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At least 307 records · Page 17Linked to original sources
PubMed1992

Different concentrations of thyroid peroxidase and thyroglobulin in the nuclear envelope and the endoplasmic reticulum throughout the cytoplasm.

Thyroid peroxidase (TPO) and thyroglobulin (TG) represent two major glycoproteins of thyroid follicular cells performing biological functions such as iodination, transcytosis of thyroglobulin, and formation of thyroid hormones. They are involved in thyroid autoimmunity and thyroid inborn metabolic disorders. Studying these processes at a molecular level includes the determination of their precise intracellular distribution. An evaluation of the relative concentrations of TG and TPO in different subcellular compartments was carried out in stimulated human follicular cells using thin-frozen sections and the immunogold technique. It is documented that TG is transported from the endoplasmic reticulum and the Golgi apparatus to the follicular lumen by transport vesicles; most of it being present in the expanded endoplasmic reticulum throughout the cytoplasm. On the other hand, gold particles indicating TPO are adjacent to the membranes of the exocytotic pathway. They do not label the basolateral membrane but show the strongest density in the nuclear envelope and the apical membrane. The labeling density of TPO is about four times higher in the nuclear envelope than in the endoplasmic reticulum throughout the cytoplasm. In contrast, TG is concentrated three times higher in the rough endoplasmic reticulum throughout the cytoplasm than in the nuclear cisternae. Our results give the first quantitative evidence that TPO and TG are concentrated in different subcompartments of the endoplasmic reticulum. Because previous studies demonstrated the nuclear envelope as the site where the synthesis of endogenous peroxidase (Brökelmann, J., D. W. Fawcett, Biol. Reprod. 1, 59-71 (1969)) begins, we suggest that synthesis of these functionally related proteins happens in specialized parts of the endoplasmic reticulum.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport↗
PubMed1976

[Isolation of highly active preparations of sarcoplasmic reticulum and Ca2-dependent ATPase from cardiac muscle].

A microsomal preparation with a high ability for Ca2+ uptake has been isolated from pigeon heart. A method of further purification of Ca2+-accumulating system of heart, based on the ability of sarcoplasmic reticulum for the energy-dependent Ca2+ accumulation in the presence of oxalate, has been developed. Upon centrifugation in the gradient of sucrose and KCl concentration the fragments of sarcoplasmic reticulum, rendered "heavy" by calcium oxalate, can be separated from foreign cell membranes. The main component of heart "calcium pump" is Ca2+-dependent ATPase (making up to about 50% of all proteins of the purified reticulum), having a molecular weight of 100.000--105.000. Specific activity of heart Ca2+-ATPase as well as the ability of purified heart sarcoplasmic reticulum for Ca2+ uptake are only slightly less than those of the skeletal muscle reticulum. The data obtained suggest that heart sarcoplasmic reticulum may be efficient for providing heart muscle relaxation.

Adenosine Triphosphatases↗
PubMedDate not supplied

Structure and molecular organisation of the sarcoplasmic reticulum of skeletal muscle fibers.

Activation of muscle contraction is a rapid event that is initiated by depolarization of the plasma membrane and transverse (T) tubules, which following transduction in the interior of the muscle cell, activate the release of calcium from the sarcoplasmic reticulum (SR). Pioneer studies using electron microscopy defined the organization of the sarcoplasmic reticulum and the details of the junctions between sarcoplasmic reticulum and T tubules, which are essential for translating the electrical signal on the plasma membrane to calcium release from the sarcoplasmic reticulum. Molecular biology and biochemistry studies have revealed the presence of several proteins located on the sarcoplasmic reticulum, some of which participate together with the ryanodine receptors to the assembly of a large multi-protein complex, while others, like the calcium pumps, have independent localization and activities. As a whole, the current view of this system contemplates the existence of a high level of structural organization in the sarcoplasmic reticulum with respect to the localization of ryanodine receptors and other proteins. In this review we shall summarize studies on the expression and possible functional significance of the ryanodine receptor type 3 in mammalian skeletal muscles and recent studies aimed to dissect the mechanisms that establish the organization of the SR in striated muscles.

