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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 247 (1987), S. 505-513 
    ISSN: 1432-0878
    Keywords: Thyroid gland (porcine, rat) ; Thyroglobulin ; Intracellular transport ; Secretion ; Low temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of cooling to 20° C on the intracellular transport and secretion of thyroglobulin was studied by incubating open thyroid follicles isolated from porcine thyroid tissue. Follicles were labeled with 3H-leucine or 3H-galactose and the secretion of labeled thyroglobulin into the incubation medium was followed by chase incubations under various experimental conditions. The observations indicate that the transport of thyroglobulin is inhibited at three sites of the intracellular pathway by cooling to 20° C, i.e., between the RER cisternae and the Golgi cisternae, between the latter and the exocytic vesicles, and between these vesicles and the extracellular space (corresponding to the follicle lumen). The secretion of 3H-leucine-labeled thyroglobulin decreased linearly between 37° and 20° C; within this temperature range the activation energy for secretion, calculated from Arrhenius plots, was found to be 37 kcal/mol. Below 20° C the secretion was scarcely measurable. It is suggested that the three transport blocks at 20° C result mainly from inhibition of membrane fission and fusion due to phase transition in membrane lipids.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 248 (1987), S. 153-160 
    ISSN: 1432-0878
    Keywords: Thyroid gland ; Thyroglobulin ; Intracellular transport ; Secretion ; Monensin ; Isolated follicles ; Pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of monensin on the secretion of thyroglobulin was studied in open follicles isolated from pig thyroid tissue; in this system, thyroglobulin is secreted into the incubation medium. When monensin was present during a 4-h chase incubation after pulse-labelling with3H-leucine, the secretion of labelled thyroglobulin was reduced by about 85%; in electron-microscopic autoradiographs of rat thyroid lobes labelled and chase-incubated under similar conditions the relative number of grains over follicle lumina was strongly reduced when monensin was present during the chase. These observations are in agreement with the consensus that monensin arrests transport of secretory proteins in the Golgi complex. In other experiments, pulse-labelled follicles were chase-incubated for 1.5 h whereby labelled thyroglobulin was transported from the RER to exocytic vesicles. Monensin present during a subsequent chase of 0.5 h caused only a moderate decrease of labelled thyroglobulin secretion. TSH present during the second chase-stimulated secretion in both control and monensin-exposed follicles. TSH also caused a drastic reduction of exocytic vesicles in rat thyroid lobes, and the number of vesicles remaining in the cells was the same in controls and lobes exposed to the ionophore. The observations are interpreted to show that monensin does not inhibit the basal or TSH-stimulated transport of thyroglobulin from the site of monensin-induced arrest in the Golgi complex to the apical cell surface or the exocytosis of thyroglobulin.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 250 (1987), S. 701-708 
    ISSN: 1432-0878
    Keywords: Thyroid gland ; Thyroglobulin ; Intracellular transport ; Secretion ; Energy deprivation ; Oxidative phosphorylation ; Pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of energy deprivation on the intracellular transport and secretion of thyroglobulin was studied in open follicles isolated from porcine thyroids. Follicles were pulse-labeled with 3H-leucine or 3H-galactose. Labeled thyroglobulin was secreted into the incubation medium where it was isolated by means of immunoprecipitation. Secretion was followed in chase incubations under various experimental conditions using CCCP (carbonyl-cyanide-mchlorophenylhydrazone) or DNP (dinitrophenol), both uncouplers of oxidative phosphorylation, or CN−, which inhibits respiration. CCCP (1 μM) was shown to inhibit exocytosis by about 80%, DNP (0.1–5 mM) by 45–85%, and CN− (0.5–1.1 mM) by 5–55%. By combining CN− with the ionophore monensin, which blocks transport through the Golgi complex but does not essentially interfere with exocytosis, evidence was obtained that CN− also inhibits transport of thyroglobulin from the Golgi cisternae to the exocytic vesicles by 40%. Electron-miroscopic autoradiography of isolated thyroid lobes from the rat also indicated that transport of 3H-leucine label into the follicle lumen is inhibited in the presence of CCCP or CN−. Intracellular ATP content was found to be about 40% of the control level in follicles incubated with CCCP (1 uM) or CN− (0.9 mM). The results show that the transport of thyroglobulin from the Golgi complex to the exocytic vesicles as well as from the exocytic vesicles into the follicle lumen is dependent upon metabolic energy. The transport blocks are probably associated with inhibited membrane fusions and fissions.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0878
    Keywords: Thyroid gland (porcine) ; Thyroglobulin ; 3H-Galactose ; Sialic acid ; Monensin ; Intracellular transport ; Secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The Na+/K+ ionophore monensin is known to arrest the intracellular transport of newly synthesized proteins in the Golgi complex. In the present investigation the effect of monensin on the secretion of 3H-galactose-labeled and 3H-sialic acid-labeled thyroglobulin was studied in open thyroid follicles isolated from porcine thyroid tissue. Follicles were incubated with 3H-galactose at 20° C for 1 h; at this temperature the labeled thyroglobulin remains in the labeling compartment (Ring et al. 1987a). The follicles were then chased at 37° C for 1 h in the absence or presence of 1 μM monensin. Without monensin substantial amounts of labeled thyroglobulin were secreted into the medium, whereas in the presence of the ionophore secretion was inhibited by 80%. Since we have previously shown (Ring et al. 1987 b) that monensin does not inhibit secretion of thyroglobulin present on the distal side of the monensin block we conclude that galactose is incorporated into thyroglobulin on the proximal side of this block. Secretion was also measured in follicles continuously incubated with 3H-galactose for 1 h at 37° C in the absence or presence of monensin. In these experiments secretion of labeled thyroglobulin was inhibited by about 85% in the presence of monensin. Identically designed experiments with 3H-N-acetylmannosamine, a precursor of sialic acid, gave similar results, i.e., almost complete inhibition of secretion of labeled thyroglobulin in the presence of monensin. The agreement between the results of the galactose and sialic acid experiments indicates that sialic acid, like galactose, is incorporated into thyroglobulin on the proximal side of the monensin block. Considering observations made in other cell systems the present results suggest that galactosylation and sialylation of thyroglobulin are completed within the Golgi complex.
    Type of Medium: Electronic Resource
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