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At least 667 records · Page 37Linked to original sources
PubMed1990

Intramembrane particles and responses of sensory axon terminals during reinnervation of the frog muscle spindle.

Changes in the density of intramembrane particles (IMPs) of sensory nerve terminals in the bullfrog muscle spindle were correlated with recovery in the response of the spindle to stretch during postcrush reinnervation. A few IMPs on the protoplasmic (P) face in summer experiments (June to October) reappeared by the 3rd week after the nerve crush, then rapidly increased to 110% and 120% of control values 2 and 2.5 months after the crush. Afferent responses to stretch could be recorded after the mean IMP density on the P-face in terminal branches had recovered to more than 25% of the control value. The discharge rate showed a plateau pattern during the period of the excessive IMPs. This was supplanted by a normal pattern after a myelinated branch of the sensory axon was cut. The IMPs in winter experiments (November to April) reappeared by day 90 after nerve crush, and then slowly increased. The sustained responses to stretch reappeared after 5 months, when the mean IMP density on the P-face was restored to 25% or more of the control. Neither excessive density of the IMPs nor plateau pattern of the discharge rate were observed in winter experiments. The relation between the regenerated IMP densities and the functional recovery is discussed.

Action Potentials↗
PubMed1991

Distribution of glial fibrillary acidic protein and vimentin immunoreactivity during rat visual cortex development.

The postnatal maturation of astrocytes in the rat visual cortex was analysed by immunostaining the astroglial proteins vimentin and glial fibrillary acidic protein with poly- and monoclonal antibodies. Vimentin immunoreactivity was present in the visual cortex up to the third postnatal week, whereas immunolabelling first disappeared in the cortical layers and then in the white matter. In the early postnatal period, vimentin antibodies labelled radial glial fibres. After the first postnatal week staining of radial glial fibres gradually disappeared and vimentin immunoreactivity was localized in a few protoplasmic astrocytes in the grey matter and fibrous astrocytes in the white matter. The development of glial fibrillary acidic protein-positive astrocytes was not fully complete until postnatal day 50. Glial fibrillary acidic protein-positive radial glial fibres were present after birth and disappeared towards the end of the third postnatal week. Staining of astrocytes in the white matter and in cortical layers I and VI reached an adult density at postnatal days 8 and 20, respectively. A progressively later development of glial fibrillary acidic protein-positive astrocytes was observed in cortical layers II-V which was completed between postnatal days 47 and 50. In the adult rat visual cortex glial fibrillary acidic protein-positive astrocytes were especially dense in layers I and VI, moderate in layers II/III and V and nearly absent in layer IV and lower layer III. The time course of the loss of vimentin and the gradual appearance of glial fibrillary acidic protein immunoreactivity in the visual cortex is considered as an index of astrocytic maturation and the spatiotemporal sequence of this maturation pattern is discussed in terms of reciprocal neuron-astrocyte interactions during brain development.

Animals↗
PubMed1991

Antibodies to Mycobacterium paratuberculosis in patients with Crohn's disease.

IgG antibodies against Mycobacterium paratuberculosis protoplasmic antigen were looked for by an enzyme immunosorbent assay in patients with Crohn's disease, Ulcerative colitis, active pulmonary tuberculosis, past pulmonary tuberculosis, and in healthy controls. Serum reactivity for these antibodies was not correlated to PPD skin test positivity without history of mycobacterial disease. A cutoff based on the mean absorbance value of a pool of healthy blood donors was chosen. Positive values were found in 12/24 (50%) patients with active pulmonary tuberculosis and 2/10 (20%) skin-test-positive subjects with past pulmonary tuberculosis as expected, because antigenic sharing is common among different mycobacteria. The control group of blood donors showed borderline positivities in 3/149 cases (2.01%). Positive values were found in 4/108 (3.70%) patients with Crohn's disease and 2/40 (5%) with ulcerative colitis. We conclude that our data do not support a causal relationship between the M. paratuberculosis and Crohn's disease, but occasional patients with inflammatory bowel diseases show unexpected positivities for these mycobacterial antibodies.

Adolescent↗
PubMed2001

Freeze-substitution of dehydrated plant tissues: artefacts of aqueous fixation revisited.

