Potassium: From Physiology to Clinical Implications

Effective lowering of α-synuclein expression by targeting G-quadruplex structures within the SNCA gene

Alpha-synuclein, encoded by the SNCA gene, is a pivotal protein implicated in the pathogenesis of synucleinopathies, including Parkinson's disease. Current approaches for modulating alpha-synuclein levels involve antisense nucleotides, siRNAs, and small molecules targeting SNCA's 5'-UTR mRNA. Here, we propose a groundbreaking strategy targeting G-quadruplex structures to effectively modulate SNCA gene expression and lowering alpha-synuclein amount. Novel G-quadruplex sequences, identified on the SNCA gene's transcription starting site and 5'-UTR of SNCA mRNAs, were experimentally confirmed for their stability through biophysical assays and in vitro experiments on human genomic DNA. Biological validation in differentiated SH-SY5Y cells revealed that well-known G-quadruplex ligands remarkably stabilized these structures, inducing the modulation of SNCA mRNAs expression, and the effective decrease in alpha-synuclein amount. Besides, a novel peptide nucleic acid conjugate, designed to selectively disrupt of G-quadruplex within the SNCA gene promoter, caused a promising lowering of both SNCA mRNA and alpha-synuclein protein. Altogether our findings highlight G-quadruplexes' key role as intriguing biological targets in achieving a notable and successful reduction in alpha-synuclein expression, pointing to a novel approach against synucleinopathies.

CRTAC1 has a Compact β-propeller-TTR Core Stabilized by Potassium Ions

Cartilage acidic protein-1 (CRTAC1) is a secreted glycoprotein with roles in development, function and repair of the nervous system. It is linked to ischemic stroke, osteoarthritis and (long) COVID outcomes, and has suppressive activity in carcinoma and bladder cancer. Structural characterization of CRTAC1 has been complicated by its tendency to form disulfide-linked aggregates. Here, we show that CRTAC1 is stabilized by potassium ions. Using x-ray crystallography, we determined the structure of CRTAC1 to 1.6 Å. This reveals that the protein consists of a three-domain fold, including a previously-unreported compact β-propeller-TTR combination, in which an extended loop of the TTR plugs the β-propeller core. Electron density is observed for ten bound ions: six calcium, three potassium and one sodium. Low potassium ion concentrations lead to changes in tryptophan environment and exposure of two buried free cysteines located on a β-blade and in the β-propeller-plugging TTR loop. Mutating the two free cysteines to serines prevents covalent intermolecular interactions, but not aggregation, in absence of potassium ions. The potassium ion binding sites are located between the blades of the β-propeller, explaining their importance for the stability of the CRTAC1 fold. Despite varying in sequence, the three potassium ion binding sites are structurally similar and conserved features of the CRTAC protein family. These insights into the stability and structure of CRTAC1 provide a basis for further work into the function of CRTAC1 in health and disease.

IGF2BP1-Mediated Regulation of CCN1 Expression by Specific Binding to G-Quadruplex Structure in Its 3'UTR

The intricate regulation of gene expression is fundamental to the biological complexity of higher organisms, and is primarily governed by transcriptional and post-transcriptional mechanisms. The 3'-untranslated region (3'UTR) of mRNA is rich in cis-regulatory elements like G-quadruplexes (G4s), and plays a crucial role in post-transcriptional regulation. G4s have emerged as significant gene regulators, impacting mRNA stability, translation, and localization. In this study, we investigate the role of a robust parallel G4 structure situated within the 3'UTR of CCN1 mRNA in post-transcriptional regulation. This G4 structure is proximal to the stop codon of human CCN1, and evolutionarily conserved. We elucidated its interaction with the insulin-like growth factor 2 binding protein 1 (IGF2BP1), a noncanonical RNA N6-methyladenosine (m6A) modification reader, revealing a novel interplay between RNA modifications and G-quadruplex structures. Knockdown experiments and mutagenesis studies demonstrate that IGF2BP1 binds specifically to the G4 structure, modulating CCN1 mRNA stability. Additionally, we unveil the role of IGF2BP1's RNA recognition motifs in G4 recognition, highlighting this enthalpically driven interaction. Our findings offer fresh perspectives on the complex mechanisms of post-transcriptional gene regulation mediated by G4 RNA secondary structures.

Development of an Evidence-Based List of Non-Antineoplastic Vesicants: 2024 Update

Infiltration of a vesicant, called extravasation, can result in severe patient injuries. Recognition of vesicants and their relative risk of injury is essential to extravasation prevention, early recognition, and appropriate treatment. In this article, the Vesicant Task Force (VTF) updates the previously published Infusion Nurses Society (INS) vesicant list from 2017. The 2024 INS list diverges from earlier vesicant lists, such as the 2017 VTF list, by adopting a risk stratification approach based upon documented patient outcomes, in contrast to the reliance on expert consensus or only surrogate risk indicators, such as pH and osmolarity. The methodology used to create the updated list is explained, and the criteria for high- and moderate-risk vesicants and cautionary vesicants are defined.

Optimising patient care: comprehensive evaluation of inpatient hypokalaemia

Hypokalaemia is a common electrolyte disorder affecting hospitalised patients. It is associated with adverse outcomes including increased mortality. Inpatients with hypokalaemia need a different approach to workup and management as the aetiologies and progression of the hypokalaemia are distinct to outpatients. Potassium homeostasis is predominantly maintained by renal potassium handling. The clinical manifestations of hypokalaemia depend on the severity of hypokalaemia, however, most of the findings are non-specific. The approach to management is guided by the severity of the hypokalaemia and the underlying aetiology. Oral potassium replacement can be used in many cases of mild hypokalaemia. Intravenous replacement of potassium is necessary for many inpatients. Close monitoring is essential to ensure adequacy and to prevent adverse outcomes. An interdisciplinary approach with critical care input is needed in severe cases, and in patients where routine intravenous replacement may not be feasible (e.g., patients with heart failure). In addition to replacement, the cornerstone of management is a comprehensive review of the patient to identify the underlying cause of the hypokalaemia and the factors sustaining it. In patients in whom the cause is not apparent, or the potassium does not improve as anticipated, a referral to nephrology or endocrinology should be considered. This paper reviews the assessment of hypokalaemia in a hospital setting. It is aimed at early career doctors on the wards to help carry out a thorough evaluation. It also provides a useful framework for management.

Facile One Pot Synthesis of Hybrid Core-Shell Silica-Based Sensors for Live Imaging of Dissolved Oxygen and Hypoxia Mapping in 3D Cell Models

Fluorescence imaging allows for noninvasively visualizing and measuring key physiological parameters like pH and dissolved oxygen. In our work, we created two ratiometric fluorescent microsensors designed for accurately tracking dissolved oxygen levels in 3D cell cultures. We developed a simple and cost-effective method to produce hybrid core-shell silica microparticles that are biocompatible and versatile. These sensors incorporate oxygen-sensitive probes (Ru(dpp) or PtOEP) and reference dyes (RBITC or A647 NHS-Ester). SEM analysis confirmed the efficient loading and distribution of the sensing dye on the outer shell. Fluorimetric and CLSM tests demonstrated the sensors' reversibility and high sensitivity to oxygen, even when integrated into 3D scaffolds. Aging and bleaching experiments validated the stability of our hybrid core-shell silica microsensors for 3D monitoring. The Ru(dpp)-RBITC microparticles showed the most promising performance, especially in a pancreatic cancer model using alginate microgels. By employing computational segmentation, we generated 3D oxygen maps during live cell imaging, revealing oxygen gradients in the extracellular matrix and indicating a significant decrease in oxygen level characteristics of solid tumors. Notably, after 12 h, the oxygen concentration dropped to a hypoxic level of PO2 2.7 ± 0.1%.

