Browsing by Subject "Osmotic Pressure"

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    Cartilage mechanics in the guinea pig model of osteoarthritis studied with an osmotic loading method.
    (Osteoarthritis and cartilage, 2004-05) Flahiff, Charlene M; Kraus, Virginia B; Huebner, Janet L; Setton, Lori A
    To determine the material properties of articular cartilage in the Hartley guinea pig model of spontaneous osteoarthritis.Cartilage-bone samples from the medial femoral condyle and tibial plateau of 12 month-old guinea pig knees were subjected to osmotic loading. Site-matched swelling strains and fixed charge density values were used in a triphasic theoretical model for cartilage swelling to determine the modulus of the cartilage solid matrix. The degree of cartilage degeneration was assessed in adjacent tissue sections using a semi-quantitative histological grading scheme.Decreased values for both moduli and surface zone fixed charge density were associated with increasing grades of cartilage degeneration. Decreases in moduli reflect damage to the collagen matrix, which give rise to greater swelling strains.Histological evidence of cartilage degeneration was associated with impaired cartilage mechanics in the aging Hartley guinea pig.
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    The effects of osmotic stress on the structure and function of the cell nucleus.
    (2010) Finan, John Desmond
    Chondrocytes maintain cartilage by transducing joint load into appropriate biosynthetic activity, a process commonly known as mechanotransduction. Malfunctioning mechanotransduction leads to cartilage degradation and osteoarthritis. The mechanism of mechanotransduction is only partially understood but osmotic stresses are thought to play an important role. This study shows that the chondrocyte nucleus shrinks and wrinkles under hyper-osmotic stress. It shrinks because the chromatin inside the nucleus contracts as the macromolecules in the cell become more crowded. It wrinkles because the nuclear lamina buckles as the nucleus contracts. These morphological changes accelerate transport across the nuclear envelope. Many cells have organized actin caps around their nuclei that constrain the nucleus from contracting under hyper-osmotic stress. Agents exist that can reverse this loss of osmotic sensitivity in vitro without damaging the cell.