Separation of septal influences on lordosis, ultrasound production, and body weight

It is well known that macromolecules like albumin are markedly restricted in their passage across the glomerular capillary wall. However, the relative importance of solute size, charge and shape is currently debated since much of the previous work is based on dextran in neutral or charge-modified forms. These polymers have certain drawbacks that make them less suitable for analysis of capillary permeability and the notion of a glomerular charge barrier has therefore been questioned. Moreover, macromolecules larger than albumin (mol. wt. 69,000) have been suggested to pass through nonselective 'shunt' pathways. In order to study glomerular permeability, isolated rat kidneys were perfused with albumin solutions containing trace amounts of two differently radiolabelled isoenzymes of lactate dehydrogenase (LDH) at low temperature to inhibit tubular function. The isoenzymes have similar size (mol. wt. 140,000) and shape but differ in charge, one carrying a negative net surface charge (LDH1, -19) and the other being slightly cationic (LDH5, +2). The urine and perfusate samples were subjected to high pressure liquid chromatography (HPLC) gel-filtration to allow for measurements of intact LDH. The fractional clearance was 0.11% +/- 0.04% for the anionic LDH1 and 0.56% +/- 0.07% for LDH5, whereas that for albumin was 0.21% +/- 0.03% at a glomerular filtration rate of 0.11 +/- 0.01 mL min-1 g-1 kidney wet weight. The results were analysed using a homogenously charged membrane model and are compatible with a charge density of 35 mEq L-1, with 95% confidence interval of 26-41 mEq L-1. These findings suggest a significant glomerular charge selectivity for proteins substantially larger than albumin. The charge density is, however, far less than estimated from dextran studies.     

Fibrillogenesis in tendon healing: an experimental study

The aim of this study was the histochemical, immunohistochemical and ultrastructural analysis of reparative fibrillogenesis in experimental lesions of Achilles' tendon. Subtotal tenotomy of Achilles' tendon was performed in twenty Wistar rats. The scar tissue was analysed 2, 4, 7, 14, 21, 30, 45 and 60 days post-operatively. Histochemical, (resorcin-fuchsin, aldehyde-fuchsin, iron haematoxylin and Fullmer and Lillie's methods) immunohistochemical (antibody against collagen I, II and elastin) and ultrastructural analyses were performed. Three phases in the healing process were distinguished: 1) inflammatory, 2) proliferative, and 3) remodelling phase. The inflammatory phase was characterised by haematoma, fibrin deposition, inflammatory cells, fibroblasts, beginning of collagen fibrillogenesis (200-400 A ? fibrils) and oxytalan fibrils. The proliferative phase was characterised by angiogenesis and fibroblast proliferation. Collagen fibres displayed a random arrangement and had a diameter of 400-600 A. Immature elastic fibres reached maximum tissutal concentration. In the remodelling phase, hypocellularity, normal vascularisation, tendon crimps, collagen fibres (800-1,000 A ?), elastic fibres with increased elastin deposition and reduction in oxytalan fibres were observed. In the course of the healing process collagen and elastic fibre fibrillogenesis exhibited consistent quantitative and qualitative variations (i.e. differences in the type and diameter of fibrils). The present study suggests that, together with other matrix macromolecules, also elastic fibres (oxytalan, elaunin and mature) are synthesised in significantly higher amounts during reparative fibrillogenesis and play a role in cell-matrix interaction.     