Mechanisms of inclusion of thallium-201 into Prussian blue nanoparticles for nuclear medicine applications

Prussian blue is known for its high affinity for thallium and other univalent metal cations and has been used as a treatment for radiocaesium and thallium/radiothallium poisoning. While Prussian blue nanoparticles (PBNPs) show potential for binding radioactive thallium for further use in nuclear medicine applications, the inclusion mechanism remains elusive. Understanding the interaction between PBNPs and 201Tl is essential for identifying the physicochemical and radiochemical properties required for optimal in vivo performance. In this work, we evaluated the binding mechanism between Tl and PBNPs with different coatings and core shapes. Combining PBNPs with [201Tl] thallium(I) chloride provided high radiolabelling yields and radiochemical stabilities under physiological conditions. Comprehensive characterisation by different X-ray techniques confirmed that Tl ions are located in the interstitial sites within the crystal structure, maintaining the integrity of the iron (Fe) 4p electronic distribution and inducing local modifications in the nearby C-N ligands. Additionally, this inclusion does not impact the core or the shell of the nanoparticles but does alter their ionic composition. The PB ionic network undergoes significant changes, with a substantial drop in K+ content, confirming that Tl+ ions replace K+ and occupy additional spaces within the crystal structure. These results open new opportunities in nuclear medicine applications with 201Tl-PBNPs where the size, shape and composition of the particles can be specifically tuned depending on the desired biological properties without affecting the radiochemical performance as a vehicle for 201Tl.

Structural biology and molecular pharmacology of voltage-gated ion channels

Voltage-gated ion channels (VGICs), including those for Na+, Ca2+ and K+, selectively permeate ions across the cell membrane in response to changes in membrane potential, thus participating in physiological processes involving electrical signalling, such as neurotransmission, muscle contraction and hormone secretion. Aberrant function or dysregulation of VGICs is associated with a diversity of neurological, psychiatric, cardiovascular and muscular disorders, and approximately 10% of FDA-approved drugs directly target VGICs. Understanding the structure-function relationship of VGICs is crucial for our comprehension of their working mechanisms and role in diseases. In this Review, we discuss how advances in single-particle cryo-electron microscopy have afforded unprecedented structural insights into VGICs, especially on their interactions with clinical and investigational drugs. We present a comprehensive overview of the recent advances in the structural biology of VGICs, with a focus on how prototypical drugs and toxins modulate VGIC activities. We explore how these structures elucidate the molecular basis for drug actions, reveal novel pharmacological sites, and provide critical clues to future drug discovery.

Structural Unfolding of G-Quadruplexes: From Small Molecules to Antisense Strategies

G-quadruplexes (G4s) are non-canonical nucleic acid secondary structures that have gathered significant interest in medicinal chemistry over the past two decades due to their unique structural features and potential roles in a variety of biological processes and disorders. Traditionally, research efforts have focused on stabilizing G4s, while in recent years, the attention has progressively shifted to G4 destabilization, unveiling new therapeutic perspectives. This review provides an in-depth overview of recent advances in the development of small molecules, starting with the controversial role of TMPyP4. Moreover, we described effective metal complexes in addition to G4-disrupting small molecules as well as good G4 stabilizing ligands that can destabilize G4s in response to external stimuli. Finally, we presented antisense strategies as a promising approach for destabilizing G4s, with a particular focus on 2'-OMe antisense oligonucleotide, peptide nucleic acid, and locked nucleic acid. Overall, this review emphasizes the importance of understanding G4 dynamics as well as ongoing efforts to develop selective G4-unfolding strategies that can modulate their biological function and therapeutic potential.

Ion carrier modulated MRI contrast

An ion-responsive MRI contrast agent based on a POPC liposomal scaffold is generated that displays a large amplitude relaxivity switch. Entrapment of MR active Gd-DOTA within cholesterol-doped, i.e., membrane rigidified, liposomes dampens the MR response through diminished water exchange across the lipid bilayer. Relaxivity is re-established by integration of ion carriers in the liposome membrane to mediate solvated ion flux.

Does the XPA-FEN1 Interaction Concern to Nucleotide Excision Repair or Beyond?

Nucleotide excision repair (NER) is the most universal repair pathway, which removes a wide range of DNA helix-distorting lesions caused by chemical or physical agents. The final steps of this repair process are gap-filling repair synthesis and subsequent ligation. XPA is the central NER scaffolding protein factor and can be involved in post-incision NER stages. Replication machinery is loaded after the first incision of the damaged strand that is performed by the XPF-ERCC1 nuclease forming a damaged 5'-flap processed by the XPG endonuclease. Flap endonuclease I (FEN1) is a critical component of replication machinery and is absolutely indispensable for the maturation of newly synthesized strands. FEN1 also contributes to the long-patch pathway of base excision repair. Here, we use a set of DNA substrates containing a fluorescently labeled 5'-flap and different size gap to analyze possible repair factor-replication factor interactions. Ternary XPA-FEN1-DNA complexes with each tested DNA are detected. Furthermore, we demonstrate XPA-FEN1 complex formation in the absence of DNA due to protein-protein interaction. Functional assays reveal that XPA moderately inhibits FEN1 catalytic activity. Using fluorescently labeled XPA, formation of ternary RPA-XPA-FEN1 complex, where XPA accommodates FEN1 and RPA contacts simultaneously, can be proposed. We discuss possible functional roles of the XPA-FEN1 interaction in NER related DNA resynthesis and/or other DNA metabolic processes where XPA can be involved in the complex with FEN1.

Malnutrition management in children with chronic kidney disease

Chronic kidney disease (CKD) encompasses diverse conditions such as congenital anomalies, glomerulonephritis, and hereditary nephropathies, necessitating individualized nutritional interventions. Early detection is pivotal due to the heightened risk of adverse outcomes, including compromised growth and increased healthcare costs. The nutritional assessment in pediatric CKD employs a comprehensive, multidisciplinary approach, considering disease-specific factors, growth metrics, and dietary habits. The prevalence of malnutrition, as identified through diverse tools and guidelines, underscores the necessity for regular and vigilant monitoring. Nutritional management strategies seek equilibrium in calorie intake, protein requirements, and electrolyte considerations. Maintaining a well-balanced nutritional intake is crucial for preventing systemic complications and preserving the remaining kidney function. The nuanced landscape of enteral nutrition, inclusive of gastrostomy placement, warrants consideration in scenarios requiring prolonged support, with an emphasis on minimizing risks for optimized outcomes. In conclusion, the ongoing challenge of managing nutrition in pediatric CKD necessitates continuous assessment and adaptation. This review underscores the significance of tailored dietary approaches, not only to foster growth and prevent complications but also to enhance the overall quality of life for children grappling with CKD.

The biogenesis of potassium transporters: implications of disease-associated mutations

The concentration of intracellular and extracellular potassium is tightly regulated due to the action of various ion transporters, channels, and pumps, which reside primarily in the kidney. Yet, potassium transporters and cotransporters play vital roles in all organs and cell types. Perhaps not surprisingly, defects in the biogenesis, function, and/or regulation of these proteins are linked to range of catastrophic human diseases, but to date, few drugs have been approved to treat these maladies. In this review, we discuss the structure, function, and activity of a group of potassium-chloride cotransporters, the KCCs, as well as the related sodium-potassium-chloride cotransporters, the NKCCs. Diseases associated with each of the four KCCs and two NKCCs are also discussed. Particular emphasis is placed on how these complex membrane proteins fold and mature in the endoplasmic reticulum, how non-native forms of the cotransporters are destroyed in the cell, and which cellular factors oversee their maturation and transport to the cell surface. When known, we also outline how the levels and activities of each cotransporter are regulated. Open questions in the field and avenues for future investigations are further outlined.

