Effects Of Changes In Concentration Research Articles

Kinetics of diffusion in a spherical cell. i. no solute buffering

Realistic neuron models that involve effects of concentration changes of second messengers on ion channels must include processes such as diffusion and solute buffering. These processes, which span a wide range of spatial and temporal scales, may impose a severe computational burden. In this paper and its companion, we examine the kinetics of diffusion and present methods for stimulating it accurately and efficiency. The problem of calcium diffusion in a spherical cell is used as a device to demonstrate the practical application of our analysis. However, the scope of these papers is not limited to this problem. The same analysis that we apply and concerns that we raise are germane to the spread of any second messenger, and can be adapted to other geometries. The focus of this paper is the simplest case: diffusion in the absence of solute buffering. This analysis also applies whenever buffering is so fast that it is instantaneous compared to diffusion, or so slow that concentration gradients have dissipated before substantial buffering takes place. The second paper investigates the more difficult situation where diffusion and buffering occur at comparable rates. In the absence of buffering, concentration changes produced by diffusion can be fit by an infinite series of exponential terms. We show how to design a model with N + 1 compartments that fits the N slowest terms of this series exactly in a shell just inside the cell membrane.

Self-consistent approach to the diffusion induced by a centrifugal field in condensed matter: Sedimentation.

A self-consistent approach to the Lamm sedimentation equation is proposed for describing the diffusion induced by a centrifugal (or gravitational) field in a two-component condensed system, particularly for a high solute concentration or a high centrifugal field. In this approach, the driving force inducing the diffusion is expressed by introduction of the effective mass of the surrounding mixture (solvent and solutes) which causes the buoyant force. It is self-consistently represented as a function of concentration in place of the constant value in the Lamm equation. The theory is constructed on the basis of nonequilibrium thermodynamics and the Nernst-Einstein relation considering the effect of concentration change. The resulting diffusion equation is presented in a nonlinear form instead of the linear one of the Lamm equation. The concentration profile in equilibrium state is found by solving the nonlinear diffusion equation. It is shown that the nonlinear effect is significant with increase either in the solute concentration or in the centrifugal field.

Hydrogen iodide in argon matrixes

The infrared spectra and HI and DI in argon matrices have been studied in the 11-25 K interval. The effects of concentration changes and of impurities have been investigated. Dimer and trimer bands have been assigned, as well as bands due to binary complexes with water, hydrogen bromide, hydrogen chloride, and atomic and molecular iodine.

Photochemically induced nuclear polarization study of the accessibility of tyrosines in insulin

The accessible tyrosines of bovine insulin were studied by the photochemically induced dynamic nuclear polarization (photo-CIDNP) method. Tyrosine 1H nuclear polarization is observed in acidic, neutral, and basic solutions at all concentrations studied, in the absence of added salts as well as in the presence of 0.05-0.1 M chloride or phosphate. At pH 2.1 in the presence of chloride, at concentrations of 640 microM and above, most of the nuclear polarization at delta 6.82 originates from one group of tyrosines. On the basis of the crystallographic model, these are assumed to be the A14 tyrosines. We explored the possibility of a genuine concentration dependence of the photo-CIDNP intensity of insulin due to aggregation. In order to discern between such effects and trivial kinetic effects traceable to the optical irradiation method, the effects of concentration changes on polarization were examined in three apparently nonassociating trypsin inhibitor proteins. In insulin, the intensity of Tyr-A 14 polarization changes slowly at concentrations above 1 mM, suggesting that these residues are similarly accessible in all association states. At insulin concentrations below 320 microM, additional tyrosine emission signals were observed. These signals are probably due to B16 and B26 tyrosines of monomers. Polarization transfer effects from Tyr-A14 are evident in the tetramer and hexamer. Enhanced absorption effects in the two histidines (B5 and B10) of the insulin monomer were observed at pH 10 in the presence of 0.1 M phosphate.