Immunohistochemical quantitation for extracellular matrix proteins in rats with glomerulonephritis induced by monoclonal anti-Thy-1.1 antibody

During clot retraction, platelets interact with fibrin resulting in marked reduction of clot volume. Altered fibrin structure has been reported to affect clot retraction as measured by serum expression. This study was performed to test whether such altered retraction was the result of increased resistance to network collapse or due to decreased force development by platelets. Altered fibrin structure was documented as variation of fibre mass/length ratios (mu) and shifts in clot elastic modulus. The force developed by platelets during clotting was measured directly. Increasing the fibrinogen concentration led to thinner fibre formation (decreased mu), and a linear increase in gel elastic modulus. Over a fibrinogen concentration range of 100 to 400 mg/dl, force development was minimally affected. Force development and clot elastic modulus increased in a linear fashion with increasing platelet concentration. Increasing the calcium concentration from 5 to 20 mM caused a 160% increase in fibrin fibre size (mu), and a 52% decline in clot modulus. Force developed at 1200 s declined by 17%. At 15 mg/ml, dextran and hydroxyethyl starch (HES) also increased mu, and decreased clot modulus; however, both agents markedly reduced force development. Increasing ionic strength or the addition of IgG decreased mu and increased gel elastic modulus. Force development increased modestly with increased ionic strength, did not change with addition of IgG in saline and declined with addition of IgG in maltose. This study indicates that force development is primarily dependent on platelet function while clot modulus depends on both fibrin structure and platelet function.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dextran on the molecular structure and tensile behaviour of human fibrin

Characteristic changes induced by dextran during the conversion of fibrinogen to fibrin have previously been shown to be associated with profound alterations in morphology of fibrin. However, whether dextran is incorporated into the fibrin molecule and whether morphological changes are associated with alterations in mechanical behaviour of formed fibrin was unclear. The investigations described show that the fibrin made in the presence of dextran has a shortened syneresis time, a lowered modulus of elasticity, an increased elongation and diminished ultimate strength at break. The molecular composition of fibrin clots remains unaltered despite the altered mechanical properties and morphological changes. Furthermore, dextran is not incorporated into the fibrin structure in any appreciable quantity. It is suggested that these several effects of dextran on clot morphology, tensile behaviour and kinetics of fibrin formation arise from increased forces of attraction between fibrin molecules such that fibrin chains are held together by weak secondary cross-links rather than by stronger primary cross-links which are hidden within the thicker fibrin chain bundles.     

Lipid composition of high density lipoproteins in familial hyperlipoproteinemias

OBJECTIVE: Comparison of side effects (fever shivering and/or allergic reactions, collapse, symptomatic hypocalcaemia) of the different substitution fluids used during therapeutical plasmapheresis. DESIGN: Multicentric retrospective comparative study designed to explore the side effects due to the replacements fluids (albumin alone or associated with dextran 40, modified fluid gelatin, hydroxyethyl starch), and to determine the best combination in patients undergoing plasmapheresis. PATIENTS: 46,895 procedures were performed on 5,167 patients between 1990 and 1994. The analysis concerns 33,962 sessions, divided into two groups (group 1: 21,079 sessions from 1990 to 1992 comparing albumin alone versus combined albumin-macromolecules and the different combinations among these, group 2: 12,883 sessions in 1993-1994 comparing albumin alone versus albumin-hydroxyethyl starch). Because of the diversity of the products used, 13,029 sessions were not studied because groups of small sample sizes were formed. MEASUREMENTS AND RESULTS: In group 1, the comparison of albumin + macromolecules with albumin alone, shows the best haemodynamic tolerance, lower frequency of fever shivering and/or allergic reactions in the albumin alone subgroup. On the other hand, hypocalcaemia is significantly higher in this subgroup. The combinations albumin + dextran 40 (but after hapten inhibition) and albumin + hydroxyethyl starch are equivalent. Albumin + modified fluid gelatin is the combination presenting the highest incidence in terms of allergic manifestations. In group 2, albumin + hydroxyethyl starch versus albumin alone, the former is preferable in terms of the three side effects studied. CONCLUSION: The results of this study show a combination of albumin 4% hydroxyethyl starch to replace plasma during plasma exchange to be the method presenting the lowest morbidity and the best cost/effectiveness ratio.     

