Temporal changes in the physical properties of healing fractures in rabbits

Temporal changes in the physical properties of healing fractures in rabbits were studied. The mechanical environment at the fracture site was measured and monitored during healing. Animals were sacrificed after 3 to 8 weeks. The results of healing were quantified by whole bone dynamic torsional strength tests. Torque-angle curves were recorded by computer. At maximum torque four parameters were calculated: torque, angle, energy absorbed and stiffness. Torque and stiffness increased while energy remained constant and angle decreased with time. However, values calculated by a constant deformation criteria showed the three strength parameters to increase with time. The rate of increase was highest for stiffness followed by torque and energy.     

The goblet cavity matrix in the larval midgut of Hyalophora cecropia

The larval midgut of the silkmoth Hyalophora cecropia was examined using scanning electron microscopy. Goblet cells were observed to contain within their cavities a matrix plug. This matrix material was extruded onto the lumen side of the epithelium when the tissue was stretched. The rôle of this matrix material in maintenance of the capacity of the midgut to transport ions in vivo and in vitro is discussed.     

Changes in protein synthesis in rats in response to endurance training

Experiments were conducted to investigate the influence of endurance exercise training on protein synthesis in skeletal muscle, heart, and liver. Training decreased incorporation of [¹⁴C]-leucine into proteins of the stromal fraction of muscle but there was no change in amino acid incorporation into proteins of the sarcoplasmic and myofibrillar fractions. Incorporation of [¹⁴C]-leucine into the protein of heart, liver, and plasma was depressed in trained rats compared to untrained rats. The specific radioactivity of [¹⁴C]-leucine was similar in tissues of trained and untrained rats and thus the depressed amino acid incorporation represents a decrease in the rate of protein synthesis. These observations demonstrate that the adaptation of muscle protein metabolism to endurance training is quite different than the alterations during work-induced hypertrophy of muscle. The difference in adaptation probably relates to the functional differences between the types of exercise. However depression of protein synthesis in trained rats is a general effect in several tissues and not an effect localized in muscle tissue.     

Endogenous lectins in chickens and slime molds: Transfer from intracellular to extracellular sites

Endogenous lectins in both cellular slime molds and chicken tissues have been localized primarily intracellularly, in contrast with the predominantly extracellular localization of the glycoproteins, glycolipids, and glycosaminoglycans with which they might interact. Here we present evidence that lectins in both of these organisms may be externalized and become associated with the cell surface and/or extracellular materials. In chicken intestine, chicken-lactose-lectin-II is shown to be localized in the secretory granules of the goblet cells, along with mucin, and to be secreted onto the intestinal surface. In embryonic muscle, chicken-lactose-lectin-I is shown to be externalized with differentiation, ultimately becoming localized on the surface of myotubes and in the extracellular spaces. In a cellular slime mold, Dictyostelium purpureum, externalization of lectin is elicited by either polyvalent glycoproteins that bind the small amount of endogenous cell surface lectin, or by slime mold or plant lectins that bind unoccupied complementary cell surface oligosaccharides. These results suggest that externalization of endogenous lectin may be a response to specific external signals. We conclude that lectins are frequently held in intracellular reserves awaiting release for specific external functions.     

Lipochromosome mediated gene transfer: Identification and probable specificity of localization of human chromosomal material and stability of the transferents

Summary Using lipochromosomes (phospholipid-entrapped chromosomes) we have transferred the human HGPRT gene into HGPRT deficient mouse cells (A9) with a frequency of approximately 1×10⁻⁵ (Mukherjee et al., Proc. Natl. Acad. Sci. USA 75: 1361–1365; 1978). Two other genes located on the long arm of the human X-chromosome were also expressed in two independently derived populations of transferents (A9/GT3 and A9/GT4). We report here the chromosomal and enzymatic composition of human HGPRT-positive clones from each subpopulation analyzed in detail with alkaline Giemsa-11 staining. All the clones expressed human PGK and HGPRT, but one (A9/GT4C6) lacked human G6PD. In each of four clones examined microscopically, a small piece of presumptive human chromatin was visible in the karyotypes of most cells. The chromatin fragment was free or attached in each cell of an individual clone. When integrated, the human chromosomal fragment in each clone appeared associated with the centromere of the same telocentric A9 chromosome (No. 6 by Q-banding). These data suggest that: (a) substantial human chromosomal fragments can be transferred into recipient cells using the lipochromosome technique; (b) clones from human HGPRT positive A9 transferent subpopulations may or may not possess other human X-linked markers; (c) the stability of lipochromosomally transferred genes varied from clone to clone and stability is generally poor in the absence of continuous selection pressure (e.g., HAT); (d) when multiple X-linked human genes were transferred to mouse cells a cytologically detectable human chromosomal fragment was identified free or attached to a host chromosome; and (e) integration of transferred human chromosomal material into mouse chromosomes may occur at preferential site(s) in the recipient genome. This research was sponsored in part by the Office of Health and Environmental Research U.S. Department of Energy under Contract W-7405-eng-26 with the Union Carbide Corporation.     