Effect of change in concentration upon lens turbidity as predicted by the random fluctuation theory

Theoretical calculations were performed to predict how the light scattering intensity would change with changes in concentration in the gel state. The theory of light scattering was applied to a random distribution of hard spheres. The spherical particles with constant diameter were embedded in a medium having a different refractive index. The light-scattering intensities obtained as a function of concentration showed that in dilute solutions the scattered light intensity increases with concentration. However, in concentrated solution greater than 0.1 or 0.2 volume fraction, the light-scattering intensity decreases with increase in concentration.

Studies on carboxymethylated cellulose: Potentiometric titrations, 2

AbstractEffect of the sizes of counterions on the dissociation constant of carboxymethylated cellulose (CMC) is studied by potentiometry. Dissociation of protons from the CMC chains is suppressed with increasing size of the counterion. A good agreement is observed between the theory of Kagawa and Gregor and the experimental results accounting for the counterion size effect; a thermodynamic analysis of ΔpK supported this conclusion. Effects of concentration changes of the polyacid were also considered.

ChemInform Abstract: RAMAN LIGHT SCATTERING STUDIES OF THE DEPOLARIZED RAYLEIGH WING OF LIQUIDS AND SOLUTIONS

Raman spectra of the depolarized Rayleigh wing region (10–300 cm−1) of a number of liquids and solutions have been recorded in digital form employing signal averaging techniques. The symmetrized I(?) spectra have been recast in an I(?)?2 format which transforms the Rayleigh spectra into forms directly comparable to far‐infrared absorption. The major advantage of this procedure is that it suppresses the exciting line and emphasizes the weak low frequency peaks. As a result, the basic characteristics of the ’’peaks’’ previously reported are confirmed with improved precision. Peaks have also been observed for the first time for cyclohexane, acetone, and n‐tetradecane. These peaks appear to reflect the short‐time behavior of the external coordinates of individual anisotropic molecules and should not be confused with fundamental vibrational or negative combination modes. For liquid benzene, studies of the effects of concentration change (in carbon tetrachloride), temperature change, and isotopic substitution clearly showed that the peak originates in hindered librational oscillations of individual benzene molecules. Temperature variation studies revealed that the peak maximum decreased with increased temperature, which was exactly the opposite of that reported from infrared studies.

The effect of changes in concentrations of dry matter, and of fat and protein in milk substitute diets for veal calves

SUMMARYThe effect of a gradual increase in dry-matter concentration from 140 g/kg (LD diets) to a maximum of 215 g/kg (HD diets), and the effect of an increase in fat concentration from 225 g/kg D.M. and reduction in protein concentration from 298 g/kg D.M. (LF diets) to 254g fat and 211g protein/kg D.M. respectively (HF diets) was examined with 32 Friesian bull calves in a 2 × 2 factorial experiment. Milk substitutes were offered ad libitum in two feeds daily from 2 days of age. The dietary changes were first introduced at 7 weeks of age and differences became progressively greater as further changes were made at 9, 11 and 13 weeks. The calves were slaughtered at 16 weeks of age.Dry-matter intake for calves given the HD diets increased faster with age after 7 weeks than that for calves given the LD diets. For the period 7–16 weeks, calves given the HD diets consumed 17% more D.M. than those given the LD diets and had a 13% greater rate of live-weight gain (1·57 v. 1·39 kg/day), although most of the increase in weight gain occurred between 9 and 13 weeks of age.There was no significant effect on D.M. intake or on live-weight gain of altering the fat and protein concentrations in the milk substitute, although feed conversion ratio (kg D.M. intake/kg weight gain) was higher for the HF than for the LF diets. Apparent digestibility of D.M., crude protein and fat were reduced with the HF diets, but the efficiency of retention of the digested nitrogen was improved. During the second and third weeks of life, D.M. intake reached a peak at approximately 67 g/kg0·75 and subsequently declined to stabilize at about 56 g/kg0·75. However, a gradual increase in concentration of the milk substitute from 140 to 215 g D.M./kg increased intake to about 62 g D.M./kg0·75. The results clearly indicate that, at a dietary concentration of 140 g D.M./kg, maximum D.M. intake cannot be achieved because the volume of fluid that needs to be ingested exceeds the capacity of the digestive system. In contrast, at reconstitution rates increasing from 140 to 215 g D.M./kg, distension of the stomach becomes less important and physiological and metabolic factors seem to assume a greater role in the control of feed intake.

