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Nucleic Acids Research Feb 2015Microsecond molecular dynamics simulations of B-DNA oligomers carried out in an aqueous environment with a physiological salt concentration enable us to perform a...
Microsecond molecular dynamics simulations of B-DNA oligomers carried out in an aqueous environment with a physiological salt concentration enable us to perform a detailed analysis of how potassium ions interact with the double helix. The oligomers studied contain all 136 distinct tetranucleotides and we are thus able to make a comprehensive analysis of base sequence effects. Using a recently developed curvilinear helicoidal coordinate method we are able to analyze the details of ion populations and densities within the major and minor grooves and in the space surrounding DNA. The results show higher ion populations than have typically been observed in earlier studies and sequence effects that go beyond the nature of individual base pairs or base pair steps. We also show that, in some special cases, ion distributions converge very slowly and, on a microsecond timescale, do not reflect the symmetry of the corresponding base sequence.
Topics: Base Sequence; Cations, Monovalent; DNA; Molecular Dynamics Simulation; Nucleic Acid Conformation; Potassium
PubMed: 25662221
DOI: 10.1093/nar/gkv080 -
Proteins maintain hydration at high [KCl] concentration regardless of content in acidic amino acids.Biophysical Journal Jul 2021Proteins of halophilic organisms, which accumulate molar concentrations of KCl in their cytoplasm, have a much higher content in acidic amino acids than proteins of...
Proteins of halophilic organisms, which accumulate molar concentrations of KCl in their cytoplasm, have a much higher content in acidic amino acids than proteins of mesophilic organisms. It has been proposed that this excess is necessary to maintain proteins hydrated in an environment with low water activity, either via direct interactions between water and the carboxylate groups of acidic amino acids or via cooperative interactions between acidic amino acids and hydrated cations. Our simulation study of five halophilic proteins and five mesophilic counterparts does not support either possibility. The simulations use the AMBER ff14SB force field with newly optimized Lennard-Jones parameters for the interactions between carboxylate groups and potassium ions. We find that proteins with a larger fraction of acidic amino acids indeed have higher hydration levels, as measured by the concentration of water in their hydration shell and the number of water/protein hydrogen bonds. However, the hydration level of each protein is identical at low (b = 0.15 mol/kg) and high (b = 2 mol/kg) KCl concentrations; excess acidic amino acids are clearly not necessary to maintain proteins hydrated at high salt concentration. It has also been proposed that cooperative interactions between acidic amino acids in halophilic proteins and hydrated cations stabilize the folded protein structure and would lead to slower dynamics of the solvation shell. We find that the translational dynamics of the solvation shell is barely distinguishable between halophilic and mesophilic proteins; if such a cooperative effect exists, it does not have that entropic signature.
Topics: Amino Acids, Acidic; Ions; Potassium; Potassium Chloride; Sodium Chloride; Water
PubMed: 34087206
DOI: 10.1016/j.bpj.2021.05.015 -
Pflugers Archiv : European Journal of... Feb 2018The renal collecting duct contains two distinct cell types, principal and intercalated cells, expressing potassium K4.1/5.1 (KCNJ10/16) and chloride ClC-K2 (ClC-Kb in...