Local hemodynamics, permeability, and oxygen metabolism during acute inflammation of innervated or denervated isolated equine joints

OBJECTIVES: To determine oxygen metabolism, permeability, and blood flow in isolated joints in response to interleukin 1beta (IL-1beta) and contribution of innervation. SAMPLE POPULATION: One metacarpophalangeal (MCP) joint of 24 adult horses. PROCEDURE: The MCP joint was isolated for 6 hours in a pump-perfused, auto-oxygenated, innervated or denervated preparation. Isolated joints were assigned to the following 4 groups: control, control-denervated, inflamed, and inflamed-denervated, and inflammation was induced by intra-articular injection of IL-1beta. Circuit arterial and venous pressures, flows, and blood gas tensions, synovial fluid production, and intra-articular pressure were measured. Total vascular resistance; oxygen delivery, consumption, and extraction ratio (ER); and permeability surface area product were calculated. Synovial membrane blood flow was determined at 0, 60, and 330 minutes. Synovial membrane wet-to-dry ratio was obtained, and permeability to macromolecules was determined by intra-articular injection of Evans blue albumin and fluorescein isothiocyanate-conjugated dextran. RESULTS: Oxygen delivery and synovial membrane blood flow progressively increased but were not different among groups. Oxygen consumption and ER significantly increased in inflamed joints, as did intraarticular pressure and synovial fluid production. Inflamed joints had greater wet-to-dry ratio. Albumin permeability significantly increased in the villous synovial membrane of the inflamed groups, and dextran permeability was increased in the innervated groups, with a trend toward increased permeability in inflamed groups. CONCLUSION: Inflammation significantly increased oxygen demand, which was initially met by increased ER. Permeability to small molecules was increased with inflammation; innervation increased permeability to large molecules. Use of an isolated joint model enabled documentation of the physiologic responses of the joint to acute inflammation.     

The role of fibrinogen degradation products in the pathogenesis of the respiratory distress syndrome

Pulmonary dysfunction in awake rabbits was induced by intravenous infusion of a highly purified human fibrin split product (fragment D). The dose of infused fragment D was chosen to achieve observed plasma concentrations of fibrin split products in hospitalized patients with severe burns or trauma (about 100mug of FSP/ml of blood). Four hours after infusion, the animals displayed a clinical and pathological pattern which closely resembled post-traumatic acute respiratory distress syndrome, including hypoxia, hypocarbia, thrombocytopenia, increased pulmonary capillary permeability to albumin, interstitial edema, hypertrophy of alveolar lining cells, and intra-alveolar hemorrhage. In vivo production of fibrin split products by infusion of thrombin with induction of secondary fibrinolysis produced similar pulmonary changes, although intravascular clots and platelet aggregates also were prominent. Infusion of human fibrinogen and human albumin at identical doses failed to induce pulmonary dysfuction. The results suggest that fibrin split products (fragment D) alone are toxic to the respiratory system and may contribute to the development of acute respiratory distress syndrome in severely traumatized or burned patients.     

Dynamic light scattering study of fine semiflexible fibrin networks

Fine fibrin networks have been investigated using the dynamic light scattering (DLS) technique. At the shortest delay times, t, the dynamic structure factor s(q,t) is found to depend on time according to an exponential function and, at intermediate delay times (up to 1 ms), to a stretched exponential. At longer times (t > 1 ms), a progressively increasing deviation from the stretched exponential behaviour has been observed. These results are in agreement with the theoretical predictions of a recently forwarded model for semiflexible polymers in semidilute solutions [K. Kroy and E. Frey, Physical Review E 55 (1996) p. 3092.], despite the fact that fibrin networks are made up of crosslinked branched polymers. The model, moreover, allows the calculation from the initial decay rate gamma q(0) of the average diameter of the fibrin fibres, a. The value of a = 30 +/- 2 nm, at fibrinogen concentration c(f) = 1676 nM and ionic strength 0.5, fits well into the data reported in electron microscopy studies. A concentration dependence of the average diameter of the fibrin fibres has been observed which saturates at the highest concentrations. The diameter of fibrin fibres is an important component in determining the physical properties of the fibrin networks, since the radial growth of fibrin fibres is limited by twisting during protofibrils aggregation. Our results indicate the importance of taking into account intrinsic semiflexibility in studying the physical properties of 'real' polymers and emphasize the high sensitivity of the DLS technique to investigate biological polymers also at the lowest concentrations where the systems are very fragile.     

