FINE STRUCTURE IN FROZEN-ETCHED YEAST CELLS

Occurrence of carotenoids and sporopollenin in Nanochlorum eucaryotum, a novel marine alga with unusual characteristics

Pigment analysis of Nanochlorum eucaryotum on two strains grown under different gaseous conditions was performed. Air-gassed control cultures did not differ qualitatively with respect to the content of chlorophylls a and b, carotenes alpha and beta, lutein, violaxanthin, neoxanthin and cryptoxanthin in comparison with cultures grown under natural gas. The absolute pigment content per cell increased in cultures grown with natural gas. Growth of N. eucaryotum depends on CO2 which is present in concentrations up to 2.0 vol% in natural gas. N. eucaryotum cannot utilize methane and is therefore not methylotrophic. In cultures of N. eucaryotum grown with natural gas and in air-gassed cultures under nitrogen deficient conditions the secondary carotenoids canthaxanthin and astaxanthin could be detected. In air-gassed cultures of strain N. eucaryotum Colona the same secondary carotenoids have been found, while secondary carotenoids were never found in strain N. eucaryotum Mainz. Cell walls of N. eucaryotum always contain sporopollenin as confirmed by isolation, elemental analysis, infrared absorption spectrophotometry, acetolysis-resistance and electron microscopy.

Rapid effects of gonadal steroids upon hypothalamic neuronal membrane ultrastructure

Freeze-fracture methodology was used to study rat hypothalamic arcuate nucleus (AN) neuronal plasma membrane organization following in vitro perfusion of brain slices with 17-beta-estradiol (17 beta E2) or other test compounds. Physiological levels (10(-10) M) of 17 beta E2 caused an increase in neuronal membrane exo-endocytotic pits within 1 min of perfusion. The increased density of pits was dose related, sustained at a constant rate during 10 min of perfusion, reverted to control values after perfusion with estradiol-free medium for 1 h, and was accompanied by an increased uptake of horseradish peroxidase by the arcuate nucleus in brain slices. The 17 beta E2-induced increase in exo-endocytotic pit density was blocked by tamoxifen (10(-8) M). Cholesterol (10(-10) M), 17-alpha-estradiol (10(-6) M) or dihydrotestosterone (10(-6) M) had no effect on exo-endocytotic pit density. Testosterone had about 50% the potency of 17 beta E2 in increasing exo-endocytotic pit density. These results indicate that physiological levels of 17 beta E2 can have rapid effects upon arcuate nucleus neuronal membrane ultrastructure.

Effect of aging on the morphology of epididymal adipose tissue in the rat

Quantitative morphometrical parameters were compared in epididymal adipose tissue of adult (6 months old) and old (24 months old) Wistar rats, using light and electron microscopy of embedded material and freeze-etch replicas, and taking into account the functional unit of adipose tissue: the capillary-adipocyte. Despite an insignificant reduction of the adipocyte number and size in old rats when the whole population was sampled, the confounding factor of size of adipocytes could be excluded from morphometric computations in adult and old rats. Morphometric measures were performed on the whole transit from capillaries to adipocytes. They revealed that the plasma membranes, as seen in freeze etching, and the thicknesses of endothelial and adipocyte cytoplasms, as seen in ultra-thin sections, remained unaltered with aging. By contrast, the basement membranes were changed but differently around capillaries and adipocytes. The capillary-adipocyte distances were shorter and the vascularization density was higher in old rats.

Further morphological (freeze-fracture) evidence for an impulse generating function of Mauthner axon collaterals in the tench (Tinca tinca L.) spinal cord

The freeze-etching technique was applied to the tench spinal cord. Replicas of Mauthner axons revealed that the non-junctional axolemma at the tip of axon collaterals alone exhibits intramembranous E-face particles whose size, distribution and overall density are comparable with those at Ranvier nodes. Since typical Ranvier nodes are lacking along the stem of the heavily myelinated Mauthner giant axon, this finding contributes further evidence to our earlier observations suggesting that the spiny Mauthner axon collaterals represent true nodal equivalents and most likely the long-sought substrate of impulse propagation.

Cholesterol-phospholipid vesicles in human bile: an ultrastructural study

Phospholipid vesicles, a newly described (bile salt independent) mode of cholesterol transport in human bile, were previously characterized by quasi-elastic light scattering and gel filtration. In the present study the ultrastructure of these vesicles was investigated by electron microscopy using freeze-fracture and negative-staining techniques. Vesicles of varying size were found in all 14 hepatic and 3 gallbladder biles examined. The diameter of the vesicles ranged from 25 to 75 nm by electron microscopy after freeze fracture and from 54 to 94 nm by quasi-elastic light scattering. They had a spherical shape and appeared to be unilamellar. The appearance of the vesicles in fresh hepatic and gallbladder biles as well as in chromatographic fractions was similar. Vesicles were dissolved by the addition of exogenous bile salts. Cholesterol is transported in human bile by both vesicles and micelles. The role of the vesicles may be particularly important in preventing cholesterol precipitation in dilute and supersaturated biles.