Animals↗
PubMed1975

[Studies on the method of removing foreign bodies from the reticulum with the use of the Eisenhut probe].

So far a number of different opinions have been published in various publications on the possibilities of preventing diseases caused by foreign bodies--by removing them from the reticulum with the use of the magnetic probe. It was decided to test the practical value of the Eisenhut probe. Studies on 58 cows were carried out in the 1967-1973 period. Among the tested animals fere those suffering persistent rumen fistula and others which were being examined after rumenotomy. The animals under observation were divided into 5 groups. The object of the experiment was to test: a) the properties of the probe and possible dangers which might have resulted from its application. b) the usefulness and effectiveness of this rather expensive instrument. On the strength of experiments carried out it was found that the possibilities in moving the end of the probe, when introduced into reticulum, are very limited and, what more, a direct application of that into the reticulum cavity is difficult in "mass-probing", thus largely restricting the efficiency of the given instrument. The "retrieving crown" of the magnetic end has no essential part in the process of removing foreign bodies from the reticulum. Results obtained after having starved the animals for a period of time were even worse. When applying the probe to animals in good health, cases of rupturing the oesophagus and thus aspiring the alimentary content into the respiratory tract were recorded. When using the above-mentioned instrument, it was never possible to recover more than 50% of the foreign bodies introduced previously into the reticulum, which was mainly due to the difficulty in introducing the magnetic end into the reticulum.

Animals↗
PubMed1991

Trafficking of lipids from the endoplasmic reticulum to the Golgi apparatus in a cell-free system from rat liver.

Trafficking and sorting of lipids during transport from the endoplasmic reticulum to the Golgi apparatus was studied using a cell-free system from rat liver. Transitional elements of the endoplasmic reticulum were prepared from liver slices prelabeled with [14C]- or [3H]acetate as the donor fraction. Non-radioactive Golgi apparatus were immobilized on nitrocellulose as the acceptor. When reconstituted, the radiolabeled donor retained a capacity to transfer labeled lipids to the non-radioactive Golgi apparatus acceptor. Transfer exhibited two kinetically different components. One was stimulated by ATP, facilitated by cytosol and inhibited by guanosine 5'-O-(thiotriphosphate) and N-ethylmaleimide. In parallel with protein transport, the ATP-dependent lipid transfer occurred with a temperature transition at about 20 degrees C. The other was not stimulated by ATP, did not require cytosol, was acceptor unspecific, was unaffected by inhibitors and, while temperature dependent, did not exhibit a sharp temperature transition. The ATP-independent transfer was non-vesicular. In contrast, the ATP-dependent transfer was vesicular. Transition vesicles isolated by preparative free-flow electrophoresis, when used as the donor fraction, transferred lipids to Golgi apparatus acceptor with a 5-6-fold greater efficiency than that exhibited by the unfractionated transitional endoplasmic reticulum. Formation of transition vesicles was ATP-dependent. Transferred lipids were chiefly phosphatidylcholine and cholesterol. Membrane triglycerides, major constituents of the transitional endoplasmic reticulum membranes, were both depleted in the transition vesicle-enriched fractions and not transferred to Golgi apparatus suggestive of lipid sorting prior to or during transition vesicle formation. The characteristics of the ATP plus cytosol-dependent transfer were similar to those for protein transfer mediated by transition vesicles. Thus, the 50-70-nm vesicles derived from transitional endoplasmic reticulum appear to function in the trafficking of both newly synthesized proteins and lipids from the endoplasmic reticulum to the Golgi apparatus.

Adenosine Triphosphate↗
PubMed1990

Purification, calcium binding properties, and ultrastructural localization of the 53,000- and 160,000 (sarcalumenin)-dalton glycoproteins of the sarcoplasmic reticulum.