IR-spectroscopic study of the effect of the CoO concentration of CoO-MgO solid solutions on the activation energy for oxidation of the surface forms of CO

1. Kinetic parameters for the oxidation of two surfaces forms of CO on CoO-MgO solid solutions have been determined by IR spectroscopy. The values obtained indicate that these forms differ in their reactivities with respect to oxygen. 2. Comparison of the effect of concentration changes on the activation energy for oxidation on cluster centers and on Weiss centers suggests that the exceptional properties of the cluster centers are due to weakening of the Co-to-surface bonding resulting from indirect exchange.

THE STABILITY OF VITAMIN B6 ACCUMULATION AND PYRIDOXAL KINASE ACTIVITY IN RABBIT BRAIN AND CHOROID PLEXUS

The effects of changes in the concentrations of pyridoxal phosphate and blogenic amines in brain on: (I) pyridoxal kinase (EC 2.7.1.35) activity in brain and choroid plexus; and (2) vitamin B6 accumulation by brain slices and isolated, intact choroid plexuses were studied. New Zealand white rabbits were treated parenterally with 200 mg/kg pyridoxine‐HCl for 3 days or 120 mg/kg 4‐deoxypyridoxine HCI or 5 mg/kg reserpine I day before death. After these treatments the mean concentration of pyridoxal phosphate in brain was elevated by 39% by pyridoxine and decreased by 57% by 4‐deoxypyridoxine. Reserpine had no effect. However, the ability of brain slices and isolated, intact choroid plexuses from the treated rabbits to accumulate [3H] vitamin B6 (with [3H]pyridoxine in the medium) was not different from untreated controls. Also, the specific activity of pyridoxal kinase in brain and choroid plexus of treated rabbits was not different from controls. These results show that vitamin B6 accumulation and pyridoxal kinase activity in brain and choroid plexus are independent of both pyridoxal phosphate and reserpine‐sensitive biogenic amine concentrations in brain. In vitro studies with pyridoxal kinase showed that. in both choroid plexus and brain. pyridoxal kinase was a single enzyme with a molecular weight of 43.000 and a Km, for pyridoxine of 2.0 μM Crude and partially‐purified pyridoxal kinase from brain was not inhibited by biogenic amines (1 mM) or pyridoxal phosphate (5 μM). These in vitro data are consistent with the lack of effect of changes in pyridoxal phosphate and biogenic amine concentrations (in brain) on pyridoxal kinase activity in brain in vivo.

Réactions chimiques oscillantes (type Belousov‐Zhabotinskii) impliquant des cétones cycliques et aliphatiques

Oscillating Chemical Reactions (Belousov‐Zhabotinskii type) involving cyclic and aliphatic KetonesFour ketonic compounds (cyclohexanone, cyclopentanone, butanone, and 3‐pentanone) have been found to generate chemical oscillations in the BrO3−/Ce4+/ketone system. The effect of changes in concentrations of the reagents has been investigated and differences in behaviour with other systems found. The dependence of these reactions on temperature has been studied and activation energies calculated.

Anionic polymerization of caprolactam. Optimization of the system NaH/N‐benzoyl caprolactam

AbstractThe effects of changes in concentration of sodium hydride as catalyst, and N‐benzoyl caprolactam as cocatalyst upon the polymerization of ε‐caprolactam were studied. The effects were monitored as changes in the intrinsic viscosity of the resultant polymer determined in m‐cresol at 25°C. Effects of changes in polymerization temperature at constant catalyst and cocatalyst concentration were also studied.Reproducibility of a given average molecular weight was variable. The highest value of intrinsic viscosity resulted from the lowest cocatalyst concentration studied. Intrinsic viscosity of the product reached a peak at 1.8 mol‐% catalyst for 1 and 2 mol‐% cocatalyst, but no clear peak occurred at the higher cocatalyst concentrations studied. The highest intrinsic viscosity resulted from the lowest polymerization temperature in the range from 120–200°C.

