Eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man

The primary purpose of this investigation was to study the eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man using a recently developed combined isometric, concentric and eccentric controlled velocity dynamometer (the SPARK System). A secondary purpose was to compare the method error associated with maximal voluntary concentric and eccentric torque output over a range of testing velocities. 21 males (21-32 years) performed on two separate days maximal voluntary isometric, concentric and eccentric contractions of the quadriceps femoris at 4 isokinetic lever arm velocities of 0 degree.s-1 (isometric), 30 degrees.s-1, 120 degrees.s-1 and 270 degrees.s-1. Eccentric peak torque and angle-specific torques (measured every 10 degrees from 30 degrees to 70 degrees) did not significantly change from 0 degrees.s-1 to 270 degrees.s-1 (p greater than 0.005) with the exception of angle-specific 40 degrees torque, which significantly increased; p less than 0.05). The mean method error was significantly higher for the eccentric tests (10.6% +/- 1.6%) than for the concentric tests (8.1% +/- 1.7%) (p less than 0.05). The mean method error decreased slightly with increasing concentric velocity (p greater than 0.05), and increased slightly with increasing eccentric velocity (p greater than 0.05). A tension restricting neural mechanism, if active during maximal eccentric contractions, could possibly account for the large difference seen between the present eccentric torque-velocity results and the classic results obtained from isolated animal muscle.     

Effect of long-term anemia and retransfusion on central circulation during exercise

The bulk modulus and the shear modulus describe the capacity of material to resist a change in volume and a change of shape, respectively. The values of these elastic coefficients for air-filled lung parenchyma suggest that there is a qualitative difference between the mechanisms by which the parenchyma resists expansion and shear deformation; the bulk modulus changes roughly exponentially with the transpulmonary pressure, whereas the shear modulus is nearly a constant fraction of the transpulmonary pressure for a wide range of volumes. The bulk modulus is approximately 6.5 times as large as the shear modulus. In recent microstructural modeling of lung parenchyma, these mechanisms have been pictured as being similar to the mechanisms by which an open cell liquid foam resists deformations. In this paper, we report values for the bulk moduli and the shear moduli of normal air-filled rabbit lungs and of air-filled lungs in which alveolar surface tension is maintained constant at 16 dyn/cm. Elevating surface tension above normal physiological values causes the bulk modulus to decrease and the shear modulus to increase. Furthermore, the bulk modulus is found to be sensitive to a dependence of surface tension on surface area, but the shear modulus is not. These results agree qualitatively with the predictions of the model, but there are quantitative differences between the data and the model.     

Implementation of periodic acid-thiosemicarbazide-silver proteinate staining for ultrastructural assessment of muscle glycogen utilization during exercise

Summary Distribution of glycogen particles in semithin and ultrathin sections of biopsy samples from human muscles subjected to either short- or long-term running were investigated using PAS and Periodic Acid-ThioSemiCarbazide-Silver Proteinate (PA-TSC-SP) staining methods. Glycogen particles were predominantly found immediately under the sarcolemma or aligned along the myofibrillar Iband. After long-term exhaustive exercise type-1 fibers with a few or no glycogen particles in the core of the fibers were frequently observed. The subsarcolemmal glycogen stores of these depleted type-1 fibers were about three times as large as after exhaustive short-time exercise. Another indication of utilization of subsarcolemmal glycogen stores during anaerobic exercise was that many particles displayed a pale, rudimentary shape. This observation suggests fragmental metabolization of glycogen. Thus, depending on type of exercise and type of fiber differential and sequential glycogen utilization patterns can be observed.     

Cellular origin of fibronectin in interspecies hybrid kidneys

The cellular origin of fibronectin in the kidney was studied in three experimental models. Immunohistochemical techniques that use cross-reacting or species-specific antibodies against mouse or chicken fibronectin were employed. In the first model studied, initially avascular mouse kidneys cultured on avian chorioallantoic membranes differentiate into epithelial kidney tubules and become vascularized by chorioallantoic vessels. Subsequently, hybrid glomeruli composed of mouse podocytes and avian endothelial-mesangial cells form. In immunohistochemical studies, cross-reacting antibodies to fibronectin stained vascular walls, tubular basement membranes, interstitium, and glomeruli of mouse kidney grafts. The species-specific antibodies reacting only with mouse fibronectin stained interstitial areas and tubular basement membranes, but showed no reaction with hybrid glomeruli and avian vascular walls. In contrast, species-specific antibodies against chicken fibronectin stained both the interstitial areas and the vascular walls as well as the endothelial-mesangial areas of the hybrid glomeruli, but did not stain the mouse-derived epithelial structures of the kidneys. In the second model, embryonic kidneys cultured under avascular conditions in vitro develop glomerular tufts, which are devoid of endothelial cells. These explants showed fluorescence staining for fibronectin only in tubular basement membranes and in interstitium. The avascular, purely epithelial glomerular bodies remained unstained. Finally, in outgrowths of separated embryonic glomeruli, the cross-reacting fibronectin antibodies revealed two populations of cells: one devoid of fibronectin and another expressing fibronectin in strong fibrillar and granular patterns. These results favor the idea that the main endogenous cellular sources for fibronectin in the embryonic kidney are the interstitial and vascular cells. All experiments presented here suggest that fibronectin is not synthesized by glomerular epithelial cells in vivo.     

