scholarly journals Force and stiffness in glycerinated rabbit psoas fibers. Effects of calcium and elevated phosphate.

1992 ◽  
Vol 99 (5) ◽  
pp. 795-816 ◽  
Author(s):  
D A Martyn ◽  
A M Gordon
Keyword(s):  
Ionic Strength ◽  
Calcium Sensitivity ◽  
Bathing Solution ◽  
Experimental Conditions ◽  
Relative Population ◽  
Calcium Dependent ◽  
All Solutions ◽  
Length Changes ◽  
Ph Buffer ◽  
Potassium 40

Force (F) and stiffness (K) were measured in glycerinated psoas fibers at various calcium levels with 0, 10, 20, and 30 mM orthophosphate (Pi) added to the bathing solutions. The concentrations of bathing solution constituents were as follows: 110 mM potassium, 40 mM sodium, 4 mM MgATP, 10 mM total EGTA, and variable amounts of MOPS (pH buffer). The pH was 7.0, the ionic strength was 200 mM, and the temperature was 10 degrees C. Calcium levels were established by adding various amounts of CaCl2. All solutions contained 4% Dextran T-500. Fiber K was measured by imposing sinusoidal length changes (0.03-0.1%) at 1 kHz and by applying rapid steps in length and measuring the resulting F changes. At all [Pi] tested, K was more sensitive to calcium than F. Elevating bathing solution [Pi] caused a decrease in the calcium sensitivity of both F and K, while the slopes of F-calcium and K-calcium relations increased. In maximally activating calcium, raising [Pi] caused a continuous decrease in F over the range tested, while from very low to 10 mM Pi K remained constant. Above 10 mM Pi K declined, but to a lesser extent than did F. The results suggest that under our experimental conditions strongly attached crossbridges can exist in both force-producing and non-force-producing states, and that the relative population of these states may be calcium dependent.

The effect of valence and Ionic-strength on the measurement of pH buffer capacity

Soil Research ◽  
1994 ◽  
Vol 32 (5) ◽  
pp. 975 ◽  
Author(s):  
RL Aitken ◽  
PW Moody
Keyword(s):  
Ionic Strength ◽  
Titration Curve ◽  
Buffer Capacity ◽  
Experimental Conditions ◽  
Linear Portion ◽  
Titration Curves ◽  
Addition Rate ◽  
Ph Buffer ◽  
Buffer Capacities ◽  
Linear Regressions

Although the measurement of pH buffer capacity (pHBC) is used to determine lime requirement and acid addition rate in acidification studies, the experimental conditions under which pHBC is determined have not been studied. The effect of valence and ionic strength on the measurement of pHBC was investigated on a range of soils. The effect of the monovalent or divalent accompanying ion was examined by establishing separate titration curves for each of 100 soils by adding incremental amounts of either Ca(OH)2, NaOH, HCl or H2SO4 to soil suspended (1 : 5) in water. Linear regressions were fitted to the linear portion of each titration curve and the slopes of these lines were used as a measure of pHBC. For each soil, the pH buffer capacities were statistically compared. The pHBC determined with Ca(OH)2 was significantly (P = 0.05) greater than that determined with NaOH in 92 soils and, on average (all soils), was 2.2 times the pHBC in NaOH. The effect of ionic strength on pHBC was investigated in each of 20 soils by titrating with HCI in water and suspensions at nominal ionic strengths of 0.006, 0.03 and 0.3 m. In all soils there was a trend for increasing pHBC with increasing ionic strength (I) and, for I < 0.03 m, there was a marked increase in pHBC with increasing I. The results are discussed in relation to the effect of valence and ionic strength on pH buffer capacity mechanisms, and the implications with respect to calculating acidification rates and lime requirements.

scholarly journals Synapsin I (protein I), a nerve terminal-specific phosphoprotein. III. Its association with synaptic vesicles studied in a highly purified synaptic vesicle preparation.

1983 ◽  
Vol 96 (5) ◽  
pp. 1374-1388 ◽  
Author(s):  
W B Huttner ◽  
W Schiebler ◽  
P Greengard ◽  
P De Camilli
Keyword(s):  
Ionic Strength ◽  
Synaptic Vesicle ◽  
Synaptic Vesicles ◽  
Immunological Methods ◽  
Synapsin I ◽  
Tail Region ◽  
Electron Microscopic ◽  
Experimental Conditions ◽  
Calcium Dependent ◽  
Dependent Protein

