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American Journal of Physiology. Renal... Mar 2023The Cl/[Formula: see text] exchanger pendrin in the kidney maintains acid-base balance and intravascular volume. Pendrin is upregulated in models associated with high...
The Cl/[Formula: see text] exchanger pendrin in the kidney maintains acid-base balance and intravascular volume. Pendrin is upregulated in models associated with high circulating aldosterone concentration, such as dietary NaCl restriction or an aldosterone infusion. However, it has not been established if pendrin is similarly regulated by aldosterone with a high-K diet because the effects of accompanying anions have not been considered. Here, we explored how pendrin is modulated by different dietary potassium salts. Wild-type (WT) and aldosterone synthase (AS) knockout (KO) mice were randomized to control, high-KHCO, or high-KCl diets. Dietary KCl and KHCO loading increased aldosterone in WT mice to the same extent but had opposite effects on pendrin abundance. KHCO loading increased pendrin protein and transcript abundance. Conversely, high-KCl diet feeding caused pendrin to decrease within 8 h of switching from the high-KHCO diet, coincident with an increase in plasma Cl and a decrease in [Formula: see text]. In contrast, switching the high-KCl diet to the high-KHCO diet caused pendrin to increase in WT mice. Experiments in AS KO mice revealed that aldosterone is necessary to optimally upregulate pendrin protein in response to the high-KHCO diet but not to increase pendrin mRNA. We conclude that pendrin is differentially regulated by different dietary potassium salts and that its regulation is prioritized by the dietary anion, providing a mechanism to prevent metabolic alkalosis with high-K base diets and safeguard against hyperchloremic acidosis with consumption of high-KCl diets. Regulation of the Cl/[Formula: see text] exchanger pendrin has been suggested to explain the aldosterone paradox. A high-K diet has been proposed to downregulate a pendrin-mediated K-sparing NaCl reabsorption pathway to maximize urinary K excretion. Here, we challenged the hypothesis, revealing that the accompanying anion, not K, drives pendrin expression. Pendrin is downregulated with a high-KCl diet, preventing acidosis, and upregulated with an alkaline-rich high-K diet, preventing metabolic alkalosis. Pendrin regulation is prioritized for acid-base balance.
Topics: Animals; Mice; Acidosis; Aldosterone; Alkalosis; Anion Transport Proteins; Bicarbonates; Diet; Potassium; Potassium, Dietary; Salts; Sodium Chloride; Sulfate Transporters
PubMed: 36656986
DOI: 10.1152/ajprenal.00128.2022 -
Analytical Chemistry Jun 2022We present spectroelectrochemical sensing of the potassium ion (K) at three very distinct analytical ranges─nanomolar, micromolar, and millimolar─when using the same...
We present spectroelectrochemical sensing of the potassium ion (K) at three very distinct analytical ranges─nanomolar, micromolar, and millimolar─when using the same ion-selective electrode (ISE) but interrogated under various regimes. The ISE is conceived in the all-solid-state format: an ITO glass modified with the conducting polymer poly(3-octylethiophene) (POT) and an ultrathin potassium-selective membrane. The experimental setup is designed to apply a potential in a three-electrode electrochemical cell with the ISE as the working electrode, while dynamic spectral changes in the POT film are simultaneously registered. The POT film is gradually oxidized to POT, and this process is ultimately linked to K transfer at the membrane-sample interface, attending to electroneutrality requirements. The spectroelectrochemistry experiment provides two signals: a voltammetric peak and a transient absorbance response, with the latter of special interest because of its correspondence with the generated charge in the POT and thus with the ionic charge expelled from the membrane. By modifying how the ion analyte (K but also others) is initially accumulated into the membrane, we found three ranges of response for the absorbance: 10-950 nM for an accumulation-stripping protocol, 0.5-10 μM in diffusion-controlled cyclic voltammetry, and 0.5-32 mM with thin-layer cyclic voltammetry. This wide response range is a unique feature, one that is rare to find for a sensor and indeed for any analytical technique. Accordingly, the developed sensor is highly appealing for many analytical applications, especially considering the versatility of samples and ion analytes that may be spotted.
Topics: Ion-Selective Electrodes; Ions; Polymers; Potassium
PubMed: 35687727
DOI: 10.1021/acs.analchem.2c01584 -
ACS Nano Oct 2022Accurate measurements of ion permeability through cellular membranes remains challenging due to the lack of suitable ion-selective probes. Here we use giant unilamellar...
