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A Maroudas

Publications and source records attributed to A Maroudas.

At least 37 records · Page 2Linked to original sources
PubMed1988

The distributions and diffusivities of small ions in chondroitin sulphate, hyaluronate and some proteoglycan solutions.

The distributions and diffusivities of Na+, Ca2+ and Cl- in chondroitin sulphate (CS), hyaluronate (HA) and proteoglycan solutions were measured using equilibrium dialysis and a capillary tube method. Measurements were made for a range of glycosaminoglycan (GAG) concentrations up to those normally found in dense connective tissue (10% CS, 2.5% HA), ionic strengths up to normal physiological concentrations (0.15 M) and for different combinations of monovalent and divalent cations. The partition coefficients, Ki, of the positive ions increased with increasing matrix concentration and with decreasing ionic strength but with one exception the selectivity coefficient KCaNa = square root of KCa/KNa was close to unity, indicating nearly ideal Donnan distributions. The ionic diffusivities decreased very much like those of small neutral solutes with increasing matrix concentration and with one exception were relatively independent of ionic strength, The exception in both cases was low matrix concentrations and low ionic strengths for which the diffusivity of Ca2+ was an order of magnitude lower and selectivity coefficients were approximately 2. We conclude that at physiological ionic strengths and GAG concentrations the distributions of small ions are determined by simple electrostatic interactions, without binding or condensation, and the diffusivities are not affected by the electrostatic field.

Calcium↗
PubMed1988

The theoretical distributions and diffusivities of small ions in chondroitin sulphate and hyaluronate.

The electrostatic interactions between polyionic glycosaminoglycans and small mobile ions are investigated using the Poisson-Boltzmann equation and a rod-in-cell model of the polyelectrolyte. Calculations are made for the range of polyelectrolyte concentrations and buffer compositions for which measurements of ion distributions and diffusivities are reported in a companion paper (Maroudas et al., Biophys. Chem. 32 (1988) 257). We conclude that the distribution of mobile ions is largely determined by the 'far-field' potential and is adequately described by the Poisson-Boltzmann theory and also by more approximate theories such as ideal Donnan or 'condensation' theory. The measured variations in cation diffusivities, particularly the increase in diffusivity with increasing matrix concentration at low ionic strengths, are predicted qualitatively using an approximate diffusion theory together with the calculated potential fields. However, the same theory applied to anion diffusion gives qualitatively wrong results.

Chondroitin↗
PubMed1987

Effects of low-amplitude pulsed magnetic fields on cellular ion transport.

Pulsed magnetic fields (PMFs) are widely used to treat difficult fractures of bone and other disorders of connective tissue. It is not clear how they interact with tissue metabolism, although it has been proposed that induced currents or electric fields impinging on cell membranes may modify their ion transport function. This hypothesis was tested by treating in vitro models for ion transport processes with short-term exposure to PMFs. No change occurred in active transport of potassium or calcium in human red cells or in calcium transport through an epithelial membrane. We considered less direct action on red cell membranes, that their permeability might be modified after PMF treatment, and also that PMFs might alter the extracellular ionic activity within connective tissue by interacting with its Donnan potential. Each of these studies proved negative, and we conclude that the PMF waveforms used here do not exert a general short-term effect on cellular ion transport.

Allantois↗
PubMed1987

"Free" and "exchangeable" or "trapped" and "non-exchangeable" water in cartilage.

We repeated some of our own previous experiments, as well as some of Torzilli's recent experiments (11) on which he bases his conclusions relating to a nonexchangeable "trapped water" in cartilage. We are unable to confirm Torzilli's findings. We observed partition coefficients for 3H.HO very close to unity. That both the extrafibrillar and most of the intrafibrillar water is freely exchangeable and behaves as available water towards small solutes has been independently shown (3) for other collagenous tissues. All the different permutations of partition experiments have yielded results that are fully consistent with our original picture of the very major fraction of cartilage water being free.

Animals↗
PubMed1986

Effects of mechanical and osmotic pressure on the rate of glycosaminoglycan synthesis in the human adult femoral head cartilage: an in vitro study.

