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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract:α-Dystroglycan (α-DG) is part of a complex of cell surface proteins linked to dystrophin or utrophin, which is distributed over the myofiber surface and is concentrated at neuromuscular junctions. In laminin overlays of muscle extracts from developing chick hindlimb muscle, α-DG first appears at embryonic day (E) 10 with an apparent molecular mass of 120 kDa. By E15 it is replaced by smaller (∼100 kDa) and larger (∼150 kDa) isoforms. The larger form increases in amount and in molecular mass (〉200 kDa) as the muscle is innervated and the postsynaptic membrane differentiates (E10-E20), and then decreases dramatically in amount after hatching. In myoblasts differentiating in culture the molecular mass of α-DG is not significantly increased by their replication, fusion, or differentiation into myotubes. Monoclonal antibody IIH6, which recognizes a carbohydrate epitope on α-DG, preferentially binds to the larger forms, suggesting that the core protein is differentially glycosylated beginning at E16. Consistent with prior observations implicating the IIH6 epitope in laminin binding, the smaller forms of α-DG bind more weakly to laminin affinity columns than the larger ones. In blots of adult rat skeletal muscle probed with radiolabeled laminin or monoclonal antibody IIH6, α-DG appears as a 〉200-kDa band that decreases in molecular mass but increases in intensity following denervation. Northern blots reveal a single mRNA transcript, indicating that the reduction in molecular mass of α-DG after denervation is not obviously a result of alternative splicing but is likely due to posttranslational modification of newly synthesized molecules. The regulation of α-DG by the nerve and its increased affinity for laminin suggest that glycosylation of this protein may be important in myofiber-basement membrane interactions during development and after denervation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-7365
    Keywords: Congenital portal-systemic shunts ; portal-systemic encephalopathy ; glutamate ; glutamine ; aromatic amino acids ; hepatic encephalopathy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Numerous studies suggest that modifications in concentrations of both excitatory and inhibitory amino acids are implicated in the pathophysiology of portal-systemic encephalopathy (PSE), a neuropsychiatric disorder associated with chronic liver disease in humans. In this study, amino acid levels were measured by High Performance Liquid Chromatography (HPLC) in Cerebrospinal Fluid (CSF) of 10 dogs (age range: 3 mo.- 3 yr 4 mo.) exhibiting a congenital portal-systemic shunt, either intra or extra-hepatic, and 8 age-matched control dogs who showed no signs of hepatic or neurologic disorders. Dogs with congenital shunts manifested signs of encephalopathy such as disorientation, head pressing, vocalization, depression, seizures and coma. CSF from dogs with congenital shunts contained significantly increased amounts of glutamate (2 to 3-fold increase, p〈0.01), glutamine (6-fold increase, p〈0.05) and aromatic amino acids (phenylalanine, tyrosine and tryptophan) compared to CSF of control dogs. Concentrations of GABA and branched chain amino acids (valine, leucine, isoleucine) were within normal limits. Modifications of brain glutamate (an excitatory amino acid) as well as tryptophan (the precursor of serotonin) could contribute to the neurological syndrome characteristic of congenital PSE in dogs.
    Type of Medium: Electronic Resource
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