterus. Their functions include the regulation of hormone release and feedback by Kir6.1 and Kir6.2, which are expressed in the luteal granulosa cells and gonadotropin-releasing hormone neurons respectively, and regulate the functioning of the hypothalamus–pituitary–ovarian axis and the production of progesterone. Both channels are regulated by subtypes of the sulfonylurea receptor (SUR), Kir6.1/SUR2B and Kir6.2/SUR1. K_v and Slo2.1 affect the transition from uterine quiescence in late pregnancy to the state of strong myometrial contractions in labor. Intermediate- and small-conductance K_Ca modulate the vasodilatation of the placental chorionic plate resistance arteries via the secretion of nitric oxide and endothelium-derived hyperpolarizing factors. Treatment with specific channel activators and inhibitors provides information relevant for clinical use that could help alter the functions of the female reproductive system.

Kv1.3 Channel as a Key Therapeutic Target for Neuroinflammatory Diseases: State of the Art and Beyond

It remains a challenge for the effective treatment of neuroinflammatory disease, including multiple sclerosis (MS), stroke, epilepsy, and Alzheimer’s and Parkinson’s disease. The voltage-gated potassium Kv1.3 channel is of interest, which is considered as a novel therapeutic target for treating neuroinflammatory disorders due to its crucial role in subsets of T lymphocytes as well as microglial cells. Toxic animals, such as sea anemones, scorpions, spiders, snakes, and cone snails, can produce a variety of toxins that act on the Kv1.3 channel. The Stichodactyla helianthus K⁺ channel blocking toxin (ShK) from the sea anemone S. helianthus is proved as a classical blocker of Kv1.3. One of the synthetic analogs ShK-186, being developed as a therapeutic for autoimmune diseases, has successfully completed first-in-man Phase 1 trials. In addition to addressing the recent progress on the studies underlying the pharmacological characterizations of ShK on MS, the review will also explore the possibility for clinical treatment of ShK-like Kv1.3 blocking polypeptides on other neuroinflammatory diseases.

Cancer-Associated Intermediate Conductance Ca2+-Activated K⁺ Channel KCa3.1

Several tumor entities have been reported to overexpress K_Ca3.1 potassium channels due to epigenetic, transcriptional, or post-translational modifications. By modulating membrane potential, cell volume, or Ca²⁺ signaling, K_Ca3.1 has been proposed to exert pivotal oncogenic functions in tumorigenesis, malignant progression, metastasis, and therapy resistance. Moreover, K_Ca3.1 is expressed by tumor-promoting stroma cells such as fibroblasts and the tumor vasculature suggesting a role of K_Ca3.1 in the adaptation of the tumor microenvironment. Combined, this features K_Ca3.1 as a candidate target for innovative anti-cancer therapy. However, immune cells also express K_Ca3.1 thereby contributing to T cell activation. Thus, any strategy targeting K_Ca3.1 in anti-cancer therapy may also modulate anti-tumor immune activity and/or immunosuppression. The present review article highlights the potential of K_Ca3.1 as an anti-tumor target providing an overview of the current knowledge on its function in tumor pathogenesis with emphasis on vasculo- and angiogenesis as well as anti-cancer immune responses.

'Gardos Channelopathy': a variant of hereditary Stomatocytosis with complex molecular regulation

The Gardos channel is a Ca²⁺ sensitive, K⁺ selective channel present in several tissues including RBCs, where it is involved in cell volume regulation. Recently, mutations at two different aminoacid residues in KCNN4 have been reported in patients with hereditary xerocytosis. We identified by whole exome sequencing a new family with two members affected by chronic hemolytic anemia carrying mutation R352H in the KCNN4 gene. No additional mutations in genes encoding for RBCs cytoskeletal, membrane or channel proteins were detected. We performed functional studies on patients’ RBCs to evaluate the effects of R352H mutation on the cellular properties and eventually on the clinical phenotype. Gardos channel hyperactivation was demonstrated in circulating erythrocytes and erythroblasts differentiated ex-vivo from peripheral CD34+ cells. Pathological alterations in the function of multiple ion transport systems were observed, suggesting the presence of compensatory effects ultimately preventing cellular dehydration in patient’s RBCs; moreover, flow cytometry and confocal fluorescence live-cell imaging showed Ca²⁺ overload in the RBCs of both patients and hypersensitivity of Ca²⁺ uptake by RBCs to swelling. Altogether these findings suggest that the ‘Gardos channelopathy’ is a complex pathology, to some extent different from the common hereditary xerocytosis.

Role of epithelial ion transports in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder with a complex pathogenesis. Diarrhea is a highly prevalent and often debilitating symptom of IBD patients that results, at least in part, from an intestinal hydroelectrolytic imbalance. Evidence suggests that reduced electrolyte absorption is more relevant than increased secretion to this disequilibrium. This systematic review analyses and integrates the current evidence on the roles of epithelial Na(+)-K(+)-ATPase (NKA), Na(+)/H(+) exchangers (NHEs), epithelial Na(+) channels (ENaC), and K(+) channels (KC) in IBD-associated diarrhea. NKA is the key driving force of the transepithelial ionic transport and its activity is decreased in IBD. In addition, the downregulation of apical NHE and ENaC and the upregulation of apical large-conductance KC all contribute to the IBD-associated diarrhea by lowering sodium absorption and/or increasing potassium secretion.