Synapsin I (protein I) is a neuron-specific phosphoprotein, which is a substrate for cAMP-dependent and Ca/calmodulin-dependent protein kinases. In two accompanying studies (De Camilli, P., R. Cameron, and P. Greengard, and De Camilli, P., S. M. Harris, Jr., W. B. Huttner, and P. Greengard, 1983, J. Cell Biol. 96:1337-1354 and 1355-1373) we have shown, by immunocytochemical techniques at the light microscopic and electron microscopic levels, that synapsin I is present in the majority of, and possibly in all, nerve terminals, where it is primarily associated with synaptic vesicles. In the present study we have prepared a highly purified synaptic vesicle fraction from rat brain by a procedure that involves permeation chromatography on controlled-pore glass as a final purification step. Using immunological methods, synapsin I concentrations were determined in various subcellular fractions obtained in the course of vesicle purification. Synapsin I was found to copurify with synaptic vesicles and to represent approximately 6% of the total protein in the highly purified synaptic vesicle fraction. The copurification of synapsin I with synaptic vesicles was dependent on the use of low ionic strength media throughout the purification. Synapsin I was released into the soluble phase by increased ionic strength at neutral pH, but not by nonionic detergents. The highly purified synaptic vesicle fraction contained a calcium-dependent protein kinase that phosphorylated endogenous synapsin I in its collagenase-sensitive tail region. The phosphorylation of this region appeared to facilitate the dissociation of synapsin I from synaptic vesicles under the experimental conditions used.

scholarly journals The Effect of pH, Ionic Strength and the Presence of PbII on the Formation of Calcium Carbonate from Homogenous Alkaline Solutions at Room Temperature

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 783
Author(s):  
Fulvio Di Lorenzo ◽  
Kay Steiner ◽  
Sergey V. Churakov
Keyword(s):  
Ionic Strength ◽  
Deep Understanding ◽  
Inhibitory Effect ◽  
Alkaline Solutions ◽  
Nucleation Kinetics ◽  
Experimental Conditions ◽  
Calcium Carbonates ◽  
Natural Systems ◽  
Geological Processes ◽  
System Variables

Precipitation of calcium carbonates in aqueous systems is an important factor controlling various industrial, biological, and geological processes. In the first part of this study, the well-known titration approach introduced by Gebauer and coworkers in 2008 s used to obtain reliable experimental dataset for the deep understanding of CaCO3 nucleation kinetics in supersaturated solutions over a broad range of pH and ionic strength conditions. In the second part, the effect of impurities, i.e., 1 mol% of Pb2+, was assessed in the same range of experimental conditions. Divalent lead has been shown to have an inhibitory effect in all ranges of the conditions tested except for pH 8 and low ionic strength (≤0.15 mol/L). Future investigations might take advantage of the methodology and the data provided in this work to investigate the effect of other system variables. The investigation of all the major variables and the assessment of eventual synergic effects could improve our ability to predict the formation of CaCO3 in complex natural systems.

scholarly journals Ferroxidase activity of ferritin: effects of pH, buffer and Fe(II) and Fe(III) concentrations on Fe(II) autoxidation and ferroxidation

1999 ◽  
Vol 338 (3) ◽  
pp. 615-618 ◽  
Author(s):  
Xiaoke YANG ◽  
N. Dennis CHASTEEN
Keyword(s):  
Ph Control ◽  
Alternative Mechanism ◽  
Experimental Conditions ◽  
Iron Storage ◽  
Ferroxidase Activity ◽  
Effects Of Ph ◽  
Ph Stat ◽  
Ph Buffer ◽  
Horse Spleen Ferritin

It is widely accepted that iron deposition in the iron storage protein ferritin in vitro involves Fe(II) oxidation, and that ferritin facilitates this oxidation at a ferroxidase site on the protein. However, these views have recently been questioned, with the protein ferroxidase activity instead being attributed to autoxidation from the buffer alone. Ligand exchange between another protein with ferroxidase activity and ferritin has been proposed as an alternative mechanism for iron incorporation into ferritin. In the present work, a pH stat apparatus is used to eliminate the influence of buffers on iron(II) oxidation. Here we show that the recent experiments questioning the ferroxidase activity of ferritin were flawed by inadequate pH control, that buffers actually retard rather than facilitate iron(II) oxidation, and that horse spleen ferritin has ferroxidase activity when measured under proper experimental conditions. Furthermore, high pH (7.0), a high Fe(II) concentration and the presence of Fe(III) all favour Fe(II) autoxidation in the presence or absence of ferritin.

