PubMed Health⌕ Search

Biomedical subjects

G Vrensen

Publications and source records attributed to G Vrensen.

At least 19 recordsLinked to original sources
PubMed2003

Nonresonant Raman imaging of protein distribution in single human cells.

A confocal Raman microscope is used to study the protein distribution inside biological cells. It is shown that high quality Raman imaging of the protein distribution can be obtained using confocal nonresonant Raman imaging (lambda(exc) = 647.1 nm). The results are shown for two different human cell types. Perpheral blood lymphocytes are used as an example of the fully maturated cells with a low level of nuclear transcription. Human eye lens epithelial cells are used as an example of cells with a high level of nuclear activity. The protein distribution in both cell types is completely different. The nuclear distribution of the protein largely varies in the peripheral blood lymphocyte cells, while proteins are more homogenously distributed over the nuclear space in the eye lens epithelial cells. The imaging time is approximately 20 min for a field of view of 10 x 10 microm(2). The size of the sampling volume is 1.4 fL using a full width at half-maximum criterion along the z axis and a 1/e(2) criterion in the xy plane. The results presented here indicate that Raman imaging is particularly of interest in the study of cellular processes, like phagocytosis, apoptosis, chromatin compaction, and cellular differentiation, which are accompanied by relatively large-scale redistributions of the materials.

Cell Nucleus↗
PubMed2003

Nonresonant confocal Raman imaging of DNA and protein distribution in apoptotic cells.

Nonresonant confocal Raman imaging has been used to map the DNA and the protein distributions in individual single human cells. The images are obtained on an improved homebuilt confocal Raman microscope. After statistical analysis, using singular value decomposition, the Raman images are reconstructed from the spectra covering the fingerprint region. The data are obtained at a step interval of approximately 250 nm and cover a field from 8- to 15- micro m square in size. Dwell times at each pixel are between 0.5 and 2 s, depending on the nature and the state of the cell under investigation. High quality nonresonant Raman images can only be obtained under these conditions using continuous wave high laser powers between 60 and 120 mW. We will present evidence that these laser powers can still safely be used to recover the chemical distributions in fixed cells. The developed Raman imaging method is used to image directly, i.e., without prior labeling, the nucleotide condensation and the protein distribution in the so-called nuclear fragments of apoptotic HeLa cells. In the control (nonapoptotic) HeLa cells, we show, for the first time by Raman microspectroscopy, the presence of the RNA in a cell nucleus.

Apoptosis↗
PubMed1998

Transient activation of cyclin B/Cdc2 during terminal differentiation of lens fiber cells.

Previous work has shown that postmitotic, differentiating fiber cells of the embryonic chicken lens express cyclin B and Cdc2. The present study explores the possible physiological role of these proteins in lens differentiation by examining the developmental regulation of cyclin B/Cdc2 expression and activity in lens fiber cells of embryonic and newborn rats. Cyclin B mRNA and protein were detected not only in the lens epithelium, which contains proliferating cells, but also in postmitotic, differentiating fiber cells. In contrast, cyclin A mRNA and protein were detected only in epithelial cells. Immunoprecipitation with cyclin B antibody coprecipitated Cdc2 from both epithelial and fiber cell extracts. Immunoprecipitates of cyclin B from both epithelial cells and fiber cells showed H1 kinase activity when assayed in vitro, but the developmental pattern of cyclin B-associated kinase activity in these two lens fractions was markedly different. In the epithelium, H1 kinase activity decreased gradually with developmental age in parallel with the decrease in epithelial cell proliferation, whereas, in the fiber cells, kinase activity peaked sharply at embryonic day 18 (E18) and E19. Microscopic examination of rat lenses indicated that peak cyclin B/Cdc2 activity was correlated with changes in chromatin structure and nuclear envelope breakdown in the terminally differentiating primary lens fiber cells. These findings suggest that cyclin B/Cdc2 activity may play an active role in nuclear changes leading to primary fiber cell denucleation.