PKA reduces the rat and human KCa3.1 current, CaM binding, and Ca2+ signaling, which requires Ser332/334 in the CaM-binding C terminus

The Ca(2+)-dependent K(+) channel, KCa3.1 (KCNN4/IK/SK4), is widely expressed and contributes to cell functions that include volume regulation, migration, membrane potential, and excitability. KCa3.1 is now considered a therapeutic target for several diseases, including CNS disorders involving microglial activation; thus, we need to understand how KCa3.1 function is regulated. KCa3.1 gating and trafficking require calmodulin binding to the two ends of the CaM-binding domain (CaMBD), which also contains three conserved sites for Ser/Thr kinases. Although cAMP protein kinase (PKA) signaling is important in many cells that use KCa3.1, reports of channel regulation by PKA are inconsistent. We first compared regulation by PKA of native rat KCa3.1 channels in microglia (and the microglia cell line, MLS-9) with human KCa3.1 expressed in HEK293 cells. In all three cells, PKA activation with Sp-8-Br-cAMPS decreased the current, and this was prevented by the PKA inhibitor, PKI14-22. Inhibiting PKA with Rp-8-Br-cAMPS increased the current in microglia. Mutating the single PKA site (S334A) in human KCa3.1 abolished the PKA-dependent regulation. CaM-affinity chromatography showed that CaM binding to KCa3.1 was decreased by PKA-dependent phosphorylation of S334, and this regulation was absent in the S334A mutant. Single-channel analysis showed that PKA decreased the open probability in wild-type but not S334A mutant channels. The same decrease in current for native and wild-type expressed KCa3.1 channels (but not S334A) occurred when PKA was activated through the adenosine A2a receptor. Finally, by decreasing the KCa3.1 current, PKA activation reduced Ca(2+)-release-activated Ca(2+) entry following activation of metabotropic purinergic receptors in microglia.

Targeting the Small- and Intermediate-Conductance Ca-Activated Potassium Channels: The Drug-Binding Pocket at the Channel/Calmodulin Interface

The small- and intermediate-conductance Ca(2+)-activated potassium (SK/IK) channels play important roles in the regulation of excitable cells in both the central nervous and cardiovascular systems. Evidence from animal models has implicated SK/IK channels in neurological conditions such as ataxia and alcohol use disorders. Further, genome-wide association studies have suggested that cardiovascular abnormalities such as arrhythmias and hypertension are associated with single nucleotide polymorphisms that occur within the genes encoding the SK/IK channels. The Ca(2+) sensitivity of the SK/IK channels stems from a constitutively bound Ca(2+)-binding protein: calmodulin. Small-molecule positive modulators of SK/IK channels have been developed over the past decade, and recent structural studies have revealed that the binding pocket of these positive modulators is located at the interface between the channel and calmodulin. SK/IK channel positive modulators can potentiate channel activity by enhancing the coupling between Ca(2+) sensing via calmodulin and mechanical opening of the channel. Here, we review binding pocket studies that have provided structural insight into the mechanism of action for SK/IK channel positive modulators. These studies lay the foundation for structure-based drug discovery efforts that can identify novel SK/IK channel positive modulators.

Effects of clotrimazol on the acute necrotizing pancreatitis in rats

This study aims to investigate the influence of clotrimazol (CLTZ) on acute necrotizing pancreatitis (ANP) induced by glycodeoxycholic acid in rats. Rats were divided into five groups as sham + saline, sham + CLTZ, sham + polyethylene glycol, ANP + saline, and ANP + CLTZ. ANP in rats was induced by glycodeoxycholic acid. The extent of acinar cell injury, mortality, systemic cardiorespiratory variables, functional capillary density (FCD), renal/hepatic functions, and changes in some enzyme markers for pancreatic and lung tissue were investigated during ANP in rats. The use of CLTZ after the induction of ANP resulted in a significant decrease in the mortality rate, pancreatic necrosis, and serum activity of amylase, alanine aminotransferase, interleukin-6, lactate dehydrogenase in bronchoalveolar lavage fluid, serum concentration of urea, and tissue activity of myeloperoxidase, and malondialdehyde in the pancreas and lung and a significant increase in concentrations of calcium, blood pressure, urine output, pO2, and FCD. This study showed that CLTZ demonstrated beneficial effect on the course of ANP in rats. Therefore, it may be used in the treatment of acute pancreatitis.

The potassium channel KCa3.1 as new therapeutic target for the prevention of obliterative airway disease

BACKGROUND

The calcium-activated potassium channel KCa3.1 is critically involved in T-cell activation as well as in the proliferation of smooth muscle cells and fibroblasts. We sought to investigate whether KCa3.1 contributes to the pathogenesis of obliterative airway disease (OAD) and whether knockout or pharmacologic blockade would prevent the development of OAD.

METHODS

Tracheas from CBA donors were heterotopically transplanted into the omentum of C57Bl/6J wild-type or KCa3.1 mice. C57Bl/6J recipients were either left untreated or received the KCa3.1 blocker TRAM-34 (120 mg/kg/day). Histopathology and immunologic assays were performed on postoperative day 5 or 28.

RESULTS

Subepithelial T-cell and macrophage infiltration on postoperative day 5, as seen in untreated allografts, was significantly reduced in the KCa3.1 and TRAM-34 groups. Also, systemic Th1 activation was significantly and Th2 mildly reduced by KCa3.1 knockout or blockade. After 28 days, luminal obliteration of tracheal allografts was reduced from 89%±21% in untreated recipients to 53%±26% (P=0.010) and 59%±33% (P=0.032) in KCa3.1 and TRAM-34-treated animals, respectively. The airway epithelium was mostly preserved in syngeneic grafts, mostly destroyed in the KCa3.1 and TRAM-34 groups, and absent in untreated allografts. Allografts triggered an antibody response in untreated recipients, which was significantly reduced in KCa3.1 animals. KCa3.1 was detected in T cells, airway epithelial cells, and myofibroblasts. TRAM-34 dose-dependently suppressed proliferation of wild-type C57B/6J splenocytes but did not show any effect on KCa3.1 splenocytes.

CONCLUSIONS

Our findings suggest that KCa3.1 channels are involved in the pathogenesis of OAD and that KCa3.1 blockade holds promise to reduce OAD development.