Orthogonal arrays of particles in the gastric parietal cell of the rat: differences between superficial and basal cells in the gland and after pentagastrin or metiamide treatment

The basolateral plasma membrane of gastric parietal cells is characterized by the presence of orthogonal arrays of particles revealed by the freeze-fracture technique. These arrays were quantitatively assessed in freeze-fracture replicas of the gastric mucosa at two different levels of the gastric gland and after pentagastrin and metiamide treatment. The arrays were small and scarce in parietal cells located in the upper part of the gland, while they were markedly more abundant in parietal cells situated at the base of the gland. In both superficial and basal cells, the concentration of the arrays was significantly decreased after pentagastrin or metiamide treatment. This decrease was not due to an increase in the surface area of the basal plasma membrane. These results indicate that the concentration of the orthogonal arrays is a distinctive feature between superficial and basal parietal cells and that the arrays can be modulated by parietal cell function.

Insulin modulates neuronal plasma membrane development in human fetal spinal cord neurons in culture

The number of intramembrane protein particles (IMP) in the protoplasmic face of the perikaryal plasma membrane was evaluated in neurons from 9 week-old and 12 week-old human fetal spinal cord in culture. An increased number of IMP was observed in membranes from 12 week-old fetal neurons when compared to membranes from 9 week-old fetal neurons. The addition of insulin (100-2500 microU/ml) to the culture media resulted in a significantly increased number of IMP in neuronal membranes. Incubation with glucose (1.5-6 mg/ml) did not modify the number of IMP and glucose did not potentiate the effect of insulin when both glucose (3 mg/ml) and insulin (500 microU/ml) were added to the culture media. The results suggest that insulin may modulate the development of neuronal membranes and that this effect is not mediated by an increased glucose utilization.

Ultrastructural study of Candida albicans yeast after application of a ribonuclease

Electron microscopy was performed on Candida albicans yeast after application of ribonuclease to clear the cytoplasmic background. In conjunction with Thiery's method of highlighting polysaccharide components, this clearing technique, which has not been used since 1959, enabled visualization of the nucleus, the mitochondria, the vacuolar system and another structure which seemed to be the Golgi apparatus. The invaginations of the plasmalemma membrane (or lomasomes) are highly developed and may be partially responsible for transporting material required for development of the cell wall, especially during budding.

Cell-to-cell fusion of lens fiber cells in situ: correlative light, scanning electron microscopic, and freeze-fracture studies

We have discovered cell-to-cell fusion between fiber cells of adult frog lenses in situ. Stereo scanning electron microscopy (SEM) revealed fusion between neighboring fiber cells in radial cell columns (RCCs) and in the same growth ring, respectively. Cell-to-cell fusion of fiber cells in the lens produced fusion zones that in cross-section were larger and of different polygonal shapes than unfused fiber cells. The shape and sizes of fiber cells surrounding fusion zones and the alignment of RCCs were also altered. Serial sectioning through fusion zones confirmed that they were areas of cell-to-cell continuity established by the union of neighboring fiber cells as seen by SEM. Fusion zones represent a previously unrecognized intercellular pathway in the adult frog lens. Although numerous fusion zones were seen throughout the lens cortex and nucleus, cell-to-cell fusion was rarely observed to have occurred between elongating fiber cells. Interestingly, communicating junctions with an unusual ultrastructure that closely resembles the appearance of membranes in the process of fusion demonstrated in other systems were frequently seen in the region of the superficial cortex where fusion zones were most numerous. The fact that such unusual communicating junctions were not found in any other region of the lens leads us to speculate that structural changes in fiber cell communicating junctions may herald the formation of fusion zones and that the initial site of cell-to-cell fusion between fiber cells may be within communicating junctional plaques.

Trans-synaptic modulation of Purkinje cell plasma membrane organization by climbing fiber axonal flow

Destruction of the inferior olivary nucleus in the rat by thermocoagulation results in the degeneration of climbing fibers in the cerebellar cortex. Under these conditions the plasma membrane of Purkinje cells was selectively affected at the level of the spines on large dendrites (LD spines), the postsynaptic targets for climbing fibers. The number of small (less than 10 nm) non-junctional intramembrane particles (IMP) was significantly decreased in E-faces during the first 3 days following the lesion (47% of control IMP values). Later, the number of IMPs progressively recovered to reach 67% of the control IMP values 1 month following the lesion. IMP numbers in the P-face and in the postsynaptic junctional aggregates of the E-face were unaffected by destruction of climbing fibers. Following injection of colchicine into the inferior olivary nucleus, a treatment that inhibits axonal transport in climbing fibers, a selective decrease in IMP numbers on the E-faces of LD spines was also found. The maximal decrease was found during the first 10 days after injection (48% of control values), and then the number of IMPs gradually increased to reach control values by 90 days post-injection. In the case of colchicine treatment also, the reduction in the number of IMPs affected selectively a class of non-junctional small IMPs, less than 10 nm in diameter. These data show that there is a similar selective modification in the membrane structure of Purkinje cells, not only following destruction of climbing fibers by thermocoagulation, but also following inhibition of axonal flow in climbing fibers by colchicine injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential distribution of intermembranous particles in the plasmalemma of the migrating cerebellar granule cells