The renal collecting duct contains two distinct cell types, principal and intercalated cells, expressing potassium K4.1/5.1 (KCNJ10/16) and chloride ClC-K2 (ClC-Kb in humans) channels on their basolateral membrane, respectively. Both channels are thought to play important roles in controlling systemic water-electrolyte balance and blood pressure. However, little is known about mechanisms regulating activity of K4.1/5.1 and ClC-K2/b. Here, we employed patch clamp analysis at the single channel and whole cell levels in freshly isolated mouse collecting ducts to investigate regulation of K4.1/5.1 and ClC-K2/b by dietary K and Cl intake. Treatment of mice with high K and high Cl diet (6% K, 5% Cl) for 1 week significantly increased basolateral K-selective current, single channel K4.1/5.1 activity and induced hyperpolarization of basolateral membrane potential in principal cells when compared to values in mice on a regular diet (0.9% K, 0.5% Cl). In contrast, basolateral Cl-selective current and single channel ClC-K2/b activity was markedly decreased in intercalated cells under this condition. Substitution of dietary K to Na in the presence of high Cl exerted a similar inhibiting action of ClC-K2/b suggesting that the channel is sensitive to variations in dietary Cl per se. Cl-sensitive with-no-lysine kinase (WNK) cascade has been recently proposed to orchestrate electrolyte transport in the distal tubule during variations of dietary K. However, co-expression of WNK1 or its major downstream effector Ste20-related proline-alanine-rich kinase (SPAK) had no effect on ClC-Kb over-expressed in Chinese hamster ovary (CHO) cells. Treatment of mice with high K diet without concomitant elevations in dietary Cl (6% K, 0.5% Cl) elicited a comparable increase in basolateral K-selective current, single channel K4.1/5.1 activity in principal cells, but had no significant effect on ClC-K2/b activity in intercalated cells. Furthermore, stimulation of aldosterone signaling by Deoxycorticosterone acetate (DOCA) recapitulated the stimulatory actions of high K intake on K4.1/5.1 channels in principal cells but was ineffective to alter ClC-K2/b activity and basolateral Cl conductance in intercalated cells. In summary, we report that variations of dietary K and Cl independently regulate basolateral potassium and chloride conductance in principal and intercalated cells. We propose that such discrete mechanism might contribute to fine-tuning of urinary excretion of electrolytes depending on dietary intake.
Topics: Action Potentials; Animals; CHO Cells; Cell Membrane; Cells, Cultured; Chloride Channels; Chlorides; Cricetinae; Cricetulus; Diet; Kidney Tubules, Collecting; Male; Mice; Mice, Inbred C57BL; Potassium; Potassium Channels, Inwardly Rectifying
PubMed: 29134279
DOI: 10.1007/s00424-017-2084-x -
The Journal of General Physiology Aug 2023K+ channel activity can be limited by C-type inactivation, which is likely initiated in part by dissociation of K+ ions from the selectivity filter and modulated by the...
K+ channel activity can be limited by C-type inactivation, which is likely initiated in part by dissociation of K+ ions from the selectivity filter and modulated by the side chains that surround it. While crystallographic and computational studies have linked inactivation to a "collapsed" selectivity filter conformation in the KcsA channel, the structural basis for selectivity filter gating in other K+ channels is less clear. Here, we combined electrophysiological recordings with molecular dynamics simulations, to study selectivity filter gating in the model potassium channel MthK and its V55E mutant (analogous to KcsA E71) in the pore-helix. We found that MthK V55E has a lower open probability than the WT channel, due to decreased stability of the open state, as well as a lower unitary conductance. Simulations account for both of these variables on the atomistic scale, showing that ion permeation in V55E is altered by two distinct orientations of the E55 side chain. In the "vertical" orientation, in which E55 forms a hydrogen bond with D64 (as in KcsA WT channels), the filter displays reduced conductance compared to MthK WT. In contrast, in the "horizontal" orientation, K+ conductance is closer to that of MthK WT; although selectivity filter stability is lowered, resulting in more frequent inactivation. Surprisingly, inactivation in MthK WT and V55E is associated with a widening of the selectivity filter, unlike what is observed for KcsA and reminisces recent structures of inactivated channels, suggesting a conserved inactivation pathway across the potassium channel family.
Topics: Protein Conformation; Potassium; Ion Channel Gating; Potassium Channels; Molecular Dynamics Simulation; Ions; Bacterial Proteins
PubMed: 37318452
DOI: 10.1085/jgp.202213166 -
Kidney International Jun 2017To maintain potassium homeostasis, kidneys exert flow-dependent potassium secretion to facilitate kaliuresis in response to elevated dietary potassium intake. This...
To maintain potassium homeostasis, kidneys exert flow-dependent potassium secretion to facilitate kaliuresis in response to elevated dietary potassium intake. This process involves stimulation of calcium-activated large conductance maxi-K (BK) channels in the distal nephron, namely the connecting tubule and the collecting duct. Recent evidence suggests that the TRPV4 channel is a critical determinant of flow-dependent intracellular calcium elevations in these segments of the renal tubule. Here, we demonstrate that elevated dietary potassium intake (five percent potassium) increases renal TRPV4 mRNA and protein levels in an aldosterone-dependent manner and causes redistribution of the channel to the apical plasma membrane in native collecting duct cells. This, in turn, leads to augmented TRPV4-mediated flow-dependent calcium ion responses in freshly isolated split-opened collecting ducts from mice fed the high potassium diet. Genetic TRPV4 ablation greatly diminished BK channel activity in collecting duct cells pointing to a reduced capacity to excrete potassium. Consistently, elevated potassium intake induced hyperkalemia in TRPV4 knockout mice due to deficient renal potassium excretion. Thus, regulation of TRPV4 activity in the distal nephron by dietary potassium is an indispensable component of whole body potassium balance.
