Myosin thick filaments from adult rabbit skeletal muscles

Myosin subfragment 1 (S1) forms dimers in the presence of Mg(2+) or MgADP or MgATP. The entire myosin molecule forms head-head dimers in the presence of MgATP. The angle between the two subunits in the S1 dimer is 95 degrees. Assuming that the length of the globular part of S1 is approximately 12 nm and that the S1/S2 joint (lever arm approximately 7 nm) is clearly bent, the cylinder tangent to this dimer should have a diameter of approximately 18 nm, close to the approximately 16-20 nm suggested by many studies for the diameter of thick filaments in situ. These conclusions led us to re-examine our previous model, according to which two heads from two opposite myosin molecules are inserted into the filament core and interact as dimers. We studied synthetic filaments by electron microscopy, enzyme activity assays, controlled digestion and filament-filament interaction analysis. Synthetic filaments formed by rapid dilution in the presence of 1 mM EDTA at room temperature ( approximately 22 degrees C) had all their myosin heads outside the backbone. These filaments are called superfilaments (SF). Synthetic filaments formed by slow dilution, in the presence of either 2 mM Mg(2+) or 0.5 mM MgATP and at low temperature ( approximately 0 degrees C) had one myosin head outside the backbone and one head inside. These filaments are called filaments (F). Synthetic filaments formed by slow dilution, in the presence of 4 mM MgATP at low temperature ( approximately 0 degrees C) had most of their heads inserted in the filament core. These filaments are called antifilaments (AF). These experimental results provide important new information about myosin synthetic filaments. In particular, we found that myosin heads were involved in filament assembly and that filament-filament interactions can occur via the external heads. Native filaments (NF) from rabbit psoas muscle were also studied by enzyme assays. Their structure depended on the age of the rabbit. NF from 4-month-old rabbits were three-stranded, i.e. six myosin heads per crown, two of which were inside the core and four outside. NF from 18-month-old rabbits were two-stranded (similar to F).     

Blood lactate accumulation and muscle deoxygenation during incremental exercise.

Near-infrared spectroscopy (NIRS) could allow insights into controversial issues related to blood lactate concentration ([La](b)) increases at submaximal workloads (). We combined, on five well-trained subjects [mountain climbers; peak O(2) consumption (VO(2peak)), 51.0 +/- 4.2 (SD) ml. kg(-1). min(-1)] performing incremental exercise on a cycle ergometer (30 W added every 4 min up to voluntary exhaustion), measurements of pulmonary gas exchange and earlobe [La](b) with determinations of concentration changes of oxygenated Hb (Delta[O(2)Hb]) and deoxygenated Hb (Delta[HHb]) in the vastus lateralis muscle, by continuous-wave NIRS. A "point of inflection" of [La](b) vs. was arbitrarily identified at the lowest [La](b) value which was >0.5 mM lower than that obtained at the following. Total Hb volume (Delta[O(2)Hb + HHb]) in the muscle region of interest increased as a function of up to 60-65% of VO(2 peak), after which it remained unchanged. The oxygenation index (Delta[O(2)Hb - HHb]) showed an accelerated decrease from 60- 65% of VO(2 peak). In the presence of a constant total Hb volume, the observed Delta[O(2)Hb - HHb] decrease indicates muscle deoxygenation (i.e., mainly capillary-venular Hb desaturation). The onset of muscle deoxygenation was significantly correlated (r(2) = 0.95; P < 0.01) with the point of inflection of [La](b) vs., i.e., with the onset of blood lactate accumulation. Previous studies showed relatively constant femoral venous PO(2) levels at higher than approximately 60% of maximal O(2) consumption. Thus muscle deoxygenation observed in the present study from 60-65% of VO(2 peak) could be attributed to capillary-venular Hb desaturation in the presence of relatively constant capillary-venular PO(2) levels, as a consequence of a rightward shift of the O(2)Hb dissociation curve determined by the onset of lactic acidosis.     

Increased neurodegeneration during ageing in mice lacking high-affinity nicotine receptors

We have examined neuroanatomical, biochemical and endocrine parameters and spatial learning in mice lacking the beta2 subunit of the nicotinic acetylcholine receptor (nAChR) during ageing. Aged beta2(-/-) mutant mice showed region-specific alterations in cortical regions, including neocortical hypotrophy, loss of hippocampal pyramidal neurons, astro- and microgliosis and elevation of serum corticosterone levels. Whereas adult mutant and control animals performed well in the Morris maze, 22- to 24-month-old beta2(-/-) mice were significantly impaired in spatial learning. These data show that beta2 subunit-containing nAChRs can contribute to both neuronal survival and maintenance of cognitive performance during ageing. beta2(-/-) mice may thus serve as one possible animal model for some of the cognitive deficits and degenerative processes which take place during physiological ageing and in Alzheimer's disease, particularly those associated with dysfunction of the cholinergic system.     