The size and distribution of intramembraneous particles in 5 different plasmalemma domains of migrating cerebellar granule cells was studied by the freeze-fracture method. The quantitative analysis in 5-20-day-old rats reveals that the membrane of the leading tip of the descending process, the soma and vertical process that are associated with Bergmann glial fibers, have a significantly higher density of small (less than 11 nm diameter) intramembraneous protein particles than the horizontal processes and their growth cones which grow along previously generated parallel fibers. This regional difference in density of membrane associated particles may be related to the selective outgrowth of the two classes of granule cell neurites along glial and neuronal surfaces.

A correlative freeze-etch and electrophysiological study of communicating junctions in crystalline lenses

We have conducted a correlative electrophysiological and morphological study of cell to cell coupling in frog and rat lenses. Electrical impedance measurements from frog and rat lenses were curve fit to a model of lens structure to obtain a value for internal resistivity (Ri). The mean and standard deviation of Ri was 550 +/- 190 ohm-cm (n = 7) in rat lenses and 3400 +/- 340 ohm-cm (n = 10) in frog lenses. These results indicate that the extent of cell to cell coupling is far more extensive in rat lenses than in frog lenses and therefore suggest that rat lens fiber cells are conjoined by greater numbers of communicating junctions than frog lens fiber cells. Freeze-etch replicas were made of fiber cells from rat and frog lenses of comparable size and from a comparable area (intermediate cortex) as that used in the electrophysiological study. A total of 987 and 1,393 square microns of replicated membrane were examined in rat and frog lenses, respectively. 1,573 communicating junctions were counted in rat lens replicas cumulatively measuring 313 square microns or 31.7% of the total membrane area. 604 communicating junctions were counted in frog lens replicas cumulatively measuring 163 square microns or 11.7% of the total membrane area. These results demonstrate that the amount of communicating junction predicted to be necessary to account for the more extensive electrotonic coupling between fiber cells in rat lenses than in frog lenses is qualitatively confirmed by morphological analysis.

Exocytosis in non-plasmolyzed and plasmolyzed tobacco pollen tubes : A freeze-fracture study

Exocytosis occurring during deposition of secondary wall material was studied by freeze-fracturing ultrarapidly frozen non-plasmolyzed and plasmolyzed tobacco pollen tubes. The secondary wall of tobacco pollen tubes shows a random orientation of microfibrils. This was observed directly on fractures through the tube wall and indirectly as imprints of microfibrils on fracture faces of the plasma membrane of non-plasmolyzed tubes. About half of the plasmatic fracture faces from non-plasmolyzed and plasmolyzed pollen tubes carried hexagonal arrays of intramembraneous particles in between randomly distributed particles. Deposition of secondary wall material was often accompanied by an undulated plasma membrane and the presence of membrane-bound vesicles in invaginations of the plasma membrane, between the plasma membrane and secondary wall and-especially in plasmolyzed tubes-within the secondary wall of tube flanks and wall cap. The findings are discussed in connection with published schemes of membrane behaviour during exocytosis.

Sex differences and maturational changes in arcuate nucleus neuronal plasma membrane organization

Intramembrane particles (IMP) are believed to represent protein-containing structures in the membrane. Hypothalamic arcuate nucleus neuronal plasma membranes from male and female rats studied from birth to adulthood were quantitatively assessed for IMP number and size using freeze-fracture techniques. We found that newborn female rats have a significantly greater number of IMP than newborn males. There is also a progressive increase in the number of IMP during the first 20 days of postnatal life in both sexes. The rate of protein particle insertion favors females, maintaining the unequal protein particle content into adulthood with female rats having more IMP than males of the same age. The differences in IMP concentration are mainly due to greater numbers of small (less than 10 nm) particles in neuronal membranes from female rats. These data extend previous reports of sexual dimorphism in the arcuate nucleus to the level of plasma membrane organization.

Postsynaptic membrane domains in the molecular layer of the cerebellum: a correlation between presynaptic inputs and postsynaptic plasma membrane organization

The intramembrane particle (IMP) content of Purkinje, basket, stellate and Golgi cell plasma membrane was quantitatively assessed in freeze-fracture replicas of the cerebellum of normal rats and Weaver mutant mice. This analysis showed that, irrespective of the cell type innervated (i.e. Purkinje, stellate, basket or Golgi cells) postsynaptic membranes for parallel fibers had a relatively low IMP content in their cytoplasmic P-face (approximately equal to 750 IMP/micron2), while postsynaptic membranes for climbing, basket and stellate axons were characterized by a significantly higher IMP content (approximately equal to 1400 IMP/micron2). This difference of IMP content between the targets for parallel fibers and those for climbing, basket and stellate axons was restricted to IMP smaller than 10 nm and appeared progressively during the development of the molecular layer, suggesting a correlation between the formation of synaptic contacts and the segregation of the postsynaptic membrane in these two different domains. In addition, the study of the Weaver mice cerebellum, which is deprived of parallel fibers, but yet shows a normal IMP content in the postsynaptic membrane for the missing fibers, indicated that this characteristic IMP content is established before or during the afferent's reaching its target, and independently of whether the contact ultimately occurs.

