Cellular Potassium Research Articles

Migraine Aura: Pathophysiology, Mimics, and Treatment Options.

Recent insights into the clinical presentation and pathophysiology of migraine aura have paved the way for new treatments for this common but frequently debilitating condition. Marked efflux of cellular potassium and glutamate contributes to the cortical spreading depression that forms the electrophysiological basis of migraine aura phenomena. Secondary vascular perturbations also contribute to the various symptoms of a migraine attack. Calcitonin gene-related peptide (CGRP) plays a key role in many of these steps, and a growing class of CGRP-antagonists have emerged as a novel, efficacious preventative therapy. It is still not fully understood why a preponderance of migraine aura symptoms is visual, and this issue is an active area of research. In addition, the pathophysiological changes responsible for visual snow syndrome are under investigation. Before diagnosing a patient with migraine aura, it is important to consider the differential diagnosis of transient visual phenomena, with attention to clinical features that may suggest conditions such as retinal disorders, transient ischemic attack, or occipital epilepsy.

Potassium-lowering agents for the treatment of nonemergent hyperkalemia: pharmacology, dosing and comparative efficacy.

Hyperkalemia represents a common and potentially life-threating electrolyte abnormality, a complication frequently observed in patients with heart failure, kidney disease, diabetes or in those receiving drug therapies influencing the renin-angiotensin-aldosterone system. Elevated serum potassium levels are often the result of impaired urinary potassium elimination, inadequate or reduced cellular potassium uptake, severe heart failure, use of medications influencing potassium levels in the circulation, or, more commonly, a combination of these factors. Strategies for the treatment of nonemergent hyperkalemia include the use of cation-exchange resins, polymers or other novel mechanisms of potassium trapping, including sodium polystyrene sulfonate, patiromer and sodium zirconium cyclosilicate. These agents differ in their pharmacology and mechanism of action, clinical efficacy, including onset and extent of potassium-lowering effect, dosage and administration, and potential safety and adverse effect profiles. In this review, an evaluation of these characteristics, including clinical evidence and safety concerns, in the management of nonemergent hyperkalemia will be explored.

G protein-coupled and ATP-sensitive inwardly rectifying potassium ion channels are essential for HIV entry

The high genetic diversity of Human Immunodeficiency virus (HIV), has hindered the development of effective vaccines or antiviral drugs against it. Hence, there is a continuous need for identification of new antiviral targets. HIV exploits specific host proteins also known as HIV-dependency factors during its replication inside the cell. Potassium channels play a crucial role in the life cycle of several viruses by modulating ion homeostasis, cell signaling, cell cycle, and cell death. In this study, using pharmacological tools, we have identified that HIV utilizes distinct cellular potassium channels at various steps in its life cycle. Members of inwardly rectifying potassium (Kir) channel family, G protein-coupled (GIRK), and ATP-sensitive (KATP) are involved in HIV entry. Blocking these channels using specific inhibitors reduces HIV entry. Another member, Kir 1.1 plays a role post entry as inhibiting this channel inhibits virus production and release. These inhibitors are not toxic to the cells at the concentration used in the study. We have further identified the possible mechanism through which these potassium channels regulate HIV entry by using a slow-response potential-sensitive probe DIBAC4(3) and have observed that blocking these potassium channels inhibits membrane depolarization which then inhibits HIV entry and virus release as well. These results demonstrate for the first time, the important role of Kir channel members in HIV-1 infection and suggest that these K+ channels could serve as a safe therapeutic target for treatment of HIV/AIDS.