We studied the effects of mechanical and osmotic compression on sulphate incorporation into glycosaminoglycans of human femoral head cartilage. We found that both mechanical and osmotic compression produce the same lowering of sulphate uptake relative to uncompressed controls. It appears that this effect is not associated with changes in solute transport or changes in solute concentration in the matrix, but is due, in part at least, to an increased osmotic pressure acting on the chondrocytes. A second mechanism of action might be involved directly through the increased proteoglycan concentration in the pericellular environment, resulting from a reduction in the water content. We also found that glycosaminoglycan synthesis returned to its control level when the conditions prevailing in the matrix, in the absence of pressure or added solute, were restored.

Adult↗
PubMed1986

The "instantaneous" deformation of cartilage: effects of collagen fiber orientation and osmotic stress.

The present study was undertaken with two objectives in view. The first was to distinguish between the "instantaneous" deformation and creep of articular cartilage when subjected to a step loading in unconfined compression. This was done by observing changes in the specimen's diameter rather than its thickness. The second objective was to investigate experimentally the anisotropic behaviour of cartilage in a compressive loading mode, corresponding to the physiological situation. An apparatus was thus developed and constructed which enabled us to follow the "instantaneous" changes of the surface area of the sample as the latter was being loaded in unconfined compression. Specimens of human articular cartilage from normal femoral heads and condyles were tested. Full thickness specimens were tested with and without the underlying bone, as well as partial thickness specimens, characterizing the different zones of cartilage. Solutions of different ionic strength were used to vary the osmotic stress and specimens covering a considerable range of proteoglycan concentrations were selected. The effects of hydration and proteoglycan removal on the "instantaneous" deformation were also studied. The "instantaneous" deformation was found to be of a strongly anisotropic nature in all zones. The deformation was always smaller along the Indian-ink prick pattern than at 90 degrees to it, and this effect was most pronounced in the superficial zone of cartilage. The results reveal an analogy with the tensile properties of cartilage and indicate that the collagen network is mainly responsible for controlling the "instantaneous" deformation. The proteoglycans play an indirect role by modulating the stiffness of the collagen network through their osmotic pressure.

Aged↗
PubMed1985

Studies of hydration and swelling pressure in normal and osteoarthritic cartilage.

An experimental study was carried out which involved comparing cartilage from normal and osteoarthritic joints with respect to (a) swelling pressure and (b) variation of hydration with applied pressure. The main conclusion was that whilst osteoarthritic cartilage is undoubtedly less able to resist water loss under a given applied pressure than normal cartilage, this is not due to a change in the "quality" of the proteoglycans, resulting in a change in the osmotic pressure of the latter, but simply to a decreased fixed charge density. The latter decrease is either caused by an increase in the water content - and this we attribute to a weakened collagen network - and/or to a loss of part of the proteoglycans from the tissue.

Aged↗
PubMed1984

The composition of normal and osteoarthritic articular cartilage from human knee joints. With special reference to unicompartmental replacement and osteotomy of the knee.

UNLABELLED: The articular cartilage from nineteen osteoarthritic and fourteen normal control adult human knee joints was analyzed for changes in water content, proteoglycan composition and structure, glycosaminoglycan synthesis rates, and cell content. We found no significant differences between visually intact cartilage from osteoarthritic knee joints and cartilage from control joints for any of the parameters studied. In osteoarthritic specimens in which the cartilage surface was not intact the biochemical changes depended on the degree of fibrillation. Surface-fibrillated specimens had a higher water content in the surface layers but no change in the content or synthesis rate of glycosaminoglycan. Deeply fibrillated cartilage, however, had an increased water content through its full depth, and there was a decrease in both the rate of synthesis and the content of glycosaminoglycans. CLINICAL RELEVANCE: The results of this study suggest that degenerative changes in osteoarthritic knees are focal in origin and that corrective osteotomy or unicompartmental joint replacement might be rational procedures for knees in which the cartilage in all of one compartment is visually intact.

Aged↗
PubMed1983

Structure of proteoglycans from different layers of human articular cartilage.