Borderline disorder in Turkey: a 2- to 4-year follow-up

1. Conventional and germ-free rats were fed a fibre-free elemental diet with or without the addition of fermentable dietary fibres. We have previously reported that fibre was associated with greatly increased epithelial cell proliferation, but only in the conventional group, implying that it is the breakdown of fibre by the colonic microflora that is the main determinant of mucosal proliferation in the hind gut. The relationship of these changes to various plasma hormones implicated in intestinal growth control are described in this paper. 2. The most dramatic finding was that plasma levels of enteroglucagon and peptide YY were greatly increased in the germ-free groups. The response of these rats to fibre differed in that fibre decreased levels of enteroglucagon and peptide YY in the germ-free animals, but increased them in the conventional rats. Gastrin and insulin levels were significantly lowered in the fibre-supplemented groups, but were not affected by the microflora. 3. These results corroborate our previous findings that the effects of fibre and its fermentation are dynamically complex, and demonstrate that, like proliferation, direct effects and indirect fermentation-derived effects on plasma hormones also coexist.     

Finding a universal low-viscosity polymer for DNA separation

We have investigated the viscosity of different commercially available polymers in solution and found that dextran has a low viscosity compared to other polymers of comparable molecular weight and resolving power. This makes it a potentially useful matrix for DNA separation in capillary electrophoresis, where either short time or low pressure are preferred for matrix replacement. We showed that dextran performs well for the separation of oligonucleotides and double-stranded DNA fragments. Together with the well-known application for protein separation, this makes dextran a universal polymer for the separation of biological macromolecules.     

The configuration of fibrin clots determines capillary morphogenesis and endothelial cell migration

In the living organism, capillary growth frequently occurs in a fibrin-rich extracellular matrix. The structure and the mechanical properties of fibrin clots are influenced by various macromolecules (i.e., hyaluronic acid and thrombospondin) and also by pH, ionic strength, and thrombin concentrations of the milieu in which they polymerize. The configuration (three-dimensional architecture) and the rigidity of fibrin clots correlate with their opacity measured by spectrophotometric absorbance readings at 350 nm. By using bovine pulmonary artery endothelial cells and bovine fibrinogen, we show here that transparent fibrin clots (A(350) < 1.0), polymerized at > or = pH 7.5 or in the presence of increased thrombin or sodium chloride concentrations, strongly stimulated capillary morphogenesis in vitro. In contrast, opaque fibrin gels (A(350) > 1.5), polymerized at pH 7.2 or in the presence of dextran, stimulated only the migration of endothelial cells but not capillary morphogenesis. We demonstrate that the angiomorphogenic effects of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) are strongly dependent on the structure of the fibrin clots. Our findings suggest that bFGF/VEGF primarily stimulate the proliferation of endothelial cells, whereas the three-dimensional architecture of the fibrin matrix is decisive for capillary morphogenesis.     

Partitioning and diffusion of proteins and linear polymers in polyacrylamide gels

The equilibrium partition coefficient (K) and diffusion coefficient (Dgel) of two proteins and two linear polymers were measured as a function of polymer content of a 2.7% cross-linked polyacrylamide (PA) gel. The gel concentration, expressed as a volume percentage of PA in the gel (phi), varied between 0 and 14%. The measurements were made by fluorescence spectroscopy; fluorescent dyes were covalently attached to the macromolecules. The dependence of K on phi for the proteins agrees with a model of the gel network as randomly placed, impenetrable rods. The diffusion data are interpreted in terms of an effective medium theory for the mobility of a sphere in a Brinkman fluid. Using values of the Brinkman parameter in the literature, the effective medium model with no adjustable parameters fits the diffusion data for the proteins very well but underpredicts Dgel for the linear polymers. The gel effect on partitioning is significantly greater than that on diffusion. The permeability (KDgel) of bovine serum albumin decreased by 10(3) over the range phi = 0 --> 8%, and the ratio of permeabilities for ribonuclease compared to BSA increased from 2 to 30.     