The plasma membrane of growing root hairs is composed of zones of local differentiation

Growing root hairs of cress (Lepidium sativum L.) were investigated using freeze-fracture and electron-microscopic techniques. Three zones of differentiation could be detected: the tip zone, the zone of vacuolation and the foot zone. Corresponding to these zones, the plasmatic fracture face of the plasma membrane showed areas of pronounced differentiation with respect to the distribution and frequency of intramembranous particles (IMPs). The tip zone was characterized by an irregular fracture plane caused by a large number of blisters which were more or less free of IMPs. These blisters coincided in size and shape with Golgi vesicles accumulated in the ground cytoplasm near the very tip. Outside these blisters, IMPs were randomly distributed. The surrounding cell wall was very thin and mainly composed of amorphous material. The plasma membrane of the vacuolation zone often revealed areas of hexagonally ordered particles (HOPS). Such patterns of particles were observed in chemically fixed and unfixed root hairs with a maximum surface density of 1200 HOPS per area. Mostly, however, 15-50 HOPS per area were found. The number of such areas increased with increasing distance from the tip up to five areas per μm(2). Additionally, imprints of large cellulose microfibrils could be detected in unfixed material; they were mainly parallel to the root-hair axis and sometimes ended in areas of HOPS. However, HOPS were observed only in approximately 60% of the root hairs. Otherwise, large areas free of IMPs were interspersed between areas of randomly distributed IMPs. The particle frequency was relatively low and varied greatly in the tip as well as in the vacuolation zone, that is, from 1200 to 2000 IMPs μm(-2). Finally, the plasma membrane of the foot zone showed a very constant number of approx. 2000 IMPs μm(-2). These particles were mainly distinct and randomly distributed. In this zone, HOPS were never observed in spite of the fact that the cell wall was composed of numerous parallel-running cellulose microfibrils. Since membrane material is mainly incorporated in the tip zone where IMPs are statistically distributed, the results indicate that the plasma membrane of the outgrowing part of the root-hair cells is characterized by a high lateral mobility of its components. Furthermore, they indicate that specifically arranged particles are involved in the synthesis of cellulose microfibrils. These areas of HOPS seem to be locally restricted and - or limited with respect to their lifetime.

Bacterial anatomy in retrospect and prospect

Progress in bacterial anatomy over a period of about 15 years is reviewed. In particular, attention is paid to developments in which the Department of Electron Microscopy and Molecular Cytology was involved. Past and present problems in bacterial anatomy as well as approaches to their solution are discussed.

A study of dynamic membrane phenomena during the gastric secretory cycle: fusion, retrieval and recycling of membranes

The possibility of recycling, fusion and retrieval of membranes during the gastric secretory process was studied in isolated gastric mucosae of the toad Bufo marinus. Incorporation and efflux of 14C-inulin and horseradish peroxidase (HRP) into the tissue as well as transmission and freeze-fracture electron microscopic studies during the secretory cycle were done. HRP and 14C-inulin were incorporated into the tubulovesicular membrane system during the secreting-resting transition. Upon restimulation, markers were released towards the lumen. Marker efflux preceded onset of H+ secretion. Morphological transformations in the oxyntic cell as evidenced from transmission and freeze-fracture electron microscopy preceded acid secretion coinciding with marker efflux. At this time, images that have been associated with membrane fusion were found in the apical membranes of oxyntic cells. The results are consistent with a model where membrane area increases by a fusion mechanism at the expense of the tubulovesicular system. This transformation precedes the onset of H+ secretion. Upon cessation of the stimulus or inhibition, membranes are retrieved and the tubulovesicular system reformed. Retrieved membranes could be then reutilized in the next secretory cycle.

Lysis of growing cells of Saccharomyces cerevisiae induced by papulacandin B

Light and electron microscopy was used to study the effect of papulacandin B on Saccharomyces cerevisiae in the exponential growth phase. At 1-2 micrograms/mL cell division in the culture continued almost in parallel with the control, at 4 micrograms/mL cell proliferation was reduced and the culture contained some cells with 2-9 buds which were not separated from the mother cell by a septum, and at higher concentrations (8, 16 and 32 micrograms/mL) the proliferation stopped within 2 h. Cessation of proliferation was due to lysis of budding cells in the bud region including perforation of thinned cell wall (most often at the bud basis and sometimes at its apex), extrusion of cytoplasm and death of cell. Lysis was also observed in cells without visible buds. Dividing cells died without visible lysis.