Impaired distal renal potassium handling in streptozotocin-induced diabetic mice

Diabetes is closely associated with K+ disturbances during disease progression and treatment. However, it remains unclear whether K+ imbalance occurs in diabetes with normal kidney function. In this study, we examined the effects of dietary K+ intake on systemic K+ balance and renal K+ handling in streptozotocin (STZ)-induced diabetic mice. The control and STZ mice were fed low or high K+ diet for 7 days to investigate the role of dietary K+ intake in renal K+ excretion and K+ homeostasis and to explore the underlying mechanism by evaluating K+ secretion-related transport proteins in distal nephrons. K+-deficient diet caused excessive urinary K+ loss, decreased daily K+ balance, and led to severe hypokalemia in STZ mice compared with control mice. In contrast, STZ mice showed an increased daily K+ balance and elevated plasma K+ level under K+-loading conditions. Dysregulation of the NaCl cotransporter (NCC), epithelial Na+ channel (ENaC), and renal outer medullary K+ channel (ROMK) was observed in diabetic mice fed either low or high K+ diet. Moreover, amiloride treatment reduced urinary K+ excretion and corrected hypokalemia in K+-restricted STZ mice. On the other hand, inhibition of SGLT2 by dapagliflozin promoted urinary K+ excretion and normalized plasma K+ levels in K+-supplemented STZ mice, at least partly by increasing ENaC activity. We conclude that STZ mice exhibited abnormal K+ balance and impaired renal K+ handling under either low or high K+ diet, which could be primarily attributed to the dysfunction of ENaC-dependent renal K+ excretion pathway, despite the possible role of NCC.NEW & NOTEWORTHY Neither low dietary K+ intake nor high dietary K+ intake effectively modulates renal K+ excretion and K+ homeostasis in STZ mice, which is closely related to the abnormality of ENaC expression and activity. SGLT2 inhibitor increases urinary K+ excretion and reduces plasma K+ level in STZ mice under high dietary K+ intake, an effect that may be partly due to the upregulation of ENaC activity.

Integrating microneedles and sensing strategies for diagnostic and monitoring applications: The state of the art

Microneedles (MNs) offer minimally-invasive access to interstitial fluid (ISF) - a potent alternative to blood in terms of monitoring physiological analytes. This property is particularly advantageous for the painless detection and monitoring of drugs and biomolecules. However, the complexity of the skin environment, coupled with the inherent nature of the analytes being detected and the inherent physical properties of MNs, pose challenges when conducting physiological monitoring using this fluid. In this review, we discuss different sensing mechanisms and highlight advancements in monitoring different targets, with a particular focus on drug monitoring. We further list the current challenges facing the field and conclude by discussing aspects of MN design which serve to enhance their performance when monitoring different classes of analytes.

Persistent Luminescence Nanosensors: A Generalized Optode-Based Platform for Autofluorescence-Free Sensing in Biological Systems

Fluorescent nanosensors have revolutionized diagnostics and our ability to monitor cellular dynamics. Yet, distinguishing sensor signals from autofluorescence remains a challenge. Here, we merged optode-based sensing with near-infrared-emitting ZnGa2O4:Cr3+ persistent luminescence nanoparticles (PLNPs) to create nanocomposites for autofluorescence-free "glow-in-the-dark" sensing. Hydrophobic modification and incorporation of the persistent luminescence nanoparticles into an optode-based nanoparticle core yielded persistent luminescence nanosensors (PLNs) for five analytes (K+, Na+, Ca2+, pH, and O2) via two distinct mechanisms. We demonstrated the viability of the PLNs by quantifying K+ in fetal bovine serum, calibrating the pH PLNs in the same, and ratiometrically monitoring O2 metabolism in cultures of Saccharomyces cerevisiae, all the while overcoming their respective autofluorescence signatures. This highly modular platform allows for facile tuning of the sensing functionality, optical properties, and surface chemistry and promises high signal-to-noise ratios in complex optical environments.

Pseudonormokalemia case report - What does it mean to have normal blood potassium?

This case report describes a case of pseudonormokalemia, true hypokalemia. Often, only laboratory values outside the normal range gain attention and false normal results are at risk of not being noticed. However, a disease state may be masked by another pathological process. Here, a 50-year old male was admitted to the Department of Internal Medicine due to sepsis from a dental infection. Initially, serum potassium measurement revealed a normal value of 4 mmol/L (reference interval 3.8-5.1 mmol/L). Thrombocyte number was above 500x109/L. Due to our policy to recommend a repeated measurement of potassium in whole blood or heparin plasma if a patient has thrombocytosis, pseudonormokalemia was identified because the heparin plasma potassium value was only 2.9 mmol/L (reference interval 3.5-4.8 mmol/L). The physiological difference between serum and plasma concentration is no more than 0.3 mmol/L. In this case, potassium concentration were falsely elevated in the serum sample, probably caused by the high number of platelets releasing potassium during clotting. Interpretative comments in patients with thrombocytosis over 500x109/L recommending plasma potassium measurement are helpful. The best way to eliminate pseudohyperkalemia and pseudonormokalemia phenomena caused by thrombocytosis is to completely change towards heparin plasma as the standard material.

Probing intracellular potassium dynamics in neurons with the genetically encoded sensor lc-LysM GEPII 1.0 in vitro and in vivo

Neuronal activity is accompanied by a net outflow of potassium ions (K+) from the intra- to the extracellular space. While extracellular [K+] changes during neuronal activity are well characterized, intracellular dynamics have been less well investigated due to lack of respective probes. In the current study we characterized the FRET-based K+ biosensor lc-LysM GEPII 1.0 for its capacity to measure intracellular [K+] changes in primary cultured neurons and in mouse cortical neurons in vivo. We found that lc-LysM GEPII 1.0 can resolve neuronal [K+] decreases in vitro during seizure-like and intense optogenetically evoked activity. [K+] changes during single action potentials could not be recorded. We confirmed these findings in vivo by expressing lc-LysM GEPII 1.0 in mouse cortical neurons and performing 2-photon fluorescence lifetime imaging. We observed an increase in the fluorescence lifetime of lc-LysM GEPII 1.0 during periinfarct depolarizations, which indicates a decrease in intracellular neuronal [K+]. Our findings suggest that lc-LysM GEPII 1.0 can be used to measure large changes in [K+] in neurons in vitro and in vivo but requires optimization to resolve smaller changes as observed during single action potentials.

Potassium-mediated bacterial chemotactic response

Bacteria in biofilms secrete potassium ions to attract free swimming cells. However, the basis of chemotaxis to potassium remains poorly understood. Here, using a microfluidic device, we found that Escherichia coli can rapidly accumulate in regions of high potassium concentration on the order of millimoles. Using a bead assay, we measured the dynamic response of individual flagellar motors to stepwise changes in potassium concentration, finding that the response resulted from the chemotaxis signaling pathway. To characterize the chemotactic response to potassium, we measured the dose-response curve and adaptation kinetics via an Förster resonance energy transfer (FRET) assay, finding that the chemotaxis pathway exhibited a sensitive response and fast adaptation to potassium. We further found that the two major chemoreceptors Tar and Tsr respond differently to potassium. Tar receptors exhibit a biphasic response, whereas Tsr receptors respond to potassium as an attractant. These different responses were consistent with the responses of the two receptors to intracellular pH changes. The sensitive response and fast adaptation allow bacteria to sense and localize small changes in potassium concentration. The differential responses of Tar and Tsr receptors to potassium suggest that cells at different growth stages respond differently to potassium and may have different requirements for potassium.

