The Investigation of Time-dependent Solute Transport through Horizontally Situated Membrane: The Effect of Configuration Membrane System

This paper presents an experimental and theoretical investigation ofsolute transport through a horizontally situated membrane. Theexperimental investigation was carried out by the laserinterferometric method in association with a computer system ofinterference image analysis. On the basis of this analysis thicknessof near-membrane layers, solution concentration drops on these layersas well as diffusion fluxes of diluted substance are determined.Different fluxes of the soluble substance are observed depending onthe configuration of the system. The results of the experimental andtheoretical investigation of diffusion fluxes are conformable inrespect of measurement error, with one adjustment parameter, i.e. thesolute partition coefficient.     

THE TECHNIQUE OF LABELLED MITOSES: ANALYSIS BY AUTOMATIC CURVE-FITTING

An improved method is described for the analysis of data obtained by the technique of labelled mitoses. It is a development of the method described by Barrett (1966) in which theoretical curves are computed on the basis of a model which assumes that the phases G¹, S and G² are described by independent log-normal distributions; the analysis consists in finding a form of this model which gives a labelled mitoses curve which is the best fit to the available data. This fitting procedure has now been made automatic. No comprehensive indication of the goodness of fit can be given, although in the analysis of over fifty sets of data the method appears to have worked well.
A supplementary computer program is described which, on the basis of three separate assumed modes of cell loss, calculates the form of the age distributions and theoretical continuous labelling curves. This allows growth fraction to be calculated in a way which takes account of the distribution of phase durations and the non-rectangular age distributions of expanding cell populations. It also gives an opportunity to study the implications of continuous labelling data as regards the mode of cell loss.
A comparison is made between the present method of labelled mitoses curve analysis and the empirical rules which have often been used.     

Impedance microbiology: quantification of bacterial content in milk by means of capacitance growth curves

The impedancimetric method is a technique for the rapid evaluation of milk bacterial content and also of its subproducts. Several authors have made use of culture conductance changes during bacterial growth for quantitative and qualitative assessments of microbial growth. However, interface capacitance curves, Ci, have not been used. In this paper, we quantify bacteria in cow raw milk by following their growth as the above-mentioned capacitance change time course event. With it, bigger growth variations, shorter detection times and a better coefficient of correlation with the plate count method were obtained than those yielded by conductance curves. Calibration was performed by plotting initial known concentrations, IC (CFU/ml), as a function of the time detection theshold (TDT).     

Static water structure detected by heat capacity measurements on aqueous solutions of a triple-helical polysaccharide schizophyllan

Heat capacity measurements were made on aqueous solutions of a triple-helical polysaccharide schizophyllan by precision adiabatic calorimetry over a wide range of concentrations 30.45-90.93 wt % at temperatures between 5 and 315 K. The heat capacity curves obtained were divided into four groups depending on the weight fraction of schizophyllan w regions I-IV. In region I, triple-helices with the sheath of bound water, structured water, and loosely structured water forming layers around the helix core are embedded in free water. In region II, there is no free water, and loosely structured water decreases until it vanishes, but structured water stays constant with increasing w. In region III, bound water remains unaffected, but structured water decreases with increasing w by overlapping each other. Finally, in region IV, only schizophyllan and bound water exist, the latter decreasing upon increasing w. The maximum thickness of each layer is 0.18(3) nm for bound water, 0.13(4) nm for structured water, and 0.23(6) nm for loosely structured water, and these layers of water are at the enthalpy levels of 53%, 93.7%, and nearly 100%, respectively, between ice (0%) and free water (100%).     

Effects of heterogeneity and cooperativity on the forms of binding curves for multivalent ligands

An exploratory investigation is made of the binding behavior that is likely to be encountered with multivalent ligands under circumstances where a single intrinsic binding constant does not suffice to describe all acceptor-ligand interactions. Numerical simulations of theoretical binding behavior have established that current criteria for recognizing heterogeneity and cooperativity of acceptor sites on the basis of the deviation of the binding curve from rectangular hyperbolic form for univalent ligands also apply to the interpretation of the corresponding binding curves for multivalent ligands. However, for systems in which the source of the departure from equivalence and independence of binding sites resides in the ligand, these criteria are reversed. On the basis of these observations a case is then made for attributing results of an experimental binding study of the interaction between pyruvate kinase and muscle myofibrils to positive cooperativity of enzyme sites rather than to heterogeneity or negative cooperativity of the myofibrillar sites.     

