Cholinergic control of the mechanical properties of the catch connective tissue in the holothurian body wall

Effects of acetylcholine (ACh), ACh-agonists and antagonists were studied on the viscosity of the dermis of the sea cucumber Holothuria leucospilota. ACh and nicotinic agonists caused an early increase in viscosity and late decrease. Muscarinic agonists produced a viscosity decrease. The viscosity increase elicited by nicotine was inhibited by tubocurarine. The viscosity decrease caused by methacholine was suppressed by atropine. The mechanical properties of this connective tissue are very likely controlled by both nicotinic and muscarinic cholinoreceptors.     

Effect of plasma exchange on blood viscosity and cerebral blood flow.

The effects of plasma exchange using a low viscosity plasma substitute on blood viscosity and cerebral blood flow were investigated in eight subjects with normal cerebral vasculature. Plasma exchange resulted in significant reductions in plasma viscosity, whole blood viscosity, globulin and fibrinogen concentration without affecting packed cell volume. The reduction in whole blood viscosity was more pronounced at low shear rates suggesting an additional effect on red cell aggregation. Despite the fall in viscosity there was no significant change in cerebral blood flow. The results support the metabolic theory of autoregulation. Although changes in blood viscosity appear not to alter the level of cerebral blood flow under these circumstances, plasma exchange could still be of benefit in the management of acute cerebrovascular disease.     

Dynamic aspect of kinetics of reaction catalyzed by lactate dehydrogenase

The influence of solvent viscosity on the kinetic parameters of the pyruvate reduction reaction catalyzed by lactate dehydrogenase has been investigated. The viscosity was adjusted by sucrose and glycerol solutions at concentrations from 0 to 44% and from 0 to 63%, respectively. The reaction rate decreased abruptly with an increase in viscosity. The study of different reaction stages (enzyme-substrate complex formation, catalysis, inhibitory complex decomposition, competitive inhibition by chlorine ions) revealed that the catalysis (and the related conformational changes) is the only stage (of the above mentioned) that depends markedly on the solvent viscosity. The reaction is insensitive to the changes in the dielectric properties of the solution induced by the addition of alcohols and dioxane. The observed power dependence of the rate constant on viscosity is explained in terms of Kramer's theory which considers the proton transition through the activation barrier to be a diffusion in the field of random forces. The influence of solvent viscosity on enzymic kinetics indicates a direct relation between solvent dynamics and relevant protein conformational movements.     

Theory of non-Newtonian viscosity of red blood cell suspension: effect of red cell deformation

The effects of the deformation of red blood cells on non-Newtonian viscosity of a concentrated red cell suspension are investigated theoretically. To simplify the problem an elastic spherical shell filled with an incompressible Newtonian fluid is considered as a model of a normal red cell. The equation of the surface of the shell suspended in a steady simple shear flow is calculated on the assumption that the deformation from a spherical shape is very small. The relative viscosity of a concentrated suspension of such particles is obtained based on the "free surface cell" method proposed by Happel. It is shown that the relative viscosity decreases as the shear rate increases.     

Cardiac mechanoenergetic cost of elevated plasma viscosity after moderate hemodilution

The purpose of this study was to investigate how plasma viscosity affects cardiac and vascular function during moderate hemodilution. Twelve anesthetized hamsters were hemodiluted by 40% of blood volume with two different viscosity plasma expanders. Experimental groups were based on the plasma expander viscosity, namely: high viscosity plasma expander (HVPE, 6.3 mPa?·?s) and low viscosity plasma expander (LVPE, 2.2 mPa?·?s). Left ventricular (LV) function was intracardiacally measured with a high temporal resolution miniaturized conductance catheter and concurrent pressure-volume results were used to calculate different LV indices. Independently of the plasma expander, hemodilution decreased hematocrit to 28% in both groups. LVPE hemodilution reduced whole blood viscosity by 40% without changing plasma viscosity, while HVPE hemodilution reduced whole blood viscosity by 23% and almost doubled plasma viscosity relative to baseline. High viscosity plasma expander hemodilution significantly increased cardiac output, stroke volume and stroke work compared to baseline, whereas LVPE hemodilution did not. Furthermore, an increase in plasma viscosity during moderate hemodilution produced a higher energy transfer per unit volume of ejected blood. Systemic vascular resistance decreased after hemodilution in both groups. Counter-intuitively, HVPE hemodilution showed lower vascular resistance and vascular hindrance than LVPE hemodilution. This result suggests that geometrical changes in the circulatory system are induced by the increase in plasma viscosity. In conclusion, an increase in plasma viscosity after moderate hemodilution directly influenced cardiac and vascular function by maintaining hydraulic power and reducing systemic vascular resistance through vasodilation.     