Native mass spectrometry of complexes formed by molecular glues reveals stoichiometric rearrangement of E3 ligases

In this application of native mass spectrometry (nMS) to investigate complexes formed by molecular glues (MGs), we have demonstrated its efficiency in delineating stoichiometric rearrangements of E3 ligases that occur during targeted protein degradation (TPD). MGs stabilise interactions between an E3 ligase and a protein of interest (POI) targeted for degradation, and these ternary interactions are challenging to characterise. We have shown that nMS can unambiguously identify complexes formed between the CRBN : DDB1 E3 ligase and the POI GSPT1 upon the addition of lenalidomide, pomalidomide or thalidomide. Ternary complex formation was also identified involving the DCAF15 : DDA1 : DDB1 E3 ligase in the presence of MG (E7820 or indisulam) and POI RBM39. Moreover, we uncovered that the DCAF15 : DDA1 : DDB1 E3 ligase self-associates into dimers and trimers when analysed alone at low salt concentrations (100 mM ammonium acetate) which dissociate into single copies of the complex at higher salt concentrations (500 mM ammonium acetate), or upon the addition of MG and POI, forming a 1 : 1 : 1 ternary complex. This work demonstrates the strength of nMS in TPD research, reveals novel binding mechanisms of the DCAF15 E3 ligase, and its self-association into dimers and trimers at reduced salt concentration during structural analysis.

Pathogenic SNPs Affect Both RNA and DNA G-Quadruplexes' Responses to Ligands

Single nucleotide polymorphisms (SNPs) are common genetic variations that are present in over 1% of the population and can significantly modify the structures of both DNA and RNA. G-quadruplex structures (G4) are formed by the superposition of tetrads of guanines. To date, the impact of SNPs on both G4 ligands' binding efficacies and specificities has not been investigated. Here, using a bioinformatically predicted G4 and SNPs found in the α-synuclein gene as a proof-of-concept, it was demonstrated that SNPs can modulate both DNA and RNA G4s' responses to ligands. Specifically, six widely recognized ligands (Phen-DC3, PDS, 360A, RHPS4, BRACO19, and TMPyP4) were shown to differentially affect both the structure and the polymerase stalling of the different SNPs. This work highlights the importance of choosing the appropriate G4 ligand when dealing with an SNP identified in a G-rich gene.

Bioluminescence Imaging of Potassium Ion Using a Sensory Luciferin and an Engineered Luciferase

Bioluminescent indicators are power tools for studying dynamic biological processes. In this study, we present the generation of novel bioluminescent indicators by modifying the luciferin molecule with an analyte-binding moiety. Specifically, we have successfully developed the first bioluminescent indicator for potassium ions (K+), which are critical electrolytes in biological systems. Our approach involved the design and synthesis of a K+-binding luciferin named potassiorin. Additionally, we engineered a luciferase enzyme called BRIPO (bioluminescent red indicator for potassium) to work synergistically with potassiorin, resulting in optimized K+-dependent bioluminescence responses. Through extensive validation in cell lines, primary neurons, and live mice, we demonstrated the efficacy of this new tool for detecting K+. Our research demonstrates an innovative concept of incorporating sensory moieties into luciferins to modulate luciferase activity. This approach has great potential for developing a wide range of bioluminescent indicators, advancing bioluminescence imaging (BLI), and enabling the study of various analytes in biological systems.

Endothelial cell serum and glucocorticoid regulated kinase 1 (SGK1) mediates vascular stiffening

BACKGROUND

Excessive dietary salt intake increases vascular stiffness in humans, especially in salt-sensitive populations. While we recently suggested that the endothelial sodium channel (EnNaC) contributes to salt-sensitivity related endothelial cell (EC) and arterial stiffening, mechanistic understanding remains incomplete. This study therefore aimed to explore the role of EC-serum and glucocorticoid regulated kinase 1 (SGK1), as a reported regulator of sodium channels, in EC and arterial stiffening.

METHODS AND RESULTS

A mouse model of salt sensitivity-associated vascular stiffening was produced by subcutaneous implantation of slow-release deoxycorticosterone acetate (DOCA) pellets, with salt (1 % NaCl, 0.2 % KCl) administered via drinking water. Preliminary data showed that global SGK1 deletion caused significantly decreased blood pressure (BP), EnNaC activity and aortic endothelium stiffness as compared to control mice following DOCA-salt treatment. To probe EC signaling pathways, selective deletion of EC-SGK1 was performed by cross-breeding cadherin 5-Cre mice with sgk1flox/flox mice. DOCA-salt treated control mice had significantly increased BP, EC and aortic stiffness in vivo and ex vivo, which were attenuated by EC-SGK1 deficiency. To demonstrate relevance to humans, human aortic ECs were cultured in the absence or presence of aldosterone and high salt with or without the SGK1 inhibitor, EMD638683 (10uM or 25uM). Treatment with aldosterone and high salt increased intrinsic stiffness of ECs, which was prevented by SGK1 inhibition. Further, the SGK1 inhibitor prevented aldosterone and high salt induced actin polymerization, a key mechanism in cellular stiffening.

CONCLUSION

EC-SGK1 contributes to salt-sensitivity related EC and aortic stiffening by mechanisms appearing to involve regulation of actin polymerization.

Mechanisms and physiological relevance of acid-base exchange in functional units of the kidney

This review discusses the importance of homeostasis with a particular emphasis on the acid-base (AB) balance, a crucial aspect of pH regulation in living systems. Two primary organ systems correct deviations from the standard pH balance: the respiratory system via gas exchange and the kidneys via proton/bicarbonate secretion and reabsorption. Focusing on kidney functions, we describe the complexity of renal architecture and its challenges for experimental research. We address specific roles of different nephron segments (the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule) in pH homeostasis, while explaining the physiological significance of ion exchange processes maintained by the kidneys, particularly the role of bicarbonate ions (HCO3-) as an essential buffer system of the body. The review will be of interest to researchers in the fields of physiology, biochemistry and molecular biology, which builds a strong foundation and critically evaluates existing studies. Our review helps identify the gaps of knowledge by thoroughly understanding the existing literature related to kidney acid-base homeostasis.

Bioluminescence Imaging of Potassium Ion Using a Sensory Luciferin and an Engineered Luciferase

Bioluminescent indicators are power tools for studying dynamic biological processes. In this study, we present the generation of novel bioluminescent indicators by modifying the luciferin molecule with an analyte-binding moiety. Specifically, we have successfully developed the first bioluminescent indicator for potassium ions (K+), which are critical electrolytes in biological systems. Our approach involved the design and synthesis of a K+-binding luciferin named potassiorin. Additionally, we engineered a luciferase enzyme called BRIPO (bioluminescent red indicator for potassium) to work synergistically with potassiorin, resulting in optimized K+-dependent bioluminescence responses. Through extensive validation in cell lines, primary neurons, and live mice, we demonstrated the efficacy of this new tool for detecting K+. Our research demonstrates an innovative concept of incorporating sensory moieties into luciferins to modulate luciferase activity. This approach has great potential for developing a wide range of bioluminescent indicators, advancing bioluminescence imaging (BLI), and enabling the study of various analytes in biological systems.

K+ontrol rapidly and efficiently reduces potassium in donor blood during ex vivo circulation

BACKGROUND

Patients with kidney failure are at risk for lethal complications from hyperkalemia. Resuscitation, medications, and hemodialysis are used to mitigate increased potassium (K+) levels in circulating blood; however, these approaches may not always be readily available or effective, especially in a resource limited environment. We tested a sorbent cartridge (KC, K+ontrol CytoSorbents Medical Inc., Monmouth Junction, New Jersey) which contains a resin adsorber for K+. The objective of this study was to test the utility of KC in an ex vivo circulation system. We hypothesized that KC reduces K+ levels in extracorporeal circulation of donor swine whole blood infused with KCl.

METHODS

A six-hour circulation study was carried out using KC, a NxStage (NxStage Medical, Inc., Lawrence, MA) membrane, blood bag containing heparinized whole blood with KCl infusion, 3/16-inch ID tubing, a peristaltic pump, and flow sensors. The NxStage permeate line was connected back to the main circuit in the Control group (n = 6), creating a recirculation loop. For KC group (n = 6), KC was added to the recirculation loop, and a continuous infusion of KCl at 10 mEq/hour was administered for two hours. Blood samples were acquired at baseline and every hour for 6 h.