An attempt at comparing CT images of petrous bone with analogical sections of anatomical specimens

The purpose of the paper was to present comparative laminar anatomy of human temporal bone on the basis of cross-sections of autopsy specimens and CT scans made in identical thin layers. The investigations were made on 20 temporal bones taken during anatomopathological dissections of cadavers of men and women (aged 40 to 60 a) without visible pathological changes in the skull. The CT examinations were made by means of a Siemens Somatom DR 2 apparatus, using high resolution programme, on 10 patients who had pathological changes in the ear. The obtained scans were compared with temporal bone cross-sections, schemas of regular anatomical relation of 8 layers corresponding to routine CT examinations were worked out.     

Analysis of receptor binding displacement curves by a nonhomologous ligand, on the basis of an equivalent competition principle

An exact method for the analysis of receptor-ligand binding data when labeled bound ligand is displaced by a nonhomologous ligand with a different dissociation constant is described. The present method, which is based on an equivalent competition principle for the homologous and the nonhomologous ligand, converts displacement curves into a linear form and is also applicable to situations in which free concentrations of ligand are significantly smaller than the added concentrations as a result of ligand binding. It is shown that the dissociation constant of the nonhomologous ligand is given directly by the concentration of this nonhomologous ligand added and the free concentration of unlabeled homologous ligand required to give the same level of displacement of labeled bound ligand. On the basis of these displacement characteristics, all binding parameters for receptor interaction of the nonhomologous ligand can be obtained and expressed, for example, in a Scatchard plot. The present method, which is referred to as the equivalent competition method, is also evaluated in this study with respect to the effects of nonspecific ligand binding and the presence of multiple receptor classes.     

Two-dimensional reconstruction of birefringence map of the skeletal muscle sarcomere in relaxed and rigor states studied by interference microscopy]

A new method of automatized quantitative interferometry of skeletal muscle fibers was developed for the investigation of birefringence. A device based on the Linnic microscope was constructed to obtain phase images, which are two-dimensional pictures of birefringence. For the first time, two-and-three-dimensional maps of both total birefringence and birefringence for individual sarcomeres in the central part of muscle fiber were visualized using large databases. It was shown that total birefringence of fibers at rest length in the rigor state was lower as compared with the relaxed. Birefringence values from individual sarcomere interferograms revealed also that normalized A-disk birefringence was lower in the rigor state. The results obtained could be explained by a decrease of thick filaments anisotropy, due to the moving away of myosin heads from the rod during transition into the rigor state.     

Local Mixed-Effects Fitting for Detecting Reproductive Hormone Surge Times

Hormone secretion processes remain part of the biological mystery as they are highly regulated and individual specific. When hormone trajectories from multiple subjects are under investigation, both population-average mechanism and subject-specific deviations are of great interest. In particular, statistical methodologies that enable us not only to identify surge times and surge magnitudes but also to make inference on these biological features is in need. In this paper, we propose a local kernel smoothing method to perform the analysis of multiple hormone curves using the nonparametric mixed-effects model. We develop a local quadratic mixed-effects (LQME) fitting procedure that detects local maxima of the population-average profile curve and the individual profile curves. Related statistical inference is established to carry out a hypothesis test for the local surge and to construct a confidence interval for a detected surge feature. This method is illustrated by simulation studies and a reproductive hormone data analysis.     