This investigation assessed the extent of rehydration of dehydrated plant tissues during aqueous fixation in comparison with the fine structure revealed by freeze-substitution. Radicles from desiccation-tolerant pea (Pisum sativum L.), desiccation-sensitive jackfruit seeds (Artocarpus heterophyllus Lamk.), and leaves of the resurrection plant Eragrostis nindensis Ficalho & Hiern. were selected for their developmentally diverse characteristics. Following freeze-substitution, electron microscopy of dehydrated cells revealed variable wall infolding. Plasmalemmas had a trilaminar appearance and were continuous and closely appressed to cell walls, while the cytoplasm was compacted but ordered. Following aqueous fixation, separation of the plasmalemma and the cell wall, membrane vesiculation and distortion of cellular substructure were evident in all material studied. The sectional area enclosed by the cell wall in cortical cells of dehydrated pea and jackfruit radicles and mesophyll of E. nindensis increased after aqueous fixation by 55, 20, and 30%, respectively. Separation of the plasmalemma and the cell wall was attributed to the characteristics of aqueous fixatives, which limited the expansion of the plasmalemma and cellular contents but not that of the cell wall. It is proposed that severed plasmodesmatal connections, plasmalemma discontinuities, and membrane vesiculation that frequently accompany separation of walls and protoplasm are artefacts of aqueous fixation and should not be interpreted as evidence of desiccation damage or membrane recycling. Evidence suggests that, unlike aqueous fixation, freeze-substitution facilitates reliable preservation of tissues in the dehydrated state and is therefore essential for ultrastructural studies of desiccation.

Artifacts↗
PubMed1990

Gravity-dependent polarity of cytoplasmic streaming in Nitellopsis.

The internodal cells of the characean alga Nitellopsis obtusa were chosen to investigate the effect of gravity on cytoplasmic streaming. Horizontal cells exhibit streaming with equal velocities in both directions, whereas in vertically oriented cells, the downward-streaming cytoplasm flows ca. 10% faster than the upward-streaming cytoplasm. These results are independent of the orientation of the morphological top and bottom of the cell. We define the ratio of the velocity of the downward- to the upward-streaming cytoplasm as the polar ratio (PR). The normal polarity of a cell can be reversed (PR < 1) by treatment with neutral red (NR). The NR effect may be the result of membrane hyperpolarization, caused by the opening of K+ channels. The K+ channel blocker TEA Cl- inhibits the NR effect. External Ca2+ is required for normal graviresponsiveness. The [Ca2+] of the medium determines the polarity of cytoplasmic streaming. Less than 1 micromole Ca2+ resulted in a PR < 1 while greater than 1 micromole Ca2+ resulted in the normal gravity response. The voltage-dependent Ca(2+)-channel blocker, nifedipine, inhibited the gravity response in a reversible manner, while treatment with LaCl3 resulted in a PR < 1, indicating the presence of two types of Ca2+ channels. A new model for graviperception is presented in which the whole cell acts as the gravity sensor, and the plasma membrane acts as the gravireceptor. This is supported by ligation and UV irradiation experiments which indicate that the membranes at both ends of the cell are required for graviperception. The density of the external medium also affects the PR of Nitellopsis. Calculations are presented that indicate that the weight of the protoplasm may provide enough potential energy to open ion channels.

Calcium↗
PubMed1982

Structural features of the rat small intestinal microvillus membrane in acute experimental diabetes.

Experimentally induced diabetes enhances the specific activity of several microvillus membrane proteins in the rat small intestine. The increase in the specific activity of sucrase-isomaltase has been shown by others to be due to an increase in enzyme protein, raising the possibility that diabetes induces a generalized increase in microvillus membrane proteins. Since intramembrane particles (IMPs) seen on freeze-fracture replicas of microvillus membranes are thought to represent integral membrane proteins, we compared microvillus IMP densities in diabetic rats with those in control rats. In addition, mucosal sucrase, maltase, and alkaline phosphatase specific activities were measured in all animals. Diabetic rats had significantly increased sucrase and maltase but not alkaline phosphatase specific activities compared with control rats. The density of microvillus IMPs on both the protoplasmic and extracellular fracture faces of undifferentiated crypt cells and villus absorptive cells was not increased in experimental diabetes. These data indicate that diabetes does not result in a generalized increase in microvillus membrane proteins. Thus the enhanced activity of microvillus membrane proteins in diabetes appears to be highly selective.

Acute Disease↗
PubMed1986

Astrocytes increase in glial fibrillary acidic protein during retrograde changes of facial motor neurons.

Concomitant with the proliferation of satellite microglial cells occurring in the process of motor neuron regeneration, an astrocytic hypertrophy is also seen. A remarkable increase of glial fibrillary acidic protein (GFAP) immunoreactivity is demonstrated in astrocytes of the facial nucleus within a few days following nerve transection. The increase of GFAP antigenicity is associated with an increased appearance of glial filaments and astrocytic processes. We suggest that resident protoplasmic astrocytes become involved in retrograde changes in facial motor neurons and transform into reactive astrocytes. They are of the fibrous type and highly positive for GFAP.

Animals↗
PubMed1986

Brain-specific hyaluronate-binding protein. A product of white matter astrocytes?