Protective Roles for Potassium SK/K(Ca)2 Channels in Microglia and Neurons

New concepts on potassium channel function in neuroinflammation suggest that they regulate mechanisms of microglial activation, including intracellular calcium homeostasis, morphological alterations, pro-inflammatory cytokine release, antigen presentation, and phagocytosis. Although little is known about voltage independent potassium channels in microglia, special attention emerges on small (SK/KCNN1-3/K(Ca)2) and intermediate (IK/KCNN4/K(Ca)3.1)-conductance calcium-activated potassium channels as regulators of microglial activation in the field of research on neuroinflammation and neurodegeneration. In particular, recent findings suggested that SK/K(Ca)2 channels, by regulating calcium homeostasis, may elicit a dual mechanism of action with protective properties in neurons and inhibition of inflammatory responses in microglia. Thus, modulating SK/K(Ca)2 channels and calcium signaling may provide novel therapeutic strategies in neurological disorders, where neuronal cell death and inflammatory responses concomitantly contribute to disease progression. Here, we review the particular role of SK/K(Ca)2 channels for [Ca(2+)](i) regulation in microglia and neurons, and we discuss the potential impact for further experimental approaches addressing novel therapeutic strategies in neurological diseases, where neuronal cell death and neuroinflammatory processes are prominent.

Relaxant effect of a novel calcium-activated potassium channel modulator on human myometrial spontaneous contractility in vitro

AIM

To investigate the effect of 4,5-dichloro-1,3-diethyl-1,3-dihydro-benzoimidazol-2-one (NS4591), a novel SK/IK channels positive modulator, on human myometrial activity.

METHODS

Organ bath studies were performed on myometrial preparations obtained from women undergoing elective caesarean section at term (N = 11) or hysterectomy (N = 11). NS4591 was added cumulatively in the concentration range of 0.3-30 μm. In separate experiments, the effects of pre-incubation of muscle preparation with the SK or IK channel blockers apamin (1 μm) and TRAM34 (10 μm) on the outcomes of NS4591 were evaluated. Simultaneous vehicle controls were performed for all experiments. The effects of drugs were studied on spontaneous contractions.

RESULTS

NS4591 exerted an inhibitory effect on myometrial contractions in muscle strips from non-pregnant and pregnant women. The contractility in non-pregnant and pregnant myometrium was reduced to the following values respectively: amplitude 20.65 ± 7.38% (P < 0.001) and 42.85 ± 11.04% (P < 0.05) and area under the curve 11.72 ± 7.39% (P < 0.001) and 34.84 ± 10.50% (P < 0.001) and are reflective of 30 μm NS4591 compared to vehicle control. In non-pregnant tissue, apamin partially reduced the inhibitory effects of NS4591, but we observed relaxation mediated by NS4591 despite pre-incubation with TRAM34. In contrast, in pregnant tissue, neither apamin nor TRAM34 could reverse the relaxatory effects of NS4591.

CONCLUSION

Our findings imply that SK/IK channels are present and functional in myometrium from pregnant and non-pregnant women. The SK/IK channel-positive modulator NS4591 exerts relaxation of human myometrium in vitro, and this may have implications for the clinical management of preterm labour.

Cell volume regulation in chondrocytes

Chondrocytes are the cells within cartilage which produce and maintain the extracellular matrix. Volume regulation in these cells is vital to their function and occurs in several different physiological and pathological contexts. Firstly, chondrocytes exist within an environment of changing osmolarity and compressive loads. Secondly, in osteoarthritic joint failure, cartilage water content changes and there is a notable increase in chondrocyte apoptosis. Thirdly, endochondral ossification requires chondrocyte swelling in association with hypertrophy. Regulatory volume decrease (RVD) and regulatory volume increase (RVI) have both been observed in articular chondrocytes and this review focuses on the mechanisms identified to account for these. There has been evidence so far to suggest TRPV4 is central to RVD; however other elements of the pathway have not yet been identified. Unlike RVD, RVI appears less robust in articular chondrocytes and there have been fewer mechanistic studies; the primary focus being on the Na(+)-K(+)-2Cl(-) co-transporter. The clinical significance of chondrocyte volume regulation remains unproven. Importantly however, transcript abundances of several ion channels implicated in volume control are changed in chondrocytes from osteoarthritic cartilage. A critical question is whether disturbances of volume regulation mechanisms lead to, result from or are simply coincidental to cartilage damage.

K(Ca)3.1 channels facilitate K+ secretion or Na+ absorption depending on apical or basolateral P2Y receptor stimulation

Human mammary epithelial (HME) cells express several P2Y receptor subtypes located in both apical and basolateral membranes. Apical UTP or ATP-γ-S stimulation of monolayers mounted in Ussing chambers evoked a rapid, but transient decrease in short circuit current (I(sc)), consistent with activation of an apical K+ conductance. In contrast, basolateral P2Y receptor stimulation activated basolateral K+ channels and increased transepithelial Na+ absorption. Chelating intracellular Ca2+ using the membrane-permeable compound BAPTA-AM, abolished the effects of purinoceptor activation on I(sc). Apical pretreatment with charybdotoxin also blocked the I(sc) decrease by >90% and similar magnitudes of inhibition were observed with clotrimazole and TRAM-34. In contrast, iberiotoxin and apamin did not block the effects of apical P2Y receptor stimulation. Silencing the expression of K(Ca)3.1 produced ∼70% inhibition of mRNA expression and a similar reduction in the effects of apical purinoceptor agonists on I(sc). In addition, silencing P2Y2 receptors reduced the level of P2Y2 mRNA by 75% and blocked the effects of ATP-γ-S by 65%. These results suggest that P2Y2 receptors mediate the effects of purinoceptor agonists on K+ secretion by regulating the activity of K(Ca)3.1 channels expressed in the apical membrane of HME cells. The results also indicate that release of ATP or UTP across the apical or basolateral membrane elicits qualitatively different effects on ion transport that may ultimately determine the [Na+]/[K+] composition of fluid within the mammary ductal network.

