ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.00673.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.t01-1-00673.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Using in parallel electron microscopy of ultrathin frozen‐hydrated sections and freeze‐fracture replicas, we compare the ultrastructural consequences of two freezing techniques: slam‐freezing at liquid helium temperature and high‐pressure freezing, on a model system, the DNA cholesteric liquid crystalline phase. Both freezing techniques are able to vitrify DNA liquid crystalline solutions containing up to 85% water, but induce structural rearrangements of the molecular organization. The cholesteric structure is preserved by the slam‐freezing method despite the formation of periodic distortions induced by the mechanical compressive stress. In contrast, high‐pressure freezing does not preserve the structure of the liquid crystal: the long‐range cholesteric stratification disappears, and the local continuous twist between molecules is modified. These results show that vitrification, though necessary, may not be a sufficient token of preservation of the native state of hydrated materials. We discuss the possible origins of the molecular rearrangements that have time to occur in the specimens as a result of the low freezing rate permitted by the high‐pressure f

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1090666.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

A rapid fixation/dehydration method of plant specimens for scanning electron microscopy is presented. Prior to critical‐point drying (CPD) the specimens are immersed in pure methanol. Methanol incubation instantly fixes the elastically extended cell walls. Owing to this instant fixation, shrinking of the specimens is prevented, resulting in an improved preservation of cell dimensions comparable toin vivoconditions. The method is most suitable for plant epidermal surfaces. It avoids the time‐consuming fixation/dehydration in routine investigation of plant surfaces prior to CPD, especially for delicate specim

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.d01-110.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

In contrast to the increase in the extinction dose for thick specimens, observed broadening rates of diffraction spots from behenic acid multiple monolayers were independent of specimen thickness. This result leads to the conclusion that specimens are always decaying at the same rate although the periodicity of crystals still remains in thick specimens. The conclusion is interpreted as being the result of the radiation damage mechanism based on longitudinal motions of long chain molecules. For the evaluation of beam damage effect the broadening rate and the extinction dose should be used as indicator for the radiation sensitivity of crystals and for the possibility of observing diffraction patterns, respectively.

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1170674.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Changes in the elemental composition of cells during isolation of glandular epithelia were studied by electron probe X‐ray microanalysis. Fine chopping of rat submandibular gland followed by enzymatic treatment for 15 min caused marked increases in Na and Cl and a decrease in K concentrations in acinar cells. After enzymatic treatment for 50 min, Na, Cl and K concentrations returned to close to the control level. Mechanical disaggregation of the acinar clumps following enzymatic treatment resulted again in minor increases in Na and Cl and a marked decrease in K concentration. Exposure of isolated acini to cholinergic stimulationin vitroresulted in secretion of Cl and K from the acinar cells. Dissection of the sweat gland from human skin caused a decrease in the K/Na ratio. Incubation of the gland for 30–45 min with collagenase gave rise to a gradual decrease in the K/Na ratio. After mechanical separation of the gland into the secretory coil and reabsorptive duct, a further reduction of the K/Na ratio was seen. However, the duct cells had a much lower K/Na ratio and higher Ca concentration than the coil cells. In primary cultures, the K/Na ratios of the coil and duct cells returned to thein situlevel. The elemental composition of sweat gland cells incubated in collagenase‐containing medium was no different from that in cells incubated in collagenase‐free medium. In the intact collagenase‐isolated tissue, Cl−secretion in the coil was elicited by carbachol but not by cAMP, whereas in the duct cells the reverse was the case. In primary cell cultures, Cl−efflux in both coil and duct cells could be elicited by both carbachol and cAMP. In conclusion, although changes in elemental composition of gland cells during the isolation procedure occur, physiological responses can be detected. When primary cell cultures are used, it should be borne in mind that cultured cells may have physiological properties different from those o

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1110668.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

We describe a Raman imaging microscope that produces high‐fidelity, large format Raman images and Raman spectra from samples as small as 1 μm in size. Laser illumination is delivered to the object by means of an infinity corrected microscope objective, either by a galvanometer scanning system or a widefield fibre optic. Wavelength selection of Raman scattered emission is achieved by an acousto‐optic tunable filter (AOTF), which maintains image fidelity and provides either continuous or random wavelength selection. The collimated AOTF output is imaged first by a tube lens and then by a projection lens onto a cooled silicon CCD array. Instrument features, including factors that determine the system’s spatial and spectral resolution, and design considerations are discussed in detail. Images and spectra of test objects and samples that demonstrate the capability of this imaging spectrometer are presented. The potential of intrinsic chemical imaging is discussed in terms of its use in the analyses of a variety of chemical and biological

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1130670.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The preparation of specimens for detailed TEM microanalysis of micrometre‐diameter, ceramic fibre cross‐sections is described. The starter material is ceramic fibre in powder form and both ultramicrotomy‐based and ion beam thinning‐based methods are described. Requirements for specimens of uniform and adequate thinness, for easy selection of representative fibre cross‐sections within the same specimen and for a reliable and time‐efficient preparation method, resulted in choice of the ultramicrotomy‐based method and the associated development of a novel extrusion and sedimentation technique of embedding the fibres to provide necessary pre‐alignm

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1030660.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

In this paper we describe a preparative procedure which allows maximal visualization of all lipid bilayers in the human stratum corneum (SC). We used 50‐μm‐thick vibratome sections of paraformaldehyde/glutaraldehyde‐fixed human skin. The sections were post‐fixed in 1% osmium tetroxide and 0.5% ruthenium tetroxide. The vibratome sections were dehydrated only in 70% ethanol in order to prevent dissolution of the lipids.  Lipid bilayers, including the alternating electron‐dense and electron‐lucent lamellae, were visible between all cell layers of the SC. In addition, this preparative procedure also appeared to be excellent for the ultrastructural preservation of l

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1070664.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY