Role Of Physical Forces Research Articles

The role of physical forces on cytotoxic T cell-target cell conjugate stability.

Theoretical considerations suggest that external forces play a significant role in cell-cell conjugate formation and may lead to the misinterpretation of adhesion data. To test this, the stability of conjugates formed between CTL and fibroblast target cells (TC) was examined in the controlled shear environment of a parallel plate flow chamber. Murine fibroblast targets expressing class I maternally transmitted Ag Mtaa or Mtab were grown on a glass slide that formed one wall of the flow chamber and were used in conjunction with anti-Mtaa and anti-Mtab specific mouse CTL clones to establish a panel of Ag-reciprocal targets and lymphocytes. Although cytolysis assays indicated that lymphocytes recognized and destroyed appropriate but not inappropriate targets, the stability of some CTL/TC conjugates was Ag independent. In all cases, the conjugate stability was shear dependent over a 100-fold range (0.04 to 4.0 dynes/cm2). For some clones, the ratio of the stabilities of Ag-specific CTL/TC conjugates to nonspecific conjugates was significantly enhanced with increasing shear. This implies that the role of Ag specificity in CTL/TC adhesion may be misinterpreted if the shear environment of CTL/TC conjugates is unknown or uncontrolled. Kinetic analysis revealed that conjugate stability was dependent on the exposure time to external forces and that there existed two populations of conjugates; weak associations that disengaged within the first 30 s of flow, and strong associations that remained attached even after a 5-min exposure to a steady shear stress. The stability of Ag-specific CTL/TC conjugates at 0.04 dynes/cm2 was enhanced by 50% as the temperature was increased from 25 to 37 degrees C, whereas the stability of nonspecific CTL/TC associations was not affected. This result indicates that significant Ag-specific strengthening may occur at physiologic temperatures. This work suggests the importance of attention to role of fluid mechanical shear stress in standard adhesion assays.

Role of physical forces in compensatory growth of the lung.

In many species, partial resection of the lung leads to rapid compensatory growth of the remaining tissue to restore normal lung mass and function. The response to partial pneumonectomy is closely controlled; both its rate and nature are subject to hormonal modulation. Physical factors, particularly distortion of the lung by altered inflation, are likely involved in regulation of the response, although the details of the regulatory mechanisms are not understood. In a number of tissues including the lung, application of external physical force leads to both acute and long-term changes in metabolism. In some cases these include cell growth and division, along with increased production of extracellular matrix components. Similar responses have been described after application of stress to isolated cells in culture. Independent lines of investigation have defined dramatic influences of cell shape on growth, differentiation, and metabolism, but stress-strain relationships at the cellular or subcellular levels are poorly defined. The mechanisms by which changes in cell shape are transduced to intracellular signals likely depend on receptor-mediated interactions with the cytoskeleton, but strain-associated transduction pathways may involve stretch-sensitive ion channels, G protein-dependent reactions, the action of locally produced autocrine or paracrine factors, or a combination of these factors. These observations suggest a general model of the response to pneumonectomy that may be used to formulate specific hypotheses as a basis for future investigations. This approach will provide insight into the mechanisms by which physical forces influence growth and metabolism in the lung and other tissues.

Role of Physical Forces in Hydrophobic Interaction Chromatography

Abstract Hydrophobic interaction chromatography (HIC) is a new non-biospecific liquid chromatography method for the separation of proteins, and other biological macromolecules; the mobile phases are aqueous and the adsorbents are agarose beads coated with ionogenic, or non-ionogenic, hydrocarbonaceous ligands. A non-traditional interpretation is given here for the mechanisms of retention and elution in HIC in terms of the several physical forces between the protein and the adsorbent, chiefly the van der Waals attraction (comprising dispersion, orientation and induction) and the electrostatic double layer interaction. From a qualitative analysis of the hydrogen-bond and the structural features of water, it is shown here that the role of the alkyl ligands on the adsorbent, the lyotropic salt effects and the effect of additives to the mobile phase such as ethylene glycol can all be unifyingly represented in the Hamaker coefficient of the van der Waals attraction between protein and adsorbent in water. An increase in the number and length of alkyl ligands, and the addition of structure-making (“salting-out”) salts at high ionic strengths increase the latter attraction while the addition of structure-breaking “salting-in” salts or organic solvents such as ethylene glycol decreases the attraction. The potentials corresponding to the different physical forces add up to the total interaction potential. The shapes of the total interaction potential relevant to HIC are identified. Coefficients of adsorption and desorption are shown to be related to this potential and the high sensitivity of the latter to its parameters such as the Hamaker coefficient, is illustrated. Retention, elution and the natures of the different fractions into which a protein mixture may be separated by HIC are visualized in terms of the interaction potential. Numerous experimental reports in HIC are classified, tabulated, and in certain cases, discussed in detail. Experimental evidence is presented for the application of ionic strength manipulations, in the low ionic strength range (electrostatic effects), in the high ionic strength range (lyotropic salt effects) as well as for the combined use of low and high ionic strength effects, retention onto adsorbents with no ligands as well as onto adsorbents with alkyl ligands of various chain lengths and number densities, temperature effects, and the effects of heterogeneities of proteins and adsorbents. Applications and variants of HIC are cited. In total, the paper summarizes various types of HIC experimental facts and explains most of them in a simple, unifying fashion.

A field and circuit thermodynamics for integrative physiology. I. Introduction to the general notions.

In this first of three articles on a physical basis for integrative physiology, statistical mechanical concepts are developed into a field thermodynamics. The development begins by comparing the different ways change is viewed in biology compared to physics. The Hamiltonian field concept unites the two. The requirements of a thermostatic description are introduced; then those of nonequilibrium thermodynamics are added. Conditions suitable for continuum, near-equilibrium analysis of systems are given; then the role of physical forces in organization is discussed. The development returns to statistical mechanics, and introduces conservation principles and equations of change for ensembles of interacting units. A general notion of systems and thermodynamic engines is discussed next, and a narrative account of the explanatory scope of field thermodynamics is given. Its applications to living systems are the subject of the subsequent two articles of this series.