Topics: Adaptation, Physiological; Animals; Calcium; Genetic Predisposition to Disease; Homeostasis; Hyperkalemia; Kidney Tubules; Large-Conductance Calcium-Activated Potassium Channels; Mice, Inbred C57BL; Mice, Knockout; Phenotype; Potassium, Dietary; Receptors, Mineralocorticoid; Renal Elimination; TRPV Cation Channels
PubMed: 28187982
DOI: 10.1016/j.kint.2016.12.010 -
Analytical Sciences : the International... 2010Two-dimensional real-time observation of potassium ion distributions was achieved using an ion imaging device based on charge-coupled device (CCD) and metal-oxide...
Two-dimensional real-time observation of potassium ion distributions was achieved using an ion imaging device based on charge-coupled device (CCD) and metal-oxide semiconductor technologies, and an ion selective membrane. The CCD potassium ion image sensor was equipped with an array of 32 × 32 pixels (1024 pixels). It could record five frames per second with an area of 4.16 × 4.16 mm(2). Potassium ion images were produced instantly. The leaching of potassium ion from a 3.3 M KCl Ag/AgCl reference electrode was dynamically monitored in aqueous solution. The potassium ion selective membrane on the semiconductor consisted of plasticized poly(vinyl chloride) (PVC) with bis(benzo-15-crown-5). The addition of a polyhedral oligomeric silsesquioxane to the plasticized PVC membrane greatly improved adhesion of the membrane onto Si(3)N(4) of the semiconductor surface, and the potential response was stabilized. The potential response was linear from 10(-2) to 10(-5) M logarithmic concentration of potassium ion. The selectivity coefficients were K(K(+),Li(+))(pot) = 10(-2.85), K(K(+),Na(+))(pot) = 10(-2.30), K(K(+),Rb(+))(pot) =10(-1.16), and K(K(+),Cs(+))(pot) = 10(-2.05).
Topics: Computer Systems; Crown Ethers; Electrodes; Hydrogen-Ion Concentration; Ions; Plasticizers; Polyvinyl Chloride; Potassium; Potentiometry; Semiconductors; Sodium; Static Electricity
PubMed: 20953045
DOI: 10.2116/analsci.26.1039 -
Chemphyschem : a European Journal of... Oct 2021Rare anionic forms of nucleic acids play a significant biological role and lead to spontaneous mutations and replication and translational errors. There is a lack of...
Rare anionic forms of nucleic acids play a significant biological role and lead to spontaneous mutations and replication and translational errors. There is a lack of information surrounding the stability and reactivity of these forms. Ion pairs of mono-sodium and -potassium salts of adenine exist in DMSO solution with possible cation coordination sites at the N1, N7 and N9 atoms of the purine ring. At increasing concentrations π-π stacked dimers are the predominant species of aggregates followed by higher order aggregation governed by coordination to metal cations in which the type of counter ion present has a central role in the aggregate formation.
Topics: Adenine; Anions; Cations; Crystallography, X-Ray; Dimethyl Sulfoxide; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Structure; Potassium; Salts; Sodium; Spectrophotometry, Ultraviolet
PubMed: 34153151
DOI: 10.1002/cphc.202100098 -
American Journal of Veterinary Research Apr 2000To assess the effect of dietary potassium citrate supplementation on the urinary pH, relative supersaturation of calcium oxalate and struvite (defined as the activity...
OBJECTIVE
To assess the effect of dietary potassium citrate supplementation on the urinary pH, relative supersaturation of calcium oxalate and struvite (defined as the activity product/solubility product of the substance), and concentrations of magnesium, ammonium, phosphate, citrate, calcium, and oxalate in dogs.
ANIMALS
12 healthy adult dogs.