The distribution of glial fibrillary acidic (GFA) protein and hyaluronectin, a hyaluronate-binding protein isolated from human brain, was compared in brain, spinal cord and optic nerves of pigs and dogs by indirect immunofluorescence with monoclonal antibodies. In spinal cord white matter the localization of the two proteins was similar, both antigens forming a mesh surrounding myelinated axons. A similar distribution of the two proteins was also observed in the periventricular glia as well as in the glia limitans of spinal cord and optic nerves. Cerebral white matter was hyaluronectin-positive, but the GFA-positive stellate astrocytes did not stain with hyaluronectin antibodies in this location. Hyaluronectin antibodies did not stain grey matter, the granular layer of the cerebellum excepted. The astrocytes identified with GFA antibodies in hyaluronectin-negative grey matter were: the fibrous astrocytes forming the glia limitans on the surface of the cerebral hemispheres; the protoplasmic astrocytes of cerebral isocortex and basal ganglia; the fibrous astrocytes of cerebral allocortex (hippocampus); Bergmann radial glia in the molecular layer of the cerebellar cortex; and fibrous astrocytes of spinal cord anterior and posterior horns. It is concluded that the hyaluronectin fraction reacting with the monoclonal antibodies is a brain-specific protein probably produced by white matter astrocytes. We propose to call this fraction brain-specific hyaluronectin, to be distinguished from other fractions reacting with polyclonal antibodies and with different localizations.

Animals↗
PubMed1988

The use of fluorochromes in the cytochemical characterization of some phytoflagellates.

Sixteen fluorochromes were tested for the cytochemical characterization of two dinoflagellates (Amphidinuim carterae, Prorocentrum micans) and one chlorophycean flagellate (Dunaliella tertiolecta). Depending on the fluorochrome used, various cellular components (including the plasma membrane, thecal plates, pusule, trichocysts, nucleus, lipid bodies and vacuoles) were revealed. The different colours obtained from single or double fluorochrome staining enabled the differentiation and identification of most cellular components. Protoplasmic staining with Fluorescein diacetate suggested the occurrence of esterases in the three phytoflagellates. Rhodamine B, Neutral Red, FluoroBora P and Nile Blue revealed extensive occurrence of lipoid bodies in A. carterae, but Nile Blue showed considerable difference from the other stains in the inclusion size and intracellular location of these bodies. Chlortetracycline binding, and its inhibition by the Ca2+ionophore A23187, indicated that the plasma membrane, pusule system and trichocysts contain sites of Ca2+ binding. Calcofluor White ST proved superior to Congo Red and Lucifer Yellow in elucidating structural details of the thecal plates of P. micans. While Acridine Orange revealed the presence of surface-coat acidic polysaccharides, the fluoresceinated lectins established their glycoconjugate nature in all the three flagellates. Possible mechanisms of fluorochrome uptake are discussed.

Animals↗
PubMed1987

Intramembrane particles and terminal responses following denervation of frog muscle spindles.

The sizes and population density of intramembrane particles in the non-myelinated sensory nerve terminals of frog muscle spindles were studied in comparison with changes in the responses to spindles to stretch 1-28 days after denervation. The sciatic nerve in the right leg was cut at the dorsal part of the hip joint. Spindle receptors in the left leg were used as controls. Muscle spindles were isolated from semitendinosus and iliofibularis muscles. The mean density of particles, which occurred mainly on the protoplasmic (P) face, declined rapidly to 60% of the control values 2 days after denervation, 30% after 4 days and to less than 10% after 7 days. The mean diameter of particles changed from 8.0 +/- 1.5 nm in the control to 12.8 +/- 2.5 nm 7 days after denervation. No significant difference between the results for the trunks (greater than 2 micron in diameter) and the branches (less than 0.5 micron) of the non-myelinated axons was observed. The peak rate of afferent discharges during a ramp-and-hold stretch survived up to 4 days after denervation, whereas the static component disappeared after 3 days. It is suggested that the decline to less than 20% of the control density of particles removes the mechanosensitivity of the sensory endings.

Animals↗
PubMed1976

Antioxidant and antitranspirant protection of apple foliage against ozone injury.

Visible injury to apple foliage from exposure to ozone includes brown stippling on lower leaf surfaces and a light yellow mosaic on upper surfaces. Histologically, chlorophyll is destroyed and palisade and spongy mesophyll cells collapse following disintegration of their protoplasm. Foliar spray applications of the antioxidant, diphenylamine (DPA) or the antitranspirant, Wilt Pruf offer protection against this visible and histological injury. Superior protection results from application of both agents in combination.

Aniline Compounds↗
PubMed1975

The effect of "ouabain" on the ultrastructure of cerebral arterioles and surrounding tissue, studied by a cannulation of a cerebral artery.