RESULTS

In the control group, K+ levels remained at ∼9 mmol/L; 9.1 ± 0.4 mmol/L at 6 h. In the KC group, significant decreases in K+ at hour 1 (4.3 ± 0.3 mmol/L) and were sustained for the experiment duration equilibrating at 4.6 ± 0.4 mmol/L after 6 h (p = 0.042). Main loop blood flow was maintained under 400 mL/min; recirculation loop flow varied between 60 and 70 mL/min in the control group and 45-55 mL/min in the KC group. Decreases in recirculation loop flow in KC group required 7% increase of pump RPM.

CONCLUSIONS

During ex-vivo extracorporeal circulation using donor swine blood, KC removed approximately 50% of K+, normalizing circulating levels.

Mycobacterium tuberculosis response to cholesterol is integrated with environmental pH and potassium levels via a lipid metabolism regulator

Successful colonization of the host requires Mycobacterium tuberculosis (Mtb) to sense and respond coordinately to disparate environmental cues during infection and adapt its physiology. However, how Mtb response to environmental cues and the availability of key carbon sources may be integrated is poorly understood. Here, by exploiting a reporter-based genetic screen, we have unexpectedly found that overexpression of transcription factors involved in Mtb lipid metabolism altered the dampening effect of low environmental potassium concentrations ([K+]) on the pH response of Mtb. Cholesterol is a major carbon source for Mtb during infection, and transcriptional analyses revealed that Mtb response to acidic pH was augmented in the presence of cholesterol and vice versa. Strikingly, deletion of the putative lipid regulator mce3R had little effect on Mtb transcriptional response to acidic pH or cholesterol individually, but resulted specifically in loss of cholesterol response augmentation in the simultaneous presence of acidic pH. Similarly, while mce3R deletion had little effect on Mtb response to low environmental [K+] alone, augmentation of the low [K+] response by the simultaneous presence of cholesterol was lost in the mutant. Finally, a mce3R deletion mutant was attenuated for growth in foamy macrophages and for colonization in a murine infection model that recapitulates caseous necrotic lesions and the presence of foamy macrophages. These findings reveal the critical coordination between Mtb response to environmental cues and cholesterol, a vital carbon source, and establishes Mce3R as a transcription factor that crucially serves to integrate these signals.

Non-steroidal Anti-inflammatory Drug (NSAID)-, Potassium Supplement-, Bisphosphonate-, and Doxycycline-Mediated Peptic Ulcer Effects: A Narrative Review

Peptic ulcers are a common condition that arises from an imbalance between acid production and gastroduodenal protective factors. Various drugs, including non-steroidal anti-inflammatory drugs (NSAIDs), potassium supplements, bisphosphonates, and doxycycline, can increase the development of peptic ulcers. NSAIDs are one of the most common medications prescribed for pain relief, and they also inhibit the formation of cyclooxygenase-1 (COX-1). COX-1 helps in the production of mucus that lines the stomach, so by inhibiting COX-1, NSAIDs reduce the mucus produced by the stomach and increase the likelihood of gastric ulcer formation. Additionally, NSAIDs are acidic, and increasing the amount of any acid in the stomach can result in promoting ulcer development. Potassium supplements are used to reduce the effects of hypertension, decrease the development of kidney stones, and treat hypokalemia. The various types of transporters and channels used to move potassium across cell membranes increase hydrogen being pumped, increasing gastric acid production and ulcer formation. Bisphosphonates are used to treat a variety of skeletal disorders that require inhibition of osteoclast activity. Nitric oxide (NO) has been shown to have a therapeutic effect on gastric ulcers, and some bisphosphonates have been shown to decrease the production of nitric oxide, resulting in increased damage to the gastric mucosa. Finally, doxycycline is a broad-spectrum tetracycline antibiotic that is typically used to treat anthrax poisoning, skin lesions, and sexually transmitted diseases. A harmful adverse effect of doxycycline is the formation of peptic and gastric ulcers related to the drug being highly acidic once it has dissolved.

Interdependence of cellular and network properties in respiratory rhythmogenesis

How breathing is generated by the preBötzinger Complex (preBötC) remains divided between two ideological frameworks, and the persistent sodium current (INaP) lies at the heart of this debate. Although INaP is widely expressed, the pacemaker hypothesis considers it essential because it endows a small subset of neurons with intrinsic bursting or "pacemaker" activity. In contrast, burstlet theory considers INaP dispensable because rhythm emerges from "pre-inspiratory" spiking activity driven by feed-forward network interactions. Using computational modeling, we discover that changes in spike shape can dissociate INaP from intrinsic bursting. Consistent with many experimental benchmarks, conditional effects on spike shape during simulated changes in oxygenation, development, extracellular potassium, and temperature alter the prevalence of intrinsic bursting and pre-inspiratory spiking without altering the role of INaP. Our results support a unifying hypothesis where INaP and excitatory network interactions, but not intrinsic bursting or pre-inspiratory spiking, are critical interdependent features of preBötC rhythmogenesis.

Pre-exposure to seawater or chloride salts influences the avoidance-selection behavior of zebrafish larvae in a conductivity gradient

The risk assessment of freshwater salinization is constructed around standard assays and using sodium chloride (NaCl), neglecting that the stressor is most likely a complex mixture of ions and the possibility of prior contact with it, triggering acclimation mechanisms in the freshwater biota. To date, as far as we are aware of, no information has been generated integrating both acclimation and avoidance behavior in the context of salinization, that may allow these risk assessments upgrading. Accordingly, 6-days-old Danio rerio larvae were selected to perform 12-h avoidance assays in a non-confined 6-compartment linear system to simulate conductivity gradients using seawater (SW) and the chloride salts MgCl2, KCl, and CaCl2. Salinity gradients were established from conductivities known to cause 50% egg mortality in a 96-h exposure (LC50,96h,embryo). The triggering of acclimation processes, which could influence organisms' avoidance-selection under the conductivity gradients, was also studied using larvae pre-exposed to lethal levels of each salt or SW. Median avoidance conductivities after a 12-h of exposure (AC50,12h), and the Population Immediate Decline (PID) were computed. All non-pre-exposed larvae were able to detect and flee from conductivities corresponding to the LC50,96h,embryo, selecting compartments with lower conductivities, except for KCl. The AC50,12h and LC50,96h overlapped for MgCl2 and CaCl2, though the former is considered as more sensitive as it was obtained in 12 h of exposure. The AC50,12h for SW was 1.83-fold lower than the LC50,96h, thus, reinforcing the higher sensitivity of the parameter ACx and its adequacy for risk assessment frameworks. The PID, at low conductivities, was solely explained by the avoidance behavior of non-pre-exposed larvae. Larvae pre-exposed to lethal levels of salt or SW were found to select higher conductivities, except for MgCl2. Results indicated that avoidance-selection assays are ecologically relevant and sensitive tools to be used in risk assessment processes. Stressor pre-exposure influenced organisms' avoidance-selection behavior under conductivity gradients, suggesting that under salinization events organisms may acclimate, remaining in altered habitats.

Comparison of effectiveness and safety of sodium polystyrene sulfonate and sodium zirconium cyclosilicate for treatment of hyperkalemia in hospitalized patients

PURPOSE

Potassium binders are frequently utilized for the treatment of hyperkalemia in hospitalized patients; however, there is limited data directly comparing individual agents. The purpose of this study was to compare the effectiveness and safety of sodium polystyrene sulfonate (SPS) and sodium zirconium cyclosilicate (SZC) for hyperkalemia treatment in hospitalized patients.