Animals↗
PubMed1994

A correlated study of metabolic cell communication and gap junction distribution in the adult frog lens.

By using low molecular weight dye injection and laser scanning confocal microscopy it has been possible to assess the degree of dye communication in several regions (intraepithelial, epithelium-fibre cell, fibre-epithelium and fibre-fibre) of the adult frog lens. These same areas of the lens have also been examined by freeze fracture electron microscopy for the presence and organisation of gap junctions. Epithelial cell lateral membranes have numerous gap junctions which efficiently transmitted dye to their neighbours though none was detectable in the underlying fibre cells. This was correlated with an apparent absence of gap junctions at the epithelium/fibre cell interface. Dye spread between cortical fibre cells was only observed in a subset of fibres in the bow region of the lens. Neither mature cortical fibres nor immature bow fibres appeared to be dye-coupled and we detected no dye passed from fibre cells to adjacent epithelial cells at their anterior ends. This pattern of dye communication was also correlated with the apparent absence of recognisable gap junctions on the lateral membranes of either the recently differentiated bow fibres or the mature cortical fibres. Classical gap junctions were only found on the membranes of fibres between five and ten cells in from the lens bow, i.e. the subset of fibres which were dye-coupled. No gap junctions were found between deeper cortical fibres or nuclear fibres, although they were characterised by a number of square arrays. Though electrically well coupled the adult frog lens may be relatively poorly dye coupled and this could depend on the age and differentiation stage of the cells concerned. The model of a freely communicating lens clearly requires re-examination by correlated physiological and morphological studies.

Animals↗
PubMed1994

Sympathetic innervation of the rat's eye and peripheral ganglia: an electron microscopic autoradiographic tracing study.

The sympathetic innervation of the rat anterior eye segment and related peripheral ganglia was studied using light and electron microscopic autoradiography after anterograde tracing with 3H-leucine from the superior cervical ganglion. In the trigeminal and pterygopalatine ganglia, unmyelinated nerve fibers were labeled. Some fibers contained accumulations of small vesicles. Close apposition of these labeled sympathetic fibers with other unmyelinated fibers was common, and was also observed at sites where accumulations of vesicles were found. In the iris, ciliary body and trabeculum, numerous fibers and vesicle-containing varicosities were labeled, which all had a similar morphology. No labeling was found in the cornea. Sympathetic fibers traversing the trigeminal and pterygopalatine ganglion closely appose other unmyelinated fibers and contain clusters of vesicles without forming classical synaptic contacts. However, non-synaptic information transfer needs further investigation. The anterior eye segment, except for the cornea, is densely innervated by sympathetic nerve terminals.

Animals↗
PubMed1992

Dysfunction of the blood-retina barrier following white light exposure. A tracer study with horseradish peroxidase and ferrous gluconate.

The aim of this investigation was to study the ultrastructural effects of white light on the retinas of pigmented rabbits. The retinas were exposed to white light (400-740 nm) at intensities between 65 and 140 mW/cm2 for 1 h. Two days after exposure, the increased leakage of fluorescein measured with vitreous fluorophotometry could be mimicked on electron microscopy by the tracers ferrous gluconate and horseradish peroxidase (HRP). In cases of minimal fluorescein leakage, traces of HRP were found in the basal folds of the retina pigment epithelium (RPE). No HRP was observed apical to the tight junctions of the RPE cells. When there was a great amount of fluorescein leakage, HRP completely filled the RPE cytoplasm, the extracellular spaces, and several cells in the neuroretina. It is concluded that after exposure to low intensities of white light, blood-retina barrier dysfunction may be due to disruption of the RPE basal fold membrane, leading to increased transcellular passage. The intact tight junctions suggest the under these circumstances intercellular leakage is not a component of BRB dysfunction.

Animals↗
PubMed1992

Membrane architecture as a function of lens fibre maturation: a freeze fracture and scanning electron microscopic study in the human lens.