A technique for cannulation of a parietal branch of the middle cerebral artery is described by which high but local concentrations of substances can be achieved in cortical vessels. Using this technique it was shown that ouabain, a specific inhibitor of the Na+-K+-ATPase enzyme system, can produce alterations in the blood brain barrier (BBB) permeability as seen by the passage of Evans Blue into cortical tissue. Electron microscopy revealed changes in the endothelium of cerebral arterioles ranging from an increase in the number of vesicles and vacuoles to complete breakdown of cytoplasm and membranes. Swelling of the peri-arteriolar end feet of protoplasmic astroglia and of dendrites was characteristic of tissue surrounding affected arterioles. Swollen fibrous astrocytes, oligodendrocytes and microglia were not seen even in areas of vasogenic edema. These results are discussed in terms of current ideas of the BBB and astroglial function.

Animals↗
PubMed1990

D2O-induced cell excitation.

The effects of deuterium oxide (D2O) on giant internodal cells of the fresh water alga Chara gymnophylla, were investigated. D2O causes membrane excitation followed by potassium leakage. The primary effect consists of an almost instantaneous membrane depolarization resembling an action potential with incomplete repolarization. A hypothesis was proposed which deals with an "osmotic stress" effect of D2O on membrane ion channels followed by the suppression of the electrogenic pump activity. The initial changes (potential spike and rapid K+ efflux) may represent the previously undetected link between the D2O-induced temporary arrest of protoplasmic streaming and the early events triggered at the plasma membrane level as the primary site of D2O action.

Cell Membrane↗
PubMed1983

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.

Animals↗
PubMed1989

Shape determinants of McLeod acanthocytes.

We have sought to elucidate the spiculated shape of McLeod erythrocytes. Red cells from a normal donor and from a McLeod patient were incubated in phosphate-buffered saline containing 0, 0.05, or 0.1 mM chlorpromazine at 0 degrees C for 5 min, then glutaraldehyde-fixed, and examined by scanning electron microscopy. The normal red cells were biconcave disks in which chlorpromazine induced inward (negative) curvature: deep cupping (stomatocytosis) and multiple invaginations. The McLeod cells were mostly spiculated. Chlorpromazine at lower concentration converted them into biconcave disks and, at higher concentration, into stomatocytes. These results support the hypothesis that the spiculation of McLeod cells is the result of an imbalance of surface area between the two lipid leaflets of the membrane; that is, a bilayer couple effect. We determined the numerical density of intramembrane particles (IMP) in replicas of both fracture faces of red cells subjected to freeze fracture and rotary shadowing. These values were as follows (expressed per microns 2 of membrane +/- SD): the normal protoplasmic fracture face had 2200 +/- 306 and the McLeod had 2300 +/- 250. The normal exoplasmic fracture face had 388 +/- 75 and the McLeod had 330 +/- 59. We conclude that there is no evidence for derangement of band 3, the principal protein in the IMP, in McLeod erythrocytes.

Acanthocytes↗
PubMed1989

Unusual in vitro formation of cyst-like structures associated with human intestinal spirochaetosis.

Spirochaetes were isolated from rectal biopsies of three patients and successfully cultured. Enzymatic reactions and electron microscopy revealed spirochaetes resembling Brachyspira aalborgi. Examination of ultrathin sections of centrifugates of cultured spirochaetes yielded unusual cyst-like structures with an outer double membrane containing spirochaetes in different developmental stages. The protoplasmic cylinders seemed to originate from a large electron-dense focus in the cyst-like structures. The axial fibrils occurred as loosely distributed solitary structures in the cyst-like structures. Cysts were not found in the biopsy tissue. The encystment of the spirochaetes could be related to their protection, multiplication, spread and transmission.

Colitis↗
PubMed1978

Volume changes and potential artifacts of epithelial cells of frog skin following impalement with microelectrodes filled with 3 m KCl.

Cells of isolated frog skin epithelium were observed microscopically during impalement with standard microelectrodes of 5 to 20 Momega resistance, filled with 3 m KCl. Impaled cells, as well as some neighboring cells, were seen to swell 10 to 100 sec after impalement, while the negative potential recorded by the microelectrode depolarized (open circuit conditions). Apparently, osmotic swelling of small epithelial cells may be caused by diffusion of KCl from such electrodes. This conclusion is supported by calculations quoted from the literature of KCl loss from microelectrodes. Intracellular recordings from epithelia with destructed cellular membranes gave negative "pre-tip potentials" of up to mV. The potentials could be altered by electrode movement, by decreasing the ambient pH or the tip-pH and by modifying the fixed charges of the tissue chemically. It is shown that even a moderate loss of KCl, which will not result in appreciable swelling, can produce negative potentials in front of the electrode tip if the protoplasm has a high density of negative fixed charges. We suggest the use of 3 m KCl electrodes with resistances above 30 Momega if after impalement compression of intracellular material by the tip can be avoided. Where such compression cannot be avoided, it is best to fill the microelectrode with an isotonic solution which mimics the electrolyte composition of the cytosol.

Animals↗