Changes in surface area and volume measured by micropipette aspiration for erythrocytes ageing in vivo.
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Animals↗
Biomedical subjects
G B Nash
Publications and source records attributed to G B Nash.
Size measurements on isolated rat heart cells using Coulter analysis and light scatter flow cytometry.
Isolated ventricular muscle cells from the adult rat heart have been examined by both Coulter analysis and light scatter flow cytometry. The dispersed cell preparations contain two main cell types: viable, rod-shaped cells and damaged, round cells. Coulter analytical techniques provided statistical data on cell volume for both cell types. The contribution of each population to the Coulter pulse height distributions were separated by a subtraction method using data obtained from digitonin-treated preparations that contain only round cells. A shape factor for cells aligned with the flow direction was computed from light microscope measurements and the effects of cell orientation within the Coulter aperture were approximately assessed. The estimated volumes for intact myocytes compare favourably with those reported in the literature. No significant size difference was observed between fresh and fixed cells. Narrow angle, forward light scatter measurements were made on individual cells flowing across a focused laser beam. Both scatter pulse height and pulse width (pulse duration) distributions were collected. Values for myocyte length calculated from pulse width information agree well with published data and confirm that the hydrodynamic forces in the flow system produced alignment of the cells with the flow direction. Scatter pulse width distributions reveal two distinct peaks assignable to either rod or round cells. Preliminary electronic gating experiments, using pulse height signals, suggest that signals derived from round cells could be eliminated entirely using a gating regime based on pulse width. This would enable flow cytometric measurements to be made on only the intact myocytes present in heterogeneous preparations.
Animals↗
Effect of neuraminidase on rigidity of the red cell membrane.
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Elasticity↗
Kinetics of the different steps during neutrophil migration through cultured endothelial monolayers treated with tumour necrosis factor-alpha.
To enable a better understanding of the regulation of neutrophil migration, we investigated the kinetics of adhesion and migration over, through and under endothelial monolayers. Neutrophils were perfused over human umbilical vein endothelial cells (HUVEC) which had been treated with tumour necrosis factor-alpha (TNF; 2-1,000 U/ml) for 4 h. Videomicroscopy showed that transendothelial migration was complete within about 5 min of completion of perfusion of a bolus of neutrophils. Separate populations of adherent cells could then be observed, either rolling, migrating over the surface of the HUVEC or migrating underneath, at different characteristic speeds. Increasing concentration of TNF had little effect on the kinetics of migration, but shifted the balance from rolling adhesion to transendothelial migration. When individual neutrophils were followed from the moment they bound to HUVEC treated with 100 U/ml TNF, we found that approximately 40% immobilised essentially immediately on contact, while approximately 40% immobilised after rolling for varying periods (average 26 s) and approximately 20% rolled continuously. Most of the immobilised cells went on to migrate through the monolayer after spending 20-200 s migrating on top, and took about 60 s to pass through. Overall, the time from first binding to completion of transmigration averaged 152 s (range approximately 60-240 s). Interestingly, neutrophils moved relatively slowly on top of the monolayer (about 8 microm/min) but more rapidly underneath (about 16 microm/min). We suggest that the different stages during neutrophil transmigration have characteristic kinetics with separate control mechanisms, which critically influence the efficiency and rate of clearance from the vasculature.
Blood Flow Velocity↗
Cell adhesion: more than just glue (review).
The ability of cells to interact with each other and their surroundings in a co-ordinated manner depends on multiple adhesive interactions between neighbouring cells and their extracellular environment. These adhesive interactions are mediated by a family of cell surface proteins, termed cell adhesion molecules. Fortunately these adhesion molecules fall into distinct families with adhesive interactions varying in strength from strong binding involved in the maintenance of tissue architecture to more transient, less avid, dynamic interactions observed in leukocyte biology. Adhesion molecules are extremely versatile cell surface receptors which not only stick cells together but provide biochemical and physical signals that regulate a range of diverse functions, such as cell proliferation, gene expression, differentiation, apoptosis and migration. In addition, like many other cell surface molecules, they have been usurped as portals of entry for pathogens, including prions. How the mechanical and chemical messages generated from adhesion molecules are integrated with other signalling pathways (such as receptor tyrosine kinases and phosphatases) and the role that aberrant cell adhesion plays in developmental defects and disease pathology are currently very active areas of research. This review focuses on the biochemical features that define whether a cell surface molecule can act as an adhesion molecule, and discusses five specific examples of how cell adhesion molecules function as more than just 'sticky' receptors. The discussion is confined to the signalling events mediated by members of the integrin, cadherin and immunoglobulin gene superfamilies. It is suggested that, by controlling the membrane organization of signalling receptors, by imposing spatial organization, and by regulating the local concentration of cytosolic adapter proteins, intercellular and cell-matrix adhesion is more than just glue holding cells together. Rather dynamic 'conversations' and the formation of multi-protein complexes between adhesion molecules, growth factor receptors and matrix macromolecules can now provide a molecular explanation for the long-observed but poorly understood requirement for a number of seemingly distinct cell surface molecules to be engaged for efficient cell function to occur.
Animals↗
Structural determinants of the rigidity of the red cell membrane.
Although the stability and viscoelasticity of the red cell membrane are undoubtedly governed by the membrane's underlying protein skeleton, the mechanism by which this network controls elasticity is uncertain. The structural constraints, that impose end-to-end spacing on the spectrin molecules well below that in free solution, may impart rubbery (entropic) elasticity to the system. However, other enthalpic and entropic contributions due to interactions between spectrin chains or between spectrin and other proteins, the lipid bilayer or the solvent must also prevail. To relate structural features to elasticity, explicit measurements of membrane rigidity are required. The most widely used measurement is that of the membrane shear elastic modulus by micropipette aspiration. Analysis of genetic variants of membrane structure have shown that the density of spectrin is directly correlated with membrane rigidity. Although cross-linking of the skeleton increases rigidity, interruption of the continuity of the network by dissociating spectrin tetramers into dimers does not reduce rigidity as might be expected. On the other hand, external ligands that cause new interactions between integral proteins and the skeletal network do increase rigidity. Moreover, hereditary ovalocytes, which have a deletion of 9 amino acids from band 3 at the first point of entry into the membrane, are extremely rigid. This mutation is associated with decreased translational and rotational mobility of the band 3, and may impair flexural freedom of its cytoplasmic domain. It thus appears that elasticity may be regulated not only by the structure of the spectrin network, but also by its interactions with and freedom of motion relative to the lipid bilayer.
Chemical Phenomena↗