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1.
Calculations of the contribution of diffusion to lung retention given previously (W. Findeisen,Pflüg. Arch. f. d. ges. Physiol.,236, 367–379, 1935; H. D. Landahl,Bull. Math. Biophysics,12, 43–56, 1950) contained an error appreciably underestimating the role of diffusion for particles less than a few microns in diameter. In the calculations (Landahl, 1950), a schematic representation of the lungs was modified to conform to the actual resting lung volume by increasing the number of alveolar sacs. A recalculation of total deposition with this chematic model gives too large a retention for very small particles. Hence it seemed appropriate to recalculate the retention for various paricle sizes in various regions of the respiratory tract for several respiratory paterns, using the original schematic model but assuming that the estimates reflect conditions in a deflated lung. For a given tidal air the sizes of the alveolar ducts and sacs were assumed to expand so that the total volume of the model was equal to 2.5 liters plus one half of the tidal air, i.e., the mean lung volume. The results of these calculations are appreciably different from those given previously, but the differences are serious only for particles of about 0.1 micron or less. Also given is an approximation method for calculating the probability of impaction of droplets against nasal hairs.  相似文献   

2.
Fumio Oosawa 《Biopolymers》1968,6(11):1633-1647
This paper gives a very simple method based on the characteristic property of the electric free energy to calculate the repulsive force between parallel rodlike macroions in a solution as a function of the charge density on rods. The total extensive force (?f/?X) of an assembly of m rods of length l and charge number n (charge density ? neo /l) at small extension X in the absence of low molecular sals is given by where z is the valency of counterions and Q (= neO2/εkTl) is a dimensionless quantity representing the charge density. The repulsion between two parallel rods is given by putting m = 2. At large charge densities the repulsion is very much smaller than the direct coulomb force between charged rods, even at small distances. The addition of low molecular salts does not depress the repulsion appreciably, as long as the average concentration of salt ions is much smaller than the concentration of counterions accumulated in the space between rods. The effect of fluctuation of the coumerion distribution is also analyzed, and it is found that the attractive force due to the ion fluctuation may predominate over the above repulsive force in the case of polyvalent counterions and rods of high charge densities at small distances.  相似文献   

3.
Design of bio-mimetic particles with enhanced vascular interaction   总被引:1,自引:0,他引:1  
The majority of particle-based delivery systems for the ‘smart’ administration of therapeutic and imaging agents have a spherical shape, are made by polymeric or lipid materials, have a size in the order of few hundreds of nanometers and a negligibly small relative density to aqueous solutions. In the microcirculation and deep airways of the lungs, where the creeping flow assumption holds, such small spheres move by following the flow stream lines and are not affected by external volume force fields. A delivery system should be designed to drift across the stream lines and interact repeatedly with the vessel walls, so that vascular interaction could be enhanced. The numerical approach presented in [Gavze, E., Shapiro, M., 1997. Particles in a shear flow near a solid wall: effect of nonsphericity on forces and velocities. International Journal of Multiphase Flow 23, 155–182.] is, here, proposed as a tool to analyze the dynamics of arbitrarily shaped particles in a creeping flow, and has been extended to include the contribution of external force fields. As an example, ellipsoidal particles with aspect ratio 0.5 are considered. In the absence of external volume forces, a net lateral drift (margination) of the particles has been observed for Stokes number larger than unity (St>1); whereas, for smaller St, the particles oscillate with no net lateral motion. Under these conditions, margination is governed solely by particle inertia (geometry and particle-to-fluid density ratio). In the presence of volume forces, even for fairly small St, margination is observed but in a direction dictated by the external force field. It is concluded that a fine balance between size, shape and density can lead to EVI particles (particles with enhanced vascular interaction) that are able to sense endothelial cells for biological and biophysical abnormalities, mimicking circulating platelets and leukocytes.  相似文献   

4.
The abilityto deliver proteins and peptides to the systemic circulation byinhalation has contributed to a rise in the number of inhalationtherapies under investigation. For most of these therapies, aerosolsare designed to comprise small spherical droplets or particles of massdensity near 1 g/cm3 and meangeometric diameter between ~1 and 3 µm, suitable for particlepenetration into the airways or lung periphery. Studies performedprimarily with liquid aerosols have shown that these characteristics ofinhaled aerosols lead to optimal therapeutic effect, both for local andsystemic therapeutic delivery. Inefficient drug delivery can stillarise, owing to excessive particle aggregation in an inhaler,deposition in the mouth and throat, and overly rapid particle removalfrom the lungs by mucocilliary or phagocytic clearance mechanisms. Toaddress these problems, particle surface chemistry and surfaceroughness are traditionally manipulated. Recent data indicate thatmajor improvements in aerosol particle performance may also be achievedby lowering particle mass density and increasing particle size, sincelarge, porous particles display less tendency to agglomerate than(conventional) small and nonporous particles. Also, large, porousparticles inhaled into the lungs can potentially release therapeuticsubstances for long periods of time by escaping phagocytic clearancefrom the lung periphery, thus enabling therapeutic action for periodsranging from hours to many days.