METHODS

This retrospective cohort study evaluated adult patients who were admitted within a 7-hospital health system and received SPS or SZC for a serum potassium level greater than 5.0 mEq/L. Patients receiving dialysis prior to SPS/SZC administration, those receiving other potassium-lowering medications within 6 hours prior to blood sampling for a repeat potassium level, and those started on kidney replacement therapy prior to sampling for a repeat potassium level were excluded.

RESULTS

Following evaluation of 3,903 patients, the mean reduction in serum potassium 4 to 24 hours after binder administration was 0.96 mEq/L with SPS and 0.78 mEq/L with SZC (P < 0.0001). The median dose of SPS was 30 g (interquartile range [IQR], 15-30 g) while the median (IQR) dose of SZC was 10 g (10-10 g). Resolution of hyperkalemia within 24 hours was achieved in a higher percentage of patients with use of SPS (74.9%) versus SZC (68.8%) (P < 0.001).

CONCLUSION

One of the largest comparisons of SPS and SZC conducted to date, this study demonstrated the effectiveness and safety of both agents. While a statistically greater reduction in serum potassium was observed with use of SPS, there was significant dosing variability among agents that limited the ability to directly compare specific doses. Further investigation is needed to determine the optimal dose of each agent for acute hyperkalemia management. This data will inform clinical decisions about the choice of potassium binder for acute hyperkalemia.

Fluorescent nano- and microparticles for sensing cellular microenvironment: past, present and future applications

The tumor microenvironment (TME) demonstrates distinct hallmarks, including acidosis, hypoxia, reactive oxygen species (ROS) generation, and altered ion fluxes, which are crucial targets for early cancer biomarker detection, tumor diagnosis, and therapeutic strategies. Various imaging and sensing techniques have been developed and employed in both research and clinical settings to visualize and monitor cellular and TME dynamics. Among these, ratiometric fluorescence-based sensors have emerged as powerful analytical tools, providing precise and sensitive insights into TME and enabling real-time detection and tracking of dynamic changes. In this comprehensive review, we discuss the latest advancements in ratiometric fluorescent probes designed for the optical mapping of pH, oxygen, ROS, ions, and biomarkers within the TME. We elucidate their structural designs and sensing mechanisms as well as their applications in in vitro and in vivo detection. Furthermore, we explore integrated sensing platforms that reveal the spatiotemporal behavior of complex tumor cultures, highlighting the potential of high-resolution imaging techniques combined with computational methods. This review aims to provide a solid foundation for understanding the current state of the art and the future potential of fluorescent nano- and microparticles in the field of cellular microenvironment sensing.

A Comparative Study on the Lysosomal Cation Channel TMEM175 Using Automated Whole-Cell Patch-Clamp, Lysosomal Patch-Clamp, and Solid Supported Membrane-Based Electrophysiology: Functional Characterization and High-Throughput Screening Assay Development

The lysosomal cation channel TMEM175 is a Parkinson's disease-related protein and a promising drug target. Unlike whole-cell automated patch-clamp (APC), lysosomal patch-clamp (LPC) facilitates physiological conditions, but is not yet suitable for high-throughput screening (HTS) applications. Here, we apply solid supported membrane-based electrophysiology (SSME), which enables both direct access to lysosomes and high-throughput electrophysiological recordings. In SSME, ion translocation mediated by TMEM175 is stimulated using a concentration gradient at a resting potential of 0 mV. The concentration-dependent K+ response exhibited an I/c curve with two distinct slopes, indicating the existence of two conducting states. We measured H+ fluxes with a permeability ratio of PH/PK = 48,500, which matches literature findings from patch-clamp studies, validating the SSME approach. Additionally, TMEM175 displayed a high pH dependence. Decreasing cytosolic pH inhibited both K+ and H+ conductivity of TMEM175. Conversely, lysosomal pH and pH gradients did not have major effects on TMEM175. Finally, we developed HTS assays for drug screening and evaluated tool compounds (4-AP, Zn as inhibitors; DCPIB, arachidonic acid, SC-79 as enhancers) using SSME and APC. Additionally, we recorded EC50 data for eight blinded TMEM175 enhancers and compared the results across all three assay technologies, including LPC, discussing their advantages and disadvantages.

Implementation of the medical emergencies in eating disorders in adults guidance on non-specialist units

The Royal College of Psychiatrists recently published data showing an 84% increase in UK hospital admissions for eating disorders over the past 5 years, highlighting the importance of the college's new Medical Emergencies in Eating Disorders (MEED) guidance. This includes a 79% increase among adults, many of whom are admitted to general medical wards that do not have input from expert eating disorder services. Consequently, the multidisciplinary nutrition support team, nutrition specialist nurses and dietitians have a potentially vital role in implementing MEED to ensure that the appropriate nutritional, fluid and electrolyte management is in place for safe refeeding and avoidance of the potentially harmful underfeeding syndrome. Furthermore, the guidance includes special recommendations for the use of nasogastric feeding in eating disorder patients, which requires input from experts in this field, including specialist nurses and dietitians. This article focuses on the implementation of MEED on hospital wards that do not have input from specialist eating disorders services.

Sudden cardiac arrest in a child with Gitelman syndrome: a case report and literature review

Salt-losing tubulopathies are well-recognised diseases predisposing to metabolic disturbances in affected patients. One of the most severe complications can be life-threatening arrhythmias causing sudden cardiac arrest. We present here the first case of a pediatric patient with Gitelman syndrome associated sudden cardiac arrest without precipitating event. A 10-year-old boy collapsed due to ventricular fibrillation in the Prague tram. Lay cardiopulmonary resuscitation was initiated and external defibrillation restored sinus rhythm within minutes. Initial laboratory examination revealed severe hypokalemia requiring large amounts of electrolyte supplementation. Genetic testing focused to tubulopathies was performed and the diagnosis of Gitelman syndrome was made following the identification of two pathogenic variants in SLC12A3 gene (c.2633 + 1G>A and c.2221G>A). Implantable cardioverter-defibrillator was implanted to prevent sudden cardiac death. The patient was in a good clinical condition with satisfactory electrolyte serum levels at the last follow-up. Causes of electrolyte abnormalities in children should be identified early to prevent the development of rare but potentially fatal complications.

The cellular pathways that maintain the quality control and transport of diverse potassium channels

Potassium channels are multi-subunit transmembrane proteins that permit the selective passage of potassium and play fundamental roles in physiological processes, such as action potentials in the nervous system and organismal salt and water homeostasis, which is mediated by the kidney. Like all ion channels, newly translated potassium channels enter the endoplasmic reticulum (ER) and undergo the error-prone process of acquiring post-translational modifications, folding into their native conformations, assembling with other subunits, and trafficking through the secretory pathway to reach their final destinations, most commonly the plasma membrane. Disruptions in these processes can result in detrimental consequences, including various human diseases. Thus, multiple quality control checkpoints evolved to guide potassium channels through the secretory pathway and clear potentially toxic, aggregation-prone misfolded species. We will summarize current knowledge on the mechanisms underlying potassium channel quality control in the secretory pathway, highlight diseases associated with channel misfolding, and suggest potential therapeutic routes.

The content of potassium in biosubstrates in young athletes

Purpose. To study the features of potassium metabolism in young athletes based on the analysis of its concentration in biological substrates.

Material and methods. The study involved 123 children aged 12 to 17 years. Four groups were formed: control (n=26), swimmers (n=33), hockey players (n=45), fencers (n=19). Samples were studied using inductively coupled plasma atomic emission spectrometry. Saliva and hair were used as substrates for analysis.