Cell surface modifications in the epithelium of rat ventral prostate during adaptation to in vitro conditions: an ultrastructural study

Sequential changes in epithelial cells of collagenase-dissociated rat ventral prostate were studied by thin-section and freeze-fracture electron microscopy. Epithelial cells did not attach to the substrate for 48 h. Pelleted cells obtained 1, 24, and 48 h after dissociation were assigned to three categories depending on morphology and cellular associations. (a) Solitary epithelial cells degenerated as determined by extensive vacuolization in the cytoplasm and aggregation of intramembranous particles (IMP). (b) Epithelial clusters consisted of a homogeneous population of well-maintained, closely packed cells. Aggregation of IMP was minimal. Tight junctions that formed between cells at the periphery of the clusters appeared normal and provided an effective permeability barrier demonstrated by the exclusion of ruthenium red tracer. (c) Tissue fragments were comprised of varying combinations of epithelial, endothelial, and smooth muscle cells as well as fibroblasts and erythrocytes. Maintenance of tissue fragments was variable. Plasma membranes often displayed aggregated IMP and proliferated tight junctional strands. An effective permeability barrier was absent. After the 48 h "latent period," epithelial cells in the clusters lost interdependence, disassociated from one another, and attached to the substrate. These isolated cells, which did not display aggregated IMP, retained the ability to form an effective permeability barrier upon reaching confluency. During the first 48 h, epithelial cells did not tolerate solitary existence, yet as participants in clusters they were well maintained. After this interval, they no longer required interactions with neighbors in order to survive. These results indicate that under our experimental conditions, an adaptation period is required by prostatic epithelial cells. The enhanced quality of maintenance associated with epithelial clusters suggests that control over the internal microenvironment, provided by a tight junctional barrier, may be important during the initial period of adaptation in vitro.

A freeze-fracture electron microscope study of Trichomonas vaginalis Donné and Tritrichomonas foetus (Riedmüller)

Two strains of Trichomonas vaginalis, JH162A , with low pathogenicity, and Balt 44, with high pathogenicity, as well as one highly pathogenic strain, KV-1, of Tritrichomonas foetus were studied by freeze-fracture electron microscopy. The protoplasmic faces ( PFs ) of the cell membranes of all three strains of both species had similar numbers of intramembranous particles (IMPs); however, the particles in the external faces (EFs) of these membranes were least abundant in Trichomonas vaginalis strain Balt 44 and most numerous in those of strain JH162A of this species. In Tritrichomonas foetus strain KV-1 the number of IMPs in the EF was close to but somewhat lower than that in the mild strain of the human urogenital trichomonad . In both species, the anterior, but not the recurrent, flagella had rosette-like formations, consisting of approximately 9 to 12 IMPs on both the PFs and EFs. The numbers and distribution of the rosettes appeared to vary among different flagella and in different areas of individual flagella of a single organism belonging to either species. The freeze-fracture electron micrographs provided a more complete understanding of the fine structure of undulating membranes of Trichomonadinae , as represented by Trichomonas vaginalis, and of Tritrichomonadinae (the Tritrichomonas augusta -type), as exemplified by Tritrichomonas foetus, than was gained from previous transmission and scanning electron microscope studies. Typically three longitudinal rows of IMPs on the PF of the recurrent flagellum of Trichomonas vaginalis were noted in the area of attachment of this flagellum to the undulating membrane. The functional aspects of the various structures and differences between certain organelles revealed in the two trichomonad species by the freeze-fracture method are discussed.

The effect of alpha-latrotoxin on the neurosecretory PC12 cell line: electron microscopy and cytotoxicity studies

Neurosecretory PC12 cells were exposed in a variety of experimental conditions to nanomolar concentrations of alpha-latrotoxin purified from the venom of the black widow spider. When applied in a modified Ringer medium containing millimolar Ca2+ the toxin rapidly elicited a marked stimulation of exocytosis, as indicated by the appearance of typical images of granule-plasmalemma interaction and by the decreased density (number/unit area) of secretion granules in the cytoplasm. Without Ca2+ in the medium this early toxin effect was delayed and evolved less rapidly, but was still clearly appreciable. These morphological results appear in good quantitative agreement with the biochemical data on dopamine release reported in the preceding article. The stimulation of exocytosis was followed after a short delay by a stimulation of endocytosis, as revealed by an increased accumulation of the extracellular tracer, [14C]sucrose, within the toxin-treated cells. At later times after the application of alpha-latrotoxin other effects appeared, but only in the presence of Ca2+: these included changes in cell shape; focal alterations of the mitochondrial matrix (clear discrete areas and dense precipitates) and frank signs of cytotoxicity (rupture of the plasmalemma, clearing of the cytoplasmatic matrix). The toxin-induced cell death was studied quantitatively by using trypan blue exclusion as well as the 51Cr test, and was found to be dependent on alpha-latrotoxin concentration, temperature of incubation and Ca2+ concentration in the medium. Ionic substitutions concerning anions as well as cations other than Ca2+ had minor or no consequences. Thus, the early effect of alpha-latrotoxin in PC12 cells (stimulation of exocytosis, at least partially Ca2+-independent) can be dissociated from the late 'toxic' effect (strictly Ca2+-dependent).