小麦糊化特性参数稳定性分析及其与其它品质性状关系的研究

通过测定黄淮麦区2年度3试点13个小麦区试品种糊化特性(RVA)参数及其它主要品质性状,研究了小麦RVA参数稳定性及其与其它主要品质性状间的关系.结果表明:基因型对峰值粘度、保持粘度、稀懈值、最终粘度、回升值起主导作用,环境对糊化温度和峰值时间影响较大.峰值粘度、保持粘度、最终粘度在品种间变幅较大,分别为2 055.50 cp～3 935.50 cp、1 046.42 cp～2 589.00 cp和2 412.00 cp～4 341.50 cp,峰值粘度、保持粘度、稀懈值的变异系数较高,分别为10.74 %、12.17 %、21.25 %.除峰值时间外,其它RVA参数品种间差异极显著.峰值粘度与保持粘度、稀懈值、最终粘度及回升值间极显著正相关.峰值粘度、保持粘度、最终粘度、回升值与蛋白质含量、湿面筋含量和Zeleny沉降值间极显著负相关.同时依据RVA参数对参试品种进行了聚类分析.峰值粘度可作为衡量小麦淀粉特性的最重要指标,由于品种间淀粉品质差异大,因此品种选育过程中应同时注重蛋白质和淀粉品质.     

Medium viscosity regulates the activity of membrane-bound and soluble phospholipase A2

Medium viscosity is a regulator of very low density lipoprotein production by cultured hepatocytes; their secretion and synthesis are inversely proportional to the extracellular fluid viscosity. The possibility that the mechanism of this extracellular effect on cell function involves modulation of cell membrane component(s) was considered. Along with this assumption, we studied the effect of medium viscosity on the activity of phospholipase A2 (PLA2), an enzyme present in the cell surface membrane, and the activity has been correlated with cellular secretion. We have found that culture medium viscosity inhibits the activity of PLA2 in the plasma membrane of cultured liver cells, concomitantly with the inhibition of lysosomal enzyme and lipoprotein secretion. It was also found that the degradation of liposomal phosphatidylcholine by soluble snake venom PLA2 is inversely proportional to the solvent viscosity. The possibility that the effect of medium viscosity on the enzymatic reaction involves the modulation of dynamic properties of membrane phospholipids was then considered. This hypothesis was examined by monitoring the fluorescence depolarization of fluorophores incorporated into phospholipid vesicles. No significant effect of the solvent viscosity on the phospholipid bilayer was observed. It is proposed that the regulation of cellular secretion by extracellular fluid viscosity involves modulation of the cell membrane PLA2 activity.     

A semi-empirical model of apparent blood viscosity as a function of vessel diameter and discharge hematocrit

A semi-empirical model is developed to describe the dependence of apparent viscosity of blood on vessel diameter (2.7 to 500 microns) and vessel discharge hematocrit (5% to 60%). The blood flow is modeled as a cell-rich core and a cell-free marginal layer in the larger vessels and an axial-train in the smaller vessels. Laminar (Poiseuille) flow is assumed in all cases. An equation is derived in which apparent viscosity is a function of vessel diameter, core viscosity, and width of marginal layer. This is then complemented by empirical equations in which core viscosity varies exponentially with discharge hematocrit while the width of marginal layer varies linearly with discharge hematocrit. The model correlates well with several sets of experimental data and behaves according to the Fahraeus-Lindqvist effect. Predicted apparent viscosity tends to the expected finite value for large vessel diameters. Dependence of apparent viscosity on vessel diameter is realistically smooth in the whole diameter range.     

Solvent Friction Changes the Folding Pathway of the Tryptophan Zipper TZ2

Because the rate of a diffusional process such as protein folding is controlled by friction encountered along the reaction pathway, the speed of folding is readily tunable through adjustment of solvent viscosity. The precise relationship between solvent viscosity and the rate of diffusion is complex and even conformation-dependent, however, because both solvent friction and protein internal friction contribute to the total reaction friction. The heterogeneity of the reaction friction along the folding pathway may have subtle consequences. For proteins that fold on a multidimensional free-energy surface, an increase in solvent friction may drive a qualitative change in folding trajectory. Our time-resolved experiments on the rapidly and heterogeneously folding β-hairpin TZ2 show a shift in the folding pathway as viscosity increases, even though the energetics of folding is unaltered. We also observe a nonlinear or saturating behavior of the folding relaxation time with rising solvent viscosity, potentially an experimental signature of the shifting pathway for unfolding. Our results show that manipulations of solvent viscosity in folding experiments and simulations may have subtle and unexpected consequences on the folding dynamics being studied.     