Accurate measurements of ion permeability through cellular membranes remains challenging due to the lack of suitable ion-selective probes. Here we use giant unilamellar vesicles (GUVs) as membrane models for the direct visualization of mass translocation at the single-vesicle level. Ion transport is indicated with a fluorescently adjustable DNA-based sensor that accurately detects sub-millimolar variations in K concentration. In combination with microfluidics, we employed our DNA-based K sensor for extraction of the permeation coefficient of potassium ions. We measured K permeability coefficients at least 1 order of magnitude larger than previously reported values from bulk experiments and show that permeation rates across the lipid bilayer increase in the presence of octanol. In addition, an analysis of the K flux in different concentration gradients allows us to estimate the complementary H flux that dissipates the charge imbalance across the GUV membrane. Subsequently, we show that our sensor can quantify the K transport across prototypical cation-selective ion channels, gramicidin A and OmpF, revealing their relative H/K selectivity. Our results show that gramicidin A is much more selective to protons than OmpF with a H/K permeability ratio of ∼10.
Topics: Gramicidin; Unilamellar Liposomes; Lipid Bilayers; Protons; Ion Transport; Ion Channels; Ions; Potassium; DNA; Octanols
PubMed: 36222833
DOI: 10.1021/acsnano.2c07496 -
Analytical Chemistry Feb 2022Sodium and potassium are biological alkali metal ions that are essential for the physiological processes of cells and organisms. In combination with small-molecule...
Sodium and potassium are biological alkali metal ions that are essential for the physiological processes of cells and organisms. In combination with small-molecule metabolite information, disturbances in sodium and potassium tissue distributions can provide a further understanding of the biological processes in diseases. However, methods using mass spectrometry are generally tailored toward either elemental or molecular detection, which limits simultaneous quantitative mass spectrometry imaging of alkali metal ions and molecular ions. Here, we provide a new method by including crown ether molecules in the solvent for nanospray desorption electrospray ionization mass spectrometry imaging (nano-DESI MSI) that combines host-guest chemistry targeting sodium and potassium ions and quantitative imaging of endogenous lipids and metabolites. After evaluation and optimization, the method was applied to an ischemic stroke model, which has highly dynamic tissue sodium and potassium concentrations, and we report 2 times relative increase in the detected sodium concentration in the ischemic region compared to healthy tissue. Further, in the same experiment, we showed the accumulation and depletion of lipids, neurotransmitters, and amino acids using relative quantitation with internal standards spiked in the nano-DESI solvent. Overall, we demonstrate a new method that with a simple modification in liquid extraction MSI techniques using host-guest chemistry provides the added dimension of alkali metal ion imaging to provide unique insights into biological processes.
Topics: Ions; Potassium; Sodium; Solvents; Spectrometry, Mass, Electrospray Ionization
PubMed: 35077136
DOI: 10.1021/acs.analchem.1c03913 -
Journal of Chemical Theory and... Nov 2021We have compared distributions of sodium and potassium ions around double-stranded DNA, simulated using fixed charge SPC/E, TIP3P, and OPC water models and the...
We have compared distributions of sodium and potassium ions around double-stranded DNA, simulated using fixed charge SPC/E, TIP3P, and OPC water models and the Joung/Cheatham (J/C) ion parameter set, as well as the Li/Merz HFE 6-12 (L/M HFE) ion parameters for OPC water. In all the simulations, the ion distributions are in qualitative agreement with Manning's condensation theory and the Debye-Hückel theory, where expected. In agreement with experiment, binding affinity of monovalent ions to DNA does not depend on ion type in every solvent model. However, behavior of deeply bound ions, including ions bound to specific sites, depends strongly on the solvent model. In particular, the number of potassium ions in the minor groove of AT-tracts differs at least 3-fold between the solvent models tested. The number of sodium ions associated with the DNA agrees quantitatively with the experiment for the OPC water model, followed closely by TIP3P+J/C; the largest deviation from the experiment, ∼10%, is seen for SPC/E+J/C. On the other hand, SPC/E+J/C model is most consistent (67%) with the experimental potassium binding sites, followed by OPC+J/C (60%), TIP3P+J/C (53%), and OPC+L/M HFE (27%). The use of NBFIX correction with TIP3P+J/C improves its consistency with the experiment. In summary, the choice of the solvent model matters little for simulating the diffuse atmosphere of sodium and potassium ions around DNA, but ion distributions become increasingly sensitive to the solvent model near the helical axis. We offer an explanation for these trends. There is no single gold standard solvent model, although OPC water with J/C ions or TIP3P with J/C + NBFIX may offer an imperfect compromise for practical simulations of ionic atmospheres around DNA.