Effects of pH and bicarbonate on the nutrient status and growth of three Lupinus species

High pH, and high bicarbonate (HCO3−) and calcium (Ca) availability characterise calcareous soils. High [Ca] only partially explains why some Lupinus species are calcifuge, so we explored high [HCO3−] and high pH. We grew six Lupinus genotypes in hydroponics with pH 5, 6.5 and 8a (adjusted by KOH), and 8b (adjusted by KHCO3). Leaf symptoms and areas, root appearance and biomass were recorded; whole leaf and root nutrient concentrations, and leaf cellular phosphorus (P), Ca and potassium (K) concentrations were determined using elemental X-ray microanalysis. Chlorosis was observed in young leaves at high pH for L. angustifolius and L. cosentinii, and P deficiency at high pH for all genotypes. High pH decreased iron (Fe) and zinc (Zn) uptake in all genotypes. It also decreased lateral root growth, the uptake of P, K, Ca, and manganese (Mn) by all sensitive species; and translocation of P, Fe, Zn, Mn, and Ca to leaves in most sensitive species. However, leaf [Ca], leaf [K], [K] within each measured cell type, and translocation of K and Ca to leaves of L. pilosus and L. cosentinii at pH 8 were greater than at pH 5 and 6.5. Compared with pH 8a, all L. angustifolius genotypes translocated more P, Fe, Zn, Mn and K from roots to leaves at pH 8b. High pH did not affect the leaf cell types that accumulated P and Ca, but decreased the leaf cellular [P]. Lupinus angustifolius and L. cosentinii were sensitive to high [HCO3−] and/or high pH; L. pilosus was relatively tolerant. High pH decreased lateral root growth and nutrient uptake, inhibiting growth of sensitive species. High [HCO3−] diminished the negative effect of pH 8 on nutrient translocation to leaves in most L. angustifolius genotypes. This knowledge provides critical insights into the habits of Lupinus species to guide breeding of calcicole plants.

Molecular Neuroprotection Induced by Zinc-Dependent Expression of Hepatitis C-Derived Protein NS5A Targeting Kv2.1 Potassium Channels.

We present the design of an innovative molecular neuroprotective strategy and provide proof-of-concept for its implementation, relying on the injury-mediated activation of an ectopic gene construct. As oxidative injury leads to the intracellular liberation of zinc, we hypothesize that tapping onto the zinc-activated metal regulatory element (MRE) transcription factor 1 system to drive expression of the Kv2.1-targeted hepatitis C protein NS5A (hepatitis C nonstructural protein 5A) will provide neuroprotection by preventing cell death-enabling cellular potassium loss in rat cortical neurons in vitro. Indeed, using biochemical and morphologic assays, we demonstrate rapid expression of MRE-driven products in neurons. Further, we report that MRE-driven NS5A expression, induced by a slowly evolving excitotoxic stimulus, functionally blocks injurious, enhanced Kv2.1 potassium whole-cell currents and improves neuronal viability. We suggest this form of "on-demand" neuroprotection could provide the basis for a tenable therapeutic strategy to prevent neuronal cell death in neurodegeneration.

Adenosine Kinase couples sensing of cellular potassium depletion to purine metabolism

Adenosine Kinase (ADK) regulates the cellular levels of adenosine (ADO) by fine-tuning its metabolic clearance. The transfer of γ-phosphate from ATP to ADO by ADK involves regulation by the substrates and products, as well as by Mg2+ and inorganic phosphate. Here we present new crystal structures of mouse ADK (mADK) binary (mADK:ADO; 1.2 Å) and ternary (mADK:ADO:ADP; 1.8 Å) complexes. In accordance with the structural demonstration of ADO occupancy of the ATP binding site, kinetic studies confirmed a competitive model of auto-inhibition of ADK by ADO. In the ternary complex, a K+ ion is hexacoordinated between loops adjacent to the ATP binding site, where Asp310 connects the K+ coordination sphere to the ATP binding site through an anion hole structure. Nuclear Magnetic Resonance 2D 15N-1H HSQC experiments revealed that the binding of K+ perturbs Asp310 and residues of adjacent helices 14 and 15, engaging a transition to a catalytically productive structure. Consistent with the structural data, the mutants D310A and D310P are catalytically deficient and loose responsiveness to K+. Saturation Transfer Difference spectra of ATPγS provided evidence for an unfavorable interaction of the mADK D310P mutant for ATP. Reductions in K+ concentration diminish, whereas increases enhance the in vitro activity of mADK (maximum of 2.5-fold; apparent Kd = 10.4 mM). Mechanistically, K+ increases the catalytic turnover (Kcat) but does not affect the affinity of mADK for ADO or ATP. Depletion of intracellular K+ inhibited, while its restoration was accompanied by a full recovery of cellular ADK activity. Together, this novel dataset reveals the molecular basis of the allosteric activation of ADK by K+ and highlights the role of ADK in connecting depletion of intracellular K+ to the regulation of purine metabolism.