Salt effects on the cross-linking mechanism of cupric-induced sol—gel transition in alginate solutions

The viscosity behaviour of alginate-Cu²⁺-NaCl systems has been experimentally examined at various concentrations of cupric and sodium salts. Dependence of the intrinsic viscosity of alginate as a function of NaCl concentration is discussed to supplement the previous study which shows a similar behaviour to that found for other polyelectrolytes in aqueous solution in the presence of an added salt. The effects of sodium ions on the cupric association in cupric-induced alginate solutions were investigated by means of viscosity measurements. The mechanisms of complex formation in the presence of the simple added salt were studied. It was found that, at a given NaCl concentration, the viscosity of the mixture will pass through a maximum with increasing cupric concentration. The amounts of cupric cations corresponding to the maximum depends on the concentration of NaCl in the solution. Comparison of salt effects on the viscosity behaviour of alginate solutions during sol—gel transition reveals that an optimum NaCl concentration of 10⁻² mol 1⁻¹ exists where the viscosity of the mixture gives a maximum value at a certain cupric amount. This result indicates that salt effects play an important role in the sol—gel transition of the polyelectrolyte solutions. The observed phenomenon was interpreted in terms of conformational change of polyelectrolyte chain due to the addition of salt resulting in a different cross-linking mode in the system.     

The effect of the solvent viscosity on the migration of small molecules through the structure of myoglobin.

The migration rate of small molecules through the structure of proteins can be monitored by quenching the light emitted from an excited optical probe located within the protein. In the present study we examined the influence of the solvent viscosity on the migration rate of the quencher anthraquinone sulfonate through myoglobin towards an excited Zn protoporphyrin molecule at the binding site of the protein. The solvent viscosity was increased by adding dextrans of different molecular weight but forming isoviscous solutions. The results demonstrate that the migration rate in the protein decreases with increasing solvent viscosity. This suggests that the fluctuations on the protein structure, which make the above migration possible, are affected by the solvent macroviscosity.     

Anisotropic viscosity of the Chara (Characeae) rhizoid cytoplasm

To characterize cellular fluidity and mechanical processes, we determined the viscous properties of the cytoplasm of Chara contraria rhizoids in vivo by injecting and displacing superparamagnetic particles. After injection and a 24-h recovery period, the particles were moved to different positions within the rhizoid by an external magnet. The system was calibrated with solutions of known viscosities. The viscosity was determined based on the velocity at which individual beads moved toward the external magnet. The viscosity of the cytoplasm varied with direction of measurement (i.e., was highly anisotropic) and also varied between sites. The highest viscosity was observed near the endogenous statoliths (139 mP·s parallel and 78 mP·s perpendicular to the rhizoid axis). Depolymerization of actin filaments with latrunculin B reduced the viscosity significantly except around the nucleus but did not change the overall viscosity pattern. Microtubule depolymerization with oryzalin reduced viscosity especially between the nucleus and the statolith zone. The data indicate that F-actin but not microtubules affects statolith sedimentation and that cytoplasmic viscosity may be important for the gravisensing system.     

Requirements for Nutrients and Minerals by Candida brumptii IFO 0731 Producing Succinic Acid from n-Paraffin

The effect of several materials on viscometric behaviour of the soluble ovomucin was determined with a cone plate viscometer.

The soluble ovomucin showed a rapid increase in viscosity above 1.5 mg/ml, and a high concentration of the soluble ovomucin led to gel whose viscosity was comparable to that of the insoluble ovomucin. The apparent viscosity of the soluble ovomucin decreased with an increase in NaCl concentration and upon addition of lysozyme as well as of CaCl₂. The soluble ovomucin in the presence of the sonicated β-ovomucin showed an increase in viscosity on addition of a small amount of CaCl₂.

It is assumed that a great increase in viscosity of egg white may result from removal of sodium ion and lysozyme.     

Effect of viscosity on the plasma decay in a magnetic field

The effect of viscosity on the evolution of an axisymmetric plasma column in a longitudinal magnetic field is considered. It is found that, under the action of viscosity, the plasma density profile tends to become Gaussian.     

Food Viscosity Influences Caloric Intake Compensation and Body Weight in Rats

Objective: To determine the effects of food viscosity on the ability of rats to compensate for calories in a dietary supplement. Research Methods and Procedures: In a series of four experiments, rats consumed dietary supplements equated for caloric and nutritive content but differing in viscosity. Experiments 1 to 3 examined the ability of the rats to compensate for the calories consumed in low‐ compared with high‐viscosity premeals by reducing intake of a subsequent test meal. Caloric compensation was assessed with a wide range of premeal viscosity levels and with two different non‐nutritive thickening agents. Experiment 4 assessed the effects of consuming daily a low‐viscosity compared with an equicaloric high‐viscosity dietary supplement on longer term body weight gain. Results: Consuming a lower viscosity premeal was followed by significantly more caloric intake (i.e., less caloric compensation) compared with consuming premeals with higher viscosity levels. This effect was not specific to one thickening agent. Furthermore, rats given a low‐viscosity supplement daily gained significantly more weight over a 10‐week period compared with rats given a high‐viscosity supplement. Discussion: The results of these experiments suggest that food viscosity may be an important determinant of short‐term caloric intake and longer term body weight gain.     