Results. As a result of our study, it was found that in the control group, the content of potassium in saliva was significantly higher than in young athletes of all groups (p<0.001). At the same time, it was also shown that the content of potassium in the hair of people professionally involved in sports is significantly higher than that of the control group (p><0.01). The use of correlation analysis made it possible to identify a negative statistically significant relationship between the indicators of potassium concentrations in saliva and in hair (R=–0.72; p><0.001). Conclusion. The results obtained indicate the formation of potassium content in saliva and hair are probably related and may reflect the peculiarities of mineral metabolism processes in young athletes. Further research is needed to determine the mechanisms of mineral metabolism in young athletes. Key words: children, young athletes, potassium, physical development, deficiency of bioelements>˂0.001). At the same time, it was also shown that the content of potassium in the hair of people professionally involved in sports is significantly higher than that of the control group (p˂0.01). The use of correlation analysis made it possible to identify a negative statistically significant relationship between the indicators of potassium concentrations in saliva and in hair (R=–0.72; p˂0.001).

Conclusion. The results obtained indicate the formation of potassium content in saliva and hair are probably related and may reflect the peculiarities of mineral metabolism processes in young athletes. Further research is needed to determine the mechanisms of mineral metabolism in young athletes. 

The sequestration mechanism as a generalizable approach to improve the sensitivity of biosensors and bioassays

Biosensors and bioassays, both of which employ proteins and nucleic acids to detect specific molecular targets, have seen significant applications in both biomedical research and clinical practice. This success is largely due to the extraordinary versatility, affinity, and specificity of biomolecular recognition. Nevertheless, these receptors suffer from an inherent limitation: single, saturable binding sites exhibit a hyperbolic relationship (the "Langmuir isotherm") between target concentration and receptor occupancy, which in turn limits the sensitivity of these technologies to small variations in target concentration. To overcome this and generate more responsive biosensors and bioassays, here we have used the sequestration mechanism to improve the steepness of the input/output curves of several bioanalytical methods. As our test bed for this we employed sensors and assays against neutrophil gelatinase-associated lipocalin (NGAL), a kidney biomarker for which enhanced sensitivity will improve the monitoring of kidney injury. Specifically, by introducing sequestration we have improved the responsiveness of an electrochemical aptamer based (EAB) biosensor, and two bioassays, a paper-based "dipstick" assay and an enzyme-linked immunosorbent assay (ELISA). Doing so we have narrowed the dynamic range of these sensors and assays several-fold, thus enhancing their ability to measure small changes in target concentration. Given that introducing sequestration requires only the addition of the appropriate concentration of a high-affinity "depletant," the mechanism appears simple and easily adaptable to tuning the binding properties of the receptors employed in a wide range of biosensors and bioassays.

Prokaryotic Na+/H+ Exchangers—Transport Mechanism and Essential Residues

Na⁺/H⁺ exchangers are essential for Na⁺ and pH homeostasis in all organisms. Human Na⁺/H⁺ exchangers are of high medical interest, and insights into their structure and function are aided by the investigation of prokaryotic homologues. Most prokaryotic Na⁺/H⁺ exchangers belong to either the Cation/Proton Antiporter (CPA) superfamily, the Ion Transport (IT) superfamily, or the Na⁺-translocating Mrp transporter superfamily. Several structures have been solved so far for CPA and Mrp members, but none for the IT members. NhaA from E. coli has served as the prototype of Na⁺/H⁺ exchangers due to the high amount of structural and functional data available. Recent structures from other CPA exchangers, together with diverse functional information, have allowed elucidation of some common working principles shared by Na⁺/H⁺ exchangers from different families, such as the type of residues involved in the substrate binding and even a simple mechanism sufficient to explain the pH regulation in the CPA and IT superfamilies. Here, we review several aspects of prokaryotic Na⁺/H⁺ exchanger structure and function, discussing the similarities and differences between different transporters, with a focus on the CPA and IT exchangers. We also discuss the proposed transport mechanisms for Na⁺/H⁺ exchangers that explain their highly pH-regulated activity profile.

Potassium Derangements: A Pathophysiological Review, Diagnostic Approach, and Clinical Management

Potassium is an essential cation critical in fluid and electrolyte balance, acid–base regulation, and neuromuscular functions. The normal serum potassium is kept within a narrow range of 3.5–5.2 meq/L while the intracellular concentration is approximately 140–150 meq/L. The total body potassium is about 45–55 mmol/kg; thus, a 70 kg male has an estimated ~136 g and 60 kg female has ~117 g of potassium. In total, 98% of the total body potassium is intracellular. Skeletal muscle contains ~80% of body potassium stores. The ratio of intracellular to extracellular potassium concentration (Ki/Ke) maintained by Na+/K+ ATPase determines the resting membrane potential. Disturbances of potassium homeostasis lead to hypo- and hyperkalemia, which if severe, can be life-threatening. Prompt diagnosis and management of these problems are important.

Targeting a G-quadruplex from let-7e pre-miRNA with small molecules and nucleolin

Let-7e precursor microRNA has the potential to adopt a G-quadruplex (rG4) structure and recently, its roles in oncology have been the focus of much attention, as it is now known that let-7e pre-miRNA is frequently dysregulated in cancers. Therefore, it is crucial to unveil and fully characterize its ability to adopt a rG4 structure, which could be stabilized or destabilized by small molecules and proteins such as nucleolin, a protein that is deeply associated with miRNA biogenesis. Herein, by combining a set of different methods such as circular dichroism (CD), nuclear magnetic resonance (NMR), UV spectroscopy (thermal difference spectra (TDS) and isothermal difference spectra (IDS)) and polyacrylamide gel electrophoresis (PAGE), we demonstrate the formation of the rG4 structure found in let-7e pre-miRNA sequence in the presence of K+ (5'-GGGCUGAGGUAGGAGG-3'). The ability of eight small molecules (or ligands) to bind to and stabilize this rG4 structure was also fully assessed. The dissociation constants for each RNA G-quadruplex/ligand complex, determined by surface plasmon resonance (SPR), ranged in the 10-6 to 10-9 M range. Lastly, the binding of the rG4 structure to nucleolin in the presence and absence of ligands was evaluated via CD, SPR, PAGE and confocal microscopy. The small molecules 360 A and PDS demonstrated attractive properties to targetthe rG4 structure of let-7e pre-miRNA and control its biology. Our findings also highlighted that the interaction of TMPyP4 with the G-quadruplex of let-7e precursor miRNA could block the formation of the complex between the rG4 and nucleolin. Overall, this study introduces an approach to target the rG4 found in let-7e pre-miRNA which opens up a new opportunity to control the microRNA biogenesis.

POCT errors can lead to false potassium results

Point-of-care-testing (POCT) facilitates rapid availability of results that allows prompt clinical decision making. These results must be reliable and the whole process must not compromise its quality. Blood gas analyzers are one of the most used methods for POCT tests in Emergency Departments (ED) and in critical patients. Whole blood is the preferred sample, and we must be aware that hemolysis can occur. These devices cannot detect the presence of hemolysis in the sample, and because of the characteristics of the sample, we cannot visually detect it either. Hemolysis can alter the result of different parameters, including potassium with abnormal high results or masking low levels (hypokalemia) when reporting normal concentrations. Severe hyperkalemia is associated with the risk of potentially fatal cardiac arrhythmia and demands emergency clinical intervention. Hemolysis can be considered the most frequent cause of pseudohyperkalemia (spurious hyperkalemia) or pseudonormokalemia and can be accompanied by a wrong diagnosis and an ensuing inappropriate clinical decision making. A complete review of the potential causes of falsely elevated potassium concentrations in blood is presented in this article. POCT programs properly led and organized by the clinical laboratory can help to prevent errors and their impact on patient care.

Dysnatremia in Gastrointestinal Disorders

The primary solute of the milieu intérieur is sodium and accompanying anions. The solvent is water. The kidneys acutely regulate homeostasis in filtration, secretion, and resorption of electrolytes, non-electrolytes, and minerals while balancing water retention and clearance. The gastrointestinal absorptive and secretory functions enable food digestion and water absorption needed to sustain life. Gastrointestinal perturbations including vomiting and diarrhea can lead to significant volume and electrolyte losses, overwhelming the renal homeostatic compensatory mechanisms. Dysnatremia, potassium and acid-base disturbances can result from gastrointestinal pathophysiologic processes. Understanding the renal and gastrointestinal contributions to homeostatis are important for the clinical evaluation of perturbed volume disturbances.