Glycogenolysis in Acquired Glioma Resistance to Temozolomide: A Role for the [Ca2+]i-dependent Activation of Na,K-ATPase/ERK1/2 Signaling.

Understanding the mechanistic basis for temozolomide (TMZ)-induced glioma resistance is an important obstacle in developing an effective form of chemotherapy for this type of tumor. Glycogenolysis is known to play an essential role in cellular proliferation and potassium homeostasis and involves the glycogen phosphorylase isoenzyme BB (GPBB). In this investigation, plasma GPBB was correlated with TMZ-resistance. Elevated plasma GPBB concentrations were found to be more frequent in a TMZ-resistant cohort of patients with poor survival rates. TMZ inhibits cell proliferation and induces TMZ resistance by upregulating the expression of O(6)-methylguanine-DNA methyltransferase (MGMT). This process requires glycogenolysis, which was confirmed herein by treatment with 1,4-dideoxy-1,4-imino-D-arabinitol hydrochloride, a glycogenolysis inhibitor and a special GPBB inhibitor. Acute TMZ treatment leads to upregulation of [Ca2+]i, extracellular-regulated kinase (ERK)1/2 phosphorylation, and chronic TMZ treatment leads to upregulation of the expression of Na,K-ATPase, ERK1/2, and MGMT protein. Upregulation was abolished for each of these by inhibitors of transient receptor potential channel 1 and the inositol trisphosphate receptor. L-channel [Ca2+]i inhibitors and RyR antagonists had no such effect. These results demonstrate that [Ca2+]i-dependent glycogenolysis participates in acquired glioma TMZ-resistance by upregulating MGMT via a Na,K-ATPase/ERK1/2 signaling pathway. GPBB and glycogenolysis may therefore represent novel therapeutic targets for overcoming TMZ-resistant gliomas.

High-density lipoprotein inhibits serum amyloid A–mediated reactive oxygen species generation and NLRP3 inflammasome activation

Serum amyloid A (SAA) is a high-density apolipoprotein whose plasma levels can increase more than 1000-fold during a severe acute-phase inflammatory response and are more modestly elevated in chronic inflammation. SAA is thought to play important roles in innate immunity, but its biological activities have not been completely delineated. We previously reported that SAA deficiency protects mice from developing abdominal aortic aneurysms (AAAs) induced by chronic angiotensin II (AngII) infusion. Here, we report that SAA is required for AngII-induced increases in interleukin-1β (IL-1β), a potent proinflammatory cytokine that is tightly controlled by the Nod-like receptor protein 3 (NLRP3) inflammasome and caspase-1 and has been implicated in both human and mouse AAAs. We determined that purified SAA stimulates IL-1β secretion in murine J774 and bone marrow-derived macrophages through a mechanism that depends on NLRP3 expression and caspase-1 activity, but is independent of P2X7 nucleotide receptor (P2X7R) activation. Inhibiting reactive oxygen species (ROS) by N-acetyl-l-cysteine or mito-TEMPO and inhibiting activation of cathepsin B by CA-074 blocked SAA-mediated inflammasome activation and IL-1β secretion. Moreover, inhibiting cellular potassium efflux with glyburide or increasing extracellular potassium also significantly reduced SAA-mediated IL-1β secretion. Of note, incorporating SAA into high-density lipoprotein (HDL) prior to its use in cell treatments completely abolished its ability to stimulate ROS generation and inflammasome activation. These results provide detailed insights into SAA-mediated IL-1β production and highlight HDL's role in regulating SAA's proinflammatory effects.

