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Infection and Immunity Mar 2021Host colonization by a pathogen requires proper sensing and response to local environmental cues, to ensure adaptation and continued survival within the host. The ionic... (Review)
Review
Host colonization by a pathogen requires proper sensing and response to local environmental cues, to ensure adaptation and continued survival within the host. The ionic milieu represents a critical potential source of environmental cues, and indeed, there has been extensive study of the interplay between host and pathogen in the context of metals such as iron, zinc, and manganese, vital ions that are actively sequestered by the host. The inherent non-uniformity of the ionic milieu also extends, however, to "abundant" ions such as chloride and potassium, whose concentrations vary greatly between tissue and cellular locations, and with the immune response. Despite this, the concept of abundant ions as environmental cues and key players in host-pathogen interactions is only just emerging. Focusing on chloride and potassium, this review brings together studies across multiple bacterial and parasitic species that have begun to define both how these abundant ions are exploited as cues during host infection, and how they can be actively manipulated by pathogens during host colonization. The close links between ion homeostasis and sensing/response to different ionic signals, and the importance of studying pathogen response to cues in combination, are also discussed, while considering the fundamental insight still to be uncovered from further studies in this nascent area of inquiry.
Topics: Animals; Anions; Bacteria; Chlorides; Disease Susceptibility; Homeostasis; Host-Parasite Interactions; Host-Pathogen Interactions; Humans; Ions; Potassium
PubMed: 33526568
DOI: 10.1128/IAI.00641-20 -
Current Genetics Feb 2018Potassium and glutamate are the most abundant ions in every living cell. Whereas potassium plays a major role to keep the cellular turgor and to buffer the negative... (Review)
Review
Potassium and glutamate are the most abundant ions in every living cell. Whereas potassium plays a major role to keep the cellular turgor and to buffer the negative charges of the nucleic acids, the major function of glutamate is to serve as the universal amino group donor. In addition, both ions are involved in osmoprotection in bacterial cells. Here, we discuss how bacterial cells maintain the homeostasis of both ions and how adaptive evolution allows them to live even at extreme potassium limitation. Interestingly, positively charged amino acids are able to partially replace potassium, likely by buffering the negative charge of DNA. A major factor involved in the control of potassium homeostasis in Gram-positive bacteria is the essential second messenger cyclic di-AMP. This nucleotide is synthesized in response to the potassium concentration and in turn controls the expression and activity of potassium transporters. We discuss the link between the two major ions, DNA and the second messenger c-di-AMP.
Topics: Adaptation, Biological; Bacillus subtilis; Cyclic AMP; Escherichia coli; Glutamic Acid; Homeostasis; Hydrogen-Ion Concentration; Ions; Potassium; Second Messenger Systems
PubMed: 28825218
DOI: 10.1007/s00294-017-0734-3 -
Analytica Chimica Acta Nov 2018A conductometric sensor for potassium ions in solution is presented. Interdigitated, planar gold electrodes were coated with a potassium-selective polymer membrane...
A conductometric sensor for potassium ions in solution is presented. Interdigitated, planar gold electrodes were coated with a potassium-selective polymer membrane composed of a poly(vinyl chloride) matrix with about 65 wt% of plasticiser and 2-5 wt% of a potassium-selective ionophore. The impedance of the membrane was measured, using the electrodes as a transducer, and related to the concentration of potassium in a sample solution in contact with the membrane. Sensitivity was optimised by varying the sensor components, and selectivity for potassium over sodium was also shown. The resulting devices are compact, miniature, robust sensors which, by means of impedance measurements, eliminate the need for a reference electrode. The sensor was tested for potassium concentration changes of 2 mM across the clinically relevant range of 2.7-18.7 mM.
