The Effects of Osmotic Stress on the Viscoelastic and Physical Properties of Articular Chondrocytes

Abstract

The metabolic activity of chondrocytes in articular cartilage is influenced by alterations in the osmotic environment of the tissue, which occur secondary to mechanical compression. The mechanism by which osmotic stress modulates cell physiology is not fully understood and may involve changes in the physical properties of the membrane or the cytoskeleton. The goal of this study was to determine the effect of the osmotic environment on the mechanical and physical properties of chondrocytes. In isoosmotic medium, chondrocytes exhibited a spherical shape with numerous membrane ruffles. Normalized cell volume was found to be linearly related to the reciprocal of the extracellular osmolality (Boyle van't Hoff relationship) with an osmotically active intracellular water fraction of 61%. In deionized water, chondrocytes swelled monotonically until lysis at a mean apparent membrane area 234 +/- 49% of the initial area. Biomechanically, chondrocytes exhibited viscoelastic solid behavior. The instantaneous and equilibrium elastic moduli and the apparent viscosity of the cell were significantly decreased by hypoosmotic stress, but were unchanged by hyperosmotic stress. Changes in the viscoelastic properties were paralleled by the rapid dissociation and remodeling of cortical actin in response to hypoosmotic stress. These findings indicate that the physicochemical environment has a strong influence on the viscoelastic and physical properties of the chondrocyte, potentially through alterations in the actin cytoskeleton.

Universal behavior of the osmotically compressed cell and its analogy to the colloidal glass transition

“…1C). Overall, the relationship conformed to the well-known Ponder's relationship (19,20), v ϭ R⌸ iso /⌸ ϩ (1 Ϫ R), with a slope of R ϭ 0.7 (black line, Fig. 1C), where ⌸ is the applied osmotic pressure, ⌸ iso is the isotonic osmotic pressure, and relative cell volume v is the current cell volume normalized by cell volume under isotonic conditions.…”

Voltage-Dependent Calcium Channels in Chondrocytes: Roles in Health and Disease

“…Chondrocytes are surrounded by a pericellular matrix and are situated in cavities called lacunae within the ECM, where they exist in a hypoxic micro-environment [3,4] and control ECM turnover and homeostasis in response to mechanical loading [5] despite having a rather slow (mainly anaerobic) metabolism. Due to the fact that chondrocytes reside within the peculiar milieu of the ECM (which is acidic, hypertonic and hyperosmotic [6][7][8]), and since their function and differentiation is strongly dependent on intracellular calcium homeostasis [9,10], they deploy a whole range of ion channels to enable ion transport across the plasma membrane; the collection of ion channels is referred to as the chondrocyte 'channelome' [11]. Albeit generally considered to be non-excitable cells, chondrocytes and chondroprogenitor cells have been reported to express various voltage-dependent potassium channels (KV), ATP dependent potassium channels (KATP), large and small conductance calcium-activated potassium channels (BK and SK), transient receptor potential channels (primarily TRPV1 and TRPV4), purinergic receptors (both P2X and P2Y subfamily members), voltage gated and epithelial sodium channels, chloride channels, and also voltage-dependent calcium channels (VDCCs) [11][12][13].…”

Mineralization and non-ideality: on nature’s foundry

“…Overall, these studies indicate that local osmotic conditions may affect mineral growth in complex environments and also lead to variations in mineral properties, including shape, polymorph and structural mechanics. At cellular levels, the osmotic environment serves functions such as tuning mineralization activity and viscoelastic properties of cellular constituents (Guilak et al 2002;Sottnik et al 2015).…”