A unique property of a plasma proteoglycan, the C1q inhibitor. An anticoagulant state resulting from its binding to fibrinogen

The C1q inhibitor, C1qI, an approximately 30-kD circulating chondroitin-4 sulfate proteoglycan, displayed concentration-dependent prolongation of plasma and fibrinogen solution clotting times. Under factor XIIIa catalyzed cross-linking conditions and maximum C1qI concentrations, minor amounts of clot formed displaying complete gamma-gamma dimer formation but virtually no alpha-polymer formation. The anticoagulant effect was undiminished by its binding to C1q, by increased ionic strength, and by CaCl2, but was abolished by incubation of C1qI with chondroitinase ABC. 125I-labeled C1qI bound to immobilized fibrinogen, fibrin monomer, fibrinogen plasmic fragments D1 and E, and fibrin polymers. Occupancy on the E domain required uncleaved fibrinopeptides together with another structure(s), and it did not decrease binding of thrombin to fibrinogen. Occupancy on the D domain did not decrease the fibrinogen binding to fibrin monomer. We conclude that the E domain occupancy impaired fibrinopeptide cleavage, and occupancy on the D domain impaired polymerization, both steric hindrance effects. C1qI binding to fibrinogen explains at least in part the well-known fibrin(ogen) presence in immune complex-related lesions, and the fibrinogen presence in vascular basement membranes and atheromata. We postulate that fibrin binding by resident basement membrane proteoglycans provides dense anchoring of thrombus, substantially enhancing its hemostatic function.     

Development of porous defects in plasma membranes of adenosine triphosphate-depleted Madin-Darby canine kidney cells and its inhibition by glycine

Studies during the past decade have led to the recognition of a fundamental, widely expressed mechanism of structural damage in energy-deprived cells, which is suppressed by physiologic levels of glycine and is independent of Ca2+ availability or alterations of cytosolic free Ca2+. To gain insight into this process, Madin-Darby canine kidney (MDCK) cells were depleted of adenosine triphosphate (ATP) by a mitochondrial uncoupler in glucose-free medium, and intracellular free Ca2+ was clamped at 100 nM to avoid calcium cytotoxicity. Although the ATP-depleted cells swelled and blebbed and their plasma membranes appeared to be under tension, they nevertheless became permeable to macromolecules. The plasma membranes of these cells retained structural continuity, as determined by morphologic observations, and confocal microscopy of a plasma membrane protein label (Biotin: Ultra Avidin-Texas Red) and a lipid label (NBD-sphingomyelin). Using fluoresceinated dextrans of graded molecular size, membrane permselectivity was examined noninvasively by confocal microscopy. Measured as inside/outside ratios of fluorescence intensity, the permeability indices showed progressively greater restriction to diffusion of increasingly larger dextran molecules across plasma membranes, with sharp break-points between 70,000 and 145,000 daltons (d). The results indicated that the membranes behaved as if they were perforated by water-filled channels or "pores," with size-exclusion limits of molecular dimensions. The membrane defects evolved from small pores permeable only to propidium iodide (668 d) and the smallest dextran (4,000 d), before enlarging with time to become permeable to larger dextrans. Inclusion of glycine during ATP depletion did not affect cell swelling or blebbing but completely prevented the development of permeability defects. Treatment of cells before ATP depletion with a membrane-impermeant homobifunctional "nearest neighbor" cross-linking agent, 3,3' dithiobis(sulfosuccinimidylpropionate), suppressed the development of permeability defects, even in the absence of glycine. These observations suggest that the cellular abnormality that is suppressed by glycine involves rearrangement of plasma membrane proteins to form water-filled pores large enough to leak macromolecules.     