  相似文献   

5.
Adeno-associated satellite virus type 4, obtained by repeated undiluted passage, failed to produce distinct bands at the expected density of 1.43 g/cm3 after density gradient centrifugation in CsCl. This phenomenon occurred regardless of the hemagglutinating activity of the starting material. Sharp bands were found at a density of 1.34 to 1.35 g/cm3. These bands contained adenovirions and numerous satellite particles. These latter particles could be distinguished by electron microscopy from standard dense satellite particles by their flattened profiles and deep penetration of negative stains. Dense bands of satellite virus at 1.43 g/cm3 were constantly observed when the inoculum was comprised of highly diluted seed virus. Light satellite particles had a particle to HA ratio comparable with dense particles, but possessed low infectivity. Measurements of contour lengths of extracted deoxyribonucleic acid (DNA) indicate that light particles contain only a small amount of DNA, possibly less than 0.5 × 106 daltons, compared to 1.4 × 106 for the complete satellite DNA molecule.  相似文献   

6.
Summary Changes in molluscan blood cell membrane structure coincided with changes in membrane amino acid permeability during cell volume regulation. Blood cells were freeze fractured after the free amino acid permeability of their membranes had been altered by modifying the extracellular Ca2+ and intracellular ATP levels and the membrane particles examined for changes in size, number/area and distribution. Test substances that altered the divalent cation or ATP levels also altered membrane particle densities, but not size or distribution, of freeze fractured blood cells. Those test substances (Ca2+-free seawater, DNP, low temperature) that inhibited volume regulation and the FAA efflux caused decreased membrane particle density, while those test substances (Co2+, Mn2+) that potentiated volume regulation and the FAA efflux increased the number of membrane particles/unit area. These changes in membrane particle density appear to result from the changes in surface area due to the treatment effects on cell volume, so that the number of membrane particles per cell remained constant. Therefore, altered membrane FAA permeability is associated with altered membrane particle density, but the effect of this structural alteration on membrane permeability is not clear.Abbreviations FAA free amino acid - DMSO dimethylsulfoxide - DNP dinitrophenol - ASW artificial seawater  相似文献   

7.
The acinus consists of complex, branched alveolar ducts and numerous surrounding alveoli, and so in this study, we hypothesized that the particle deposition can be much influenced by the complex acinar geometry, and simulated the airflow and particle deposition (density = 1.0 g/cm3, diameter = 1 and 3 μm) numerically in a pulmonary acinar model based on synchrotron micro-CT of the mammalian lung. We assumed that the fluid–structure interaction was neglected and that alveolar flow was induced by the expansion and contraction of the acinar model with the volume changing sinusoidally with time as the moving boundary conditions. The alveolar flow was dominated by radial flows, and a weak recirculating flow was observed at the proximal side of alveoli during the entire respiratory cycle, despite the maximum Reynolds number at the inlet being 0.029. Under zero gravity, the particle deposition rate after single breathing was less than 0.01, although the particles were transported deeply into the acinus after inspiration. Under a gravitational field, the deposition rate and map were influenced strongly by gravity orientation. In the case of a particle diameter of 1 μm, the rate increased dramatically and mostly non-deposited particles remained in the model, indicating that the rate would increase further after repeated breathing. At a particle diameter of 3 μm, the rate was 1.0 and all particles were deposited during single breathing. Our results show that the particle deposition rate in realistic pulmonary acinar model is higher than in an idealized model.  相似文献   