Abstract 566: High-density Lipoprotein Inhibits Serum Amyloid a -Mediated Inflammasome Activation

Objectives: Interleukin-1beta (IL-1β) has been implicated in inflammatory diseases, including atherosclerosis and abdominal aortic aneurysm (AAA). Production of bioactive IL-1β is controlled by the inflammasome, a multi-protein complex that regulates caspase-1 activity. Serum Amyloid A (SAA) is an acute-phase protein whose levels in circulation is elevated in individuals with chronic inflammation. We previously reported that deficiency of SAA protects mice from angiotensin II (AngII)-induced AAA. Here we report that reduced AngII-induced AAA in SAA-deficient mice is accompanied by significant reductions in plasma IL-1β, indicating that SAA is required for inflammasome activation in AngII-infused mice. The objective of this study is to investigate mechanisms involved in SAA-mediated inflammasome activation. Methods/Results: SAA dose-dependently induced both caspase-1 activation and IL-1β secretion in J774 macrophage-like cells incubated with 0-25 μg/ml purified mouse SAA. The ability of SAA to induce IL-1β secretion was significantly reduced in bone marrow-derived macrophages deficient in NLRP3. A caspase-1inhibitor, Z-YVAD-FMK, significantly suppressed IL-1β secretion induced by SAA, whereas the P2X7-receptor antagonist, AA38079, had no effect. Inhibition of reactive oxygen species (ROS), cathepsin-B activation, and cellular potassium efflux by N-acetyl-L-cysteine, CA-074, and glyburide, respectively, blocked NLRP3 inflammasome activation by SAA. Pre-incubating SAA with HDL prior to cell treatments completely abrogated SAA-mediated inflammasome activation. In contrast, HDL did not alter inflammasome activation triggered by ATP. Conclusions: SAA-mediated NLRP3 inflammasome activation in macrophages is dependent on ROS generation, release of cathepsin-B, and potassium efflux, and is independent of the P2X7 receptor. Moreover, our data identify a novel mechanism by which HDL may exert cardioprotective effects.

PI(3,5)P2 Regulates Vacuole Cation Transport to Mediate Cellular Osmoregulation

Lysosomes are dynamic organelles with critical roles in cellular physiology. The lysosomal signaling lipid phosphatidylinositol 3,5‐bisphosphate (PI(3,5)P2) is a key regulator that has been implicated to control lysosome ion homeostasis, but the scope of ion transporters targeted by PI(3,5)P2 and the purpose of this regulation is not well understood. We identified loss‐of‐function mutations in the vacuolar H+‐ATPase (V‐ATPase) and in Vnx1, a vacuolar monovalent cation/proton antiporter that suppress the growth defects and osmotic swelling of vacuoles (lysosomes) in Saccharomyces cerevisiae lacking PI(3,5)P2 synthesis. The loss of PI(3,5)P2 synthesis in yeast causes a robust accumulation of multiple cations, most notably a ~3‐fold increase in cellular potassium, a primary osmolyte that regulates cellular/organellar water content. The accumulation of potassium and other cations in yeast lacking PI(3,5)P2 is relieved by Vnx1 or V‐ATPase inactivation, or by increased activation of a vacuolar cation export channel, Yvc1. Furthermore, inactivating the V‐ATPase or Vnx1 rescued several vacuole functions that are defective in PI(3,5)P2‐deficient cells. Thus, our data demonstrates that a critical function of PI(3,5)P2 signaling is to orchestrate vacuole/lysosome ion transport to maintain cellular osmoregulation and lysosome homeostasis.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Bunyavirus requirement for endosomal K+ reveals new roles of cellular ion channels during infection.