Frequency dependence of cyclic AMP in mammalian myocardium

ALTHOUGH there is now good evidence that cyclic AMP is a mediator of positive inotropic effects of catecholamines in the heart, the details of the metabolism of this nucleotide in the intact myocardial cells are still unknown. It has been shown that the intracellular concentration of cyclic AMP oscillates during each contraction cycle of the frog heart1,2. But little information is available for the influence of frequency of stimulation, which regulates myocardial contractility in physiological conditions3, on the intracellular level of cyclic AMP. We therefore investigated the relationship between cyclic AMP level and the strength of contraction of the ventricular myocardium during the induction of different contractile states by changing frequency of stimulation. In order to analyse the influence of frequency of stimulation on cyclic AMP level, the effects of changes in concentrations of extracellular calcium ions or of D600, which is thought to inhibit the influx of calcium ions through the myocardial cell membrane4, were also investigated. It was found that the intracellular level of cyclic AMP and the contractile force of isolated rabbit papillary muscles had a reciprocal relationship during induction of different contractile states by changing frequencies of stimulation. The influence of frequency was simulated by reduction of the extracellular calcium ions or by D600.

Effects of change in concentration of calcium on myocardial contractility depressed by thiamylal and halothane.

The effects of change in the concentration of Ca++ on myocardial contractility depressed by thiamylal and halothane were studied in isolated dog heart muscle. The concentration of Ca++ in the bathing medium was increased stepwise from 1.9 to 20.9 mM. An increase in Ca++ concentration resulted in an increase both in net-shortening (delta1) and in maximum velocity of shortening at 0.4 g preload (V'max) which reached the maximum values at 11.4mM of Ca++. A further increase in Ca++ concentration rather decreased delta1 and V'max. The concentration-response relation curves in the presence of thiamylal (3.3 mg%) shifted to the right almost parallel to the control curve, with the peaks at 15.2 mM of Ca++. The result indicates that the depression of myocardial contractility produced by thiamylal is counteracted competitively by Ca++. However, the curves in the presence of halothane (5.0 +/- 0.4 mg%) were kept lower than those of the control, with the peaks at 7.6 mM of Ca++. The result shows that the counteraction of Ca++ to the depression of myocardial contractility was limited in the presence of halothane. A similar tendency was observed in maximum force of isometric contraction (Fm). Moreover, in the presence of halothane, the administration of higher concentrations of Ca++ almost always accompanied "after-contraction". From the result obtained and the literature concerned it was suggested that the mechanism for producing the depression of myocardial contractility might be different between thiamylal and halothane in relation to Ca++ movements at the Ca++ storage sites within the myocardium.

Effect of Concentration Changes on Permittivity of Electrolyte Solutions

Effect of Concentration Changes on Permittivity of Electrolyte Solutions

The effects of change in concentration of carbon dioxide and oxygen on storage behaviour of Jonathan apples

The behaviour of Jonathan apples in storage was studied in relation to the concentrations of carbon dioxide and oxygen in the storage atmosphere. A factorial design of 2, 4, and 6 per cent carbon dioxide and 1.2, 2.2, and 13.2 per cent oxygen was used and apples were removed from storage at 32�F after 20, 23, and 26 weeks. The concentrations of carbon dioxide and oxygen in the storage atmosphere were related quantitatively to weight loss, ground colour, firmness, titratable acidity, and to the incidence of superficial scald and breakdown. Rest retention of weight, acids, ground colour, and firmness, and least wastage from superficial scald were found in atmospheres with high carbon dioxide and low oxygen concentrations, but more of the fruit in these atmospheres had breakdown.