Formulation-based approach to support early drug discovery and development efforts: a case study with enteric microencapsulation dosage form development for a triarylmethane derivative TRAM-34; a novel potential immunosuppressant

BACKGROUND

Enteric microencapsulation of the potential immunosuppressant TRAM-34 was investigated as a means of enhancing oral drug delivery and minimizing or eliminating hydrolysis of pyrazole-substituted triarylmethane to the respective alcohol.

METHOD

TRAM-34 was successfully enteric microencapsulated by a coacervation method using the pH-sensitive Eudragit L 100 polymer. In this study, we utilized water-miscible organic solvents such as acetone and ethanol, which are considered safe class 3 solvents according to the ICH guideline. We deemed such an approach suitable for safe scale up and for enteric coating application to other compounds of a similar lipophilicity.

RESULTS

The resulting microparticles were spherical and uniform with an average particle size of 460 microm at 15% theoretical loading. The encapsulation efficiency was 90 +/- 1.9% and the percentage yield was found to be 91.5 +/- 0.3%. The oral administration in rhesus macaques of TRAM-34-loaded enteric-coated microparticles illustrated six times enhancement in its oral bioavailability. However, the TRAM-34 plasma concentration was less than the therapeutic effective level.

CONCLUSION

The low oral bioavailability, even after enteric coating, could be attributed to the compound's inherent absorption characteristics and high lipophilicity.

N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs as potent Kv1.3 inhibitors. Part 1

We report the synthesis and in vitro activity of a series of novel N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs. These analogs showed potent inhibitory activity against Kv1.3. Several compounds, including compound 8b, showed similar potency to the known Kv1.3 inhibitor PAP-1 when tested under the IonWorks patch clamp assay conditions.

Reduced expression of SK3 and IK1 channel proteins in the cavernous tissue of diabetic rats

The small (SK3) and intermediate (IK1) conductance calcium-activated potassium channels could have key roles in the endothelium-dependent hyperpolarization factor pathway, which is believed to contribute to normal penile erection function. We aimed to investigate the expression of SK3 and IK1 in diabetic rodents. The experimental diabetes model was induced in 8-week-old male Sprague-Dawley rats (250-300 g) by a single administration of streptozotocin. Both the diabetes mellitus group (DM group, n = 20) and the control group (NDM group, n = 10) were injected with a low dose of apomorphine to allow for the measurement and comparison of the corresponding penile erections. The mRNA and protein expression levels of SK3 and IK1 were measured by reverse transcription polymerase chain reaction and western blot, respectively. Erectile function was significantly decreased in the DM group compared with control group (P < 0.05). The mRNA and protein expression levels of SK3 and IK1 were reduced in the cavernous tissue of diabetic rats compared with the control group (P < 0.05). Diabetes inhibits mRNA and protein expression of both SK3 and IK1 in the cavernous tissue of diabetic rats. This could play a key role in the development of erectile dysfunction in diabetic rats.

An investigation of the occurrence and properties of the mitochondrial intermediate-conductance Ca2+-activated K+ channel mtKCa3.1

The mitochondrial intermediate-conductance Ca2+-activated K+ channel mtKCa3.1 has recently been discovered in the HCT116 colon tumor-derived cell line, which expresses relatively high levels of this protein also in the plasma membrane. Electrophysiological recordings revealed that the channel can exhibit different conductance states and kinetic modes, which we tentatively ascribe to post-translational modifications. To verify whether the localization of this channel in mitochondria might be a peculiarity of these cells or a more widespread feature we have checked for the presence of mtKCa3.1 in a few other cell lines using biochemical and electrophysiological approaches. It turned out to be present at least in some of the cells investigated. Functional assays explored the possibility that mtKCa3.1 might be involved in cell proliferation or play a role similar to that of the Shaker-type KV1.3 channel in lymphocytes, which interacts with outer mitochondrial membrane-inserted Bax thereby promoting apoptosis (Szabò, I. et al., Proc. Natl. Acad Sci. USA 105 (2008) 14861-14866). A specific KCa3.1 inhibitor however did not have any detectable effect on cell proliferation or death.

Identification of the large-conductance background K+ channel in mouse B cells as TREK-2

Mouse B cells and their cell line (WEHI-231) express large-conductance background K(+) channels (LK(bg)) that are activated by arachidonic acids, characteristics similar to TREK-2. However, there is no evidence to identify the molecular nature of LK(bg); some properties of LK(bg) were partly different from the reported results of TREK type channels. In this study, we compared the properties of cloned TREK-2 and LK(bg) in terms of their sensitivities to ATP, phosphatidylinositol 4,5-bisphosphate (PIP(2)), intracellular pH (pH(i)), and membrane stretch. Similar to the previous findings of LK(bg), TREK-2 showed spontaneous activation after membrane excision (i-o patch) and were inhibited by MgATP or by PIP(2). The inhibition by MgATP was prevented by wortmannin, suggesting membrane-delimited regulation of TREKs by phosphoinositide (PI) kinase. The same was observed with the property of LK(bg); the activation of TREK-2 by membrane stretch was suppressed by U73122 (PLC inhibitor). As with the known properties of TREK-2, LK(bg) were activated by acidic pH(i) and inhibited by PKC activator. Finally, we confirmed the expression of TREK-2 in WEHI-231 by using RT-PCR and immunoblot analyses. The amplitude of background K(+) current and the TREK-2 expression in WEHI-231 were commonly decreased by genetic knockdown of TREK-2 using small interfering RNA. The downregulation of TREK-2 attenuated Ca(2+)-influx induced by arachidonic acid in WEHI-231. As a whole, these results strongly indicate that TREK-2 encodes LK(bg) in mouse B cells. We also newly suggest that the low activity of TREK-2 in intact cells is due to the inhibition by intrinsic PIP(2).