In order to multiply and cause disease a virus must transport its genome from outside the cell into the cytosol, most commonly achieved through the endocytic network. Endosomes transport virus particles to specific cellular destinations and viruses exploit the changing environment of maturing endocytic vesicles as triggers to mediate genome release. Previously we demonstrated that several bunyaviruses, which comprise the largest family of negative sense RNA viruses, require the activity of cellular potassium (K+) channels to cause productive infection. Specifically, we demonstrated a surprising role for K+ channels during virus endosomal trafficking. In this study, we have used the prototype bunyavirus, Bunyamwera virus (BUNV), as a tool to understand why K+ channels are required for progression of these viruses through the endocytic network. We report three major findings: First, the production of a dual fluorescently labelled bunyavirus to visualize virus trafficking in live cells. Second, we show that BUNV traffics through endosomes containing high [K+] and that these K+ ions influence the infectivity of virions. Third, we show that K+ channel inhibition can alter the distribution of K+ across the endosomal system and arrest virus trafficking in endosomes. These data suggest high endosomal [K+] is a critical cue that is required for virus infection, and is controlled by cellular K+ channels resident within the endosome network. This highlights cellular K+ channels as druggable targets to impede virus entry, infection and disease.

Inhibition of aldose-reductase-2 by a benzofuroxane derivative bf-5m increases the expression of kcne1, kcnq1 in high glucose cultured H9c2 cardiac cells and sudden cardiac death.

Long QT syndrome (LQTS) is characterized by prolonged QT interval, leading to sudden cardiac death. Hyperglycemia is an important risk factor for LQTS, inhibiting the cardiac rapid component delayed rectifier K+ current (Iks), responsible for QT interval. We previously showed that the new ALR2 inhibitor BF-5m supplies cardioprotection from QT prolongation induced by high glucose concentration in the medium, reducing QT interval prolongation and preserving morphology. Here we investigated the effects of BF-5m on cell cytotoxicity and viability in H9c2 cells, and on cellular potassium ion channels expression.H9c2 cells were grown in medium with high glucose and high glucose plus the BF-5m by assessing the cytotoxic effects and the cell survival rate. In addition, KCNE1 and KCNQ1 expression in plasma and mitochondrial membranes were monitored. Also, the expression levels of miR-1 proved to suppress KCNQ1 and KCNE1, were analyzed.BF-5m treatment reduced the cytotoxic effects of high glucose on H9c2 cells by increasing cell survival rate and improving H9c2 morphology. Plasmatic KCNE1 and KCNQ1 expression levels were restored by BF-5m in H9c2 exposed to high glucose, down-regulating miR-1.These results suggest that BF-5m exerts cardioprotection from high glucose in rat heart ventricle H9c2 cells exposed to high glucose.

Early Effects of Rhodomyrtone on Membrane Integrity in Methicillin-Resistant Staphylococcus aureus.

Strong evidence of high potency of rhodomyrtone as a promising antibacterial agent against pathogenic gram-positive bacteria has been clearly demonstrated in our previous work. The aim of this study was to provide insight into early action of rhodomyrtone, an acylphloroglucinol, on membrane damage in multidrug-resistant methicillin-resistant Staphylococcus aureus (MRSA). Early effects of rhodomyrtone on the bacterial membrane integrity were detected in a time-course study. Flow cytometry revealed a reduction in green fluorescent emission and increase in uptake of propidium iodide in rhodomyrtone-treated bacterial cells in a concentration- and time-dependent manner. Disruption of cytoplasmic membrane was further monitored by measuring cellular adenosine triphosphate (ATP) and potassium ion (K+). Leakage of both ATP and K+ and significant decrease in intracellular ATP in MRSA were observed following treatment. Pronounced changes in the bacterial ultrastructure and morphology were confirmed by transmission electron microscopy and scanning electron microscopy. Bacterial cell disruption, holes in cell surface, and bulge formations were noted in rhodomyrtone-treated cells. In this study, we provided relevant data to clarify that rhodomyrtone is a bacterial cell membrane-damaging agent. A possible early effect of this novel compound involves bacterial membrane disruption.

