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A J Powell

Publications and source records attributed to A J Powell.

9 recordsLinked to original sources
PubMed1989

A treadmill-mounted force platform.

Muscle, bone, and tendon forces; the movement of the center of mass, and the spring properties of the body during terrestrial locomotion can be measured using ground-mounted force platforms. These measurements have been extremely time consuming because of the difficulty in obtaining repeatable constant speed trials (particularly with animals). We have overcome this difficulty by mounting a force platform directly under the belt of a motorized treadmill. With this arrangement, vertical force can be recorded from an unlimited number of successive ground contacts in a much shorter time. With this treadmill-mounted force platform it is possible to accurately make the following measurements over the full range of steady speeds and under various perturbations of normal gait: 1) vertical ground reaction force over the course of the contact phase; 2) peak forces in bone, muscle, and tendon; 3) the vertical displacement of the center of mass; and 4) contact time for the limbs. In our treadmill-force platform design, belt forces and frictional forces cause no measurable cross-talk problem. Natural frequency (160 Hz), nonlinearity (less than 5%), and position independence (less than 2%) are all quite acceptable. Motor-caused vibrations are greater than 150 Hz and thus can be easily filtered.

Biomechanical Phenomena↗
PubMed1979

Mechanisms of cellular adhesion. IV. Role of serum glycoproteins in fibroblast spreading on glass.

We have investigated the exogenous factors required for the transition from the round shape of suspended fibroblasts to the characteristic spread shape on serum-coated glass. Following the evidence of others that the transition is facilitated by adsorbed component(s) related to CIG/LETS (cold-insoluble globulin/large external transformation-sensitive) proteins, we have isolated 2 such preparations from chick serum. Their influence has been investigated on fibroblast adhesion, spreading and growth and they have been characterized by gel electrophoresis, immunological cross-reactivity, amino acid and carbohydrate residue analysis, sedimentation velocity behaviour and circular dichroism spectroscopy. The preparations have molecular weights of 225/215,000 and 140,000 Daltons respectively and are closely similar in composition and secondary structure. The 225/215 000 Dalton doublet is probably a product of limited proteolysis which almost certainly occurred in the avian circulation. For cells seeded on glass precoated in different ways and in different supplemented media we could detect no change in the extent of attachment but there were profound influences on cell shape following this initial adhesion. We confirm that prior adsorption of either CIG-related preparation to glass does indeed promote fibroblast spreading in the absence of other serum components and that CIG is the sole serum component with this type of activity. We now add 2 important qualifications: (i) the presence of substrate-adsorbed serum CIG is not essential for spreading when other serum components are present in the medium; and (ii) the adhesive organization shown by interference reflexion microscopy is incompletely formed unless the additional serum components are present in the medium. We therefore conclude that 16C fibroblasts have the ability when given the stimulus of soluble serum components other than CIG, but not otherwise, to synthesize all the components necessary for the highly organized contacts with glass, including endogenous CIG/LETS proteins.

Amino Acids↗
PubMed1977

Rapid isolation of plasma membranes in high yield from cultured fibroblasts.

1. A method was developed which allows the rapid preparation of pure plasma membranes in high yield from cultured fibroblasts. 2. Cells are lysed in hypo-osmotic borate/EDTA and, after differential centrifugation, the membranes collected by centrifugation on a sucrose barrier. 3. Electron microscopy of the isolated material shows large membrane vesicles essentially free from contaminating organelles. 4. There is no detectable activity of the endoplasmic-reticulum enzyme marker, NADH2--lipoamide oxidoreductase (EC 1.6.4.3), and that of succinate dehydrogenase (EC 1.3.99.1), a marker for mitochondria, is substantially decreased. Chemical compositions are in good agreement with previous observations. 5. This study confirms the usefulness of applied isotopic markers for isolating plasma membranes.

Borohydrides↗