Inhibitors of potassium channels KV1.3 and IK-1 as immunosuppressants

New structural classes of K(V)1.3 and IK-1 ion channel blockers have been identified based on a virtual high throughput screening approach using a homology model of KcsA. These compounds display inhibitory effects on T-cell and/or keratinocyte proliferation and immunosuppressant activity within a DTH animal model.

Lactobacillus reuteri enhances excitability of colonic AH neurons by inhibiting calcium-dependent potassium channel opening

Probiotics are live non-pathogenic commensal organisms that exert therapeutic effects in travellers' diarrhea, irritable bowel syndrome and inflammatory bowel disease. Little is known about mechanisms of action of commensal bacteria on intestinal motility and motility-induced pain. It has been proposed that probiotics affect intestinal nerve function, but direct evidence for this has thus far been lacking. We hypothesized that probiotic effects might be mediated by actions on colonic intrinsic sensory neurons. We first determined whether sensory neurons were present in rat colon by their responses to chemical mucosal stimulation and identified them in terms of physiological phenotype and soma morphotype. Enteric neuron excitability and ion channel activity were measured using patch clamp recordings. We fed 10(9)Lactobacillus reuteri (LR) or vehicle control to rats for 9 days. LR ingestion increased excitability (threshold for evoking action potentials) and number of action potentials per depolarizing pulse, decreased calcium-dependent potassium channel (IK(Ca)) opening and decreased the slow afterhyperpolarization (sAHP) in sensory AH neurons, similar to the IK(Ca) antagonists Tram-34 and clotrimazole. LR did not affect threshold for action potential generation in S neurons. Our results demonstrate that LR targets an ion channel in enteric sensory nerves through which LR may affect gut motility and pain perception.

Genes and pathways differentially expressed in the brains of Fxr2 knockout mice

Fragile X syndrome is a common inherited form of mental retardation and originates from the absence of expression of the FMR1 gene. This gene and its two homologues, FXR1 and FXR2, encode for a family of fragile X related (FXR) proteins with similar tissue distribution, together with sequence and functional homology. Based on these characteristics, it has been suggested that these proteins might partly complement one another. To unravel the function of Fxr2 protein, the expression pattern of 12,588 genes was studied in the brains of wild-type and Fxr2 knockout mice, an animal model which shows behavioral abnormalities partly similar to those observed in Fmr1-knockout mice. By genome expression profiling and stringent significance tests we identify genes and gene groups de-regulated in the brains of Fxr2 knockout mice. Differential expression of candidate genes was validated by real-time PCR, in situ hybridization, immunohistochemistry and western blot analysis. A number of differentially expressed genes associated with the Fxr2 phenotype have been previously involved in other memory or cognitive disorders.

Ethanol Interactions With Calcium-Dependent Potassium Channels

In most neurons and other excitable cells, calcium-activated potassium channels of small (SK) and large conductance (BK; MaxiK) control excitability and neurotransmitter release. The spontaneous activity of dopamine neurons of the ventral tegmental area is increased by ethanol. This ethanol excitation is potentiated by selective blockade of SK, indicating that SK channels modulate ethanol stimulation of neurons that are critical in reward and reinforcement. On the other hand, ethanol directly modulates BK channel activity in a variety of systems, including rat neurohypophysial nerve endings, primary sensory dorsal root ganglia, nucleus accumbens neurons, Caenorhabditis elegans type-IV dopaminergic CEP neurons, and nonneuronal preparations, such as rat pituitary cells, cerebrovascular myocytes and human umbilical vein endothelial cells. Ethanol action on BK channels can modify neuropeptide and growth hormone release, nociception, cerebrovascular tone, and endothelial proliferation. Ethanol modulates BK channels even when the drug is evaluated using recombinant BK channel-forming alpha (slo) subunits or channel reconstitution in artificial, binary lipid bilayers, indicating that the slo subunit and its immediate lipid microenvironment are the essential targets of ethanol. Consistent with this, single amino acid slo channel mutants display altered ethanol sensitivity. Furthermore, C. elegans slo1 null mutants are resistant to ethanol-induced motor incoordination. On the other hand, Drosophila melanogaster slo null mutants fail to acquire acute tolerance to ethanol sedation. Ethanol action on slo channels, however, may be tuned by a variety of factors, including posttranslational modification of slo subunits, coexpression of channel accessory subunits, and the lipid microenvironment, resulting in increase, refractoriness, or even decrease in channel activity. In brief, both SK and BK channels are important targets of ethanol throughout the body, and interference with ethanol effects on these channels could form the basis for novel pharmacotherapies to ameliorate the actions or consequences of alcohol abuse.

Venom therapy in multiple sclerosis

To date many people with multiple sclerosis (MS) seek complementary and alternative medicines (CAM) to treat their symptoms as an adjunct to conventionally used therapies. Among the common CAM therapies, there is a renewed interest in the therapeutic potential of venoms in MS. The efficacy of this therapeutic method remains unclear. However, venom-based therapy using bee, snakes and scorpions venom and/or sea anemones toxin has been recently developed because current investigations have identified the various components and molecular mechanism of the effects of venoms under in vitro and in vivo conditions. The aim of this review is to describe the recent findings regarding the role of venoms and their components in treatment of MS disease and that whether venom therapy could be recommended as a complementary treatment or not.