8.
Atmospheric nitrogen (N) deposition is a serious problem on the North China Plain (NCP) because it imposes a considerable nutrient burden on the local environment. However, it also makes a substantial contribution to agricultural crop N requirements. The integrated total N input (ITNI) system is a method to quantify total atmospheric N deposition by using 15N-labeled monitor plants grown in pots. The effect of pot surface area and variety of indicator plant on the amount of airborne N input quantified by the ITNI system was investigated in this study. Total N deposition to the soil-maize/soil-wheat plant system at key growth stages was also quantified to improve N-fertilizer recommendations. When indicator plants having a high space requirement were used a correction factor was needed and this could be obtained only by simulating commercial field conditions, especially plant density, because the factor depends largely on pot area or the difference in plant density between pot conditions and field conditions. The total airborne N input measured by the ITNI system was not influenced by the variety of monitoring plant. N deposition was 20?C25 kg N ha?1 during growth from three expanded leaf to ten expanded leaf and also from ten expanded leaf to maturity of maize. N deposition was 29.1 kg N ha?1 between planting and the jointing stage and 10.1 kg N ha?1 from jointing to maturity of wheat. This high measured N deposition indicates that N deposition should be taken into account when calculating the N fertilizer requirements of maize and wheat in this region.  相似文献   

9.
During exocytosis the fusion pore opens rapidly, then dilates gradually, and may subsequently close completely, but what controls its dynamics is not well understood. In this study we focus our attention on forces acting on the pore wall, and which are generated solely by the passage of transmitter, ions and water through the open fusion pore. The transport through the charged cylindrical nano-size pore is simulated using a coupled system of Poisson-Nernst-Planck and Navier-Stokes equations and the forces that act radially on the wall of the fusion pore are then estimated. Four forces are considered: a) inertial force, b) pressure, c) viscotic force, and d) electrostatic force. The inertial and viscotic forces are small, but the electrostatic force and the pressure are typically significant. High vesicular pressure tends to open the fusion pore, but the pressure induced by the transport of charged particles (glutamate, ions), which is predominant when the pore wall charge density is high tends to close the pore. The electrostatic force, which also depends on the charge density on the pore wall, is weakly repulsive before the pore dilates, but becomes attractive and pronounced as the pore dilates. Given that the vesicular concentration of free transmitter can change rapidly due to the release, or owing to the dissociation from the gel matrix, we evaluated how much and how rapidly a change of the vesicular K+-glutamate concentration affects the concentration of glutamate and ions in the pore and how such changes alter the radial force on the wall of the fusion pore. A step-like rise of the vesicular K+-glutamate concentration leads to a chain of events. Pore concentration (and efflux) of both K+ and glutamate rise reaching their new steady-state values in less than 100 ns. Interestingly within a similar time interval the pore concentration of Na+ also rises, whereas that of Cl diminishes, although their extra-cellular concentration does not change. Finally such changes affect also the water movement. Water efflux changes bi-phasically, first increasing before decreasing to a new, but lower steady-state value. Nevertheless, even under such conditions an overall approximate neutrality of the pore is maintained remarkably well, and the electrostatic, but also inertial, viscotic and pressure forces acting on the pore wall remain constant. In conclusion the extrusion of the vesicular content generates forces, primarily the force due to the electro-kinetically induced pressure and electrostatic force (both influenced by the pore radius and even more by the charge density on the pore wall), which tend to close the fusion pore.  相似文献   

10.
We have found that two different temperature-sensitive mutations in gene 22, tsA74 and ts22-2, produce high frequencies (up to 85%) of petite phage particles when grown at a permissive or intermediate temperature. Moreover, the ratio of petite to normal particles in a lysate depends upon the temperature at which the phage are grown. These petite phage particles appear to have approximately isometric heads when viewed in the electron microscope, and can be distinguished from normal particles by their sedimentation coefficient and by their buoyant density in CsCl. They are biologically active as detected by their ability to complement a co-infecting amber helper phage. Lysates of both mutants grown at a permissive temperature reveal not only a significant number of petite phage particles in the electron microscope, but also sizeable classes of wider-than-normal particles, particles having abnormally attached tails, and others having more than one tail.Striking protein differences exist between the purified phage particles of tsA74 or ts22-2 and wild-type T4. B11, a 61,000 molecular weight head protein, is completely absent from the phage particles of both mutants, and the internal protein IPIII1 is present in reduced amounts as compared to wild type. The precursor to B11 is present in the lysates, but these mutations appear to prevent its incorporation into heads, so it does not become cleaved.The product of gene 22 (P22) is known to be the major protein of the morphogenetic core of the T4 head. Besides the mutations reported here, several mutations which affect head length have been found in gene 23, which codes for the major capsid protein (Doermann et al., 1973b). We suggest a model in which head length is determined by an interaction between the core (P22 and IPIII) and the outer shell (P23).  相似文献   