Full-depth plugs of adult human articular cartilage were cut into serial slices from the articular surface and analysed for their glycosaminoglycan content. The amount of chondroitin sulphate was highest in the mid-zone, whereas keratan sulphate increased progressively through the depth. Proteoglycans were isolated from each layer by extraction with 4M-guanidinium chloride followed by centrifugation in 0.4M-guanidinium chloride/CsCl at a starting density of 1.5 g/ml. The efficiency with which proteoglycans were extracted depended on slice thickness, and extraction was complete only when cartilage from each zone was sectioned at 20 microns or less. When thick sections (250 microns) were extracted, hyaluronic acid was retained in the tissue. Most of the proteoglycans, extracted from each layer under optimum conditions, could interact with hyaluronic acid to form aggregates, although the extent of aggregation was less in the deeper layers. Two pools of proteoglycan were identified in all layers by gel chromatography (Kav. 0.33 and 0.58). The smaller of these was rich in keratan sulphate and protein, and gradually increased in proportion through the cartilage depth. Chondroitin sulphate chain size was constant in all regions. The changes in composition and structure observed were consistent with the current model for hyaline-cartilage proteoglycans and were similar to those observed with increasing age in human articular cartilage.

Adult↗
PubMed1982

Nutrition of the intervertebral disc: effect of fluid flow on solute transport.

Adult dogs were injected intravenously with 35S-sulphate, and moderately exercised for one to six hours to measure isotope concentrations and profiles throughout the intervertebral discs. The isotope profiles were also observed in control animals that had been under anesthesia between injections and death. In both sets of animals, the profiles were in agreement with those expected for isotope transport by diffusion. This agreement indicates that fluid "pumping" during movement has an insignificant effect on transport of nutrients into the disc. Small solutes, e.g., O2, glucose, and sulphate, are transported into the disc chiefly by diffusion. However, calculations show that because of their low diffusivities, "pumping" may increase the rate of transport of large solutes into the disc, as it does in articular cartilage.

Anesthesia↗
PubMed1981

Nutrition of the intervertebral disc: solute transport and metabolism.

The metabolism of the canine nucleus pulposus was investigated at different oxygen tensions. It was found that even at high oxygen tensions the metabolism is mainly anaerobic, only approximately 1.5% of the glucose being converted to carbon dioxide. The concentration dependence of oxygen consumption is limited to very low oxygen tensions. Values of oxygen consumption and lactic acid production were used to calculate the concentration profiles of these substances within the nucleus pulposus, using a diffusion theory. The predicted concentration profiles were compared with the experimental measurements of concentration at various positions in the disc. The good agreement in these values found in the nucleus confirms that the main mechanism of metabolite transport is diffusion, and the main route of nutrient supply into the nucleus is via the endplate.

Anaerobiosis↗
PubMed1981

Swelling of the intervertebral disc in vitro.

Slices of the intervertebral disc swell rapidly in aqueous solutions. Following swelling, a large proportion of the proteoglycans leach out. These changes can introduce artifacts into in vitro experimental work. Swelling results from the large Gibbs-Donnan osmotic pressure of the proteoglycans which the collagen network of the disc is unable to oppose alone. Swelling can be prevented by applying pressure to disc slices either mechanically or with iso-osmotic solutions.

False Negative Reactions↗
PubMed1980

Further studies on the composition of human femoral head cartilage.

This report continues our previous studies on the composition and swelling of articular cartilage. When the protein part of the proteoglycan moiety has been taken into consideration, there is no longer a large fraction of the tissue which is not accounted for. In fact, the collagen, proteoglycans, and free electrolyte represent over 92% of the dry weight of adult femoral head cartilage, the remainder consisting most probably of other glycoproteins. Once the composition of cartilage had been well defined, it was possible to calculate the overall wet volume of tissue per unit weight of collagen for both normal and osteoarthritic cartilage. This is an important parameter, as it constitutes a direct measure of the extensibility of the collagen network. By determining the fixed charge density profile close to the articular surface, we have also been able to estimate the swelling pressure due to the proteoglycans in this region of the tissue, and to show that there is a gentle grading of osmotic stresses.

Adolescent↗