Topics: Electric Impedance; Electrochemical Techniques; Ions; Potassium
PubMed: 30193638
DOI: 10.1016/j.aca.2018.06.044 -
Progress in Neurobiology Oct 2020Throughout the nervous system, ion gradients drive fundamental processes. Yet, the roles of interstitial ions in brain functioning is largely forgotten. Emerging... (Review)
Review
Throughout the nervous system, ion gradients drive fundamental processes. Yet, the roles of interstitial ions in brain functioning is largely forgotten. Emerging literature is now revitalizing this area of neuroscience by showing that interstitial cations (K, Ca and Mg) are not static quantities but change dynamically across states such as sleep and locomotion. In turn, these state-dependent changes are capable of sculpting neuronal activity; for example, changing the local interstitial ion composition in the cortex is sufficient for modulating the prevalence of slow-frequency neuronal oscillations, or potentiating the gain of visually evoked responses. Disturbances in interstitial ionic homeostasis may also play a central role in the pathogenesis of central nervous system diseases. For example, impairments in K buffering occur in a number of neurodegenerative diseases, and abnormalities in neuronal activity in disease models disappear when interstitial K is normalized. Here we provide an overview of the roles of interstitial ions in physiology and pathology. We propose the brain uses interstitial ion signaling as a global mechanism to coordinate its complex activity patterns, and ion homeostasis failure contributes to central nervous system diseases affecting cognitive functions and behavior.
Topics: Animals; Calcium; Cations; Central Nervous System; Humans; Magnesium; Nervous System Physiological Phenomena; Potassium; Signal Transduction
PubMed: 32413398
DOI: 10.1016/j.pneurobio.2020.101802 -
Postgraduate Medicine Jun 2015Hypokalemia is a common electrolyte disturbance, observed in > 20% of hospitalized patients. Hypokalemia, although not formally defined, is generally considered to be... (Review)
Review
Hypokalemia is a common electrolyte disturbance, observed in > 20% of hospitalized patients. Hypokalemia, although not formally defined, is generally considered to be when serum potassium levels fall below the normal value of 3.6 mmol/L. In contrast to other electrolytes, potassium is primarily an intracellular ion: only 2% of all potassium in the body is present in the extracellular fluid, so a small decrease in serum potassium may represent a significant decrease in intracellular potassium. Individuals with mildly decreased potassium levels (3.0-3.5 mmol/L) may be asymptomatic, but patients with more pronounced decreases may report symptoms including muscle weakness, fatigue, and constipation. Very low serum potassium levels (≤ 2.5 mmol/L) can lead to muscle necrosis, paralysis, cardiac arrhythmias, and impaired respiration, which can be life-threatening. Absent comprehensive and robust treatment guidelines, strategies for the prevention or treatment of hypokalemia, such as how to diagnose hypokalemia, when to treat patients, what dosage regimen of potassium supplementation to use and for how long, are often based on the experience of the physician and empirical evidence. However, proper evaluation and treatment of hypokalemia in patients is essential because of associated morbidities. Because small potassium deficits in serum represent large body losses, potassium repletion requires substantial and prolonged supplementation. For patients with known risk factors for hypokalemia (e.g. hypertension, heart failure, or diabetes), careful monitoring is crucial to avoid the adverse sequelae associated with potassium deficits and to ensure that adequate and timely preventive measures can be taken. In this review, we provide practical insights into the etiology, differential diagnosis, and treatment of hypokalemia, including treatment strategies for patients with known risk factors.
Topics: Dietary Supplements; Humans; Hypokalemia; Potassium, Dietary
PubMed: 25960118
DOI: 10.1080/00325481.2015.1045814 -
Current Opinion in Nephrology and... Sep 2017The current review combines past findings with recent advances in our understanding of the homeostatic response to potassium imbalance. (Review)
Review
PURPOSE OF REVIEW
The current review combines past findings with recent advances in our understanding of the homeostatic response to potassium imbalance.
RECENT FINDINGS
Following the ingestion of a dietary potassium load, a combination of extrarenal and renal mechanisms act to maintain extracellular K+ within a tight window. Through hormonal regulation and direct K+ sensing, the nephron is ideally suited to respond to wide shifts in external K+ balance. Current evidence indicates that dietary K+ loading triggers a coordinated kaliuretic response that appears to involve voltage-dependent changes in sodium transport across multiple nephron segments, including the proximal tubule, medullary loop of Henle, and distal tubule. Inhibition of sodium transport in these segments would accomplish the final goal of enhancing distal NaCl delivery, luminal flow, and K+ secretion in the aldosterone sensitive distal nephron (ASDN).