Evidence for long-range electrostatic repulsion between HeLa cells

Agglutination curves obtained on addition of low molecular weight poly-l-lysines (mol. wt 4 000–23 000) to HeLa cells, show a deviation from linearity at low polymer concentration. This probably indicates the existence of a ζ-potential which has to be lowered before agglutination can take place. Experiments with dilysine support the assumption that cell surface charge is lowered on addition of low concentrations of short chain poly-l-lysines.Long poly-l-lysine molecules (mol. wts 70 000; 100 000) yield linear agglutination curves already at the lowest polymer concentrations. This might indicate that these polymers are able to bridge the original repulsion gap between HeLa cells.After removal of peripheral sialic acid by neuraminidase, linear agglutination curves are obtained with all poly-l-lysines irrespective of their chain lengths. This is interpreted as evidence for involvement of sialic acid residues in the charge organization responsible for electrostatic repulsion.The magnitude of the presumed repulsion effect is shown to vary with the cell density at the time the HeLa cells were harvested from the culture. The largest repulsion effect is obtained with cells from density inhibited cultures which also have the lowest tendency for mutual adhesion. With fast growing cells from low density cultures linear agglutination curves are obtained with short chain poly-l-lysines. This is interpreted as evidence for a strong diminishment or absence of long-range electrostatic repulsion between such cells.     

The atypical velocity response by pyruvate carboxylase to increasing concentrations of acetyl-coenzyme A

An investigation was made of the interaction of pyruvate carboxylase with its allosteric effector, acetyl-CoA, and the velocity profile of the deacylation of acetyl-CoA as a function of acetyl-CoA concentration indicated that this ligand does not bind to this enzyme in a positive homotropic co-operative manner. An examination was therefore made of the factors that contribute to the sigmoidicity of the rate curves obtained for pyruvate carboxylation with various concentrations of acetyl-CoA. Hill coefficients for acetyl-CoA obtained with both sheep and chicken liver pyruvate carboxylases were found to be dependent on the fixed pyruvate concentration used in the assay solution. Thus, by varying the acetyl-CoA concentration, the degree of saturation of the enzyme by pyruvate was also changed. A further consequence of non-saturating concentrations of pyruvate was that the non-productive hydrolysis of the enzyme- carboxybiotin complex increased, resulting in an under-estimate of the reaction velocity measured by oxaloacetate formation. Another factor contributing to the sigmoidicity is that, at non-saturating concentrations of acetyl-CoA, the enzyme undergoes inactivation upon dilution to low protein concentrations, again resulting in an under-estimate of the reaction velocity. Under conditions where none of the above factors was operating and the only effect of varying acetyl-CoA concentrations was to alter the proportion of the enzyme catalysing the carboxylation reaction at acetyl-CoA-dependent and -independent rates, the sigmoidicity of the acetyl-CoA velocity profile was completely eliminated.     

The genus Luppovia and the phylogeny of Cretaceous heteromorphic ammonoids

The unique preservation of heteromorphic shells of Luppovia Kakabadze, Bogdanova & Mikhailova 1978 from the Aptian deposits of Bolshoj Balkhan (western Turkmenia) made it possible to study the microstructure, internal shell characteristics and suture ontogeny of this genus. Microstructural investigations revealed that the dorsal shell wall in Luppovia is composed of three layers in contrast to that of monomorphic ammonoids, which is single-layered. This ability of secreting different numbers of layers in monomorphs and heteromorphs demonstrates plasticity of secreting activity of the mantle epithelium. Data obtained from the study of internal shell structure and suture ontogeny have been compared. Both these methods of investigation lead to the conclusion that the genus Luppovia belongs to the order Ammonitida. The results obtained confirm the viewpoint that the Cretaceous heteromorphic superfamilies Turrilitaceae and Ancylocerataceae have independent origins and belong to two different orders, Lytoceratida and Ammonitida, respectively. □ Ammonoidea , Luppovia, shell structure, ontogeny, phylogeny, Cretaceous.     

Evolution of concentration field in a membrane system

This paper deals with the evolution of concentration field at a single membrane system. Concentration field evolution is described by concentration effect of stable boundary layers, which originate in this system. The concentration effect of boundary layers (CBLE) is studied experimentally on the basis concentration profiles obtained from computer analysis of interferometric pictures of near-membrane regions. Besides experimental results, we also report theoretical investigations and numerical calculations of this effect for two models of membranes (an infinite thin wall and the wall of thickness l). Evolution of concentration field at different distances from membrane surface describes accurately the spatio-temporal structure of the concentration boundary layers (CBLs). Results have shown that their spatial structure is fully established and these layers develop diffusively.     