Topics: DNA; Ions; Lithium; Molecular Dynamics Simulation; Potassium; Sodium; Solvents; Water
PubMed: 34633813
DOI: 10.1021/acs.jctc.1c00332 -
Metal Ions in Life Sciences 2016The group I alkali metal ions Na(+) and K(+) are ubiquitous components of biological fluids that surround biological macromolecules. They play important roles other than...
The group I alkali metal ions Na(+) and K(+) are ubiquitous components of biological fluids that surround biological macromolecules. They play important roles other than being nonspecific ionic buffering agents or mediators of solute exchange and transport. Molecular evolution and regulated high intracellular and extracellular M(+) concentrations led to incorporation of selective Na(+) and K(+) binding sites into enzymes to stabilize catalytic intermediates or to provide optimal positioning of substrates. The mechanism of M(+) activation, as derived from kinetic studies along with structural analysis, has led to the classification of cofactor-like (type I) or allosteric effector (type II) activated enzymes. In the type I mechanism substrate anchoring to the enzyme active site is mediated by M(+), often acting in tandem with a divalent cation like Mg(2+), Mn(2+) or Zn(2+). In the allosteric type II mechanism, M(+) binding enhances enzyme activity through conformational transitions triggered upon binding to a distant site. In this chapter, following the discussion of the coordination chemistry of Na(+) and K(+) ions and the structural features responsible for the metal binding site selectivity in M(+)-activated enzymes, well-defined examples of M(+)-activated enzymes are used to illustrate the structural basis for type I and type II activation by Na(+) and K(+).
Topics: Binding Sites; Catalysis; Cations; Enzyme Activation; Models, Molecular; Potassium; Protein Conformation; Sodium
PubMed: 26860304
DOI: 10.1007/978-3-319-21756-7_8 -
Journal of Dairy Science Nov 1984Objectives were to study effects of heat stress, 0 or .85% sodium bicarbonate, 0 or 1.0% potassium bicarbonate, and 1.0 or 1.5% total dietary potassium on production and...
Objectives were to study effects of heat stress, 0 or .85% sodium bicarbonate, 0 or 1.0% potassium bicarbonate, and 1.0 or 1.5% total dietary potassium on production and physiological responses of dairy cows. Eighteen lactating Holsteins were assigned to shade (control) or no shade (heat stress) lots continuously for three consecutive 35-day periods and to different dietary treatments each period. Basal diet was 25% cottonseed hulls and 75% concentrate. Daytime and nighttime feed intake and production were measured the last 2 wk of each period, and milk and blood were sampled the final day of each period. Black globe temperature, rectal temperature, respiration rate, and blood pH were higher in no shade. Daytime intake was 132% greater in shade, nighttime intake was not different between environments. Milk production was about 19% greater for evening and morning milkings in shade. Daytime intake, daytime and nighttime milk production were higher with sodium bicarbonate. Potassium bicarbonate reduced intake and production. Higher total dietary potassium increased total daily milk production. Lactating cows appear adept at withstanding environmental and dietary challenges to acid-base homeostasis. Supplementation of sodium bicarbonate and 1.5% dietary potassium, but not potassium bicarbonate, were beneficial to lactating dairy cows.
Topics: Animals; Bicarbonates; Blood Gas Analysis; Body Temperature; Cattle; Cattle Diseases; Female; Food, Fortified; Hot Temperature; Lactation; Milk; Potassium; Potassium Compounds; Pregnancy; Rectum; Respiration; Sodium Bicarbonate; Stress, Physiological
PubMed: 6097604
DOI: 10.3168/jds.S0022-0302(84)81611-2 -
The Journal of Physical Chemistry. B Jan 2017An experimentally well-studied model of RNA tertiary structures is a 58mer rRNA fragment, known as GTPase-associating center (GAC) RNA, in which a highly negative pocket...