SUMMARY
Ongoing research seeks to define the relationship between potassium and volume homeostasis by elucidating pathways that couple renal K+ sensing and tubular function during the potassium stress response.
Topics: Animals; Homeostasis; Humans; Ion Transport; Nephrons; Potassium; Potassium, Dietary; Sodium; Stress, Physiological
PubMed: 28614118
DOI: 10.1097/MNH.0000000000000352 -
Molecular Plant Mar 2024Plant high-affinity K transporters (HKTs) mediate Na and K uptake, maintain Na/K homeostasis, and therefore play crucial roles in plant salt tolerance. In this study,...
Plant high-affinity K transporters (HKTs) mediate Na and K uptake, maintain Na/K homeostasis, and therefore play crucial roles in plant salt tolerance. In this study, we present cryoelectron microscopy structures of HKTs from two classes, class I HKT1;1 from Arabidopsis thaliana (AtHKT1;1) and class II HKT2;1 from Triticum aestivum (TaHKT2;1), in both Na- and K-bound states at 2.6- to 3.0-Å resolutions. Both AtHKT1;1 and TaHKT2;1 function as homodimers. Each HKT subunit consists of four tandem domain units (D1-D4) with a repeated K-channel-like M-P-M topology. In each subunit, D1-D4 assemble into an ion conduction pore with a pseudo-four-fold symmetry. Although both TaHKT2;1 and AtHKT1;1 have only one putative Na ion bound in the selectivity filter with a similar coordination pattern, the two HKTs display different K binding modes in the filter. TaHKT2;1 has three K ions bound in the selectivity filter, but AtHKT1;1 has only two K ions bound in the filter, which has a narrowed external entrance due to the presence of a Ser residue in the first filter motif. These structures, along with computational, mutational, and electrophysiological analyses, enable us to pinpoint key residues that are critical for the ion selectivity of HKTs. The findings provide new insights into the ion selectivity and ion transport mechanisms of plant HKTs and improve our understanding about how HKTs mediate plant salt tolerance and enhance crop growth.
Topics: Arabidopsis Proteins; Cryoelectron Microscopy; Symporters; Arabidopsis; Ion Transport; Ions; Potassium; Plant Proteins
PubMed: 38335958
DOI: 10.1016/j.molp.2024.01.007 -
The Journals of Gerontology. Series A,... Nov 2020Aging is associated with a progressive difficulty to maintain ion regulation, which might impair the capacity for muscle contraction. Thus, the aim of this study was to...
BACKGROUND
Aging is associated with a progressive difficulty to maintain ion regulation, which might impair the capacity for muscle contraction. Thus, the aim of this study was to examine the association between 5-year changes in dietary intake of sodium and potassium and changes in physical performance among older adults.
METHODS
We performed a prospective study with 868 participants from the Seniors-ENRICA cohort. Diet was measured with a validated diet history and physical performance was measured with the Short Physical Performance Battery (SPPB), both in 2012 and 2017. Analyses were performed with linear regression models adjusted for sociodemographic variables, lifestyle, and morbidity, using changes in the intake of sodium and potassium and changes in the sodium/potassium ratio during follow-up as independent variables, and the continuous change in the SPPB score as the dependent variable.
RESULTS
Over 5 years of follow-up, a 1 SD increase in sodium intake (ie, 0.73 g/d) was associated with a 0.13 (95% confidence interval [CI]: 0.26-0.01) points reduction in the SPPB score, while a 1 SD increase in potassium intake (ie, 0.70 g/d) was associated with a 0.19 (0.05-0.34) points increment in the score. In addition, a 1 SD increase in the sodium-to-potassium ratio (ie, 0.30) was associated with worse SPPB (-0.58 [-0.95 to -0.21]). Participants who adhered to dietary recommendations for minerals at baseline but became noncompliant during follow-up decreased their result in the SPPB.