RING CONTRACTION DURING THE LEAD TETRAACETATE OXIDATION OF REDUCING SUGARS

The rate of oxidation of D-glucose by lead tetraacetate in acetic acid is affected little by a large change in concentration of reactants, showing that the glycol cleavage step is not rate-controlling. Oxidation of 3-O-methyl-6-O-trityl-D-glucose yields 3-O-formyl-2-O-methyl-5-O-trityl-D-arabinose; the latter is not derived by production initially of a 4-O-formyl derivative that undergoes acyl migration. It is probable that the oxidation of D-glucose proceeds with conversion of the pyranose sugar into a furanose intermediate. By contrast, D-mannose appears to be oxidized mainly in the pyranose form, as shown by the oxidation patterns of D-mannose-1- and -2-14C and 5-O-methyl-D-mannofuranose, and the effects of concentration change on the reaction of D-mannose and derivatives. The proximity of the ring oxygen atom to the 1,2-diol group may contribute to the unusually high reactivity of D-mannopyranose as compared with other types of monocyclic six-membered ring vic-diols.Intermediate proportions of furanose and pyranose pathways characterize the lead tetraacetate oxidation of the other six aldohexoses. Similarities in the behavior of glucose and idose, gulose and mannose, and allose and talose may originate in steric similarities between these pairs of sugars.

DETERMINATION OF CONCENTRATIONS OF AIRBORNE RADIOACTIVITY.

Airborne radioactivity may be measured by three main methods: sampling techniques followed by suitable monitoring, sampling techniques concurrent with suitable monitoring, or by directly measuring the radioactivity from a known volume of air. The interpretation of air sampling and monitoring data obtained from the first two techniques, including the effect of half life om sample radioactivity is discussed. Subjects covered are: derivation of air sampling equations; evaluation of data from fixed collecting medium continuous air monitors; evaluation of data from moving collecting medium continuous air monitors, with immediate counting or with post collection counting; evaluation of data for the above air monitoring instruments when the half life is short compared to the sampling interval of concern, the half life is long compared to the sampling interval of concern, and the half life is similar to the sampling interval of concern. The effect of changes in concentration as a function of time is also discussed. Examples are given for each condition. (auth)

The effects of carbon dioxide and oxygen concentrations on superficial scald of Granny Smith apples

In the past, experiments on controlled atmosphere storage have tested specific combinations of carbon dioxide and oxygen, usually in a manner which precludes determination of the effect of change in concentration of these gases. The data from the series of trials discussed in this paper permitted an investigation of the effect of concentrations of carbon dioxide and oxygen on the incidence of scald with simple and multiple linear regression techniques. The method was applied to data from three types of controlled atmosphere storage: (1) Carbon dioxide 2.5–10% at 2.5% oxygen, (2) Oxygen 1.25–20%, at near zero carbon dioxide, (3) Carbon dioxide 3.3–10.9% oxygen 2.2–16%. The relation between scald (Y), carbon dioxide concentration (x), and the reciprocal of oxygen concentration (z), was described by the regression equation: Y = y + b(x – x) + c(z – z), which implies that scald is directly proportional to carbon dioxide concentration and indirectly proportional to oxygen concentration. The effects of changes in concentration of the gases, as estimated by the regression coefficients, were consistent for size of fruit, season, and orchard, but the effect for oxygen was dependent on the method of maintaining the atmosphere. Good control of scald was obtained with low oxygen atmospheres, even after storage for 6–7 months.

Voltage-Clamp Experiments with Nitella

HOPE1 has suggested that in the large internodal cells of Chara australis, the depolarization of the plasmalemma during an action potential is caused by a sudden transient increase in the permeability of this membrane to calcium ions, and a consequent inward movement of these ions. This suggestion followed from an investigation of the effects of changes in concentration of various ions on the action potential in single Chara cells.