SAXS-data-based structural modeling of DNA–gadolinium complexes fixed in particles of cholesteric liquid-crystalline dispersions

Structure of cholesteric liquid-crystalline dispersions (CLCDs) formed by double-stranded DNA molecules and treated with gadolinium salts was studied by small-angle X-ray scattering (SAXS). The obtained SAXS data open the way for structural modeling of these complexes to obtain a reasonable explanation for the correlated decrease in amplitude of an abnormal negative band in the circular dichroism (CD) spectra and the characteristic Bragg peak in the experimental small-angle X-ray scattering curves observed on treatment of CLCD by gadolinium salts. Model simulations of different kinds of structural organizations of the DNA–gadolinium complex were performed using novel SAXS data analysis methods in combination with several new, complementary modeling techniques, enabling us to build low-resolution three-dimensional structural models of DNA–gadolinium complexes fixed in CLCD particles. The obtained models allow us to suggest that a change takes place in the helical twist of quasinematic layers formed by these molecules at high concentrations of gadolinium salt. This change in the twist can be used to explain the experimentally observed increase in amplitude of an abnormal band in the CD spectra of DNA CLCD.     

Approximate treatment of the formation of a difference in the concentrations of an ion at the two sides of a membrane

The recent extension of the approximation method is applied to enable us to arrive at the time course of the concentrations at both sides of a membrane. From the differential equations which govern these, the steady-state solution is obtained in terms of the parameters, which are determined by the thickness of the diffusion layers, the chemical composition and reactions, and the diffusion constant of the membrane.     

Monitoring membrane protein rotational diffusion using time-averaged phosphorescence

Rotational motions of membrane proteins have previously been measured using time-dependent phosphorescence techniques. This paper discusses a method of examining membrane protein mobility at temperatures relevant to biological systems, using a technique similar to steady-state fluorescence. The method is demonstrated using sarcoplasmic reticulum ATPase labelled with erythrosin isothiocyanate, both in its natural condition and crosslinked by incubation with glutaraldehyde. The experimentally-observed dependence of phosphorescence anisotropy on temperature is compared to a calculated anisotropy-temperature curve. Comparison is made between the anisotropy decay curves obtained by time-averaged phosphorescence and steady-state fluorescence.     

Evidence for osmotic constraint in F-type bacterial mating

Abstract An investigation was made into the relationship between extracellular solute concentration and transfer frequency in F-type mating in Escherichia coli . Solute concentrations above a certain level correlated with a sharp decrease in transfer frequency which was not due to a loss of cell viability; this effect was obtained both with electrolyte (sodium chloride) and with osmotically equivalent non-electrolyte ( myo -inositol), despite the contrasting effects of these solutes at lower concentrations. It is hypothesized that the inhibition of conjugal transfer at high solute concentrations is due to plasmolytic rupture of adhesion sites ("Bayer's junctions").     

Interferometric studies of the radiation wave front on the Luch setup

A radial shear interferometer for studying the shape of the wave front and aberrations of the optical system of the Luch setup were designed and created. To improve the interferometric pattern, the interferometer was simulated numerically by using the Fresnel software package. The parameters of the interferometer were optimized. The interferometer allows one to record interferograms of pulsed radiation at the first and second harmonics of a neodymium laser, as well as of continuous IR radiation with a short coherence length. A new method was developed for recovering the wave front by using the WinFringe software for interferograms with a reference front. Aberrations introduced by different parts and the entire optical system of the setup were measured. The wave fronts of the first and second harmonics obtained in full-scale experiments are presented. The experimental results agree with the radiation divergence measured by other methods.     

Action potentials in gastrointestinal smooth muscle.

Recent investigation of the ultrastructure and electrophysiology of gastrointestinal smooth muscle layers has revealed a fascinating heterogeneity in cell type, cell structure, intercellular communication, and generated electrical activities. Networks of interstitial cells of Cajal (ICC) have been identified in many muscle layers and evidence is accumulating for a role of these networks in gut pacemaking activity. Synchronized motility in the organs of the gut result from interaction between ICC, neural-tissue, and smooth muscle cells. Regulation of cell to cell communication between the different cell types will be an important area for further research. Progress has been made in the elucidation of the ionic basis of the slow wave type action potentials and the spike-like action potentials. The mechanism underlying smooth muscle autorhythmicity seems different from that encountered in cardiac tissue, and evidence exists for metabolic regulation of the frequency of slow wave type action potentials.