The Ca2+-activated K+ channel KCNN4/KCa3.1 contributes to microglia activation and nitric oxide-dependent neurodegeneration

Brain damage and disease involve activation of microglia and production of potentially neurotoxic molecules, but there are no treatments that effectively target their harmful properties. We present evidence that the small-conductance Ca2+/calmodulin-activated K+ channel KCNN4/ KCa3.1/SK4/IK1 is highly expressed in rat microglia and is a potential therapeutic target for acute brain damage. Using a Transwell cell-culture system that allows separate treatment of the microglia or neurons, we show that activated microglia killed neurons, and this was markedly reduced by treating only the microglia with a selective inhibitor of KCa3.1 channels, triarylmethane-34 (TRAM-34). To assess the role of KCa3.1 channels in microglia activation and key signaling pathways involved, we exploited several fluorescence plate-reader-based assays. KCa3.1 channels contributed to microglia activation, inducible nitric oxide synthase upregulation, production of nitric oxide and peroxynitrite, and to consequent neurotoxicity, protein tyrosine nitration, and caspase 3 activation in the target neurons. Microglia activation involved the signaling pathways p38 mitogen-activated protein kinase (MAPK) and nuclear factor kappaB (NF-kappaB), which are important for upregulation of numerous proinflammatory molecules, and the KCa3.1 channels were functionally linked to activation of p38 MAPK but not NF-kappaB. These in vitro findings translated into in vivo neuroprotection, because we found that degeneration of retinal ganglion cells after optic nerve transection was reduced by intraocular injection of TRAM-34. This study provides evidence that KCa3.1 channels constitute a therapeutic target in the CNS and that inhibiting this K+ channel might benefit acute and chronic neurodegenerative disorders that are caused by or exacerbated by inflammation.

Histidine phosphorylation of the potassium channel KCa3.1 by nucleoside diphosphate kinase B is required for activation of KCa3.1 and CD4 T cells

The Ca2+ -activated K+ channel KCa3.1 is required for Ca2+ influx and the subsequent activation of B and T cells. Inhibitors of KCa3.1 are in development to treat autoimmune diseases and transplant rejection, underscoring the importance in understanding how these channels are regulated. We show that nucleoside diphosphate kinase B (NDPK-B), a mammalian histidine kinase, functions downstream of PI(3)P to activate KCa3.1. NDPK-B directly binds and activates KCa3.1 by phosphorylating histidine 358 in the carboxyl terminus of KCa3.1. Endogenous NDPK-B is also critical for KCa3.1 channel activity and the subsequent activation of CD4 T cells. These findings provide one of the best examples whereby histidine phosphorylation regulates a biological process in mammals, and provide an example whereby a channel is regulated by histidine phosphorylation. The critical role for NDPK-B in the reactivation of CD4 T cells indicates that understanding NDPK-B regulation should uncover novel pathways required for T cell activation.

Vertebrate rod photoreceptors express both BK and IK calcium-activated potassium channels, but only BK channels are involved in receptor potential regulation

In salamander rods, Ca(2+)-activated K(+) current (I(KCa)) provides an effective "clamp" of the dark membrane potential to its normal resting level. By a combination of electrophysiological, pharmacological, and immunohistochemical approaches, we show that salamander rods functionally express large-conductance Ca(2+)- and voltage-dependent potassium (BK) channel and intermediate-conductance Ca(2+)-dependent potassium (IK) channel, but not small-conductance Ca(2+)-dependent potassium channel (SK) subtypes. Application of 100 nM iberiotoxin and 100 nM clotrimazole reduced net I(KCa) to 36% and 63%, respectively, whereas the current was unaffected by application of 1 microM apamin. Consistently, anti- SK1, -SK2, and -SK3 antibodies were unable to stain rod photoreceptors, whereas both anti-BK and -SK4/ IK1 antibodies heavily stained the ellipsoid region of the inner segments of the rods. Moreover, by using current-clamp experiments, it was clearly seen that the strong clamping effect of the total I(KCa) was lost when IbTx, but not CLTZ, was applied to the bath. This behavior strongly suggests that of BK and IK channels, only the former are responsible for the clamping effect on the photoreceptor membrane potential.

Effects of the antifungal antibiotic clotrimazole on human cardiac repolarization potassium currents

The antifungal antibiotic clotrimazole (CLT) shows therapeutic effects on cancer, sickle cell disease, malaria, etc. by inhibiting membrane intermediate-conductance Ca2+ -activated K+ channels (IKCa). However, it is unclear whether this drug would affect human cardiac K+ currents. The present study was therefore designed to investigate the effects of CLT on transient outward K+ current (Ito1), and ultra-rapid delayed rectifier K+ current (IKur) in isolated human atrial myocytes, and cloned hERG channel current (IhERG) and recombinant human cardiac KCNQ1/KCNE1 channel current (IKs) expressed in HEK 293 cells. It was found that CLT inhibited Ito1 with an IC50 of 29.5 microM, accelerated Ito1 inactivation, and decreased recovery of Ito1 from inactivation. In addition, CLT inhibited human atrial I(Kur) in a concentration-dependent manner (IC50 = 7.6 microM). CLT substantially suppressed IhERG (IC50 = 3.6 microM), and negatively shifted the activation conductance of IhERG. Moreover, CLT inhibited IKs (IC50 = 15.1 microM), and positively shifted the activation conductance of the current. These results indicate that the antifungal antibiotic CLT substantially inhibits human cardiac repolarization K+ currents including Ito1, IKur, IhERG, and IKs. However, caution is recommended when correlating the observed in vitro effects on cardiac ion currents to the clinical relevance.