The ultrastructure of fibre membranes in human lenses, varying in age from premature to 40 years, was investigated using a strict protocol regarding their localization within the lens. The ultrastructural approaches used were scanning electron microscopy (SEM), and transmission electron microscopy (TEM) of ultrathin sections and freeze-fracture replicas. Irrespective of the age of the lens, superficial fibre membranes are characterized by a high density of intramembrane particles (IMPs) and numerous gap junctions (GJs). In contrast deep cortical fibres, at the SEM-level characterized by grooves and ridges, are largely free of IMPs but still contain numerous GJs. In between these regions a transitional zone was observed. At the SEM-level the transitional fibres are characterized by wrinkled membranes and formation of grooves and ridges. In freeze-fracture replicas the presence of numerous square arrays (SAs) associated with GJs is most remarkable. It is concluded that at all ages studied, the maturation and compaction of lens fibres results in a transformation of membrane architecture leading to clear-cut ultrastructural differences between superficial and deep cortical membranes. It is argued that this ultrastructural heterogeneity parallels the gradients observed biochemically for intrinsic membrane proteins and cholesterol:phospholipid ratios. The observations confirm the electrophysiological view that superficial membranes have an 'average' permeability and that deep cortical membranes are 'degenerate' or 'non-leaky'.

Adolescent↗
PubMed1990

The Hermansky-Pudlak syndrome. Variable reaction to 1-desamino-8D-arginine vasopressin for correction of the bleeding time.

The effect of the synthetic vasopressin derivative 1-desamino-8D-arginine vasopressin (DDAVP = Minrin) on bleeding time was studied in nine patients with Hermansky-Pudlak syndrome; four of them were Dutch, five were Belgian. Shortening of bleeding time was observed in four of the patients with this type of storage pool disease; in one patient the response was equivocal, in two patients the response was not dramatic and in two there was no response at all. DDAVP may be useful in managing the bleeding disorder in some patients with Hermansky-Pudlak syndrome. Therefore, every patient with this syndrome should be tested with DDAVP as a preventive measure.

Adolescent↗
PubMed1990

Square arrays in early cortical lens opacities.

A combined freeze-fracture and scanning electron microscopic study of early opaque spots in the aging human lens showed the absence of gap junctions and the presence of square arrays in the membranes of disturbed fibers and neighboring unaffected fibers. Square arrays, with membrane particles of 6-7 nm, are considered as rearranged gap junctions and/or intramembranous particles, with particle sizes between 8.5-9.5 nm; they are a sign of electric and metabolic uncoupling. These ultrastructural observations lend support to the idea of an uncoupling mechanism in the aging human lens, conserving the transparency of unaffected parts of the lens, as postulated previously.

Aging↗
PubMed1990

Morphology of the aging human lens. II. Ultrastructure of clear lenses.

Clear human post mortem lenses, varying in age between 23 and 82 years, were investigated using scanning and transmission electron microscopy. The lenses were obtained from the Corneabank Amsterdam. The post mortem delay ranged from 8-24 hours. Apart from some minor mitochondrial changes no hypoxic post mortem disturbances in epithelial cells and lens fibers were observed. In the lens fibers three main age-related fine structural alterations were found: i) membrane ruptures, ii) watervacuoles and iii) multilamellar bodies. The frequency of these alterations increased with age and they remained restricted to the superficial equatorial cortex. They were absent in the anterior and posterior cortex, supranuclear equatorial cortex and nucleus. The relevance of these observations in relation to the etiology and early pathogenesis of senile cataract is discussed. The membrane ruptures and watervacuoles are in morphological support of the view, based on biochemical evidence, that oxidative stress leads to destabilization and desintegration of membranes and consequently disturbs the waterbalance of fibers. It is postulated that the lamellar bodies are involved in the repair of ruptured membranes and breakdown of affected proteins thus explaining the late onset of senile cataractous changes.