Cytochemical analysis of intracellular calcium distribution in the anterior pituitary of the rat

Summary In an attempt to assign morphologic identities to previously distinguished functional calcium compartments in the anterior pituitary of the rat, we employed the potassium pyroantimonate technique for cation localization. Tissues were incubated for In at 37°C in control medium; with 10mM theophylline; or with depolarizing amounts of potassium. Precipitate was quantified on photomicrographs of tissue prepared for electron microscopy with a Talos Systems Digitizer. The nature of the electron dense precipitate was dependent on the experimental state of the tissue. Treatment with 5 mM EGTA abolished the dense precipitate. Electron microprobe analysis also confirmed that calcium was the predominant cation in the observed precipitate. The most significant changes in precipitate deposition occurred along the plasma membrane, the limiting membrane of secretory granules and within mitochondria. Dense precipitate was present along the plasma membrane only in cells treated with potassium. Control tissue exhibited higher levels of precipitate associated with the limiting membrane of secretory granules than either theophylline-treated or potassium-treated tissue. Mitochondria contained more precipitate in potassium-treated tissue than in controls; the mitochondria of theophylline-treated tissue contained intermediate levels of precipitate. Addition of either theophylline or depolarizing amounts of potassium has been associated with hormone secretion in anterior pituitary tissue of normal rats. Kinetic studies in our laboratory indicate that intracellular calcium shifts occur. The pyroantimonate technique is useful in verifying morphologically the calcium compartments involved in shifts in intracellular calcium.     

Procedures for the production and separation of H and M antigens in histoplasmin: Chemical and serological properties of the isolated products

Two strains of Histoplasma capsulatum were required to prepare maximum yields of H and of M antigen from histoplasmin. The antigens were separated and partially purified by a series of procedures yielding an overall recovery of 70 to 90% of the individual antigens. Stable products suitable for use as reference products were obtained when the final purification step employed DEAE-cellulose with phosphate buffer elution at increasing molarity and decreasing pH. A final step of purification of each antigen with slab acrylamide gel electrophoresis gave products which were highly reactive and specific in a variety of serological tests with sera from persons with proven cases of histoplasmosis and with natural infections of heterologous deep mycoses. These antigens were maximally active at concentrations of 2 to 16 g protein in the complement fixation, capillary precipitin, microimmunodiffusion, or immunoelectrophoresis tests; 0.5 g gave a maximum delayed cutaneous hypersensitivity reaction in homologously infected animals and caused no appreciable reaction in control animals. Although these antigens appeared to be specific when tested with sera from persons with natural infections, the M and H antigens demonstrated the presence of an additional antigen reacting with sera of rabbits immunized with cell membrane and cell particulate fractions of Blastomyces dermatitidis. After purification by electrophoresis, both the H and M antigens of some preparations showed some decomposition and loss of reactivity after storage at 5 C for more than six months. The overall results suggest that the purified H and M antigens of Heiner (12) have multiple serological reactivity and may function in precipitin reactions, complementfixing reactions, hemagglutination of formalin-fixed goose red blood cells, and as antigens for delayed cutaneous tests.     

Effect of the fluctuations in electron density within a globular protein on the excess small-angle X-ray scattering

Excess small angle X-ray scattering in solvents of differing electron density has been calculated from the crystal structures obtained for rubredoxin, trypsin inhibitor, myogen, ferricytochrome c₂, ribonuclease S, lysozyme, nuclease, myoglobin, α-chymotrypsin, elastase, subtilisin, carboxypeptidase A, thermolysin, methemoglobin, deoxyhemoglobin, and a single polypeptide chain of M₄ lactate dehydrogenase. The scattering curves for each protein can be reproduced by the sum of three curves, with the weighting of the three curves depending on the electron density of the solvent. The radius of gyration obtained from the small angle X-ray scattering by globular proteins in aqueous solution will usually exceed the values defined by the shape of the macromolecule. Deviations for certain of the proteins cited are calculated to be as large as 6%. These deviations arise from the tendency for the amino acid residues with low electron density to be situated closer to the center of the protein than the amino acid residues of high electron density. An upper limit of 19% is obtained for the discrepancy between the radius of gyration defined by the shape of a spherical globular protein of typical amino acid composition and the apparent radius of gyration measured for that protein in water by small angle X-ray scattering.     

A paradigm for axonal transport

Axonal transport has been extensively studied for a period of 20–30 years, but there is still no general consensus concerning the mechanism by which this transport process operates. An important development in this regard is the recent studies in the physical biochemistry group in the Department of Biochemistry at Monash University where it has been demonstrated that ordered flows may be generated spontaneously in polymer systems under non-equilibeium conditions. The new phenomenon exhibits many novel features, particularly with respect to polymer transport, which bear marked similarity to the behaviour of components in axonal transport. This article sets out to essentiallybring to the attention of those in the neurosciences some of the properties of ordered structured flows in polymer solutions. These properties may generate a different view in the understanding of the mechanism of axonal transport.