The 53-kDa glycoprotein and sarcalumenin (160-kDa glycoprotein) were extracted from rabbit skeletal muscle sarcoplasmic reticulum with EGTA and purified by fractionation on DEAE-Sephadex A-25 and lentil lectin-Sepharose 4B. Sarcalumenin was shown to bind up to 400 nmol of Ca2+/mg of protein at pH 7.5, which is equivalent to binding of approximately 35 mol of Ca2+/mol of protein. The apparent dissociation constant was 300 microM in the presence of 20 mM KCl and 600 microM in 150 mM KCl. The 53-kDa glycoprotein did not bind any Ca2+ under the conditions examined. Immunoblot analysis of isolated sarcoplasmic reticulum subfractions demonstrated the presence of the two glycoproteins in both the longitudinal sarcoplasmic reticulum and the terminal cisternae. Their concentrations were higher, however, in the longitudinal sarcoplasmic reticulum vesicles. Comparative immunoelectron microscopic studies using monoclonal antibodies revealed a codistribution of the 53-kDa glycoprotein with the Ca2(+)-ATPase in all regions of the free sarcoplasmic reticulum. A similar distribution was found for sarcalumenin, although immunolabeling was much weaker. The colocalization of the 53-kDa glycoprotein and sarcalumenin with the Ca2(+)-ATPase and the Ca2+ binding properties of sarcalumenin suggest that the glycoproteins may be involved in the sequestration of Ca2+ in the nonjunctional regions of the sarcoplasmic reticulum.

Animals↗
PubMed1987

Role of sarcoplasmic reticulum in digitalis-induced electrical and mechanical oscillations in the heart.

The mechanism of cardiac oscillatory activity induced by digitalis was studied in the canine ventricular muscle. We determined the role of sarcoplasmic reticulum in the phenomenon of oscillatory afterpotential and mechanical aftercontractions. Additionally we wished to study the interaction between changes in stimulus interval, which are known to affect sarcoplasmic reticulum function and these oscillatory phenomena. Aftercontraction was induced by ouabagenin but it required previous stimulation of the heart. The production of aftercontraction depended on short stimulus interval and bore no relation with the size of the releasable pool of Ca in the sarcoplasmic reticulum as indicated by the size of the driven contraction. Aftercontraction was often seen without an accompanying action potential. When a depolarization was present during aftercontraction, its temporal relation with the contraction often did not show the usual delay, suggesting that electrical activity may not necessarily initiate contraction. This was supported by the finding that Mn, a Ca channel blocker, blocked normal contractions more than aftercontraction. However, inhibition of Ca release from the sarcoplasmic reticulum by ryanodine or of Ca reuptake by caffeine were effective in blocking aftercontraction and when present, oscillatory afterpotential. Abolition of aftercontraction was not due to slowing of relaxation. These studies confirm the role of sarcoplasmic reticulum in causing aftercontraction and oscillatory afterpotential during ouabagenin toxicity and also suggest that there is a relationship between the 'repriming' ability of the sarcoplasmic reticulum and the oscillatory phenomena.

Animals↗
PubMed1988

Variation of scallop sarcoplasmic reticulum Ca2+-ATPase activity with temperature.

Methods for preparing native scallop sarcoplasmic reticulum vesicles, largely purified membranous scallop sarcoplasmic reticulum Ca2+-ATPase, and nonionic detergent-solubilized sarcoplasmic reticulum Ca2+-ATPase are described. The effect of a range of polyoxyethylene-based detergents on the solubilized Ca2+-ATPase was tested. Decaethylene glycol dodecyl ether (C12E10) supported the highest levels of activity, although C12E8 and C12E9 were more routinely used. Arrhenius plots of Ca2+-ATPase activity, where the assays were carried out with the same pH at all temperatures (7.4), showed a region of nonlinearity at 10 degrees C. A very similar plot was obtained when no compensation was made for pH variation with temperature. Both the break in the Arrhenius plot and the activation energies for the scallop sarcoplasmic reticulum above and below the break were very similar to those found for lobster sarcoplasmic reticulum (Madeira, V. M. C., Antunes-Madeira, M. C., and Carvalho, A. R. (1974) Biochem. Biophys. Res. Commun. 65, 997-1003). The Arrhenius plot of the scallop Ca2+-ATPase in C12E8 no longer showed the nonlinearity at 10-12 degrees C seen with the native sarcoplasmic reticulum, but instead a break now appeared at 20-21 degrees C. This is close to the Arrhenius break temperature of rabbit Ca2+-ATPase in C12E8 and of a perturbation in C12E8 (Dean, W. L. (1982) Biophys. J. 37, 56-57).