Evidence for a Role of Vascular Endothelium in the Control of Arterial Wall Viscosity in Humans.

URL: https://eudract.ema.europa.eu. Unique identifier: RCB2007-A001-10-53.

Responses of the freshwater fish Cyprinus carpio exposed to different concentrations of butachlor and oxadiazon

The toxic effects of butachlor and oxadiazon, widely used herbicides in South Korea were evaluated in the common carp Cyprinus carpio. Fingerlings of C. carpio were exposed to 0.5, 5 and 50 µg L-1 concentrations of herbicides for 96 h under static bioassay method and hematological and biochemical parameters were assessed. At all concentrations of butachlor and oxadiazon, white blood cell (WBC), serum sodium (Na+), chloride (Cl-), glucose, cholesterol and triglyceride levels were significantly (P < 0.05) increased compared to that of their control groups. Mean cellular volume (MCV), mean cellular haemoglobin (MCH), potassium (K+) and alkaline phosphatase (ALP) levels were significantly increased in all the concentrations of oxadiazon exposed groups. Total protein, albumin and globulin levels were induced in butachlor treated fish. Both the herbicides caused a decrease in haemoglobin (Hb), hematocrit (Hct) and red blood cell (RBC) counts in all the concentrations. However, no significant changes were found in the mean cellular haemoglobin concentration (MCHC) levels. The importance of these parameters in monitoring of the aquatic ecosystem contaminated with pesticides is discussed in detail. Furthermore, chronic effects of these herbicides on these parameters along with other parameters such as hormonal and histopathological studies need to be investigated in the future studies.

Selection and functional analysis of a Pyropia yezoensis ammonium transporter PyAMT1 in potassium deficiency

Seaweeds are believed to have developed unique mechanisms to maintain optimal cellular potassium and sodium concentrations in order to survive in the saline marine environment. To gain a molecular understanding of underlying potassium/sodium homeostasis in seaweeds, full-length cDNA libraries from the multiple stages in the life cycle, including gametophytes, conchosporangia and sporophytes of a marine red alga, Pyropia yezoensis, were constructed. A large portion of genes from each library through the life cycle was revealed to be functionally unknown reconfirming the uniqueness of P. yezoensis genes in terms of evolutionary lineage. Genes that could potentially contribute to potassium deficiency tolerance were selected from the potassium uptake defective Escherichia coli strain expressing gametophytes and conchosporangia libraries under the low potassium conditions. Of those, an ammonium transporter gene, PyAMT1, was demonstrated to enhance potassium deficiency tolerance effectively when expressed in the E. coli strain. Potential roles of PyAMT1 and other candidate components in this context are discussed.

Crystal structure of the potassium-importing KdpFABC membrane complex.

Cellular potassium import systems play a fundamental role in osmoregulation, pH homeostasis and membrane potential in all domains of life. In bacteria, the kdp operon encodes a four subunit potassium pump that maintains intracellular homeostasis as well as cell shape and turgor under conditions where potassium is limiting1. This membrane complex, called KdpFABC, has one channel-like subunit (KdpA) belonging to the Superfamily of Potassium Transporters and another pump-like subunit (KdpB) belonging to the Superfamily of P-type ATPases. Although there is considerable structural and functional information about members from both superfamilies, the mechanism by which uphill potassium transport through KdpA is coupled with ATP hydrolysis by KdpB remains poorly understood. Here we report the 2.9 Å X-ray structure of the complete Escherichia coli KdpFABC complex with a potassium ion within the selectivity filter of KdpA as well as a water molecule at a canonical cation site in the transmembrane domain of KdpB. The structure also reveals two structural elements that appear to mediate the coupling between these two subunits. Specifically, a protein-embedded tunnel runs between these potassium and water sites and a helix controlling the cytoplasmic gate of KdpA is linked to the phosphorylation domain of KdpB. Based on these observations, we propose an unprecedented mechanism that repurposes protein channel architecture for active transport across biomembranes.

