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  • 1
    Electronic Resource
    Electronic Resource
    Progressive depletion of complexin II in a transgenic mouse model of Huntington's disease (2001)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 76 (2001), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by motor, emotional and cognitive dysfunction. There is no treatment or cure for this disease, and after the onset of symptoms, usually in the fourth decade of life, there is an inexorable decline to death. In many patients there is a complex deterioration of function before the onset of neuronal loss and, at least in mouse models, abnormalities in neurotransmission represent early events in the development of the disease. Here we describe the specific and progressive loss of complexin II from the brains of mice carrying the HD mutation (R6/2 line), and the later appearance of this protein in a subpopulation of neuronal intranuclear inclusions. Although the precise role of complexin II is still unclear, it is known to bind to the SNARE complex, and is therefore likely to be involved in the control of exocytosis. Our results suggest that changes in neurotransmitter release might contribute to the neuronal dysfunction seen in these mice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2001.00059.x
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  • 2
    Electronic Resource
    Electronic Resource
    Involvement of Receptor Cycling and Receptor Reserve in Resensitization of Muscarinic Responses in SH-SY5Y Human Neuroblastoma Cells (1998)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 70 (1998), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Preexposure of SH-SY5Y cells to the muscarinic agonist carbachol caused a rapid desensitization of subsequent carbachol-stimulated intracellular Ca2+ responses and a slower decrease in the number of receptors at the plasma membrane. Desensitization (to 30% of the control response) was maximal after 1 min of exposure to agonist, whereas the number of cell surface receptors reached a minimum (33% of control) only after 5 min. Following agonist washout, the recovery of response was complete within 12 min, whereas the recovery of surface receptor number reached a plateau at 65% of control after 30 min. Treatment with inhibitors of endocytosis (concanavalin A) or recycling (nigericin) did not affect rapid desensitization but did decrease resensitization, suggesting that receptor cycling is involved in resensitization. Experiments with the irreversible antagonist propylbenzilylcholine mustard demonstrated that the receptor reserve for the Ca2+ response to 1 mM carbachol is ∼50%. Removal of this receptor reserve led to a decrease in the rate of resensitization. We propose that the existence of a receptor reserve might explain the poor correlation between functional response and surface receptor number, and that one of its roles might be to permit rapid resensitization after a significant agonist-induced decrease in surface receptor number. The purpose of receptor cycling might be to allow dephosphorylation (and reactivation) of receptors that have become phosphorylated (and inactivated) in response to agonist stimulation, because the protein phosphatase inhibitor calyculin A significantly reduced resensitization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1998.70041694.x
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of G Protein-Coupled Receptor Kinase 2 on the Sensitivity of M4 Muscarinic Acetylcholine Receptors to Agonist-Induced Internalization and Desensitization in NG108-15 Cells (1999)
    Oxford UK : Blackwell Science Ltd
    Journal of neurochemistry 73 (1999), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract : NG108-15 cells express predominantly the M4 subtype of the muscarinic receptor for acetylcholine. Stimulation of these receptors by the agonist carbachol causes an inhibition of cellular adenylyl cyclase and a consequent fall in the intracellular cyclic AMP concentration. Pretreatment of the cells with carbachol caused both internalization and desensitization of the M4 receptor. Overexpression of G protein-coupled receptor kinase (GRK) 2 caused an increase in the rate constant for receptor endocytosis (from 0.06 to 0.18 min-1) and a decrease in the EC50 for carbachol stimulation of internalization (from 15 to 3 μM). Overexpression of a dominant negative form of GRK2 had more modest effects, reducing the rate constant for endocytosis (from 0.11 to 0.07 min-1) and increasing the EC50 for carbachol stimulation of internalization (from 8 to 17 μM). Neither GRK2 nor dominant negative GRK2 overexpression had any effect on the rate constant for receptor recycling following agonist removal. The time course and extent of receptor desensitization in control cells were identical to the corresponding values for receptor internalization, and the rate and extent of desensitization were again increased by GRK2 overexpression. Exposure of the cells to hyperosmolar sucrose (0.6 M) almost completely blocked agonist-induced receptor internalization in both control and GRK2-overexpressing cells. Sucrose treatment also blocked agonist-induced desensitization. We conclude that the internalization and desensitization of the M4 muscarinic receptor in NG108-15 cells can be modulated in response to changes in GRK2 activity and also that internalization plays a key role in desensitization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1999.0731236.x
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetics of amiloride action in the hen coprodaeum in vitro (1982)
    Springer
    Pflügers Archiv 392 (1982), S. 340-346 
    Details
    ISSN: 1432-2013
    Keywords: Amiloride ; Benzamil ; Hen coprodaeum ; Sodium transport ; Short circuit current ; Dependence on Na concentration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The kinetics of amiloride action on the isolated epithelium of the hen coprodaeum are reported. Tissues were taken from birds fed on low salt diets for 9–10 days, conditions which induce a high resting short circuit current due to sodium and sensitive to amiloride. The relation between the inhibition of amiloride sensitive short circuit current and blocker concentration obeyed simple mass laws with an apparent stoichiometry of 1:1 between amiloride and the sodium entry sites. The concentration of amiloride producing its half maximal effect (K i) was 1.77±0.20 μM at a sodium concentration of 130 mM. There was a shallow dependence ofK i on sodium concentration, the value ofK i falling to 0.78±0.1 μM at 1.3 mM Na. The relation ofK i to Na concentration was linear indicating competitive antagonism. The sodium concentration which half saturates the amiloride site (K Na) was 80 mM. This value is very different from the concentration of sodium which half saturates SCC (K SCC=5–7 mM) suggesting there are at least two sites at which sodium can modify the transporting characteristics. These data are compared to those for other epithelia whereK SCC andK Na are rather similar. The benzyl derivative of amiloride (benzamil) was found to be 11.6 times more potent than amiloride on this tissue. The potency ratio is similar to that for other sodium transporting epithelia suggesting that the structure of the ion translocation mechanism is partly conserved between species although theK i for amiloride may vary by an order of magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581629
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  • 5
    Electronic Resource
    Electronic Resource
    Identification of potential components of the transport mechanism for Na+ in the hen colon and coprodaeum (1982)
    Springer
    Pflügers Archiv 392 (1982), S. 347-351 
    Details
    ISSN: 1432-2013
    Keywords: 3H-Benzamil ; Hen colon ; Hen coprodaeum ; Sodium channels ; Sodium transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The binding of3H-benzamil to homogenates of epithelium removed from the colon and coprodaeum of hens was studied. A low capacity high affinity binding component was detected. The binding constants for benzamil and amiloride to this component were similar to those obtained when these ligands were used to inhibit transport in intact epithelia. The mean potency ratio of benzamil to amiloride was 12.8 measured by binding compared with 11.6 from functional inhibition. Binding activity was present in tissues taken from animals fed on low sodium diets and those containing a normal sodium content. In the presence of sodium the affinity of benzamil was slightly reduced, but only in tissues taken from animals on a low salt diet. Only a small fraction of the total binding activity was present in the apical surface of low salt tissues indicating that in homogenates a small percentage of the total activity is associated with functional sodium entry sites. It is suggested that the major part of the binding activity detected in homogenates represents components of the sodium ion translocation mechanism which are en route for the apical membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581630
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular mechanisms in exocytosis (1995)
    Springer
    The journal of membrane biology 146 (1995), S. 113-122 
    Details
    ISSN: 1432-1424
    Keywords: Exocytosis ; Membrane fusion ; Neurotransmitter release ; GTP-binding proteins ; Fusion pore
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238002
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