Animals↗
PubMed1985

Purification and characterization of phospholamban from canine cardiac sarcoplasmic reticulum.

Phospholamban, the putative protein regulator of the Ca2+ pump of cardiac sarcoplasmic reticulum, was purified to apparent homogeneity from canine cardiac sarcoplasmic reticulum vesicles by selective extraction with sodium cholate, followed by adsorption to calcium oxalate, solubilization in Zwittergent 3-14, and specific elution from p-hydroxymercuribenzoate-agarose. Phospholamban, isolated in the dephosphorylated state, was purified 80-fold in 15% yield (approximately 2 mg of phospholamban/g of sarcoplasmic reticulum protein). Nondissociated phospholamban exhibited an apparent Mr = 25,000 in sodium dodecyl sulfate-polyacrylamide gels. Partially dissociated phospholamban, induced by boiling in sodium dodecyl sulfate, exhibited five distinct mobility forms in sodium dodecyl sulfate-polyacrylamide gels, of apparent molecular weights between 5,000-6,000 and 25,000. Phospholamban was phosphorylated to a level of 190 nmol of Pi/mg of protein by cAMP-dependent protein kinase, consistent by minimum stoichiometry with a subunit molecular weight of approximately 5,000. Phospholamban prepared by the present method was different in several respects from the proteins that have been isolated in other laboratories. Pure phospholamban was cysteine rich, containing 6 residues/100 amino acid residues. Dephosphorylated phospholamban was strongly basic with a pI = 10; phosphorylation decreased the pI to approximately 6.7. Pure phospholamban (and phospholamban present in sarcoplasmic reticulum vesicles) was not readily extracted into acidified chloroform/methanol, suggesting that the protein does not behave as an acidic proteolipid. The purified protein was highly antigenic. Phospholamban was localized by immunochemical methods to cardiac membranes enriched in sarcoplasmic reticulum, but was absent from sarcoplasmic reticulum membranes prepared from fast skeletal muscle. The method described for isolation of cardiac phospholamban is highly reproducible and relatively simple, and should be useful for further detailed studies designed to probe the molecular structure of the protein.

Adenosine Triphosphatases↗
PubMed1988

Isolation of a vesicular intermediate in the cell-free transfer of membrane from transitional elements of the endoplasmic reticulum to Golgi apparatus cisternae of rat liver.

Preparations enriched in part-smooth (lacking ribosomes), part-rough (with ribosomes) transitional elements of the endoplasmic reticulum when incubated with ATP plus a cytosol fraction responded by the formation of blebbing profiles and approximately 60-nm vesicles. The 60-nm vesicles formed resembled closely transition vesicles in situ considered to function in the transfer of membrane materials between the endoplasmic reticulum and the Golgi apparatus. The transition elements following incubation with ATP and cytosol were resolved by preparative free-flow electrophoresis into fractions of differing electronegativity. The main fraction contained the larger vesicles of the transitional membrane elements, while a less electronegative minor shoulder fraction was enriched in the 60-nm vesicles. If the vesicles concentrated by preparative free-flow electrophoresis were from material previously radiolabeled with [3H]leucine and then added to Golgi apparatus immobilized to nitrocellulose, radioactivity was transferred to the Golgi apparatus membranes. The transfer was rapid (T1/2 of about 5 min), efficient (10-30% of the total radioactivity of the transition vesicle preparations was transferred to Golgi apparatus), and independent of added ATP but facilitated by cytosol. Transfer was specific and apparently unidirectional in that Golgi apparatus membranes were ineffective as donor membranes and endoplasmic reticulum vesicles were ineffective as recipient membranes. Using a heterologous system with transition vesicles from rat liver and Golgi apparatus isolated from guinea pig liver, coalescence of the small endoplasmic reticulum-derived vesicles with Golgi apparatus membranes was demonstrated using immunocytochemistry. Employed were polyclonal antibodies directed against the isolated rat transition vesicle preparations. When localized by immunogold procedures at the electron microscope level, regions of rat-derived vesicles were found fused with cisternae of guinea pig Golgi apparatus immobilized to nitrocellulose strips. Membrane transfer was demonstrated from experiments where transition vesicle membrane proteins were radioiodinated by the Bolton-Hunter procedure. Additionally, radiolabeled peptide bands not present initially in endoplasmic reticulum appeared following coalescence of the derived vesicles with Golgi apparatus. These bands, indicative of processing, required that both Golgi apparatus and transition vesicles be present and did not occur in incubated endoplasmic reticulum preparations or on nitrocellulose strips to which no Golgi apparatus were added.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1986