The diffusion of 75Se(IV) in Beishan granite – temperature, oxygen condition and ionic strength effects

2018 ◽  
Vol 107 (1) ◽  
pp. 39-54
Author(s):  
Chunli Wang ◽  
Xiaoyu Yang ◽  
Jiangang He ◽  
Fangxin Wei ◽  
Zhong Zheng ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Effective Diffusion ◽  
Aerobic Condition ◽  
Double Layers ◽  
Solution Viscosity ◽  
Formation Factor ◽  
Experimental Conditions ◽  
Beishan Granite ◽  
Oxygen Condition ◽  
The Difference

Abstract To explore the diffusion behavior of 75Se(IV) in Beishan granite (BsG), the influences of temperature, oxygen condition and ionic strength were investigated using the through-diffusion experimental method. The effective diffusion coefficient De of 75Se(IV) in BsG varied from 4.21×10−14 m2/s to 3.19×10−13 m2/s in our experimental conditions, increased with increasing temperature. The formation factor Ff of BsG was calculated to be nearly constant in the range of temperatures investigated, suggesting that the inner structure of BsG had no significant change in the temperature range of 20–55°C. Meanwhile, the De values of 75Se(IV) in BsG under anaerobic condition was significantly larger than that under aerobic condition, which may be attributed to the difference in the sorption characteristics and species distribution of Se and pH values. Moreover, the diffusion of 75Se(IV) was promoted with ionic strength increased from 0.01 M to 0.1 M, and then decreased at 0.5 M, mainly due to the combined effects of reduced double layers with increased ionic strength and increase of the solution viscosity at higher ionic strength.

scholarly journals Speciation Studies of L-Histidine Complexes of Pb(II), Cd(II), and Hg(II) in DMSO-Water Mixtures

2012 ◽  
Vol 2012 ◽  
pp. 1-9
Author(s):  
K. Bharath Kumar Naik ◽  
B. Ananda Kumar ◽  
S. Raju ◽  
G. Nageswara Rao
Keyword(s):  
Dielectric Constant ◽  
Ionic Strength ◽  
Complex Formation ◽  
Species Distribution ◽  
Statistical Parameters ◽  
Experimental Conditions ◽  
Equilibrium Study ◽  
Predominant Species ◽  
Chemical Models ◽  
Best Fit

Equilibrium study on complex formation of L-histidine with Pb(II), Cd(II), and Hg(II) has been investigated pH metrically in DMSO-water mixtures (0–60% v/v) at 303 K and 0.16 mol L−1 ionic strength. The predominant species detected for Pb(II) and Cd(II) are ML2H4, ML2H3, ML2H2, ML2H, and ML2 and those for Hg(II) are ML2H4, ML2H3, ML2, and ML. The appropriateness of experimental conditions is verified by introducing errors intentionally in the concentrations of ingredients. The models containing different numbers of species were refined by using the computer program MINIQUAD75. The best-fit chemical models were arrived at based on statistical parameters. The trend in variation of stability constants of the complexes with dielectric constant of the medium is attributed to the electrostatic and nonelectrostatic forces. The species distribution and the plausible equilibria for the formation of the species are also presented.

scholarly journals Calcium Activation of Ryanodine Receptor Channels—Reconciling RyR Gating Models with Tetrameric Channel Structure

2005 ◽  
Vol 126 (5) ◽  
pp. 515-527 ◽  
Author(s):  
Ivan Zahradník ◽  
Sándor Györke ◽  
Alexandra Zahradníková
Keyword(s):  
Experimental Data ◽  
Binding Sites ◽  
Linear Models ◽  
Experimental Studies ◽  
Calcium Sensitivity ◽  
Channel Structure ◽  
Calcium Dependence ◽  
Calcium Dependent ◽  
Monomer Composition ◽  
The Best Approximation

Despite its importance and abundance of experimental data, the molecular mechanism of RyR2 activation by calcium is poorly understood. Recent experimental studies involving coexpression of wild-type (WT) RyR2 together with a RyR2 mutant deficient in calcium-dependent activation (Li, P., and S.R. Chen. 2001. J. Gen. Physiol. 118:33–44) revealed large variations of calcium sensitivity of the RyR tetramers with their monomer composition. Together with previous results on kinetics of Ca activation (Zahradníková, A., I. Zahradník, I. Györke, and S. Györke. 1999. J. Gen. Physiol. 114:787–798), these data represent benchmarks for construction and testing of RyR models that would reproduce RyR behavior and be structurally realistic as well. Here we present a theoretical study of the effects of RyR monomer substitution by a calcium-insensitive mutant on the calcium dependence of RyR activation. Three published models of tetrameric RyR channels were used either directly or after adaptation to provide allosteric regulation. Additionally, two alternative RyR models with Ca binding sites created jointly by the monomers were developed. The models were modified for description of channels composed of WT and mutant monomers. The parameters of the models were optimized to provide the best approximation of published experimental data. For reproducing the observed calcium dependence of RyR tetramers containing mutant monomers (a) single, independent Ca binding sites on each monomer were preferable to shared binding sites; (b) allosteric models were preferable to linear models; (c) in the WT channel, probability of opening to states containing a Ca2+-free monomer had to be extremely low; and (d) models with fully Ca-bound closed states, additional to those of an Monod-Wyman-Changeaux model, were preferable to models without such states. These results provide support for the concept that RyR activation is possible (albeit vanishingly small in WT channels) in the absence of Ca2+ binding. They also suggest further avenues toward understanding RyR gating.

