Signaling pathways between the plasma membrane and endoplasmic reticulum calcium stores

This review discusses multiple ways in which the endoplasmic reticulum participates in and is influenced by signal transduction pathways. The endoplasmic reticulum provides a Ca2+ store that can be mobilized either by calcium-induced calcium release or by the diffusible messenger inositol 1,4,5-trisphosphate. Depletion of endoplasmic reticulum Ca2+ stores provides a signal that activates surface membrane Ca2+ channels, a process known as capacitative calcium entry. Depletion of endoplasmic reticulum stores can also signal long-term cellular responses such as gene expression and programmed cell death or apoptosis. In addition to serving as a source of cellular signals, the endoplasmic reticulum is also functionally and structurally modified by the Ca2+ and protein kinase C pathways. Elevated cytoplasmic Ca2+ causes a rearrangement and fragmentation of endoplasmic reticulum membranes. Protein kinase C activation reduces the storage capacity of the endoplasmic reticulum Ca2+ pool. In some cell types, protein kinase C inhibits capacitative calcium entry. Protein kinase C activation also protects the endoplasmic reticulum from the structural effects of high cytoplasmic Ca2+. The emerging view is one of a complex network of pathways through which the endoplasmic reticulum and the Ca2+ and protein kinase C signaling pathways interact at various levels regulating cellular structure and function.     

Electron probe x-ray microanalysis and cryoultramicrotomy of unstained myocardial sarcoplasmic reticulum,in situ and fragmented

Summary Myocardial sarcoplasmic reticulum of cats in situ and fragmented sarcoplasmic reticulum (FSR) were analysed using X-ray microanalysis, cryoultramicrotomy and scanning transmission electron microscopy. 2 types of FSR vesicles can be distinguished morphologically and by their different elemental composition especially by different Ca loading. The Ca content of the sarcoplasmic reticulum can also be detected in situ.Acknowledgments. We thank Drs A.V. Somlyo and A.P. Somlyo for helpful advice and valuable discussion.This work was supported by the Deutsche Forschungsgemeinschaft.     

Der Einfluss von Halothan und Chloroform auf die Feinstruktur und Proteinsynthese der Rattenleber

Summary Examinations by electron microscopic and autoradiographic techniques of whether chloroform and halothane alter protein synthesis in rat liver, demonstrate, that chloroform causes an early destruction of the granular endoplasmatic reticulum accompanied by a marked decrease of the protein synthesis in the centre of the acini. After anaesthesia with halothane, the granular endoplasmatic reticulum and the protein synthesis proved to remain unaffected.     

Distension of the reticulum decreased food but not water intake by sheep

Summary The intakes of pelleted alfalfa by hungry sheep were depressed in a rectilinear manner in relation to the amount of water (0–800 ml) added to a balloon in the reticulum (p<0.005). Since the consumption of water by thirsty sheep was not altered by these treatments, the reduction in food intake produced by distending the reticulum was a specific response. The intakes of food were not significantly affected by distending the rumen with 800 ml water in a balloon so it is possible that the amount of fill in the reticulum rather than in the rumen may be important in signalling satiery in sheep.Acknowledgments. The technical assistance of Karen Gordon and funding from the National Research Council of Canada and the Ontario Ministry of Agriculture and Food are gratefully acknowledged.     

Über das Vorkommen von Lymphocyten in Reticulumzellen

Summary The incidence of lymphoid cells in the cytoplasm of thymus reticulum cells of white rats will be reported. The localisation of these cells has been clearly demonstrated by the electron-microscope. We regard them as immature lymphocytes apparently formed in the cytoplasm of reticulum cells, certain compounds of phagocytised cellular and nuclear fragments of dead lymphocytes being used in this process.     

Colchicine-induced appearance (proliferation) of smooth sarcoplasmic reticulum in arterial smooth muscle cells

Colchicine treatment resulted in the appearance and proliferation of smooth sarcoplasmic reticulum in some smooth muscle cells of the aortic and pulmonary trunk walls in the rabbit. The significance of cytoplasmic microtubules and/or membrane-bound tubulin for the morphogenesis, functioning and control of smooth endoplasmic reticulum in different kinds of cells is discussed.     

Colchicine-induced appearance (proliferation) of smooth sarcoplasmic reticulum in arterial smooth muscle cells

Summary Colchicine treatment resulted in the appearance and proliferation of smooth sarcoplasmic reticulum in some smooth muscle cells of the aortic and pulmonary trunk walls in the rabbit. The significance of cytoplasmic microtubules and/or membrane-bound tubulin for the morphogenesis, functioning and control of smooth endoplasmic reticulum in different kinds of cells is discussed.     

Morphological differentiation of the growing oocyte of Ctenomys torquatus (Rodentia, Octodontidae)

The ultrastructural changes observed during the growth phase of oocytes of Ctenomys torquatus (Rodentia, Octodontidae) are reported. Interest was particularly centered on the transformation and/or distribution of the components of the endoplasmic reticulum. According to the observations made it is suggested that the endoplasmic reticulum stores some kind of material which may support early stages of development.     

Morphological differentiation of the growing oocyte ofCtenomys torquatus (Rodentia,Octodontidae)

Summary The ultrastructural changes observed during the growth phase of oocytes ofCtenomys torquatus (Rodentia, Octodontidae) are reported. Interest was particularly centered on the transformation and/or distribution of the components of the endoplasmic reticulum. According to the observations made it is suggested that the endoplasmic reticulum stores some kind of material which may support early stages of development.     