11.
Using linear sucrose gradients, particulates derived from pea (Pisum sativum L. cv. Alaska) epicotyls have been fractionated and examined for marker enzyme activity. The coincidence of three reputed plasma-membrane markers [cellulase (EC 3.2.1.4), K+-stimulated Mg2+-ATPase, and glucan synthetase] at the same position on sucrose density gradients, in combination with electron microscopic evidence reported by G. Shore and G. Maclachlan (J. Cell Biol. 64, 557–571; 1975), indicates that plasma membrane of pea epicotyl has a buoyant density of about 1.13 g/cm3. This density disagrees with those usually reported for plant plasma membranes and also with recent reports for Pisum. It is, however, shown to be distinct from the equilibrium densities of enzymic markers for particulate components derived from Pisum endoplasmic reticulum (1.10–1.11 g/cm3), Golgi (1.12 g/cm3) and mitochondria (1.18 g/cm3). Furthermore, other recent literature indicates that the 1.13 g/cm3 buoyant density may be characteristic of the plasma membrane of many members of the Leguminosae. Our data indicate that the conditions of differential centrifugation (time, centrifugal force), coupled with the amount of protein utilized, affect the resolution and interpretation of profiles of marker enzymes on sucrose gradients (e.g. glucan synthetase and K+-stimulated Mg2+-ATPase were sometimes found to be associated not only with particles of 1.13 g/cm3 density, but with particles of higher densities as well). Particulate cellulase was found to be associated only with particles with equilibrium densities of about 1.13 g/cm3. Cellulase thus proved to be the most useful marker for establishing a differential centrifugation regime which would permit examination of the 1.13 g/cm3 particulate components with minimal contamination by particles of higher densities.  相似文献   

12.
A method is proposed for determining the electron density N e and the electric field E in the non-equilibrium nitrogen plasma of a low-pressure discharge from the spectra of the second positive system of N2. The method is based on measuring the specific energy deposition in the plasma and the distribution of nitrogen molecules over the vibrational levels of the C 3Π u state, as well as on modeling this distribution for a given energy deposition. The fitting parameters of the model are the values of N e and E. A kinetic model of the processes governing the steady-state density of the C 3Π u nitrogen molecules is developed. The testing of this method showed it to be quite reliable. The method is of particular interest for diagnosing electrodeless discharges and provides detailed information on the processes occurring in the discharge plasma. Preliminary data are obtained on the plasma parameters in a cavity microwave discharge and an electrode microwave discharge. In particular, it is found that the electric field in an electrode microwave discharge in nitrogen is lower than that in a hydrogen discharge. This effect is shown to be produced by stepwise and associative processes with the participation of excited particles in nitrogen.  相似文献   

13.

Background

Human paracoccidioidomycosis (PCM) is an endemic fungal disease of pulmonary origin. Follow-up of pulmonary lesions by image studies in an experimental model of PCM has not been previously attempted. This study focuses on defining patterns, topography and intensity of lung lesions in experimentally infected PCM mice by means of a comparative analysis between High Resolution Computed Tomography (HRCT) and histopathologic parameters.

Methodology

Male BALB/c mice were intranasally inoculated with 3×106 Paracoccidioides brasiliensis (Pb) conidia (n = 50) or PBS (n = 50). HRCT was done every four weeks to determine pulmonary lesions, quantify lung density, reconstruct and quantify lung air structure. Lungs were also analyzed by histopathology and histomorphometry.

Results

Three different patterns of lesions were evidenced by HRCT and histopathology, as follows: nodular-diffuse, confluent and pseudo-tumoral. The lesions were mainly located around the hilus and affected more frequently the left lung. At the 4th week post-challenge HRCT showed that 80% of the Pb-infected mice had peri-bronchial consolidations associated with a significant increase in upper lung density when compared with controls, (−263±25 vs. −422±10 HU, p<0.001). After the 8th and 12th weeks, consolidation had progressed involving also the middle regions. Histopathology revealed that consolidation as assessed by HRCT was equivalent histologically to a confluent granulomatous reaction, while nodules corresponded to individual compact granulomas. At the 16th week of infection, confluent granulomas formed pseudotumoral masses that obstructed large bronchi. Discrete focal fibrosis was visible gradually around granulomas, but this finding was only evident by histopathology.