The band 3-rich membrane of llama erythrocytes: studies on cell shape and the organization of membrane proteins

The erythrocyte membrane of the llama was characterized in comparison to that of the human. The llama erythrocyte was an elliptical disk that resisted shape alterations in hyperosmotic buffers and following metabolic depletion, both of which induce speculation of the human red cell. Lysophosphatidylcholine incorporation produced minor serrations of the edge of the llama disk but no spicules, whereas human red cells became sphero-echinocytes. The polypeptide profiles in the membranes of the two species were similar, except for several noteworthy differences: a marked elevation in the relative content of band 3; the absence of membrane-bound band 6; and simpler glycoprotein pattern in the llama. The concentration of band 3 in llama was about two and a half to three times that in the human and intramembrane particles in the protoplasmic leaflet of freeze-fractured llama membrane were correspondingly increased. The selective solubilization of bands 1, 2 and 5 in low ionic strength buffer, and all of the peripheral proteins in high alkaline buffer were similar except for increased retention of ankyrin by the llama membrane. These data suggest a similar disposition of membrane proteins. The llama membrane was markedly resistant to the solubilization of integral proteins by the nonionic detergent, Triton X-100. This property and the general resistance to shape changes may be related to the high concentration of band 3.

On the linkage of exoplasmatic freeze-fracture particles to phycobilisomes

The thylakoids of the thermophilic cyanobacterium Mastigocladus laminosus were examined by freeze-fracture analysis. The expolasmatic (EF)-freeze-fracture particles are organized in rows, separated by 45 nm or more with a 12-nm center-tocenter spacing of neighboring particles. Phycobilisomes, associated to the outer thylakoid surfaces show a similar spacing pattern. Fractures exposing simultaneously phycobilisomes and EF-freeze-fracture particles on the same thylakoid show a direct alignment of both systems. Consequently the phycobilisomes are concluded to be associated peripherally on top of the EF-freeze-fracture particles in a 1:1 assembly pattern. The periodicity of the EF-freeze-fracture particles determines the arrangement of the phycobilisomes in the rows. The planar phycobilisome model of Mörschel et al. (1977) easily allows a successive arrangement of the phycobilisomes in a row, whereas with the staggered model developed by Bryant et al. (1979), only a cogged arrangement of neighboring phycobilisomes is possible.

Intramitochondrial ATP and cell functions: yeast cells depleted of intramitochondrial ATP lose the ability to grow and multiply

Cells of the yeast Saccharomyces cerevisiae could be depleted of their intramitochondrial ATP bu culturing on glucose in the presence of antimycin A, which prevents production of ATP in mitochondria, along with bongkrekic acid, which prevents transport of ATP from the cytosol into mitochondria. Alternatively, the depletion could be achieved by culturing respiration-deficient mutants in the presence of bongkrekic acid. The depleted cells of the respiration-deficient mutant did not grow on glucose in a synthetic medium and growth for a few generations was made possible by adding peptone, yeast extract or some amino acids into the medium. The depleted cells did not differ from control cells in their content of amino acids, proteins, nucleic acids and major phospholipids and had preserved the ability to carry on protein and nucleic acid syntheses and to mate to other cells. No conspicuous cytological differences were found between the control and depleted cells. After culturing in a semi-synthetic medium in the presence of bongkrekic acid the cells of the respiration-deficient mutant exhibited almost no cytochrome c in their spectra and their azide-sensitive ATPase activity was drastically reduced. The results suggest that intramitochondrial syntheses of some low-molecular compounds as well as import and/or assembly of some cytoplasmically synthesized mitochondrial proteins into mitochondria may be impaired in cells lacking intramitochondrial ATP and this may be responsible for their inability to grow and multiply.

Junctional pattern in the squamous metaplasia of the female trigone. A freeze-fracture study

The junctional pattern of squamous metaplasia in the female trigone was studied by the freeze-fracture technique. Desmosomes were observed in all epithelial layers and varied in complexity from the basal to the superficial layers. Gap junctions were observed in the lower and upper epithelial layers. Tight junctions were detected occasionally in the superficial layer only, which appeared as maculae and did not form zonulae occludens. These data support previous suggestions that the squamous metaplastic epithelium is not waterproof and may interfere with the contraction-expansion mechanism of the bladder.

