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Biomedical subjects

A K Harris

Publications and source records attributed to A K Harris.

25 records · Page 2Linked to original sources
PubMed1981

Fibroblast traction as a mechanism for collagen morphogenesis.

To make visible the traction forces exerted by individuals cells, we have previously developed a method of culturing them on thin distortable sheets of silicone rubber. We have now used this method to compare the forces exerted by various differentiated cell types and have examined the effects of cellular traction on re-precipitated collagen-matrices. We find that the strength of cellular traction differs greatly between cell types and this traction is paradoxically weakest in the most mobile and invasive cells (leukocytes and nerve growth cones). Untransformed fibroblasts exert forces very much larger than those actually needed for locomotion. This strong traction distorts collagen gels dramatically, creating patterns similar to tendons and organ capsules. We propose that this morphogenetic rearrangement of extracellular matrices is the primary function of fibroblast traction and explains its excessive strength.

Animals↗
PubMed1981

Motion of particles adhering to the leading lamella of crawling cells.

Time-lapsed films of particle motion on the leading lamella of chick heart fibroblasts and mouse peritoneal macrophages were analyzed. The particles were composed of powdered glass or powdered aminated polystyrene and were 0.5-1.0 micrometer in radius. Particle motions were described by steps in position from one frame to the time-lapse movies to the next. The statistics of the step-size distribution of the particles were consistent with a particle in Brownian motion subject to a constant force. From the Brownian movement, we have calculated the two-dimensional diffusion coefficient of different particles. These vary by more than an order of magnitude (10(-11)-10(-10) cm2/s) even for particles composed of the same material and located very close to each other on the surface of the cell. This variation was not correlated with particle size but is interpretable as a result of different numbers of adhesive bonds holding the particles to the cells. The constant component of particle movement can be interpreted as a result of a constant force acting on each particle (0.1-1.0 x 10(-8) dyn). Variations in the fractional coefficient for particles close to each other on the cell surface do not yield corresponding differences in velocity, suggesting that the frictional coefficient and the driving force vary together. This is consistent with the hypothesis that the particles are carried by flow of the membrane as a whole or by flow of some submembrane material. The utility of our methods for monitoring cell motile behavior in biologically interesting situations, such as a chemotactic gradient, is discussed.

Animals↗
PubMed1981

Anomalous preferences of cultured macrophages for hydrophobic and roughened substrata.

Peritoneal macrophages were plated out on a series of artificial haptotactic substrata consisting of grid patterns of vacuum-evaporated palladium metal alternating with hydrophobic untreated polystyrene and with hydrophilic sulphonated polystyrene. By their active locomotion the macrophages accumulated preferentially onto the less hydrophilic of either pair of these alternative substrata. This order of substratum preference is precisely the opposite to that shown by fibroblastic cells. Macrophages were also found to accumulate preferentially onto roughened culture surfaces as opposed to smooth ones, which is again opposite to the behaviour of fibroblasts. These opposite substratum preferences shown by macrophages may reflect physical as well as functional differences in their surfaces, and could serve as assay criteria for macrophages and cell types putatively equivalent to macrophages.

Animals↗
PubMed1980

Silicone rubber substrata: a new wrinkle in the study of cell locomotion.

When tissue cells are cultured on very thin sheets of cross-linked silicone fluid, the traction forces the cells exert are made visible as elastic distortion and wrinkling of this substratum. Around explants this pattern of wrinkling closely resembles the "center effects" long observed in plasma clots and traditionally attributed to dehydration shrinkage.

Animals↗