PROCEDURE
Canned dog food was fed to dogs for 37 days. Dogs were randomly allocated to 3 groups and fed test diets for a period of 8 days. Study periods were separated by 6-day intervals. During each study period the dogs were fed either standard diet solus (control) or standard diet plus 1 of 2 types of potassium citrate supplements (150 mg potassium citrate/kg of body weight/d) twice daily. Urinary pH, volume and specific gravity, relative supersaturation of calcium oxalate and struvite, and concentrations of magnesium, ammonium, phosphate, calcium, oxalate, and citrate were assessed for each treatment.
RESULTS
Mean urine pH was not significantly affected by dietary potassium citrate supplementation, although urine pH did increase by 0.2 pH units with supplementation. Diets containing potassium citrate maintained a higher urine pH for a longer part of the day than control diet. Three Miniature Schnauzers had a significantly lower urinary relative calcium oxalate supersaturation when fed a diet supplemented with potassium citrate, compared with control diet.
CONCLUSIONS AND CLINICAL RELEVANCE
Dietary potassium citrate supplementation has limited effects on urinary variables in most healthy dogs, although supplementation results in maintenance of a higher urine pH later in the day. Consequently, if supplementation is introduced, dogs should be fed twice daily and potassium citrate should be given with both meals or with the evening meal only.
Topics: Animals; Body Weight; Calcium Oxalate; Circadian Rhythm; Dogs; Energy Intake; Female; Hydrogen-Ion Concentration; Magnesium Compounds; Male; Phosphates; Potassium Citrate; Potassium, Dietary; Struvite; Urine
PubMed: 10772109
DOI: 10.2460/ajvr.2000.61.430 -
The Journal of General Physiology Nov 1958Potassium-free artificial sea water causes a loss of cell potassium and a gain of cell sodium in Porphyra perforata, which is not attributable to an inhibition of...
Potassium-free artificial sea water causes a loss of cell potassium and a gain of cell sodium in Porphyra perforata, which is not attributable to an inhibition of respiration. On adding KCl or RbCl to such low potassium, high sodium tissues, net accumulation of potassium or rubidium takes place, accompanied by net extrusion of sodium. Rates of potassium or rubidium accumulation and sodium extrusion are proportional to the amount of KCl or RbCl added only at low concentrations. Saturation of rates is evident at KCl or RbCl concentrations above 20-30 mM, suggesting the role of an ion carrier mechanism of transport. Evidence for and against mutually dependent sodium extrusion and potassium or rubidium accumulation is discussed.
Topics: Eukaryota; Ions; Porphyra; Potassium; Rubidium; Sodium
PubMed: 13587912
DOI: 10.1085/jgp.42.2.281 -
Journal of Dairy Science May 1997We studied the balance of Na+, K+, Cl-, and water in six high yielding (> 39 kg/d of milk) cows between wk 2 to 1 prepartum and at 2 and 7 wk postpartum during winter in...
We studied the balance of Na+, K+, Cl-, and water in six high yielding (> 39 kg/d of milk) cows between wk 2 to 1 prepartum and at 2 and 7 wk postpartum during winter in Israel. Cows were fed complete diets; Na+ and Cl- contents exceeded dietary recommendations, and K+ content was equal to dietary recommendations. Milk yield was related positively and significantly to retention of Cl- and K+, indicating that ions that are the main constituents of sweat can limit the ability of cows to express full genetic potential. The highest ion retention was recorded for cows that had the highest dry matter intake and, hence, the highest ion intake. Retention of Cl- was highest for cows that were most efficient in retaining Cl- in the kidney. In hot climates, increasing the concentrations of ions in the diet of early lactation cows according to the actual dry matter intake could prevent or reduce the severity of ion deficiencies. Water turnover rate of the cows was dependent on dry matter intake, milk yield, and respiratory-cutaneous water loss. The milk-free water balance (water turnover rate minus water secreted in milk) could be very efficiently predicted for lactating and nonlactating cows by the following equation: milk-free water balance (kilograms per day) = digestible energy intake (megacalories per day) x 0.58 + respiratory-cutaneous loss (kilograms per day) x 0.97 (n = 18; R2 = 0.97). This formula provides a tool to assess the evaporative-cutaneous water loss from feed and water intake measurements to evaluate the severity of heat stress.
Topics: Animals; Body Temperature; Body Water; Body Weight; Cattle; Chlorides; Chlorine; Eating; Female; Lactation; Potassium; Sodium; Sweat
PubMed: 9178136
DOI: 10.3168/jds.S0022-0302(97)76019-3