Effect of praseodymium on drug metabolism in rat liver smooth and rough endoplasmic reticulum

Summary A small i.v. dose (3 mg/kg) of a light lanthanon, praseodymium, impairs the drug metabolizing capacity of both the smooth and rough fractions of rat liver endoplasmic reticulum. This decrease in the activity of drug metabolizing enzymes and in the amount of cytochromes P-450 and b₅ is more pronounced in the rough endoplasmic reticulum fraction.     

Développement cyclique du réticulum endoplasmique agranulaire dans les glandes thoraciques (glandes ecdysiales) deRhodnius prolixus Stäl (Insecte: Hétéroptère) aux deux derniers stades larvaires

Summary Ultrastructural study of the thoracic glands ofRhodnius prolixus at the 2 last larval instars demonstrates the cyclic differentiation of meshed networks of agranular endoplasmic reticulum. At the time of abdomen apolysis the ecdysial cells are compartmentalized into a peripheral array of agranular reticulum with sparsely mitochondria. The close association of agranular reticulum and mitochondria is interpreted as indicative of functional coupling in relation with steroid like ecdysone synthesis.

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Les auteurs tiennent à remercier le Dr J.-M. Pinet (I.N.A., Paris) pour l'envoi de la souche deRhodnius utilisée dans nos élevages.     

Development of the myocardial contractile system

Recent studies regarding developmental changes in the myocardial contractile system from fetal, newborn, and adult animals are reviewed. From the data obtained so far, we conclude that in the early fetus myocardial contraction is mainly dependent on Ca which enters via the sarcolemma. Ca release from the sarcoplasmic reticulum is minimal. The role of the sarcoplasmic reticulum as a source of contractile Ca increases and the role of Ca influx across the sarcolemma in contractile system decreases with development.     

Extravesicular noradrenaline in developing peripheral adrenergic nerves

Summary Using a fluorescence technique numerous developing noradrenergic nerve terminals were observed in the muscle coat of the rat ductus deferens, between 2 and 6 days postpartum. In the electron microscope similar developing nerve terminals possessed an extensive system of tubular endoplasmic reticulum but did not contain the small dense cored vesicles characteristic of mature noradrenergic nerve terminals. Thus the tubular reticulum is proposed as an alternative storage site for noradrenaline in developing adrenergic nerves.     

Inhibitors of protein translocation across membranes of the secretory pathway: novel antimicrobial and anticancer agents

Proteins routed to the secretory pathway start their journey by being transported across biological membranes, such as the endoplasmic reticulum. The essential nature of this protein translocation process has led to the evolution of several factors that specifically target the translocon and block translocation. In this review, various translocation pathways are discussed together with known inhibitors of translocation. Properties of signal peptide-specific systems are highlighted for the development of new therapeutic and antimicrobial applications, as compounds can target signal peptides from either host cells or pathogens and thereby selectively prevent translocation of those specific proteins. Broad inhibition of translocation is also an interesting target for the development of new anticancer drugs because cancer cells heavily depend on efficient protein translocation into the endoplasmic reticulum to support their fast growth.     

Morphometrische Untersuchungen an der Rattenleber — Parenchymzelle nach Anwendung verschiedener Fixationspuffer

Summary The effect of 2 fixatives, (1) s-Collidin buffered OsO₄, (2) phosphate buffered OsO₄, on the liver cell was studied by morphometric analysis. After fixation with solution 2, large areas of smooth endoplasmic reticulum were covered by electron-opaque deposits of glycogen. No such masking was noticed by using solution 1. Other cell organelles showed no significant differences in their relative volumes. By using fixative solution 2, decrease in glycogen can simulate relative volume increase of the smooth endoplasmic reticulum.

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Wesentliche Teile der vorliegenden Arbeit wurden von Frl. F.Stockmann der Medizinischen Fakultät der Universität Basel als Inaugural-Dissertation vorgelegt.     

Presence of presumptive interdigitating cells in the spleen of the natterjack,Bufo calamita

Summary The periphery of splenic lymphoid follicles, an area rich in reticulum fibers, contains presumptive interdigitating cells characterized by low electron density, scantiness of cytoplasmic organelles, abundant surface foldings and, sometimes, electrondense granules of unknown significance.     

Comparative analysis of phospholamban phosphorylation in crude membranes of vertebrate hearts

Phospholamban, a sarcoplasmic reticulum phosphoprotein, is present in the hearts of mammalian, avian, amphibian, and fish species. Phylogenetic changes are indicated by marked differences among species in cardiac phospholamban content and by the absence of Ca2+/calmodulin-dependent phospholamban phosphorylation at an early developmental stage.     

Ketoconazole,an inhibitor of calcium transport in skeletal muscle sarcoplasmic reticulum

Summary Ketoconazole, an antimycotic agent, inhibits calcium binding and accumulation, and induces calcium release in sarcoplasmic reticulum. The Mg²⁺-ATPase and the (Ca²⁺+Mg²⁺)-ATPase activities are stimulated at low but inhibited at high concentrations of ketoconazole.The author wishes to thank Dr K. S. Cheah for discussion and Mr C. C. Ketteridge for preparing the sarcoplasmic reticulum and carrying out the ATPase assays.     

A reticulum of nerve-like cells from trochophores of Phyllodoce mucosa (Polychaeta)

Summary The positions of and connections between the 12 principal cells of the larval reticulum are described from Golgi-Cox preparations and sections.Supported by the National Research Council of Canada and carried out in part at the Huntsman Marine Laboratory, St. Andrews, N.B.     

The presence of an endogenous peroxidase activity in hairy cell leukemia cells]

Mononuclear cells from hairy cell leukemia have been studied in three cases by ultrastructural immunocytochemistry. Cells have fairly detectable surface immunoglobulins, without monoclonal distribution however. In addition these cells have a peroxidatic activity which is revealed in the perinuclear space and strands of endoplasmic reticulum.