CONCLUSION
An increase of dietary sodium intake, a decrease of potassium intake and the resulting increment in the sodium-to-potassium ratio were prospectively associated with worse physical performance in older adults.
Topics: Aged; Diet; Female; Geriatric Assessment; Humans; Male; Middle Aged; Physical Functional Performance; Potassium; Prospective Studies; Sodium; Spain
PubMed: 32009144
DOI: 10.1093/gerona/glaa031 -
Molecular Pharmacology Apr 2019The ligand-gated ion channel P2X7 receptor attracts special attention due to its widespread presence as well as its unusual responses. Besides relatively well-understood... (Review)
Review
The ligand-gated ion channel P2X7 receptor attracts special attention due to its widespread presence as well as its unusual responses. Besides relatively well-understood mechanisms such as intracellular Ca increase and K depletion, the P2X7 receptor activates other peculiar responses whose mechanisms are not fully understood. The best known among these is the permeabilization of the cell membrane to large molecules. This permeabilization has been explained by the activation of a nonselective permeation pathway by the P2X7 receptor, a phenomenon called "pore formation." However, with the emergence of new data, it became apparent that large molecules enter the cell directly through the pore of the ion channel, similar to the smaller ions. This explanation seems to be true for cationic large molecules. On the other hand, there is still convincing evidence indicating that the P2X7 receptor activates a separate pathway that permeates anionic large molecules in some cell types. Furthermore, there exist functional data suggesting that the P2X7 receptor may also activate other intracellular signaling molecules or other ion channels. Interestingly and contrary to what is expected from a ligand-gated channel, these activations occur in a seemingly direct manner. Somewhat overshadowed by the pore formation hypothesis, these action mechanisms may lead to a better understanding of not only the P2X7 receptor itself but also some important physiologic functions such as the release of anionic autocoids/neurotransmitters in the central nervous system. This review discusses, assesses, and draws attention to the data concerning these neglected but potentially important points in the P2X7 receptor field.
Topics: Calcium; Cations; Cell Membrane; Humans; Permeability; Potassium; Receptors, Purinergic P2X7; Signal Transduction
PubMed: 30737253
DOI: 10.1124/mol.118.115022 -
Seminars in Dialysis May 2017People with kidney disease are advised to restrict individual nutrients, such as sodium, potassium, and phosphate, in line with current best practice guidelines....
People with kidney disease are advised to restrict individual nutrients, such as sodium, potassium, and phosphate, in line with current best practice guidelines. However, there is limited evidence to support the efficacy of single nutrient strategies, and compliance remains a challenge for clinicians to overcome. Many factors contribute to poor compliance with dietary prescriptions, including conflicting priorities for single nutrient restriction, the arduous self-monitoring required, and the health-related knock-on effects resulting from targeting these nutrients in isolation. This paper reviews the evidence base for the overall pattern of eating as a potential tool to deliver a diet intervention in which all the nutrients and foods work cumulatively and synergistically to improve clinical outcomes. These interventions may assist in kidney disease management and overcome these innate challenges that single nutrient interventions possess. Healthy dietary patterns are typically plant-based and lower in sodium and animal proteins. These patterns may have numerous mechanistic benefits for cardiovascular health in kidney disease, most notably through the increase in fruit, vegetables, and plant-based protein, as well as improved gut health through the increase in dietary fiber. The evidence to date on optimal dietary patterns points toward use of a predominantly plant-based diet, and suggests its adoption may improve clinical outcomes in dialysis patients. However, clinical trials are needed to determine whether these diet interventions are feasible, safe, and effective in this patient population.
Topics: Diet, Sodium-Restricted; Dietary Supplements; Humans; Kidney Diseases; Phosphates; Potassium; Renal Dialysis; Sodium
PubMed: 28239979
DOI: 10.1111/sdi.12580