Search PubMed⌕ Search

Biomedical subjects

H Robenek

Publications and source records attributed to H Robenek.

At least 127 records · Page 7Linked to original sources
PubMed1982

Primary cultures of rat hepatocytes as a model system of canalicular development, biliary secretion, and intrahepatic cholestasis. I. Distribution of filipin-cholesterol complexes during de novo formation of bile canaliculi.

Hepatocytes in primary monolayer culture reconstitute structural intact bile canaliculi sealed by tight junctions. Using filipin as a cytochemical marker for cholesterol-like membrane components in conjunction with the techniques of freeze fracture and thin sectioning, we have studied the distribution of cholesterol during the development of the biliary pole of cultured hepatocytes. It was found that the development of bile canaliculi is characterized in its very early stage by huge accumulations of filipin-cholesterol complexes located at distinct domains of the contiguous membrane. They were surrounded by junction formation zones almost devoid of these complexes, in which the alignment of intramembranous particles takes place. Maturation of the bile canaliculi was accompanied by dispersion of cholesterol within the canalicular membrane and its removal by segregation of cholesterol-rich membrane whorls and vesicles into the lumen. Finally, the luminal membranes, and particularly the areas studied with microvilli, contained only very few filipin-cholesterol complexes. In some cases, these seemed to be still arranged in small clusters. These alterations suggest a crucial role of cholesterol-rich membrane domains during initiation of a biliary polarity. On the other hand, cholesterol-poor (thus probably more fluid) areas might be required for the assembly of tight junctions, and appear to constitute the secretory active apical membrane present in the mature bile canaliculus.

Animals↗
PubMed1982

Primary cultures of rat hepatocytes as a model system of canalicular development, biliary secretion, and intrahepatic cholestasis. II. Taurolithocholate-induced alterations of canalicular morphology and of the distribution of filipin-cholesterol complexes.

Hepatocytes in primary monolayer culture treated with taurolithocholate showed distinct ultrastructural changes localized primarily to the bile canalicular membrane. These alterations comprised disturbance and proliferation of tight junctions, dilatation of the canaliculi, loss of microvilli, thickening of the pericanalicular ectoplasm, and bizarre lamellar transformations of canaliculi. In freeze-fracture replicas the lamellae projecting into the canalicular lumen were found to be devoid of intramembranous particles. Localization by the use of filipin of cholesterol in plasma membranes of taurolithocholate affected hepatocytes revealed an extensive accumulation of cholesterol in membranes of dilated canaliculi, and also in outpouchings of the contiguous membrane in the ultimate vicinity. Furthermore, a pronounced segregation of cholesterol-rich membrane material into the lumen of dilated canaliculi and into enlargements of the intercellular space could be observed in thin sections. In contrast, a total absence of cholesterol was noted in the lamellar projections of the bizarre transformed canaliculi. The reliability of these findings and their consequences for the mechanism of taurolithocholate-induced cholestasis are discussed and it is suggested that the incorporation of cholesterol into the canalicular membrane reflects only one aspect of the cholestatic effect of taurolithocholate. An additional aspect seems to comprise the dislocation of membrane bound proteins and perhaps other membrane components. This is probably caused by independent mechanisms.

Animals↗
PubMed1981

Quantitative analysis of intramembranous particles in the membranous system of rat liver cells at different stages of development and aging.

The density of intramembranous protein particles was studied by freeze-fracture. Particle density on the fracture faces of the plasmalemma and the rough endoplasmic reticulum (RER), as well as the outer and inner membranes of the nucleus and the mitochondria in rat hepatocytes were quantified. Comparison among different age groups sampled days postcoitum (dpc), days postpartum (dpp), and months postpartum (mpp) showed age-related changes in particle density in each membrane system. With the exception of the RER, particle densities increased after the 16th dpc, reached a maximum at birth, and then decreased with increasing age. Simultaneously, the number of nuclear pores shows a positive correlation with the particle density of the nuclear membranes. The particle density on the membranes of the RER shows a maximum on the 16th dpc and on the 6th dpp. Thereafter, the density of the RER decreases slightly. In all membrane systems, the density of the particles on the external fracture faces is more variable than density of the particles on the protoplasmic fracture faces.