Deep sequencing of atrial fibrillation patients with mitral valve regurgitation shows no evidence of mosaicism but reveals novel rare germline variants

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Valvular heart disease is a strong predictor, yet the underlying molecular mechanisms are unknown. The purpose of this study was to investigate the prevalence of somatic variants in AF candidate genes in an AF patient population undergoing surgery for mitral valve regurgitation (MVR) to determine whether these patients are genetically predisposed to AF. DNA was extracted from blood and left atrial tissue from 44 AF patients with MVR. Using next-generation sequencing, we investigated 110 genes using the HaloPlex Target Enrichment System. MuTect software was used for identification of somatic point variants. We functionally characterized selected variants using electrophysiologic techniques. No somatic variants were identified in the cardiac tissue. Thirty-three patients (75%) had a rare germline variation in ≥1candidate genes. Fourteen variants were novel. Fifteen variants were predicted damaging or likely damaging in ≥6 in silico predictions. We identified rare variants in genes never directly associated with AF: KCNE4, SCN4B, NEURL1, and CAND2. Interestingly, 7 patients (16%) had variants in genes involved in cellular potassium handling. The variants KCNQ1 (p.G272S) and KCNH2 (p.A913V) resulted in gain of function due to faster activation (KCNQ1) and slowed deactivation kinetics (KCNQ1, KCNH2). We did not find any somatic variants in patients with AF and MVR. Surprisingly, we found that our cohort of non-lone AF patients might, like lone AF patients, be predisposed to AF by rare germline variants. Our findings emphasize the extent of still unknown factors in the pathogenesis of AF.

A highly selective, colorimetric, and environment-sensitive optical potassium ion sensor.

Potassium ions (K+) play vital roles in many biological processes and thus highly selective sensors for K+ are critical for disease diagnosis and health monitoring. Herein, we report a colorimetric K+ sensor (KS7) in which a hemicyanine dye was used as a fluorophore and phenylaza-[18]crown-6 lariat ether (ACLE) was utilized as a K+ ligand. The maximum absorption peak of KS7 shifted hypsochromically by 77 nm (from 515 to 438 nm) with an isosbestic point at 452 nm upon the addition of K+ to its aqueous solution accompanied by a color change from red to yellow. This sensor exhibited a linear response range to K+ from 1 to 200 mM, indicating its wide detection range for cellular, urinary, and environmental potassium ions. Further, this sensor is solvent-sensitive, implying its environmental sensitivity. For the demonstration of its applications, we prepared filter paper-based K+ test strips, which were used to detect K+ in urine conveniently.

Running out of time: the decline of channel activity and nucleotide activation in adenosine triphosphate-sensitive K-channels.

KATP channels act as key regulators of electrical excitability by coupling metabolic cues—mainly intracellular adenine nucleotide concentrations—to cellular potassium ion efflux. However, their study has been hindered by their rapid loss of activity in excised membrane patches (rundown), and by a second phenomenon, the decline of activation by Mg-nucleotides (DAMN). Degradation of PI(4,5)P2 and other phosphoinositides is the strongest candidate for the molecular cause of rundown. Broad evidence indicates that most other determinants of rundown (e.g. phosphorylation, intracellular calcium, channel mutations that affect rundown) also act by influencing KATP channel regulation by phosphoinositides. Unfortunately, experimental conditions that reproducibly prevent rundown have remained elusive, necessitating post hoc data compensation. Rundown is clearly distinct from DAMN. While the former is associated with pore-forming Kir6.2 subunits, DAMN is generally a slower process involving the regulatory sulfonylurea receptor (SUR) subunits. We speculate that it arises when SUR subunits enter non-physiological conformational states associated with the loss of SUR nucleotide-binding domain dimerization following prolonged exposure to nucleotide-free conditions. This review presents new information on both rundown and DAMN, summarizes our current understanding of these processes and considers their physiological roles.This article is part of the themed issue ‘Evolution brings Ca2+ and ATP together to control life and death’.