Porcine malignant hyperthermia susceptibility: hypersensitive calcium-release mechanism of skeletal muscle sarcoplasmic reticulum.

This study tested the hypothesis that calcium-release from sarcoplasmic reticulum isolated from malignant hyperthermia swine had abnormal concentration-dependency on release modulators. Halothane stimulated half-maximal calcium-release at similar concentrations for malignant hyperthermia and control sarcoplasmic reticulum (0.10 +/- 0.04 mM). However, concentrations causing half-maximal calcium-release were lower for malignant hyperthermia sarcoplasmic reticulum (P less than 0.001) by an order of magnitude for Ca2+ (28.1 +/- 8.3 versus 1.23 +/- 0.45 nM), adenosine triphosphate (0.33 +/- 0.09 versus 0.023 +/- 0.014 mM) and caffeine (7.79 +/- 1.56 versus 0.80 +/- 0.44 mM). Half-maximal inhibition by Mg2+ occurred at threefold higher concentrations for malignant hyperthermia sarcoplasmic reticulum (0.23 +/- 0.02 versus 0.78 +/- 0.17 mM). The Ca2+-sensitivity curves for calcium-release by sarcoplasmic reticulum isolated from heterozygotes for the malignant hyperthermia-defect were indistinguishable from the averages of the curves for controls and malignant hyperthermia-homozygotes. Results of this study suggest that malignant hyperthermia is initiated due to a hypersensitive calcium-release mechanism which is inherited in an autosomal, codominant pattern and may be diagnosed using calcium-release sensitivity-tests on isolated sarcoplasmic reticulum.

Animals↗
PubMed1985

Metabolism of benzo(a)pyrene by subcellular fractions of rat liver: evidence for similar patterns of cytochrome P-450 in rough and smooth endoplasmic reticulum but not in nuclei and plasma membrane.

Since our earlier work (P. Stasiecki, F. Oesch, G. Bruder, E.D. Jarasch, and W.W. Franke, Eur. J. Cell Biol., 21: 79-92, 1980) had shown that carcinogen-metabolizing monooxygenase activity was present in almost all investigated cellular membranes, the possibility of differential control of the various metabolic pathways in the individual cellular membranes arose. Using high pressure liquid chromatography we have now studied the benzo(a)pyrene metabolites formed by rough and smooth endoplasmic reticulum, nuclei, and plasma membrane as well as mitochondrial fractions and investigated the metabolic cooperation between the monooxygenases and epoxide hydrolase in these fractions. Since various cytochrome P-450 isozymes catalyze the oxidative attack on the benzo(a)pyrene molecule at defined preferential sites, this analysis also provides an indirect trace of potential differences in the pattern of cytochrome P-450 isozymes present in the individual membranes. The metabolic profiles produced by the two most active fractions, smooth and rough endoplasmic reticulum, were very similar to each other but different from those produced by the other three preparations. The metabolite pattern produced by incubations containing nuclear fractions differed slightly from that produced by the fractions of endoplasmic reticulum, but plasma membrane and mitochondria produced markedly different patterns. Since the similarity of the benzo(a)pyrene metabolite pattern produced by the smooth and rough endoplasmic reticulum suggested similar cytochrome P-450 isozyme patterns in these two subfractions, they were further investigated by the use of selective inducers as well as a broad spectrum substrate, 7-ethoxy-coumarin, in the absence and presence of selective inhibitors. Treatment of animals with trans-stilbene oxide or phenobarbital (a) increased the total amount of metabolites per protein mass and time, (b) changed the pattern of metabolites, but (c) induced a pattern of metabolites which was again very similar in rough and smooth endoplasmic reticulum. Even more distinct changes were found following treatment with 3-methylcholanthrene or beta-naphthoflavone. Both of these compounds (a) preferentially induced the activity of rough endoplasmic reticulum, (b) changed the profile of metabolites, but (c) again did not disturb the similarities of the benzo(a)pyrene metabolite pattern between both fractions.(ABSTRACT TRUNCATED AT 400 WORDS)