Freeze-fracture studies on tardigrade cuticle

The cuticles of the heterotardigrade Echiniscus testudo and the eutardigrades Macrobiotus hufelandi and Milnesium tardigradum have been studied using freeze-fracture technique. Most of the layers seen in conventional TEM micrographs can be visualized. There is no clear evidence that the trilaminar components of the cuticle such as the outer epicuticle and the tripartite layer separating epi- and intracuticle or procuticle (whose membranous origin has been suggested by previous authors) fracture like a lipid bilayer. Microfibres not resolved or only poorly resolved by TEM can be recognized in the procuticle of all three species. Obviously their visualization depends upon the fracture angle. In Echiniscus testudo and Milnesium tardigradum the intracuticle or at least parts of it show a wavy arrangement of microfibres. Parts of the ventral intracuticle of E. testudo fracture in an obviously non-random pattern revealing distinct sublayers.

Ultrastructural studies of the nuclear envelope in human sperm

In freeze fracture preparations of normal human spermatozoa, nuclear pores were revealed in hexagonal arrangement over the sperm nucleus. The pores were 85 nm in diameter and were studded with numerous particles. The membrane of normal spermatozoa incubated without ionophore or calcium ions appeared continuous and enclosed the condensed chromatin closely. When the sperm were incubated with ionophore A23187 plus calcium ions to induce the acrosome reaction the nuclear envelope appeared to undergo dramatic topographical and morphological changes. Stretching, expanding, and loosening of the nuclear envelope and breaking down in certain regions was seen in thin sections. The importance of this phenomenon is discussed in relation to similar events occurring when the sperm penetrate the ovum.

Effects of climbing fiber destruction on large dendrite spines of Purkinje cells

The number and freeze-fracture membrane organization of spines on Purkinje cell dendrites were studied in rats after destruction, by intraperitoneal injection of 3-acetyl-pyridine (3-AP), of the climbing fiber afferents to the cerebellum. The results obtained show that: (1) there is a 1.6 fold increase in the total number of dendritic spines in the 3-AP-treated animals as compared to controls, but no change in the total number of spine synaptic profiles; (2) the spines from main dendrites in both control and 3-AP-treated animals have more than 1,000 IMP/micron 2 of P-face membrane; and, (3) the spines formed on Purkinje cell dendrites in the absence of their presynaptic axons have the same P-face membrane organization (i.e. more than 1,000 IMP/micron 2) as spines normally innervated by afferent climbing fibers. These data suggest that each type of Purkinje cell spine has a specific P-face membrane organization which does not appear to be influenced by presynaptic terminals.

Reliable use of resistance evaporation of Pt and C for high resolution freeze-fracturing and a crystal surface image complementary to the E-face of yeast plasma membranes

Freeze-fracture specimens of bakers yeast plasma membranes faces were prepared in both a modified Denton DFE-2-freeze-etch module and a modified Balzers BAF-301 freeze-etch unit. Each unit was equipped with a liquid nitrogen cooled shroud, resistance evaporators with PT-C and C sources 7 cm from the specimens and with a resistance monitor to control PT-C shadow film thickness. Optical diffraction patterns of specimens prepared in these units have fourth, fifth or sixth order spots. Therefore, on the basis of optical diffraction patterns, resolution of yeast plasma membrane specimens prepared in these units is equivalent to or better than that obtained by others with an ultrahigh vacuum system equipped with specially redesigned electron guns. A new image with tube-like particles in hexagonal arrays, each surrounded by six substructure particles, nearly perfect high-resolution complement to the hexagonal array of ring-like depressions and the six surrounding subunit depressions of the E-face, has been revealed on the surfaces of cubic crystals (presumably ice) which formed in the gap between the P- and E-faces within fissures that occurred when the samples were frozen in liquid Freon 22. When the samples were subsequently freeze-fractured at 77 K at a chamber vacuum of 13 microPa in which the specimens were protected from surface contamination by a liquid nitrogen cooled shroud, these crystals remained attached to the P-face but pulled away from the E-face against which they had apparently made molecular contact.

Further freeze-fracture studies on the uterine epithelium of Salamandra salamandra (L.) (Amphibia, Urodela) using the antibiotic filipin

The apical portion of the uterine lining of the ovoviviparous fire salamander, Salamandra salamandra, was studied by the freeze-fracture technique in conjunction with the polyene antibiotic filipin. Filipin-sterol complexes were found in the luminal plasmalemma and in the membranes limiting the mucous secretory granules typical of this epithelium. In all females, but particularly in non-pregnant females, more or less discrete clusters of filipin-sterol complexes were occasionally found overlying heavily affected secretory granules. The findings are discussed with regard to comparable results (Orci et al. 1980) based on the examination of collapsed and stretched urinary bladders of toads.