Aging↗
PubMed1981

Tissue connections in a transplantable virus-producing sebaceous adenoma of the mouse.

In this study a transplantable sebaceous adenoma is presented, which maintained its histological structure with similarities to normal sebaceous glands over a long series of transplantations. From the periphery toward the center a basal lamina, an outer layer of undifferenciated stem cells, loosely connected secreting tissue, a tightly packed zone of close cell attachment, and finally a central sebaceous zone can be distinguished. Special reference is made to the belt-like region around the zone of cell lysis and sebum accumulation, which forms a barrier to the surrounding tissue by means of numerous cell adhesions in the form of desmosomes. Relatively few virus particles of the retrovirus group, particularly type A particles, were found in any of the examined tumors.

Adenoma↗
PubMed1981

Paracrystalline inclusions in lysosomes of mouse kidney tubule cells induced by vinblastine and vincristine.

Following the simultaneous administration of vinblastine and vincristine, crystalline and paracrystalline structures were observed in the lysosomes of kidney tubule cells of mice. These structures appeared as hexagonal elements with an average diameter of 22 nm, with filaments about 5,5 nm thick located at each angle of the hexagons. They were formed following the aggregation and fusion of several mitochondria, probably from the mitochondrial cristae. In addition, highly osmiophilic, membrane-bound lysosomes were observed, which in cross-section exhibited regular arrays of straight membrane plates with a periodicity of about 10 nm. The extent to which, or even whether, these are associated with the above-mentioned paracrystalline inclusions could not be clearly established.

Animals↗
PubMed1981

Combined effects of vinblastine and vincristine on mouse hepatocytes with respect to ultrastructural elements.

The results of a single dose of the microtubule-destroying agents vinblastine/vincristine (0.5 mg/0.05 mg) on the ultrastructural elements of mouse hepatocytes was studied using the techniques of thin-sectioning and freeze-fracture following intravenous injection of the drugs. Several cytoplasmic modifications were observed in the hepatocytes. These included the storage of lipid droplets, a heavy accumulation of autophagosomes and vacuoles with very low density lipoprotein (VLDL)-like vesicles, large glycogen fields and dilated intercellular spaces with intrahepatocytic vacuoles. The rough endoplasmic reticulum exhibited pathological changes with loss of ribosomes and the bile canaliculi exhibited in some cases the loss of microvilli as well as dilatation of the lumen. The tight junctions surrounding the bile canaliculi exhibited alterations as well. The strands were reduced in number and showed a less organized arrangement. The gap junction showed an increase in size as well as an irregular outline in contrast to controls. These findings are interpreted as non-specific toxic phenomena. However, the possibility cannot be precluded that certain phenomena, such as alterations in the cell junctions, may be attributable to specific microtubule-destroying properties of the drugs.

Animals↗
PubMed1981

Comparative ultrastructure of eyespot membranes in gametes and zoospores of the green alga Ulva lactuca (Ulvales).

Eyespot membranes in zoospores, and male and female gametes of the green alga Ulva lactuca, were studied comparatively by the freeze-fracture technique. The plasmalemma and the outer chloroplast envelope membrane overlying the eyespot lipid globules are specialized in all 3 types of reproductive cells. In the eyespot region the protoplasmic face (PF) of the outer chloroplast envelope membrane contains significantly more intramembraneous particles (IMP) compared to membrane areas outside the eyespot: in female gametes there are 2.5 times more IMP/micrometers 2, in zoospores 3 and in male gametes about 4. Small size-class IMP (4--6 nm diameter) are particularly abundant on both fracture faces of the outer chloroplast membrane, but size-class distribution is not significantly different between membrane areas inside and outside the eyespot region. The total number of IMP/eyespot on the PF of the outer chloroplast membrane was calculated to be 4900 in male gametes, 5500 in female gametes and 11 200 in zoospores. The results are discussed in accordance with the view that these membrane specializations participate in photoreception relating to green algal phototaxis. Evidence is presented that there is a correlation between IMP numbers per eyespot in the outer chloroplast envelope membrane and the different phototactic behaviour of gametes compared to zoospores in Ulva.