7-Alkoxycoumarin O-Dealkylase↗
PubMed1982

Active calcium uptake by islet-cell endoplasmic reticulum.

Active calcium uptake was demonstrated in a subcellular fraction of islets which was enriched in endoplasmic reticulum. Calcium uptake was stimulated by ATP in a magnesium-dependent manner. The rate of calcium accumulation was sustained by oxalate (10 mM) and uptake was prevented or reversed by addition of the calcium ionophore A23187. This calcium uptake process was not affected by azide or ruthenium red. Direct comparison of calcium uptake by endoplasmic reticulum-enriched and plasma membrane-enriched fractions indicated that the uptake was not due to contamination of the fraction with plasma membrane vesicles. These factors as well as the purity of the fraction indicate that the calcium uptake system resides in the endoplasmic reticulum. The properties of the islet endoplasmic reticulum calcium uptake system are similar to properties reported for endoplasmic reticulum derived from other cell types. These properties include stimulation by potassium and a Km for ionized calcium of 1.5 +/- 0.3 microM. The islet-cell endoplasmic reticulum may play a critical role in cellular calcium homeostasis and contribute to the regulation of insulin secretion.

Adenosine Triphosphate↗
PubMed1982

Permeability of canine cardiac sarcoplasmic reticulum vesicles to K+, Na+, H+, and Cl-.

Cardiac muscle sarcoplasmic reticulum appears to contain channel-like structures that render the membrane permeable to small univalent ions. Canine heart microsomes fractionated according to buoyant density were examined by Millipore filtration, light scattering, and membrane potential m easurements. Enzymatic analysis and measurement of D-glucose permeation and Na/Ca exchange systems indicated two membrane fractions suitable for the permeability studies, one enriched in surface membranes with a buoyant density of 1.04-1.11 (10-25% sucrose) and one enriched in sarcoplasmic reticulum with a buoyant density of 1.13-1.15 (30-34% sucrose). Surface membrane vesicles impermeable to [3H]sucrose were largely impermeable to K+, Na+, and Cl-, while sarcoplasmic reticulum vesicles impermeable to [3H]sucrose were readily permeable to K+, Na+, H+, and Cl-. Sarcoplasmic reticulum vesicles were essentially impermeable to Ca2+, Mg2+, choline+, gluconate-, 1,4-piperazinediethanesulfonic acid (Pipes-), and D-glucose. These results suggest that cardiac muscle sarcoplasmic reticulum contains structures that facilitate the movement of small univalent ions. A possible function of these putative ion-conducting structures may be to allow rapid ion fluxes to counter electrogenic Ca2+ fluxes across sarcoplasmic reticulum during cardiac muscle contraction and relaxation.

Animals↗
PubMed1980

Proton permeability of sarcoplasmic reticulum vesicles.

The proton permeability of rabbit skeletal muscle sarcoplasmic reticulum vesicles was investigated by means of membrane potential measurements. Diffusion potentials were generated in sarcoplasmic reticulum vesicles, rat liver microsomes, and sarcoplasmic reticulum phospholipid vesicles by transferring vesicles from low to high pH. Potentials were measured using the voltage-sensitive fluorescent dye 3,3'-dipentyl-2,2'-oxacarbocyanine. Diffusion potentials were generated readily in sarcoplasmic reticulum vesicles using H+ gradients. Generation of a similar potential in phospholipid vesicles or liver microsomes required the presence of an uncoupler of oxidative phosphorylation. H+ and K+ gradient competition experiments indicated that both K+,Na+-permeable and -impermeable sarcoplasmic reticulum vesicles were permeable to H+. These studies suggested that a mechanism of H+ transport exists in sarcoplasmic reticulum that is independent of the K,Na channel, and that transient or steady state membrane potentials may be effected by the movement of H+.

