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Biomedical subjects

F A Meyer

Publications and source records attributed to F A Meyer.

At least 37 records · Page 2Linked to original sources
PubMed1981

Platelet adhesion to collagen is inhibited by adenosine diphosphate but unaffected by cell shape.

The effect of limited platelet activation, in the absence of aggregation, on the subsequent ability of rabbit platelets to adhere to collagen was studied in vitro. ADP at concentrations that initiate shape change ( greater than 0.01 micro M) reduce platelet adhesion. Shape change per se however, was not responsible since the time-dependence of the effect of ADP on shape change and adhesion is different and ADP induces reduced adhesion even when shape change is prevented with PGE or fixatives. Platelets shape-changed without ADP addition, e.g. by chilling or by low ethanol concentrations, display normal adhesion to collagen. It appears likely that upon binding to the platelet ADP induces a time-dependent alteration in the membrane, akin to refractoriness, that influences binding sites for collagen. The effect of ADP can be blocked by prior addition of AMP but not if the additions are reversed. The implications of the present finding for platelet adhesion studies are discussed.

Adenosine Diphosphate↗
PubMed1980

Fluid transport in a thick layer above an active ciliated surface.

The discrete cilia approach is employed to describe the flow field above an active ciliated surface in a layer of finite depth. The infinite-size cilia surface model predicts a uniform flow above the cilia surface. Modifications as a result of a finitely extending cilia surface inside a finite-size dish predict a backward parabolic profile above an active cilia surface. Experiments are described which demonstrate a good fit between theoretical predictions and observations. The results provide a sound physical basis for the proper interpretation of fluid-flow observations close to an active ciliary field.

Animals↗
PubMed1979

Mucociliary transference rate and mucus viscoelasticity dependence on dynamic storage and loss modulus.

Various samples of estrous bovine cervical mucus were collected, and their dynamic viscoelastic properties were determined at between 2.7 and 4.4 rad/s. Comparing the loss modulus with the rigidity (storage) modulus for the samples taken, the former was found to increase markedly as the latter increased. Limited exposure of mucus to increased temperatures removed crosslinks, whereas treatment with glutaraldehyde introduced additional ones. In the case of one sample, the number of crosslinks was altered in this way. As the number of crosslinks decreased or increased, the storage modulus decreased or increased, but the loss modulus remained relatively unaffected. The transference (ability to move particle loads) of native and modified samples on the ciliated epithelium of a frog palate depleted of mucus was determined. All data for transference rate correlated against changes in the storage modulus. The rate was maximal for a storage modulus of 1.6 dynes.cm-2 and decreased rather sharply to either side of this value. No such correlation could be found against the loss modulus. In fact, whereas very different values of the loss modulus corresponded to the same storage modulus, the transference rate was the same. Hence, the storage rather than the loss modulus determines transference rate.

Animals↗
PubMed1978

Structure and function of mucus.

A glycoprotein building block is common to mammalian mucins. This structure is composed of several protein chains having the same sequence. The carbohydrate side chains, which constitute over three-quarters of the weight, coat only some two-thirds of the backbone chain. The bare protein chains are linked by disulphide bridges and can be digested away with trypsin. Either procedure rapidly solubilizes mucus and results in a structural unit of about 500 000 molecular weight. Mucus solubilizes spontaneously. The first size unit which reaches solution is about 15 X 10(6) molecular weight but continues to break down further. Mechanical agitation considerably speeds up this process. The gel-like character which is an essential feature of mucus--which cannot otherwise act as transport coupler--is thus a transient phenomenon. The problem of how such a structure can arise from the building blocks known to be available is discussed.

Amino Acid Sequence↗
PubMed1977

Structural investigation of loose connective tissue by using a series of dextran fractions as non-interacting macromolecular probes.

The ability of the uncharged open-coil dextran molecules to penetrate tissue space, without coil-shape change, was utilized to probe (by partitioning experiments) the structural arrangement of the collagen-fibre network and the proteoglycan system. Hyaluronidase digests most of the proteoglycans away and enables the respective contributions to the exclusion volume to be evaluated by using a series of different-molecular-weight dextrans. It appears that the major part of the exclusion volume is due to the collagen-fibril as a rod and the dextran coil as an impenetrable sphere. The additional exclusion due to the proteoglycans could be accounted for by a set of points (regions of high proteoglycan-segment density) over which the dextran coild cannot pass. These points are an average of 50 nm apart and are indicative of local extensive entanglement of high-molecular-weight proteoglycans with each other. Reasons are given why these entanglements could not act as cross-links in long-term elastic loading of the tissue.

Connective Tissue↗
PubMed1976

Aging and the interstitial content of loose connective tissue. A brief note.

The concentration of hyaluronic acid which is the fixed loose connective tissue component determining water and other potentials in the interstitium remains constant with age. Since the collagen fiber network in the native tissue state is unstressed, changes in collagen fiber morphology and in collagen content with age have no influence.

Aging↗
PubMed1975

On the role of sialic acid in the rheological properties of mucus.

The importance of sialic acid in the rheological properties of mucus has been investigated. Both bovine cervical mucus, which is a gel, and the structural glycoprotein derived from it were studied before and after treatment with neuraminidase which selectively cleaves terminal sialic acid residues. The storage modulus, viscosity and circular dichroism spectrum were all essentially changed after removal of the sialic acid. These results would indicate that removal of sialic acid does not affect the physical structure of the glycoprotein and it is concluded that sialic acid has no significant role in the rheological properties of cervical mucus.

Animals↗