Partitioning of proteins in dextran/hydrophobically modified dextran aqueous two-phase systems

Partitioning of proteins was studied in aqueous two-phase systems composed of the polymers dextran and hydrophobically modified dextran. The modified dextrans were benzoyl dextran with a degree of substitution of 0.17 and valeryl dextran with a degree of substitution of 0.20. Phase diagrams for the systems of dextran/benzoyl dextran and dextran/valeryl dextran were determined at room temperature. The proteins studied were beta-galactosidase, bovine serum albumin, beta-lactoglobulin, lysozyme, myoglobin and cytochrome C. The partition coefficients of a series of salts were determined in dextran/benzoyl dextran two-phase systems. The addition of salts had strong effect on the partitioning of proteins. This effect was related to protein net charge and the position of the ions in the Hofmeister series. Cross partitioning of bovine serum albumin was studied in a dextran/benzoyl dextran aqueous two-phase system.     

Stress reactions and stress fractures in the high performance athlete. Causes, diagnosis and therapy

The plasmatic albumin concentration (3.5-4.5 g/dl) represents about 60% of the total plasma protein. Only 25-40% of whole albumin belongs to the intravascular pool, the majority is distributed in the interstitial space especially of the skin. Main physiological effects of plasmatic albumin are the control of the plasmatic volume by preservation of the colloid oncotic pressure (COP) and the plasmatic transport including the binding of drugs. The COP is the main factor for fixation of the intravascular volume and the prevention of interstitial oedema. The acute volume effects of albumin can be totally replaced by synthetic colloids like hydroxyethyl starch, gelatine, and dextran, with the exception of volume substitution in neonates. In intensive care medicine, the COP-effects of albumin can almost be replaced by synthetic colloids as well. A positive COP-effect by administration of human or synthetic macromolecules is unlikely in patients with capillary leak. For therapy control, the direct measurement of COP is superior to the calculation derived from albumin or total protein. The global clinical situation of the patient and the course of haematocrit should be respected as well. For prevention of interstitial pulmonary oedema, a COP of 15-20 mmHg should be achieved. Up to now, no clinical study verified a positive effect of albumin substitution regarding outcome or incidence of complications in intensive-care patients. Thus, an albumin therapy to maintain a COP of 15-20 mmHg in intensive-care patients is only recommended if a capillary leak is unlikely and the dose limits of synthetic colloids are attained.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fibre uniformity and cavitation during the consolidation of metal-matrix composite via fibre-mat and matrix-foil diffusion bonding

Fibre uniformity is important for ensuring overall mechanical properties of a composite. The conditions for achieving uniform fibre distribution in solid-state consolidated composites are quantitatively analysed. It is shown that the uniformity is influenced by initial fibre spacing, fibre packing and foil thickness before consolidation and matrix flow during consolidation. A graphical technique is presented to determine optimum pre-consolidation arrangement of fibres and foils for a given volume fraction. Residual cavities in partially bonded composites are observed in both hexagonally and rectangularly packed fibre arrays. Foil bending is mainly the cause for the cavities found in the former case, whereas in the rectangular array an ear defect is observed after an intermediate stage of bonding and is believed to be responsible for the voids which form during matrix flow in this case. The initiation of the ear defect is determined by matrix volume incompressibility and quantitatively analysed with respect to different conditions of the flow constraint imposed during consolidation. These predictions are compared favourably with experimental results.     

Decreased protein kinase C activation mediates inhibitory effect of norathyriol on serotonin-mediated endothelial permeability