A lipophilic iron chelator can replace transferrin as a stimulator of cell proliferation and differentiation

Of the different growth supplements used in chemically defined media, only transferrin is required for differentiation of tubules in the embryonic mouse metanephros. Since transferrin is an iron-carrying protein, we asked whether iron is crucial for tubulogenesis. Differentiation of metanephric tubules both in whole embryonic kidneys and in a transfilter system was studied. The tissues were grown in chemically defined media containing transferrin, apotransferrin, the metal-chelator complex ferric pyridoxal isonicotinoyl hydrazone (FePIH), and excesses of ferric ion. Although we found that apotransferrin was not as effective as iron-loaded transferrin in promoting proliferation in the differentiating kidneys, excess ferric ion at up to 100 microM, five times the normal serum concentration, could not promote differentiation or proliferation. However, iron coupled to the nonphysiological, lipophilic iron chelator, pyridoxal isonicotinoyl hydrazone, to form FePIH, could sustain levels of cell proliferation and tubulogenesis similar to those attained by transferrin. Thus, the role of transferrin in cell proliferation during tubulogenesis is solely to provide iron. Since FePIH apparently bypasses the receptor-mediated route of iron intake, the use of FePIH as a tool for investigating cell proliferation and its regulation is suggested.     

Exogenous fibronectin is not required for organogenesis in vitro

The biological effect of plasma fibronectin on the differentiation of embryonic mouse kidney and tooth was studied in organ cultures. Transferrin (50 micrograms/ml) was a strong mitogen for kidney cells, whereas the addition of soluble fibronectin (50 to 250 micrograms/ml) had no detectable effect on differentiation or proliferation. The same serum-free, transferrin-containing medium did not support tooth differentiation. However, fibronectin was not a necessary serum component because fibronectin-free serum supported tooth development. It was demonstrated with antibodies specific for human fibronectin that the exogenously added human fibronectin at 50 micrograms/ml did not become incorporated to the cultured organs. Only minimal incorporation to the kidney basement membrane area was observed when fibronectin concentration was 250 micrograms/ml. The mesenchymal stroma and the basement membranes of the kidney and tooth rudiments cultured in fibronectin-free media stained intensely with conventional fibronectin antibodies, indicating endogenous production of fibronectin. Outgrowing epithelial cells from isolated kidney tubules produced fibronectin as well as laminin. The results suggest that the fibronectin found in the stroma and basement membranes is an endogenous product of the developing tissues and that plasma fibronectin is not required for in vitro organogenesis. The results also indicate that it is difficult to study the effect of fibronectin on morphogenetic processes because it may not penetrate the organ explants in vitro.     

Differentiation and vascularization of the metanephric kidney grafted on the chorioallantoic membrane

The origin and development of mouse kidney vasculature were examined in chorioallantoic grafts of early kidney rudiments and of experimentally induced explants of separated metanephric mesenchymes. Whole kidney rudiments developed into advanced stages, expressed the segment-specific antigenic markers of tubules and the polyanionic coat of the glomeruli. In contrast to development in vitro, these grafts regularly showed glomeruli with an endothelial component and a basement membrane expressing type IV collagen and laminin. The glomerular endothelial cells in these grafts were shown to carry the nuclear structure of the host. This confirms the outside origin of these cells and the true hybrid nature of the glomeruli. When in vitro induced mesenchymes were grafted on chorioallantoic membranes, abundant vascular invasion was regularly found but properly vascularized glomeruli were exceptional. Uninduced, similarly grafted mesenchymal explants remained avascular as did the undifferentiated portions of partially induced mesenchymal blastemas. It is concluded that the stimulation of the host endothelial cells to invade into the differentiating mesenchyme requires the morphogenetic tissue interaction between the ureter bud and the mesenchyme. The induced metanephric cells presumably start to produce chemoattractants for endothelial cells at an early stage of differentiation. Kidney development thus seems to require an orderly, synchronized development of the three cell lineages: the branching ureter, the induced, tubule-forming mesenchyme, and the invading endothelial cells of outside origin.     

Developmentally regulated conversion of mesenchyme to epithelium

Polarized epithelial cells perform many critical physiological functions in multicellular organisms. Recent embryological studies of the conversion of nonpolar mesenchymal cells to epithelium in the developing mouse kidney have provided vital information on the molecular mechanisms that initiate epithelial cell polarization. To become polar, the cells first attach to the basement membrane that is produced by the developing epithelial cells themselves. Of the basement membrane components, laminin has a key role in the development of epithelial cell polarity. Laminin is a multidomain glycoprotein composed of three subunits: A, B1, and B2. One binding site for epithelial cells is found in the carboxyl-terminal part of the A chain of laminin. Antibodies reacting with this part of laminin inhibit polarization of developing epithelial cells in organ cultures of embryonic kidneys. Expression studies also suggest that the A chain of laminin is important for epithelial cell polarization; the A chain appears when the cells begin to polarize, whereas B chains are expressed at an earlier stage of development. The studies of conversion of mesenchyme to epithelium suggest that morphogenesis can be controlled by differential expression of laminin chains.     

Demonstration of laminin,a basement membrane glycoprotein,in routinely processed formalin-fixed human tissues

Summary Laminin was demonstrated by immunoperoxidase and immunofluorescence staining in sections of normal human tissues fixed in formalin and routinely processed in paraffin. Exposure of the sections to a solution of pepsin (Burns et al. (1980) Histochemistry 6773–78) revealed the antigenicity of this basement membrane glycoprotein. Sections from paraffin blocks stored for years at room temperature could be stained with this procedure. Normal human tissues, developing fetal tissues and tumors could be stained with this method. The staining patterns were similar to those seen in unfixed frozen sections. It thus appears that basement membrane components can be detected by immunohistological means from routinely processed histological samples, once the sections are pretreated with proteases. Staining for laminin could be used in embryonic studies and in histopathology to study the relation of cells to basement membranes and for the visualization of normal and abnormal vascularization.To whom offprint requests should be sent