Conclusions/Significance

This study demonstrated that conventional HRCT is a useful tool for evaluation and quantification of pulmonary damage occurring in experimental mouse PCM. The experimental design used decreases the need to sacrifice a large number of animals, and serves to monitor treatment efficacy by means of a more rational approach to the study of human lung disease.  相似文献   

14.
A modified Parsegian formula for calculating the image force in a water pore, which takes into account nonlocal electrostatic effects, has been applied to analysis of changes in the permeability of K+ channels. It is shown that the channel permeability increases ~3000 times as the width of the pore increases from 4 to 10 Å when the energy is calculated by the modified formula, but only 16 times if the classical Parsegian formula is used. We conclude that the image force in the K+ channel water pore plays an important part in the change of channel permeability, and the sensitivity of channel permeability to the pore width is greatly enhanced by nonlocal electrostatic effects.  相似文献   

15.
Abstract

We report results of molecular dynamics simulations of the limiting conductance of Na2+, Cl2?, Na°, and Cl° in supercritical water using the SPC/E model for water in conjuction with our previous study (Lee et al., Chem. Phys. Lett. 293, 289 (1998)). The behavior of the limiting conductances of Na2+ and Cl2? in the whole range of water density shows almost the same trend as those of Na+ and Cl?, but the deviation from the assumed linear dependence of limiting conductances of Na2+ and Cl2? on the water density is smaller than that of Na+ and Cl?. The ratio of the limiting conductance of the divalentions to that of the corresponding monovalentions over the whole range of water density is almost constant. In the cases of Na2+ and Cl2?, the dominating factor of the number of hydration water molecules around ions in the higher-density region and the dominating factor of the interaction strength between the ions and the hydration water molecules in the lower-density region are also found as was the cases for Na+ and Cl?. These factors, however, are not so strong as for the corresponding monovalent ions because the change in the energetics, structure, and dynamics are very small mainly due to the strong Coulomb interaction of the divalent ions with the hydration water molecules. The diffusion coefficient of Na° and Cl° monotonically increases with decreasing water density over the whole range of water density. The increase of the diffusion coefficient with decreasing water density is attributed only to the dramatic decrease of the hydration number of water in the first solvation shell around the uncharged species. Among the two important competing factors in the limiting conductance of Na+ and Cl?, the effect of the number of hydration water molecules around the uncharged species is the only existing factor over the whole range of water density since the interaction strength between the uncharged species and the hydration water molecules very small through the LJ interaction. This result has confirmed the dominating factor of the number of hydration water molecules around ions in the higher-density region in the explanation of the limiting conductance of Na+ and Cl? in supercritical water at 673 K.  相似文献   

16.
Biological response of exposure to radon progeny has long been investigated, but there are only few studies in which absorbed doses in lungs of laboratory animals were estimated. The present study is the first attempt to calculate the doses of inhaled radon progeny for mice. For reference, the doses for rats and humans were also computed with the corresponding models. Lung deposition of particles, their clearance, and energy deposition of alpha particles to sensitive tissues were systematically simulated. Absorbed doses to trachea and bronchi, bronchioles and terminal bronchioles, alveolar-interstitial regions, and whole lung were first provided as a function of monodisperse radon progeny particles with an equilibrium equivalent radon concentration of 1?Bq?m?3 (equilibrium factor, 0.4 and unattached fraction, 0.01). Based on the results, absorbed doses were then calculated for (1) a reference mine condition and (2) a condition previously used for animal experiments. It was found that the whole lung doses for mice, rats, and humans were 34.8, 20.7, and 10.7?nGy (Bq?m?3)?1?h?1 for the mine condition, respectively, while they were 16.9, 9.9, and 6.5?nGy (Bq?m?3)?1?h?1 for the animal experimental condition. In both cases, the values for mice are about 2 times higher than those for rats, and about 3 times higher than those for humans. Comparison of our data on rats and humans with those published in the literature shows an acceptable agreement, suggesting the validity of the present modeling for mice. In the future, a more sophisticated dosimetric study of inhaled radon progeny in mice would be desirable to demonstrate how anatomical, physiological, and environmental parameters can influence absorbed doses.  相似文献   