Membrane differentiation in the Golgi apparatus of mammalian urinary bladder epithelium

The endomembrane system in superficial and intermediate epithelial cells of mammalian urinary bladder was studied by cytochemistry, thin-section and freeze-fracture electron microscopy to determine the sites where special forms of membrane differentiation first appear. Glutaraldehyde-resistant NADH-ferricyanide reductase, distinctive 11-12 nm intramembrane particles (IMP), and asymmetry of membrane leaflets served as markers of membrane maturation. The three markers were specifically associated with the maturing face of Golgi apparatus and were absent from the remainder of the endomembrane system. Activity of this enzyme was associated with the lateral regions of the maturing face, fusiform vesicles, and the plasmalemma. Asymmetric unit membrane (AUM) plaques were not observed in the Golgi apparatus per se but were present in immature fusiform vesicles that had not detached from the maturing face. When freeze-fracture replicas and thin sections were compared, randomly arranged 11-12 nm IMP first appeared in maturing face membranes that were adjacent to clusters of "free" polyribosomes in the Golgi apparatus region. The proximity of these polyribosomes suggests that they may be related to the coincident appearance of the 11-12 nm IMP in the maturing face membrane. Our observations support the hypothesis that membranes undergo differentiation during "flow" through compartments of the endomembrane system. The lateral regions of the maturing face of the Golgi apparatus appear to be a critical location for the morphogenesis of plasma membranes in urinary bladder.

Ultrastructural study of cholestasis induced by longterm treatment with estradiol valerate. I. Tight junctional analysis and tracer experiments

Over a period of 20 weeks estradiol valerate (1.5 mg/kg body weight/week) was administered subcutaneously to male Wistar rats from which the livers were examined at four week intervals employing a freeze-fracture technique and colloidal lanthanum tracer studies. In connection with intrahepatic cholestasis, distinct alterations in the tight junctions were observed, consisting of disorganization, rarification and proliferation. Disruption of the tight junctions was not seen and colloidal lanthanum did not penetrate into the bile canalicular lumen. Holding the view that the term "leakiness" of tight junctions should be defined with reference to the tracer employed, we conclude that in the liver one tight junctional strand is sufficient to prevent the escape of larger bile constituents such as bile acids and that a back diffusion of bile acids over the tight junctional barrier does not play a role in the pathogenesis of the estrogen-induced cholestasis. Interruptions of tight junctions, as described by other authors, are interpreted as a secondary mechanical effect. On the other hand, we consider an increased permeability of the tight junctions to water and small solute molecules as probable; possibly this increased permeability is brought about by alterations in the microfilaments. A model for the pathogenesis of the estrogen-induced intrahepatic cholestasis is proposed.

Gap junctions and impulse propagation in embryonic epithelium of Amphibia. A freeze-etching study

Epithelium of amphibian embryos (Cynops orientalis, Xenopus laevis) was found in preceding experiments to generate and conduct impulses during a limited stage (26-37) of development . In order to elucidate the structural basis of impulse propagation, epithelial cells of four stages were examined by the freeze-etching method: (I) before and (II) during acquisition of conductivity; (III) when propagation was fully established, and (IV) when it was no longer present. Only few gap junctions (GJ) of small size were found in groups I and IV. GJ in epithelia of group III were increased in number and size, and appeared morphologically "coupled", i.e., with more loosely arranged connexons. the size of gap-junctional particles did not differ significantly between coupled and uncoupled stages. Zonulae occludentes seemed "leaky" in stage *, and "tight" in stages II-IV. Thus, the morphological characteristics of specialized junctions between "non excitable cells" correlated with the opening and closing of low resistance intercellular current pathways during embryonic development. Gap junctions in particular seem to form an essential link in the non-neural stimulus-response system, which may facilitate the mobility of the embryo during early phases of aquatic life before the reflex pathways have been established. Coupling and uncoupling of gap junctions may also play an important role in the regulation of cell differentiation and morphogenetic movement. The experimental model used in this study provides a useful tool for further investigations of structural correlates of gap junctional permeability under physiological conditions.

Studies on sarcoplasmic reticulum from slow-twitch muscle

Vesicles were isolated from membranes of the sarcoplasmic reticulum (SR) of rabbit slow-twitch muscle by differential and sucrose density gradient centrifugation after homogenization. In some experiments, the vesicles were further fractionated by loading them with calcium oxalate followed by centrifugation in a sucrose density gradient. Protein composition of the isolated vesicles was complex and differed from the protein composition of fast-twitch muscle vesicles. However, other protein components, which were also present in fast-twitch muscle SR vesicles, have been identified: Ca2 + -dependent ATPase, calsequestrin, 160 000 molecular weight glycoprotein and 53 000 molecular weight glycoprotein. The amount of the Ca2 + -dependent ATPase and calsequestrin was several times lower in the slow-twitch muscle SR vesicles. This has been observed in both the original and the loaded vesicles. The slow-twitch muscle SR vesicles showed active calcium transport, Ca2 + -dependent ATPase activity, and the formation of the phosphorylated intermediate under conditions similar to those established for fast-twitch muscle SR. However, these activities, when expressed per mg of total protein, were several times lower than the analogous activities in the SR vesicles isolated from fast-twitch skeletal muscle. When the same enzyme activities were expressed per mg of the 105 000 molecular weight ATPase, the values obtained were very similar in both kinds of vesicles. The results indicate that the slow rate of calcium transport, found in slow-twitch muscle SR vesicles, may be related to a low content of the calcium-transporting ATPase in the membrane.