Novel 384-Well Population Patch Clamp Electrophysiology Assays for Ca2+-Activated K+ Channels

Planar array electrophysiology techniques were applied to assays for modulators of recombinant hIK and hSK3 Ca2+-activated K+ channels. In CHO-hIK—expressing cells, under asymmetric K+ gradients, small-molecule channel activators evoked time- and voltage-independent currents characteristic of those previously described by classical patch clamp electrophysiology methods. In single-hole (cell) experiments, the large cell-to-cell heterogeneity in channel expression rendered it difficult to generate activator concentration-response curves. However, in population patch clamp mode, in which signals are averaged from up to 64 cells, well-to-well variation was substantially reduced such that concentration-response curves could be easily constructed. The absolute EC50 values and rank order of potency for a range of activators, including 1-EBIO and DC-EBIO, corresponded well with conventional patch clamp data. Activator responses of hIK and hSK3 channels could be fully and specifically blocked by the selective inhibitors TRAM-34 and apamin, with IC50 values of 0.31 μM and 3 nM, respectively. To demonstrate assay precision and robustness, a test set of 704 compounds was screened in a 384-well format of the hIK assay. All plates had Z′ values greater than 0.6, and the statistical cutoff for activity was 8%. Eleven hits (1.6%) were identified from this set, in addition to the randomly spiked wells with known activators. Overall, our findings demonstrate that population patch clamp is a powerful and enabling method for screening Ca2+-activated K+ channels and provides significant advantages over single-cell electrophysiology (IonWorksHT) and other previously published approaches. Moreover, this work demonstrates for the 1st time the utility of population patch clamp for ion channel activator assays and for non—voltage-gated ion channels.

Expression and function of calcium-activated potassium channels in human glioma cells

Ca(2+)-activated K(+) (K(Ca)) channels are a unique family of ion channels because they are capable of directly communicating calcium signals to changes in cell membrane potential required for cellular processes including but not limited to cellular proliferation and migration. It is now possible to distinguish three families of K(Ca) channels based on differences in their biophysical and pharmacological properties as well as genomic sequence. Using a combination of biochemical, molecular, and biophysical approaches, we show that human tumor cells of astrocytic origin, i.e. glioma cells, express transcripts for all three family members of K(Ca) channels including BK, IK, and all three SK channel types (SK1, SK2, and SK3). The use of selective pharmacological inhibitors shows prominent expression of currents that are inhibited by the BK channel specific inhibitors iberiotoxin and paxilline. However, despite the presence of transcripts for IK and SK, neither clotrimazole, an inhibitor of IK channels, nor apamin, known to block most SK channels inhibited any current. The exclusive expression of functional BK channels was further substantiated by shRNA knockdown experiments, which selectively reduced iberiotoxin sensitive currents. Western blotting of patient biopsies with antibodies specific for all three KCa channel types further substantiated the exclusive expression of BK type KCa channels in vivo. This finding is in sharp contrast to other cancers that express primarily IK channels.

Properties of ion channels in rabbit mesenchymal stem cells from bone marrow

The present study was designed to investigate properties of ion channels in undifferentiated rabbit mesenchymal stem cells (MSCs) from bone marrow using whole-cell patch-clamp and RT-PCR techniques. It was found that three types of outward currents were present in rabbit MSCs, including an inward rectifier K(+) current (I(Kir)), a noise-like Ca(2+)-activated K(+) current (I(KCa)) co-present with delayed rectifier K(+) current (IK(DR)). I(Kir) was inhibited by Ba(2+), while I(KCa) was inhibited by paxilline (a blocker of big conductance I(KCa) channels) and clotrimazole (an inhibitor of intermediate conductance I(KCa) channels). IK(DR) exhibited a slow inactivation, "U-shaped" voltage-dependent inactivation, and slow recovery from inactivation, and the current was inhibited by tetraethylammonium or 4-aminopyridine. RT-PCR revealed the molecular identities for the functional ionic currents, including Kir1.1 (possibly responsible for I(Kir)), KCa1.1 and KCa3.1 (possibly responsible for I(KCa)), and Kv1.2, Kv2.1, and Kv2.2 (possibly responsible for IK(DR)). These results demonstrate for the first time that three types of functional ion channel currents (i.e., I(Kir), I(KCa), and IK(DR)) are present in rabbit MSCs from bone marrow.

Voltage-dependent Ca2+-channel block by openers of intermediate and small conductance Ca2+-activated K+ channels in urinary bladder smooth muscle cells

We examined effects of small and intermediate conductance Ca(2+)-activated K(+) (SK and IK) channel openers, DCEBIO (5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one) and NS309 (3-oxime-6,7-dichloro-1H-indole-2,3-dione), on L-type Ca(2+) channel current (I(Ca)) that was measured in smooth muscle cells isolated from mouse urinary bladder under whole cell voltage-clamp. The I(Ca) was concentration-dependently inhibited by DCEBIO and NS309; half inhibition was obtained at 71.6 and 10.6 muM, respectively. The specificity of NS309 to the IK channel over the Ca(2+) channel appears to be high and higher than that of DCEBIO. DCEBIO and even NS309 may, however, substantially block Ca(2+) channels when used as SK channel openers.

Ion channels in mesenchymal stem cells from rat bone marrow

Mesenchymal stem cells (MSCs) from bone marrow are believed to be an ideal cell source for cardiomyoplasty; however, cellular electrophysiology is not understood. The present study was designed to investigate ion channels in undifferentiated rat MSCs. It was found that three types of outward currents were present in rat MSCs, including a small portion of Ca(2+)-activated K(+) channel (I(KCa)) sensitive to inhibition by iberiotoxin and/or clotromazole, a delayed rectifier K(+) current (IK(DR)), and a transient outward K(+) current (I(to)). In addition, tetrodotoxin (TTX)-sensitive sodium current (I(Na.TTX)) and nifedipine-sensitive L-type Ca(2+) current (I(Ca.L)) were found in a small population of rat MSCs. Moreover, reverse transcription-polymerase chain reaction revealed the molecular evidence of mRNA for the functional ionic currents, including Slo and KCNN4 for I(KCa); Kv1.4 for I(to); Kv1.2 and Kv2.1 for IK(DR); SCN2a1 for I(Na.TTX); and CCHL2a for I(Ca.L). These results demonstrate for the first time that multiple functional ion channel currents (i.e., I(KCa), I(to), IK(DR), I(Na.TTX), and I(Ca.L)) are present in rat MSCs from bone marrow; however, physiological roles of these ion channels remain to be studied.

Blockade of Ca2+-activated K+ channels in T cells: an option for the treatment of multiple sclerosis?