Non-invasive radionuclide imaging of trace metal trafficking in health and disease: "PET metallomics"

Several specific metallic elements must be present in the human body to maintain health and function. Maintaining the correct quantity (from trace to bulk) and location at the cell and tissue level is essential. The study of the biological role of metals has become known as metallomics. While quantities of metals in cells and tissues can be readily measured in biopsy and autopsy samples by destructive analytical techniques, their trafficking and its role in health and disease are poorly understood. Molecular imaging with radionuclides - positron emission tomography (PET) and single photon emission computed tomography (SPECT) - is emerging as a means to non-invasively study the acute trafficking of essential metals between organs, non-invasively and in real time, in health and disease. PET scanners are increasingly widely available in hospitals, and methods for producing radionuclides of some of the key essential metals are developing fast. This review summarises recent developments in radionuclide imaging technology that permit such investigations, describes the radiological and physicochemical properties of key radioisotopes of essential trace metals and useful analogues, and introduces current and potential future applications in preclinical and clinical investigations to study the biology of essential trace metals in health and disease.

Fluorescence lifetime imaging microscopy reveals sodium pump dimers in live cells

The sodium-potassium ATPase (Na/K-ATPase, NKA) establishes ion gradients that facilitate many physiological functions including action potentials and secondary transport processes. NKA comprises a catalytic subunit (alpha) that interacts closely with an essential subunit (beta) and regulatory transmembrane micropeptides called FXYD proteins. In the heart, a key modulatory partner is the FXYD protein phospholemman (PLM, FXYD1), but the stoichiometry of the alpha-beta-PLM regulatory complex is unknown. Here, we used fluorescence lifetime imaging and spectroscopy to investigate the structure, stoichiometry, and affinity of the NKA-regulatory complex. We observed a concentration-dependent binding of the subunits of NKA-PLM regulatory complex, with avid association of the alpha subunit with the essential beta subunit as well as lower affinity alpha-alpha and alpha-PLM interactions. These data provide the first evidence that, in intact live cells, the regulatory complex is composed of two alpha subunits associated with two beta subunits, decorated with two PLM regulatory subunits. Docking and molecular dynamics (MD) simulations generated a structural model of the complex that is consistent with our experimental observations. We propose that alpha-alpha subunit interactions support conformational coupling of the catalytic subunits, which may enhance NKA turnover rate. These observations provide insight into the pathophysiology of heart failure, wherein low NKA expression may be insufficient to support formation of the complete regulatory complex with the stoichiometry (alpha-beta-PLM)2.

Pre-miRNA-149 G-quadruplex as a molecular agent to capture nucleolin

One of the most significant challenges in capturing and detecting biomarkers is the choice of an appropriate biomolecular receptor. Recently, RNA G-quadruplexes emerged as plausible receptors due to their ability to recognize with high-affinity proteins. Herein, we have unveiled and characterized the capability of the precursor microRNA 149 to form a G-quadruplex structure and determined the role that some ligands may have in its folding and binding capacity to nucleolin. The G-quadruplex formation was induced by K+ ions and stabilized by ligands, as demonstrated by nuclear magnetic resonance and circular dichroism experiments. Surface plasmon resonance measurements showed a binding affinity of precursor microRNA 149 towards ligands in the micromolar range (10-5-10-6 M) and a strong binding affinity to nucleolin RNA-binding domains 1 and 2 (8.38 × 10-10 M). Even in the presence of the ligand PhenDC3, the binding remains almost identical and in the same order of magnitude (4.46 × 10-10 M). The molecular interactions of the RNA G-quadruplex motif found in precursor miRNA 149 (5'-GGGAGGGAGGGACGGG- 3') and nucleolin RNA-binding domains 1 and 2 were explored by means of molecular docking and molecular dynamics studies. The results showed that RNA G-quadruplex binds to a cavity between domains 1 and 2 of the protein. Then, complex formation was also evaluated through polyacrylamide gel electrophoresis. The results suggest that precursor microRNA 149/ligands and precursor microRNA 149/nucleolin RNA-binding domains 1 and 2 form stable molecular complexes. The in vitro co-localization of precursor microRNA 149 and nucleolin in PC3 cells was demonstrated using confocal microscopy. Finally, a rapid and straightforward microfluidic strategy was employed to check the ability of precursor microRNA 149 to capture nucleolin RNA-binding domains 1 and 2. The results revealed that precursor microRNA 149 can capture nucleolin RNA-binding domains 1 and 2 labeled with Fluorescein 5-isothiocyanate in a concentration-dependent manner, but PhenDC3 complexation seems to decrease the ability of precursor microRNA 149 to capture the protein. Overall, our results proved the formation of the G-quadruplex structure in the precursor microRNA 149 and the ability to recognize and detect nucleolin. This proof-of-concept study could open up a new framework for developing new strategies to design improved molecular receptors for capture and detection of nucleolin in complex biological samples.

Paracrine and endocrine regulation of renal potassium secretion

The seminal studies conducted by Giebisch and colleagues in the 1960s paved the way for understanding the renal mechanisms involved in K+ homeostasis. It was demonstrated that differential handling of K+ in the distal segments of the nephron is crucial for proper K+ balance. Although aldosterone had been classically ascribed as the major ion transport regulator in the distal nephron, thereby contributing to K+ homeostasis, it became clear that aldosterone per se could not explain the kidney's ability to modulate kaliuresis in both acute and chronic settings. The existence of alternative kaliuretic and antikaliuretic mechanisms was suggested by physiological studies in the 1980s but only gained form and shape with the advent of molecular biology. It is now established that the kidneys recruit several endocrine and paracrine mechanisms for adequate kaliuretic response. These mechanisms include the direct effects of peritubular K+, a gut-kidney regulatory axis sensing dietary K+ levels, the kidney secretion of kallikrein during postprandial periods, the upregulation of angiotensin II receptors in the distal nephron during chronic changes in the K+ diet, and the local increase of prostaglandins by low K+ diet. This review discusses recent advances in the understanding of endocrine and paracrine mechanisms underlying the modulation of K+ secretion and how these mechanisms impact kaliuresis and K+ balance. We also highlight important unknowns about the regulation of renal K+ excretion under physiological circumstances.

The effect of imatinib and nilotinib on blood calcium and blood potassium levels in chronic myeloid leukemia patients: a literature review

Imatinib and nilotinib are first-line treatments for chronic myeloid leukemia (CML) patients, which act specifically against target cells. However, these drugs may cause side effects, such as electrolyte disturbances. This literature review aimed to provide a comparison of the effects of imatinib and nilotinib on blood potassium and calcium levels. It also summarized their hypothetical mechanism. A comprehensive electronic search of the different databases was conducted using ‘chronic myeloid leukemia’, ‘tyrosine kinase inhibitors’, ‘imatinib’, ‘nilotinib’, ‘potassium’, ‘calcium’, ‘electrolytes’ as keywords. This review used PubMed- MEDLINE, Cochrane Library, and Google Scholar as the source databases. Sixteen articles published from 2006 to 2020 were reviewed. Changes in blood potassium levels range from increased to decreased levels, while changes in blood calcium levels range from the lower normal values to below normal values (hypocalcemia). Tyrosine kinase inhibitors (TKIs), including imatinib and nilotinib, have a non-specific target, namely plateletderived growth factor receptor (PDGFR), which indirectly affects blood potassium and calcium levels in CML patients. The clinical manifestations of these changes vary from being visible only in laboratory tests to displaying a variety of clinical signs and symptoms.