Influence of the Partitioning of Osmolytes by the Cytoplasm on the Passive Response of Cells to Osmotic Loading

Abstract

Due to the dense organization of organelles, cytoskeletal elements, and protein complexes that make up the intracellular environment, it is likely that membrane-permeant solutes may be excluded from a fraction of the interstitial space of the cytoplasm via steric restrictions, electrostatic interactions, and other long-range intermolecular forces. This study investigates the hypothesis that the intracellular partitioning of membrane-permeant solutes manifests itself as a partial volume recovery in response to hyperosmotic loading, based on prior theoretical and biomimetic experimental studies. Osmotic loading experiments are performed on immature bovine chondrocytes using culture conditions where regulatory volume responses are shown to be insignificant. Osmotic loading with membrane-permeant glycerol (92 Da) and urea (60 Da) are observed to produce partial volume recoveries consistent with the proposed hypothesis, whereas loading with 1,2-propanediol (76 Da) produces complete volume recovery. Combining these experimental results with the previous theoretical framework produces a measure for the intracellular partition coefficient of each of these solutes. At 1000 mOsm, 1,2-propanediol is the only osmolyte to yield a partition coefficient not statistically different from unity, kappa(p)(i) = 1.00 +/- 0.02. For glycerol, the partition coefficient increases with osmolarity from kappa(p)(i) = 0.48 +/- 0.19 at 200 mOsm to kappa(p)(i) = 0.80 +/- 0.07 at 1000 mOsm; urea exhibits no such dependence, with an average value of kappa(p)(i) = 0.87 +/- 0.07 for all osmolarities from 200 to 1000 mOsm. The finding that intracellular partitioning of membrane-permeant solutes manifests itself as a partial volume recovery under osmotic loading offers a simple method for characterizing the partition coefficient. These measurements suggest that significant partitioning may occur even for small membrane-permeant osmolytes. Furthermore, a positive correlation is observed, suggesting that a solute's cytoplasmic partition coefficient increases with increasing hydrophobicity.

Finite Element Implementation of Mechanochemical Phenomena in Neutral Deformable Porous Media Under Finite Deformation

“…Experimental findings have demonstrated that this partitioning may vary with the state of solid matrix strain [5, 6] as well as solute concentration [44, 45]. Furthermore, partitioning may also explain partial volume recovery responses, in gels [5] and cells [43] subjected to osmotic loading, as a result of passive transport mechanisms rather than active regulatory processes as usually assumed in cells [62]. Partial volume recovery was illustrated in the problem of osmotic loading of a spherical gel (Fig.…”

“…(2) Momentum exchange between solutes and the solid matrix, which is responsible for increased hindrance to transport [2, 36] as well as enhanced convection under dynamic loading [37, 38, 39, 40]. (3) Changes in tissue and cell volume due to alterations in their osmotic environment [41, 5, 42, 43]. (4) Partial solute exclusion from pore spaces due to steric volume and short-range electrostatic effects [2, 3, 4], which may depend on solid matrix deformation [5, 6] and solute concentration [44, 45].…”

Hypotonic challenge modulates cell volumes differently in the superficial zone of intact articular cartilage and cartilage explant

“…The effects of articular cartilage structure, composition and mechanical properties on cell deformations have been studied earlier also theoretically (Likhitpanichkul et al 2005;Korhonen et al 2010a). That kind of models combined with cell volume regulation mechanisms (e.g., Kedem and Katchalsky 1958;Kleinhans 1998;Ateshian et al 2006;Albro et al 2009) could give better explanations for the effect of cutting of the sample on the tissue integrity and cell responses. Performing experiments in confined compression might also yield additional insights for interpretation, particularly regarding the role of the collagen network.…”

Mechanics of cell growth

“…Solvent will thus be driven into the cell, down its mechano-chemical potential gradient, until this gradient returns to zero. The transient active transport of solutes and passive transport of solutes and solvent into the cell may be modeled explicitly in a general mixture framework (Ateshian et al, 2006, 2010; Ateshian, 2011) and validated experimentally (Albro et al, 2007, 2009), extending the classical presentation based on irreversible thermodynamics (Weiss, 1996). However, for the purposes of growth modeling it may suffice to analyze the steady-state response when mechano-chemical potential gradients have returned to zero.…”