In silico biophysics and hemorheology of blood hyperviscosity syndrome

Hyperviscosity syndrome (HVS) is characterized by an increase of the blood viscosity by up to seven times the normal blood viscosity, resulting in disturbances to the circulation in the vasculature system. HVS is commonly associated with an increase of large plasma proteins and abnormalities in the properties of red blood cells, such as cell interactions, cell stiffness, and increased hematocrit. Here, we perform a systematic study of the effect of each biophysical factor on the viscosity of blood by employing the dissipative particle dynamic method. Our in silico platform enables manipulation of each parameter in isolation, providing a unique scheme to quantify and accurately investigate the role of each factor in increasing the blood viscosity. To study the effect of these four factors independently, each factor was elevated more than its values for a healthy blood while the other factors remained constant, and viscosity measurement was performed for different hematocrits and flow rates. Although all four factors were found to increase the overall blood viscosity, these increases were highly dependent on the hematocrit and the flow rates imposed. The effect of cell aggregation and cell concentration on blood viscosity were predominantly observed at low shear rates, in contrast to the more magnified role of cell rigidity and plasma viscosity at high shear rates. Additionally, cell-related factors increase the whole blood viscosity at high hematocrits compared with the relative role of plasma-related factors at lower hematocrits. Our results, mapped onto the flow rates and hematocrits along the circulatory system, provide a correlation to underpinning mechanisms for HVS findings in different blood vessels.     

Microviscosity and enzyme-ligand dissociation

The effect of viscosity on the rate constant for the dissociation of an enzyme-ligand complex has been calculated from a microscopic theory. Using the Kubo representation for the rate constant and the second quantization formalism a Stokes-Einstein-Debye expression is obtained. A microscopic expression for the viscosity is derived. The equation for the microviscosity shows how important information on the enzyme-ligand complex can be obtained from studies on the viscosity dependence of the dissociation rate constant.     

Effect of solution viscosity on intraprotein electron transfer between the FMN and heme domains in inducible nitric oxide synthase

The FMN-heme intraprotein electron transfer (IET) kinetics in a human inducible NOS (iNOS) oxygenase/FMN construct were determined by laser flash photolysis as a function of solution viscosity (1.0-3.0 cP). In the presence of ethylene glycol or sucrose, an appreciable decrease in the IET rate constant value was observed with an increase in the solution viscosity. The IET rate constant is inversely proportional to the viscosity for both viscosogens. This demonstrates that viscosity, and not other properties of the added viscosogens, causes the dependence of IET rates on the solvent concentration. The IET kinetics results indicate that the FMN-heme IET in iNOS is gated by a large conformational change of the FMN domain. The kinetics and NOS flavin fluorescence results together indicate that the docked FMN/heme state is populated transiently.     

Influence of resonant charge exchange on the viscosity of partially ionized plasma in a magnetic field

The influence of resonant charge exchange for ion-atom interaction on the viscosity of partially ionized plasma embedded in the magnetic field is investigated. The general system of equations used to derive the viscosity coefficients for an arbitrary plasma component in the 21-moment approximation of Grad’s method is presented. The expressions for the coefficients of total and partial viscosities of a multicomponent partially ionized plasma in the magnetic field are obtained. As an example, the coefficients of the parallel and transverse viscosities for the ionic and neutral components of the partially ionized hydrogen plasma are calculated. It is shown that the account for resonant charge exchange can lead to a substantial change of the parallel and transverse viscosity of the plasma components in the region of low degrees of ionization on the order of 0.1.     

Influence of breed and husbandry on viscosity of Israeli goat milk yogurt

Goat’s milk yogurt prepared from milk of different goat breeds on different farm types resulted in different viscosity. Yogurt from milk of goat breeds browsing on pasture was richer in solids and resulted in significantly higher viscosity compared with that of cow milk yogurt and yogurt produced from milk of goats fed hay and concentrate indoors. Milk from goats browsing on pasture was diluted in total solids content close to that of milk from goats kept indoors and cows. Yogurt made from this diluted milk still resulted in higher viscosity. It appears that milk from goat breeds browsing on pastures contains certain factor(s) that causes an increase in the viscosity of yogurt produced from it.