We examined the mechanisms of norathyriol on the serotonin-induced increased permeability of rat heart endothelial cell monolayers. The present study showed that the activation of rat heart endothelial cell protein kinase C by phorbol myristate acetate led to the dose-dependent increase in endothelial permeability to albumin, an effect that was inhibited by staurosporine (a protein kinase inhibitor). Staurosporine also attenuated the serotonin-induced increase in permeability. Norathyriol abolished both serotonin- and phorbol myristate acetate-induced permeability. We investigated whether norathyriol, by inhibiting protein kinase C activation, attenuated the serotonin-induced permeability. Immunofluorescence studies demonstrated that norathyriol prevented the redistribution of protein kinase C isozymes following stimulation with serotonin. Western blot analysis showed that norathyriol significantly inhibited the serotonin-induced translocation of the alpha protein kinase C isozyme from the cytosolic to the particulate fraction. In conclusion, norathyriol attenuates the serotonin-induced permeability of rat heart endothelial cells to macromolecules in association with inhibition of protein kinase C activation. This decrease in endothelial cell permeability may be one of the mechanisms for the protective effects of norathyriol against edema formation in response to inflammatory agonists in vivo.     

Region- and age-dependent variations of muscle fibre properties

The cytophotometric-morphometrical analysis of extensor digitorum longus and soleus muscles of 2.5 and 18 months old rats revealed regional and age-dependent differences in fibre type distribution, fibre area and fibre type related-enzyme activities which characterize contractility and metabolic profile. Variations along the longitudinal axis from the origin to the insertion and along three transversal axes from superficial to deep were found dependent on the muscle investigated. For example, the fibres of extensor digitorum longus muscle showed increased contractile and glycolytic capacities near insertion and the fibres of soleus muscle increased oxidative capacity in its middle part. Furthermore, the contribution of the fibre type that is dominant in a muscle (fast-glycolytic fibre type in extensor digitorum longus and slow-oxidative fibre type in soleus muscle) to the total number of fibres increased from origin to insertion by 15 and 30%, respectively. Along the superficial-deep axes the oxidative capacity of all fibres increased, the most in fast fibres of the soleus muscle by approximately 50%. In soleus muscle, a decrease of cross areas of all fibre types from superficial to deep was found, correlating negatively with the succinate dehydrogenase activity of the fibres. In extensor digitorum longus muscle the change in cross areas of slow-oxidative and fast-oxidative glycolytic fibres was dependent on the position of the transversal axis in the muscle. The results suggest that distribution patterns of fibre types and the metabolic make up of individual muscle fibres are adapted on the basis of local functional demands. In both muscles, higher numbers and increased oxidative capacity of fast-glycolytic fibres were found during ageing, but variations from superficial to deeper regions were irrespective of age.     

Sprint-training effects on some contractile properties of single skinned human muscle fibres

The effects of sprint training on the contractile properties of human muscle fibres obtained by needle biopsy were investigated. Individual fibres were mechanically skinned and activated by Ca(2+)- and Sr(2+)-buffered solutions at pH 7.1, and allocated to distinct populations on the basis of their contractile characteristics. The majority of fibres sampled pre-training could be separated into the three major fibre groups: Populations I (24/70, 34%), II (25/70, 36%) and III (18/70, 26%), which exhibited characteristics similar to those of histochemically classified type I, IIA and IIB fibres, respectively. The remainder (3/70, 4%) represented another fibre group, with intermediate characteristics. The muscle fibres were also activated by Ca2+ at a reduced pH of 6.6, to mimic the intracellular acidification that occurs during intense exercise. Lowering pH increased the threshold for contraction by Ca2+, reduced Ca2+ sensitivity, and increased the steepness of the force-pCa relationship, in all fibres sampled from the three major fibre groups. Maximum force was not significantly reduced in any fibre population. In the post-training sample, the three major fibre types were present in different proportions: Populations I (10/52, 19%), II (20/52, 38.5%) and III (11/52, 21%). Three other fibre groups sampled in low numbers exhibited contractile characteristics intermediate between Population I and Population II. Following sprint training all of the three main fibre populations exhibited higher thresholds for contraction by, and lower sensitivities to, Sr2+ but not Ca2+, compared with the fibres sampled pre-training. Maximum force was significantly lower in Population II fibres after sprint training. At pH 6.6, post-trained Population III fibres exhibited even lower Ca2+ sensitivity, with concomitant increases in the threshold for contraction and force-pCa curve steepness.