Chlorophyta↗
PubMed1981

Structural relationship between desmosomes and mitochondria in human livers exhibiting a wide range of diseases.

Liver biopsies from ten patients (five women and five men, aged 25-63) with a number of different diseases were studied with a transmission electron microscope. In addition to many different pathologic changes in the hepatocytes, all clinical diagnoses showed 5-70% of mitochondria with paracrystalline inclusions. A peculiar finding was that the desmosomes that join two cells had mitochondria associated with the intracytoplasmic component in both cells in 5-15% of desmosomes observed. In addition, the association involved only one side in one cell in 7-23% of desmosomes observed. Only speculation can be made regarding the function of these mitochondrial-desmosomal associations.

Adult↗
PubMed1981

New aspects of the origin of hepatocellular vacuoles. An ultrastructural study on rat and mice liver after different intoxications.

The stages of vacuolar formations in liver parenchymal cells of rats and mice following application of phalloidine, amanitine, o-phenylphenol, hexachlorophene and p-chloro-m-cresol were demonstrated by electron microscopic investigations. After treatment the intercellular spaces are markedly widened and in restricted regions exhibit large sacculi penetrating into the cytoplasm of adjacent hepatocytes. In cross-sections these invaginations frequently appear as intracellular vacuoles. Our present investigations, however, clearly demonstrate that these vacuoles are still in direct connection with the intercellular space. The vacuolar formation is more pronounced in older animals and it is suggested that an increased patho-physiological portal hypertension leads to the swelling of the intercellular space.

Aging↗
PubMed1981

Ultrastructural changes in mouse hepatocytes exposed to vinblastine sulfate with special reference to the intercellular junctions.

The effects of a single dose (0.5 mg) of the antimicrotubular drug vinblastine sulfate on the ultrastructure of mouse hepatocytes was studied by thin sectioning and freeze-fracturing after intravenous injection of the drug. The following cytoplasmic modifications occurred in the hepatocytes: storage of lipid droplets, heavy accumulation of autophagosomes and vacuoles with very low density lipoprotein (VLDL)-like vesicles, pathological changes in the mitochondria, and dilatation of the Golgi complexes. From 30 minutes onwards the bile canaliculi appeared altered. The tight junctions surrounding the bile canaliculi became permeable to lanthanum. This increased permeability was correlated with a disorganized arrangement of tight junctional strands and localized interruptions within the zonulae occludentes. In contrast to controls the gap junctions appeared more numerous and larger in size, exhibiting a high degree of pleomorphism. In the cytoplasm gap junctional vesicles could be observed indicating the removal of gap junctions from the surface by a process of internalization. We cannot establish whether the described changes are a direct or indirect effect of vinblastine sulfate treatment. In view of the antimicrotubular effect of vinblastine sulfate we hypothesize that normal formation of gap- and tight junctions is dependent directly or indirectly on intact microtubules.

Animals↗
PubMed1981

Freeze-fracture evidence for high cholesterol content in nuclear membranes of a larval urodelan epidermis.

The treatment of the larval epidermis of the ovoviviparous salamander, Salamandra salamandra (L.), with filipin produces a high number (193/micrometer 2) of filipin-sterol complexes in the outer nuclear membrane and a markedly lower number (27/micrometer 2) in the inner membrane of the pavement cells as revealed by freeze-fracturing. Frequently a small zone immediately surrounding nuclear pores is free of membrane lesions. The nuclear envelopes of other cell types in the epidermis are free of filipin-induced protuberances. The results provide evidence for a high cholesterol content in nuclear membranes hitherto believed to be low in cholesterol.

Animals↗
PubMed1981

Sterol-deficient domains correlate with intramembrane particle arrays in the plasma membrane of Chlamydomonas reinhardii.