17.
Summary Seventy-three rats were exposed to an aerosol of enriched uranium dioxide (UO2), giving initial lung burdens of 26 to 447 µg at 6 days post-inhalation (PI). At 7 days PI 35 of these rats were further exposed to thermalised neutrons at a fluence of 1 x 1012 neutrons CM–2. There was no significant difference between the two groups in the clearance rate of the UO2 particles from the lung, up to 590 days PI. The particles cleared relatively slowly over this period with a retention halftime in the lung of 160 to 176 days.Transmission electron microscope (TEM) studies of tissue from the alveolar region at 8 days PI showed that inhalation of UO2 particles significantly increased the sizes of macrophage and type II cells, and the number of macrophage and type I cells. There was also a significant increase in the size of lysosomal granules within the macrophages after exposure to the UO2 particles. The exposure to UO2, neutrons and235U fission fragments had no significant effect on any of the cells above that observed in the animals exposed to UO2 alone.Additional rats were exposed to the same neutron fluence without prior UO2 inhalation. The alveolar cells of neutron-only exposed rats were, in size and number, typically no different from those in the completely unexposed control rats.  相似文献   

18.
The pollution of the marine environment with microplastics is pervasive. However, microplastic concentrations in the seawater are lower than the number of particles entering the oceans, suggesting that plastic particles accumulate in environmental sinks. Yet, the exact long-term sinks related to the “missing plastic” phenomenon are barely explored. Sediments in nearshore biogenic habitats are known to trap large amounts of microplastics, but also the three-dimensional structures of coral reefs might serve as unique, living long-term sinks. The main framework builders, reef-building corals, have been shown to ingest and overgrow microplastics, potentially leading to a deposition of particles in reef structures. However, little is known about the number of deposited particles and the underlying processes determining the permanent deposition in the coral skeletons. To test whether corals may act as living long-term sink for microplastic, we exposed four reef-building coral species to polyethylene microplastics (200 particles L?1) in an 18-month laboratory experiment. We found microplastics in all treatment specimens, with low numbers of particles trapped in the coral tissue (up to 2 particles per cm2) and much higher numbers in the skeleton (up to 84 particles per cm3). The numbers of particles accumulated in the coral skeletons were mainly related to coral growth (i.e., skeletal growth in volume), suggesting that deposition is a regularly occurring stochastic process. We estimate that reef-building corals may remove 0.09%–2.82% of the bioavailable microplastics from tropical shallow-reef waters per year. Our study shows for the first time that microplastic particles accumulate permanently in a biological sink, helping to explain the “missing plastic” phenomenon. This highlights the importance of coral reefs for the ecological balance of the oceans and reinforces the need to protect them, not only to mitigate the effects of climate change but also to preserve their ecosystem services as long-term sink for microplastic.  相似文献   

19.
Dissociation and Reassociation of Infectious Poliovirus Particles   总被引:3,自引:0,他引:3  
THE first reconstitution of an infectious virion was achieved when Fraenkel-Conrat and Williams1 obtained the typical rods of tobacco mosaic virus (TMV) from its components, RNA and protein. Later, the conditions for the “self-assembly” of TMV were improved so that up to 50% of the viral RNA could be coated with the protein. The reconstituted TMV was shown to be infectious and indistinguishable from native virions by several criteria2. Recent studies revealed that the reconstitution of TMV is a highly specific multi-step procedure, beginning at the 5′-end of the TMV-RNA3–5. In the past five years a number of spherical plant viruses have also been reconstituted6. In experiments with small RNA-bacteriophages very low efficiencies of reconstitution in the range of 10–8 to 10–7 p.f.u. (plaque forming units) per input molecule of RNA were obtained7,8. Reconstitution was improved by the addition of a minor viral protein, the A-protein, to the mixture of RNA and the structural protein. Even so the efficiency of conversion of RNA into infectious particles was in the range of 2×10–6 (refs. 9 and 10). We have reported the first successful restoration of poliovirus infectivity lost on dissociation of the virion by urea-mercapto-ethanol treatment11. Here we present evidence for reconstitution of infectious poliovirus particles from a mixture of poliovirus RNA and polypeptides.  相似文献   

20.
The effect of cell density on morphological transformation of chick embryo cells by Rous Sarcoma Virus (RSV) was examined in this study, and a cell density optimum for transformation was found. Less than 10% of the transformed foci appearing at the optimum density (2.5 × 104 cells per cm2) developed at high cell densities, and the diameters of the foci (an indication of the number of cells per focus) decreased with increasing cell density. No correlation was found between the decrease in transformation at high cell densities and the effect of cell density on the initial rate of cell proliferation, although dissociation of transformation from incorporation of radioactive precursors into nucleic acids could not be established. Redistribution of cells infected at high density showed that only a small proportion of successfully infected cells developed into foci. The results indicate that transformation of cells containing the RSV genome can be suppressed by physiological factors accompanying high cell density.  相似文献   

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