Animals↗
PubMed1993

Three-dimensional visualization of the smooth endoplasmic reticulum in Purkinje cell dendrites.

The three-dimensional organization of the smooth endoplasmic reticulum (SER) in Purkinje cell dendrites in the chick cerebellum was investigated to assess the connectivity between its various components. Three-dimensional reconstructions of the SER within portions of Purkinje cell dendrites were performed from serial sections through the cerebellar molecular layer. In addition, semithick and thick sections (0.25-1 micron) of chick cerebellum in which the endomembrane system had been selectively stained were examined with an intermediate high-voltage electron microscope. Three-dimensional information was extracted from thick sections using stereo pairs and tomographic reconstructions from single axis tilt series. In contrast to its discontinuous appearance in thin sections, in both the three-dimensional reconstructions and selectively stained thick sections the endoplasmic reticulum formed a highly interconnected network of tubules and cisterns extending throughout the dendritic shaft and into the spines. Several distinct morphological domains of endoplasmic reticulum were noted, including the hypolemmal cisternae, the endomembranes associated with the dendritic spines, and the tubular and cisternal endoplasmic reticulum in the dendritic shaft. In older chicks (aged 2 weeks), stacks of endoplasmic reticulum were also noted within the dendritic shaft. All elements of the SER within the dendritic shaft and spine appeared to be continuous with one another. The results of this study strongly suggest that the endoplasmic reticulum forms a complicated network that may be part of a single endomembrane system within Purkinje cell dendrite.

Aging↗
PubMedDate not supplied

Radiological method for investigation of the motor activity of the reticulum in sheep.

Radiological method for investigation of the motor activity of the reticulum in sheep. Acta Physiol. Pol., 1977, 28 (1): 85-91. Using a TUR-D 1001 X-ray apparatus, Chirana electronic image intensifier equipped with an Admira 16 film camera the authors studied the motor activity of the reticulum in sheep. The investigations were carried out on 5 young sheep. Barium suspension was used as contrast medium. The successive phases of reticulum contractions were visualized on X-ray films obtained with a seriograph. The authors determined the time of complete reticulum contraction in films obtained at a rate of 16 frames per second. It was found that the mean time of reticulum contractions in sheep is 6 seconds. The high accuracy and usefulness of radiocinematography for studying reticulum contractions in sheep is stressed.

Animals↗
PubMed1995

Changes in endoplasmic reticulum associated with beta-naphthoflavone-inducible cytochrome P450 in murine liver: a quantitative analysis.

Cytochrome P450s are found associated with membranes of endoplasmic reticulum where they catalyse the oxidation and biotransformation of a wide range of substances. It is therefore expected that their induction and catalytic activities would correlate with the ultrastructure of the cell. In this study, we compared the structure of the hepatocytes of C57BL/6 mice at the basal level in the untreated control animal, and followed induction with the beta-naphthoflavone in the experimental animal. Qualitative analysis of liver sections from control, corn oil-treated mice, and the induced, beta-naphthoflavone-treated mice were essentially similar with no obvious differences between the two groups. Direct morphometry was utilized to quantify the amounts of smooth and rough endoplasmic reticulum in the hepatocytes. A computerized Bioquant Image Analysis System was used to determine the areas of endoplasmic reticulum in the hepatocytes. Morphometric analysis showed 1.004-fold increase in the amount of smooth endoplasmic reticulum and 1.018-fold increase in amount of rough endoplasmic reticulum following treatment of C57BL/6 mice with beta-naphthoflavone. These increases were not significantly different from amounts in control hepatocytes (P). In conclusion, induction of cytochrome P450 by beta-naphthoflavone does not appear to elicit increased proliferation of the endoplasmic reticulum.

Animals↗