Voltage- and Ca(2+)-dependent K(+) channels in the membrane of both T and B lymphocytes are important for the cellular immune response. In the current issue of the European Journal of Immunology, Reich et al. demonstrate that selective blockade of the intermediate-conductance Ca(2+)-activated K(+) channel (the IK channel encoded by the KCNN4 gene) prevents cytokine production in the spinal chord and ameliorates the development of EAE caused by injection of myelin oligodendrocyte glycoprotein (MOG)(35-55) in mice. These data renew the focus on the IK channel as a potential target for the development of new immune-suppressant drugs for the treatment of autoimmune diseases.

The phosphatidylinositol 3-phosphate phosphatase myotubularin- related protein 6 (MTMR6) is a negative regulator of the Ca2+-activated K+ channel KCa3.1

Myotubularins (MTMs) belong to a large subfamily of phosphatases that dephosphorylate the 3' position of phosphatidylinositol 3-phosphate [PI(3)P] and PI(3,5)P(2). MTM1 is mutated in X-linked myotubular myopathy, and MTMR2 and MTMR13 are mutated in Charcot-Marie-Tooth syndrome. However, little is known about the general mechanism(s) whereby MTMs are regulated or the specific biological processes regulated by the different MTMs. We identified a Ca(2+)-activated K channel, K(Ca)3.1 (also known as KCa4, IKCa1, hIK1, or SK4), that specifically interacts with the MTMR6 subfamily of MTMs via coiled coil (CC) domains on both proteins. Overexpression of MTMR6 inhibited K(Ca)3.1 channel activity, and this inhibition required MTMR6's CC and phosphatase domains. This inhibition is specific; MTM1, a closely related MTM, did not inhibit K(Ca)3.1. However, a chimeric MTM1 in which the MTM1 CC domain was swapped for the MTMR6 CC domain inhibited K(Ca)3.1, indicating that MTM CC domains are sufficient to confer target specificity. K(Ca)3.1 was also inhibited by the PI(3) kinase inhibitors LY294002 and wortmannin, and this inhibition was rescued by the addition of PI(3)P, but not other phosphoinositides, to the patch pipette solution. PI(3)P also rescued the inhibition of K(Ca)3.1 by MTMR6 overexpression. These data, when taken together, indicate that K(Ca)3.1 is regulated by PI(3)P and that MTMR6 inhibits K(Ca)3.1 by dephosphorylating the 3' position of PI(3)P, possibly leading to decreased PI(3)P in lipid microdomains adjacent to K(Ca)3.1. K(Ca)3.1 plays important roles in controlling proliferation by T cells, vascular smooth muscle cells, and some cancer cell lines. Thus, our findings not only provide unique insights into the regulation of K(Ca)3.1 channel activity but also raise the possibility that MTMs play important roles in the negative regulation of T cells and in conditions associated with pathological cell proliferation, such as cancer and atherosclerosis.

Cytotoxicity of RNases is increased by cationization and counteracted by KCa channels

K(Ca) channels are involved in control of cell proliferation and differentiation. Here we have revealed their role in overcoming the RNase-induced cytotoxicity. Toxic effects of Streptomyces aureofaciens RNases Sa, Sa2, Sa3, and of RNase Sa charge reversal mutants on the human embryonic kidney cell lines differing only by the presence of K(Ca) channels were characterized. In contrast to other RNases, a basic variant of RNase Sa and RNase Sa3 exhibit significant cytotoxic activity of the same order of magnitude as onconase. Our data indicate the absence of a correlation between catalytic activity and stability of RNases and cytotoxicity. On the other hand, cationization enhances toxic effect of an RNase indicating the major role of a positive charge. Essentially lower sensitivity to cytotoxic microbial RNases of cells expressing K(Ca) channels was found. These results suggest that cells without the K(Ca) channel activity cannot counteract toxic effect of RNases.

Role of the NH2 terminus in the assembly and trafficking of the intermediate conductance Ca2+-activated K+ channel hIK1

The role of the NH(2)-terminal leucine zipper and dileucine motifs of hIK1 in the assembly, trafficking, and function of the channel was investigated using cell surface immunoprecipitation, co-immunoprecipitation (Co-IP), immunoblot, and whole-cell patch clamp techniques. Mutation of the NH(2)-terminal leucine zipper at amino acid positions 18 and 25 (L18A/L25A) resulted in a complete loss of steady-state protein expression, cell surface expression, and whole-cell current density. Inhibition of proteasomal degradation with lactacystin restored L18A/L25A protein expression, although this channel was not expressed at the cell surface as assessed by cell surface immunoprecipitation and whole-cell patch clamp. In contrast, inhibitors of lysosomal degradation (leupeptin/pepstatin) and endocytosis (chloroquine) had little effect on L18A/L25A protein expression or localization. Further studies confirmed the rapid degradation of this channel, having a time constant of 19.0 +/- 1.3 min compared with 3.2 +/- 0.8 h for wild type hIK1. Co-expression studies demonstrated that the L18A/L25A channel associates with wild type channel, thereby attenuating its expression at the cell surface. Co-IP studies confirmed this association. However, L18A/L25A channels failed to form homotetrameric channels, as assessed by Co-IP, suggesting the NH(2) terminus plays a role in tetrameric channel assembly. As with the leucine zipper, mutation of the dileucine motif to alanines, L18A/L19A, resulted in a near complete loss in steady-state protein expression with the protein being similarly targeted to the proteasome for degradation. In contrast to our results on the leucine zipper, however, both chloroquine and growing the cells at the permissive temperature of 27 degrees C restored expression of L18A/L19A at the cell surface, suggesting that the defect in the channel trafficking is the result of a subtle folding error. In conclusion, we demonstrate that the NH(2) terminus of hIK1 contains overlapping leucine zipper and dileucine motifs essential for channel assembly and trafficking to the plasma membrane.