Adult↗
PubMed1990

Biomicroscopy and scanning electron microscopy of early opacities in the aging human lens.

A large sample of lenses obtained from donor eyes spended for cornea transplantation were biomicroscopically screened and a representative subsample of lenses (about 30) exhibiting early opacities were studied at the scanning electron microscopic (SEM) level. Two types of early cortical opacities (Lens Opacities Classification System cortical grade 1a, 1b) could be distinguished biomicroscopically: (1) radial shades, and (2) circular shades. The prevalence of both types is age related, with an earlier occurrence of radial shades than of circular shades. In addition, radial shades proved to occur as single entities in isolation in lenses from people younger than the age of 40, whereas circular shades are only occasionally found in isolation in older lenses. SEM analysis substantiated the existence of the two early forms of opacity. Radial shades were found to consist of restricted parts of a small group of fibers in the deep cortex. These affected parts had membranes with a fine globular aspect and in cross-section proved to be filled with medium to large globular elements. Neighboring fibers and the nonaffected parts of the fibers involved in the radial shades had a normal SEM ultrastructure. Circular shades proved to originate as fractures of a large cohort of fibers in the deep equatorial cortex perpendicular to the course of the fibers. The fractured faces were slightly swollen, but the membranes on both sides of the fracture had a normal ultrastructure. In cross-sections of more advanced circular shades it proved that the broken fibers are filled with globular elements and are opaque. This opacification proved to extend only in one direction: either anteriorly or posteriorly. The results strongly suggest that two distinct early cataractogenic cellular processes are operating in the aging human lens. The possible induction of circular shades by radial shades, as can tentatively be concluded on account of the difference in appearance during aging of circular and radial shades, needs further verification by SEM analysis of more severely affected lenses. The observations corroborate the suggestion by Bron and Brown of the existence of mechanisms within the lens that separate damaged from undamaged fibers (segregation) or separate affected parts from unaffected parts of individual fibers (sealing).

Adolescent↗
PubMed1989

Lamellar separation in the human lens: the case for fibre folds. A combined in vivo and electron microscopy study.

Lamellar separation is seen as parallel lines in the lens cortex. It has been the subject of a joint study between Oxford and Amsterdam. The condition was studied in vivo by macro photography and in vitro by scanning electron microscopy. The lines are seen to run concentric with the lens equator, crossing the lens fibres at right angles. The lines are commonly limited by a spoke cataract, a water cleft, or a lens suture. The line may continue beyond these features with a change in direction. The lines may branch and rejoin. The lines extend in depth into the lens, polarised light showing that the lines are due to reflection. The name 'lamellar separation' implied that the appearance is due to separation between the lens lamellae. Lamellar separation is now shown by electron microscopy to be due to folds crossing the lens fibres. The clinical study showed the lines occurring with spoke cataract and the electron microscopy showed the association with the novel finding of peripheral breaks in the fibres. A new name 'Fibre Folds' is proposed.

Aged↗
PubMed1985

Lens fiber organization in four avian species: a scanning electron microscopic study.