The planar distribution of 3-beta-hydroxysterols in the plasmalemma of the green flagellate Chlamydomonas reinhardii has been studied with the freeze-fracture technique using the polyene antibiotic filipin and the saponin tomatin as cytochemical markers. Filipin-sterol complexes were predominantly observed as 25 to 30 nm protuberances on the E-face of the plasmalemma with corresponding invaginations on the P-face. Generally filipin-sterol and tomatin-sterol complexes were randomly distributed, but were virtually absent from sites of intramembrane particle arrays (IMP-arrays, i.e. the flagellar necklace, the flagellar bracelet including strut arrays, the eyespot membrane). The results suggest that IMP-arrays of Chlamydomonas are deficient in 3-beta-hydroxysterols and may therefore be regarded as special lipid arrays. IMP-arrays might require an altered lipid environment for proper function. Some functional aspects of IMP-arrays in Chlamydomonas are discussed.

Cell Membrane↗
PubMed1981

Ultrastructural alterations in the mouse liver following vincristine administration.

The damage pattern in mouse liver was investigated following a single administration of 0.15 mg vincristine sulfate using the conventional thin-section technique and freeze-fracture. Numerous cytoplasmic changes were observed. Foremost of these was the increase in autophagosomes and vacuoles with very-low-density-lipoprotein (VLDL)-like vesicles. The rough endoplasmic reticulum exhibited a vesicular structure. The mitochondria also exhibited alterations such as enlargement and polymorphism. Both the interstitium and bile canaliculi were dilated. Lanthanum penetrated into the lumen of the canaliculi, i.e. the sinusoid/canaliculus compartmentalization did not remain intact, thus permitting bile to pass into the blood. Of particular significance are the alterations in the intercellular junctions. In contrast to the controls, the tight junctions were reduced and irregularly arranged. The gap junctions exhibited hypertrophy as well as a very irregular contour. The alterations may either be attributed to non-specific toxic effects of vincristine and/or the destructive properties of the agent on microtubules.

Animals↗
PubMed1981

Structure and function of the junctional complement of spontaneous and transplanted murine mammary carcinomas.

In this study the morphology of intercellular junctions in a murine mammary adenocarcinoma and in a solid carcinoma which resulted from continuous transplantations of this spontaneous tumor are described employing the techniques of ultrathin-sectioning after conventional fixation and tannic acid fixation and freeze-fracturing. The acini of the original adenocarcinoma are separated from the intercellular spaces by tight junctions which form a narrow belt-like zonula around the adluminal parts of all epithelial cells. The apical-to-basal width of the tight junctions varies from 0.4 to 0.8 micrometer. Desmosomes and gap junctions are located close to the zonulae occludentes. The size of gap junctions ranges from small spots 0.2 micrometer in diameter to large areas approximately 1.5 micrometer in diameter. In the solid carcinoma these cellular junctions appear without acinar organization randomly between the cells. In addition, special contact zones can be observed. The contact zones seem to be the precursors of a formation plaque for gap or tight junction formation. The sizes of the gap junctions show a wide range of variation, from as small as 5 particles to as large as 0.5 micrometer in diameter. Tight junctions do not form continuous belt-like zonulae indicating that they have lost their significance as a permeability barrier. They are interpreted as mechanical links. In addition to isolated gap junctions and tight junctions there exist gap junctions adjacent to tight junction fibrils suggesting a probable biogenetic relationship of these two structures.

Adenocarcinoma↗
PubMed1980

Intercellular junctions in the uterine epithelium of Salamandra salamandra (L.) (Amphibia, Urodela). A freeze-fracture study.

Intercellular junctions in the uterine epithelium of the ovoviviparous urodele Salamandra salamandra were studied in pregnant and non-pregnant females by freeze-fracture technique. Junctional complexes consist of zonulae occludentes (tight junctions) and numerous maculae adhaerentes (desmosomes); z. adhaerentes and nexuses (gap junctions) could not be identified. Tight junctions are of the "flexible" type exhibiting loosely interconnected fibrils. The fibrillary network appears stretched more often in pregnant females possibly due to the mechanical stress of pregnancy. The structure and occurrence of the junctions identified, especially that of the tight junctions, is discussed with regard to the functions of the uterus during pregnancy.

Animals↗