Calcium-dependent secretory and redox response to CCK-8 in isolated perfused rat pancreas

1985 ◽  
Vol 248 (3) ◽  
pp. C228-C234 ◽  
Author(s):  
I. Shibuya ◽  
T. Kanno
Keyword(s):  
Redox State ◽  
Gradual Increase ◽  
Pancreatic Acinar Cell ◽  
Bathing Solution ◽  
Transfer System ◽  
Perfused Rat Pancreas ◽  
Continuous Stimulation ◽  
Calcium Dependent ◽  
Standard Solution ◽  
Protein Output

Continuous stimulation with 8 pM cholecystokinin octapeptide (CCK-8) induced a gradual increase in pancreatic protein output and little if any change in redox state of cytochromes aa3, b, and c + c1. The protein output was completely abolished when CaCl2 was removed from the perfusing and bathing solution. Continuous stimulation with 200 pM CCK-8 induced the rapid and largest protein output and a distinct reduction of cytochromes and nicotinamide nucleotides. These responses were partially decreased in the Ca2+-deficient environment and enhanced immediately after the replacement with the standard solution. These and other results are compatible with the view that reduction of electron transfer system in the pancreatic acinar cell may be induced by stimulation with the secretagogue in pharmacological concentration and that the reduction may coincide with uptake and retention of cytoplasmic excess Ca2+ by mitochondria.

High-throughput assessment of calcium sensitivity in skinned cardiac myocytes

2001 ◽  
Vol 281 (2) ◽  
pp. H969-H974 ◽  
Author(s):  
Chee Chew Lim ◽  
Michiel H. B. Helmes ◽  
Douglas B. Sawyer ◽  
Mohit Jain ◽  
Ronglih Liao
Keyword(s):  
Cardiac Myocytes ◽  
High Throughput ◽  
High Throughput Screening ◽  
Rapid Determination ◽  
Isometric Force ◽  
Calcium Sensitivity ◽  
Pharmacological Agents ◽  
Length Changes ◽  
Myofilament Calcium Sensitivity ◽  
High Degree

Isolated permeabilized cardiac myocytes have been used in the study of myofilament calcium sensitivity through measurement of the isometric force-pCa curve. Determining this force-pCa relationship in skinned myocytes is relatively expensive and carries a high degree of variability. We therefore attempted to establish an alternative high-throughput method to measure calcium sensitivity in cardiac myocytes. With the use of commercially available software that allows for precise measurement of sarcomere spacing, we measured sarcomere length changes in unloaded skinned cardiac myocytes over a range of calcium concentrations. With the use of this technique, we were able to accurately detect acute increases or decreases in myofilament calcium sensitivity after exposure to 10 mM caffeine or 5 mM 2,3-butanedione monoxime, respectively. This technique allows for the simple and rapid determination of myofilament calcium sensitivity in cardiac myocytes in a reproducible and inexpensive manner and could be used for high-throughput screening of pharmacological agents and/or transgenic mouse models for changes in myofilament calcium sensitivity.

Comparison between specific surface complexation and Donnan ion-exchange models for describing the adsorption of cations on kraft fibres – literature evidence and EXAFS study of Cu(II) binding

2010 ◽  
Vol 25 (2) ◽  
pp. 178-184 ◽  
Author(s):  
Ola Sundman ◽  
Per Persson ◽  
Lars-Olof Öhman
Keyword(s):  
Ionic Strength ◽  
Ion Exchange ◽  
Metal Ion ◽  
Experimental Conditions ◽  
Cellulose Fibres ◽  
Metal Ion Adsorption ◽  
Literature Evidence ◽  
Trivalent Cations ◽  
Exafs Study ◽  
Low Ionic Strength

Abstract A compilation of the applied experimental conditions when studying metal ion adsorption onto kraft fibres, and the resulting conclusion, revealed that the ionic strength conditions used during the experiments were an important dividing factor. At low ionic strengths, the conclusion has regularly been that the Donnan ion-exchange model could correctly predict the adsorption while, at higher ionic strengths, it has often been concluded that the formation of specific metal-ion fibre complexes must be assumed. To study this apparent influence from the presence of monovalent sodium ions, Cu K-edge EXAFS spectra of Cu2+ ions adsorbed to kraft fibres were collected in media of “0” to 100 mM NaCl. Combined with previous data, these measurements confirmed that at very low ionic strength, the importance of specific interactions between the chemically modified cellulose fibres and the Cu(II) ions significantly decreased. For a detailed description of the adsorption phenomenon, both types of interactions must be considered simultaneously. For most technical and engineering applications, however, the Donnan model can be used at low ionic strength conditions, i.e. I ≲ 10 mM. At higher ionic strengths, though, the inclusion of specific complexes in the model is necessary for correctly describing the adsorption of di- and trivalent cations with strong complex forming properties.

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