An experimentally well-studied model of RNA tertiary structures is a 58mer rRNA fragment, known as GTPase-associating center (GAC) RNA, in which a highly negative pocket walled by phosphate oxygen atoms is stabilized by a chelated cation. Although such deep pockets with more than one direct phosphate to ion chelation site normally include magnesium, as shown in one GAC crystal structure, another GAC crystal structure and solution experiments suggest potassium at this site. Both crystal structures also depict two magnesium ions directly bound to the phosphate groups comprising this controversial pocket. Here, we used classical molecular dynamics simulations as well as umbrella sampling to investigate the possibility of binding of potassium versus magnesium inside the pocket and to better characterize the chelation of one of the binding magnesium ions outside the pocket. The results support the preference of the pocket to accommodate potassium rather than magnesium and suggest that one of the closely binding magnesium ions can only bind at high magnesium concentrations, such as might be present during crystallization. This work illustrates the complementary utility of molecular modeling approaches with atomic-level detail in resolving discrepancies between conflicting experimental results.
Topics: Binding Sites; GTP Phosphohydrolases; Ions; Magnesium; Molecular Dynamics Simulation; Potassium; RNA
PubMed: 27983843
DOI: 10.1021/acs.jpcb.6b08764 -
Proceedings of the National Academy of... Mar 2019With-no-lysine (WNK) kinases regulate renal sodium-chloride cotransporter (NCC) to maintain body sodium and potassium homeostasis. Gain-of-function mutations of WNK1 and...
With-no-lysine (WNK) kinases regulate renal sodium-chloride cotransporter (NCC) to maintain body sodium and potassium homeostasis. Gain-of-function mutations of WNK1 and WNK4 in humans lead to a Mendelian hypertensive and hyperkalemic disease pseudohypoaldosteronism type II (PHAII). X-ray crystal structure and in vitro studies reveal chloride ion (Cl) binds to a hydrophobic pocket within the kinase domain of WNKs to inhibit its activity. The mechanism is thought to be important for physiological regulation of NCC by extracellular potassium. To test the hypothesis that WNK4 senses the intracellular concentration of Cl physiologically, we generated knockin mice carrying Cl-insensitive mutant WNK4. These mice displayed hypertension, hyperkalemia, hyperactive NCC, and other features fully recapitulating human and mouse models of PHAII caused by gain-of-function WNK4. Lowering plasma potassium levels by dietary potassium restriction increased NCC activity in wild-type, but not in knockin, mice. NCC activity in knockin mice can be further enhanced by the administration of norepinephrine, a known activator of NCC. Raising plasma potassium by oral gavage of potassium inactivated NCC within 1 hour in wild-type mice, but had no effect in knockin mice. The results provide compelling support for the notion that WNK4 is a bona fide physiological intracellular Cl sensor and that Cl regulation of WNK4 underlies the mechanism of regulation of NCC by extracellular potassium.
Topics: Animals; Chlorides; Mice; Mice, Transgenic; Potassium; Protein Serine-Threonine Kinases; Pseudohypoaldosteronism
PubMed: 30765526
DOI: 10.1073/pnas.1817220116 -
The Journal of Physiology Jul 19791. Dietary sodium depletion and subsequent repletion was studied in rabbits. Potassium intake was maintained constant. 2. during sodium depletion and repletion blood...
1. Dietary sodium depletion and subsequent repletion was studied in rabbits. Potassium intake was maintained constant. 2. during sodium depletion and repletion blood pressure, packed cell volume, food consumption and body weight remained at control values. 3. Decreased sodium excretion was observed in both urine and faeces during sodium depletion and the physiological control of these changes is discussed in relation to the renin-angiotensin-aldosterone system. 4. Potassium excretion during sodium depletion initially fell as a result of reduced urine volume and gradually returned to normal. Urine potassium concentration remained constant. 5. Faecal excretion of potassium rose by 63% during sodium depletion and there was a rise from a control value of 17-25% in the proportion of total potassium excretion accounted for by the faecal component. 6. Water consumption and urine volume both decreased in the initial phase of sodium depletion and then returned to control levels. 7. It is important to consider both urinary and faecal excretion of sodium and potassium when calculating balance status for either ion. Faecal excretion, as well as kidney function, shows important physiological adaptations.
Topics: Animals; Blood Pressure; Body Weight; Diet, Sodium-Restricted; Eating; Feces; Female; Hematocrit; Male; Potassium; Rabbits; Sodium; Water
PubMed: 490371
DOI: 10.1113/jphysiol.1979.sp012860