The three-dimensional organization of the eye lenses of the chicken, the canary, the song-thrush and the kestrel was studied using light and scanning electron microscopy. The lenses of birds are characterized by the presence of two distinct compartments: the annular pad and the main lens body, separated by a cavum lenticuli. The annular pad fibers had a hexagonal circumference all contained a round nucleus and except for the canary were smooth-surfaced and lacking anchoring devices. In the canary, however, the annular pad fibers were studded with edge protrusions and ball-and-socket junctions. The semicircular main lens body fibers of all four species were studded with ball-and-socket junctions and edge protrusions. In contrast with mammals these anchoring devices were present throughout the lens up to the embryonal nucleus. Superficially the main lens body fibers were extremely flat. Additionally membrane elevations and depressions and globular elements were found on these central fibers in three species, the kestrel being the exception. At the transition between annular pad and main lens body the fibers turned their course and the nuclei became oval and disappeared in the deeper aspect of the main lens body. The cavum lenticuli was filled with globules tied off from the annular pad fibers. It seems attractive to assume that the presence of a separated annular pad, a cavum lenticuli filled with globular elements, the extreme flatness of the superficial central fibers and the studding of these central fibers with anchoring devices up to the embryonal nucleus are morphological expressions of the mouldability of the bird's eye lenses and consequently would explain their efficient accommodative mechanism including formation of a lenticonus. The presence of nuclei in the annular pad fibers and their typical change at the transitional zone between annular pad and main lens body are suggestive for a two-phased differentiation in bird's lens fibers: differentiation of the germinative epithelial cells to annular pad fibers which migrate to the main lens body after which they differentiate further to main lens body fibers.

Animals↗
PubMed1984

Variations in presynaptic grid size in the granular and molecular layer of the cerebellar cortex of the cat. I. A quantitative ultrastructural study on semithin E-PTA sections.

The size distribution of synapses in the cerebellar cortex of the cat was defined on 0.5-micron semithin sections stained with ethanolic phosphotungstic acid (E-PTA). The surface area (SA) of synaptic grids was measured and the number of dense projections per grid (NDP) was counted. The results show large differences in mean values between molecular and granular layer. Within the molecular layer the differences in mean values at different levels below the pial surface were small; however, the frequency distributions differed significantly. In the granular layer a confined unimodal frequency distribution of SA and NDP was observed (mean NDP, 7.02 +/- 0.10), in the molecular layer a considerable variation in the size of the synaptic discs was observed (mean NDP, 20.40 +/- 0.43). Only a small percentage of the synaptic discs have less than 5 or more than 47 DPs. The sharply defined differences in synaptic size between the granular and molecular layer and the smaller differences within the granular and molecular layer are discussed in the context of the congruity hypothesis of Chan-Palay.

Animals↗
PubMed1984

Neodymium YAG laser effects on rabbit lenses. A scanning electron microscopic investigation using Q-switched and mode-locked lasers.

The immediate and long-term effects of Q-switched and mode-locked neodymium (Nd) yttrium-aluminum-garnet (YAG) lasers on the fine structure of lens fibers were studied with stereomicroscopic and scanning electron microscopic methods. This study shows that both laser systems produced very restricted lesions that, at a 1-h survival time, were characterized by an empty central hole surrounded by a thin amorphous wall. Fibers adjacent to the hole looked normal, apart from some compression in the immediate vicinity of the hole. At medium and long-term survival times the empty bubbles now appeared to be filled with a crystal-clear amorphous mass. The wall surrounding the empty lesions had disappeared, and at medium survival times adjacent fibers incidentally showed fiber alterations like local swellings and microplicae. At 180 days the fibers surrounding the central mass showed numerous swellings, microplicae and confluence of fibers. These fiber alterations are also seen in different types of cataracts. Thus, short-pulsed laser lesions may act as cataractogenic centers.

Animals↗
PubMed1984

The ultrastructure of the lens of the cephalopod Sepiola: a scanning electron microscopic study.

The ultrastructure of the eye lens of Sepiola atlantica was investigated using scanning electron microscopy. The main lens elements in both the anterior and posterior half of the Sepiola lens are plate-like configurations with fiber-like extensions at their margins. Anteriorly the plates are plano-convex, posteriorly subspherical. The central, primordial, posterior plates are spherical with no marginal extensions. The plates are mutually anchored by protrusions and invaginations and by push-button attachments. The posterior and anterior halves are separated by a septum which consists of concentric zones of radially orientated elongated cells. The marginal extensions of the plates and the septal elements are closely associated. The unique structure of the septum makes it a good candidate for the high resistance barrier between the posterior and anterior halves of the Sepiola lens (Jacob and Duncan, 1981).

Animals↗