Vascular endothelial growth factor (VEGF) and other common tissue prognostic indicators in breast cancer: a case-control study

VEGF is a specific mitogen and survival factor for endothelial cells and a key promoter of angiogenesis in physiological and pathological conditions. Nevertheless, VEGF tissue evaluation in cancer patients as a prognostic factor compared to the conventional histological and biological parameters is still controversial. In this case-control study, tissue VEGF was retrospectively determined by immunohistochemistry and related to T, N, ER, PgR, c-erbB-2, p53, MIB-1 and cyclin D1 in 129 breast cancer patients. Seventy-four of these patients had developed distant metastases postoperatively. The remaining 55 patients had remained disease-free >10 years after surgery. In 17 (13%) of the 129 patients (six with distant metastases and eleven disease-free) tissue and plasma VEGF were concomitantly evaluated. In univariate analysis no significant differences in VEGF and tumor size were found between metastatic and disease-free patients, whereas there were significant differences in N, ER, PgR, c-erbB-2, p53, MIB-1 and cyclin D1 (p ranging from 0.001 to 0.0001). In multivariate analysis VEGF showed less significance than N, ER, c-erbB-2, MIB-1 and cyclin D1 (p = 0.012, p = 0.007, p = 0.005, p = 0.005, p = 0.002 and p = 0.001, respectively). VEGF was a significant unfavorable prognostic indicator only in the N+ subset (p = 0.015), while ER (p = 0.05 and p = 0.021) and MIB-1 (p = 0.031 and p = 0.022) were significant in both the N+ and N- subgroups. In multivariate analysis in the 74 metastatic cases VEGF did not show any significance in relation to disease-free interval and overall survival from the time of mastectomy and from the time of relapse, whereas N and PgR did (p ranging from 0.018 to 0.001). In conclusion, tissue VEGF does not seem a suitable candidate to replace conventional histological and other common biological prognostic factors in breast cancer.     

The surface roughness of lactose particles can be modulated by wet-smoothing using a high-shear mixer

The purpose of this research was to encapsulate superoxide dismutase (SOD) and catalase (CAT) in biodegradable microspheres (MS) to obtain suitable sustained protein delivery. A modified water/oil/water double emulsion method was used for poly(D,L-lactide-co-glycolide) (PLGA) and poly(D,L-lactide) PLA MS preparation co-encapsulating mannitol, trehalose, and PEG400 for protein stabilization. Size, morphology, porosity, mass loss, mass balance, in vitro release and in vitro activity were assessed by using BCA protein assay, scanning electron microscopy, BET surface area, and particle-sizing techniques. In vitro activity retention within MS was evaluated by nicotinammide adenine dinucleotide oxidation and H₂O₂ consumption assays. SOD encapsulation efficiency resulted in 30% to 34% for PLAMS and up to 51% for PLGA MS, whereas CAT encapsulation was 34% and 45% for PLGA and PLAMS, respectively. All MS were spherical with a smooth surface and low porosity. Particle mean diameters ranged from 10 to 17 μm. CAT release was prolonged, but the results were incomplete for both PLA and PLGA MS, whereas SOD was completely released from PLGA MS in a sustained manner after 2 months. CAT results were less stable and showed a stronger interaction than SOD with the polymers. Mass loss and mass balance correlated well with the release profiles. SOD and CAT in vitro activity was preserved in all the preparations, and SOD was better stabilized in PLGA MS. PLGA MS can be useful for SOD delivery in its native form and is promising as a new depot system.     

Nanotechnology and tumor imaging: seizing an opportunity

Nanoparticles, labeled with a signaling moiety for in vivo imaging, and one or more ligands for molecularly targeted specificity, hold considerable promise in oncology. Nanoparticles can serve as modular platforms, from which a wide variety of highly sensitive and specific imaging agents can be created. For example, many hundreds or thousands of atoms that provide imaging signals, such as radioisotopes, lanthanides, or fluorophores, can be attached to each nanoparticle, to form imaging agents that would provide higher sensitivity that can be obtained from agents based on small molecules. Similarly, many copies of targeted ligands can be attached to nanoparticles to markedly increase specific binding. Drugs or therapeutic isotopes can be added to create multifunctional nanoparticles. Appropriately labeled and targeted nanoparticles could lead to a paradigm change in which cancer detection, diagnosis, and therapy are combined in a single molecular complex.     

Abstraction in mathematics

Some current interpretations of abstraction in mathematical settings are examined from different perspectives, including history and learning. It is argued that abstraction is a complex concept and that it cannot be reduced to generalization or decontextualization only. In particular, the links between abstraction processes and the emergence of new objects are shown. The role that representations have in abstraction is discussed, taking into account both the historical and the educational perspectives. As languages play a major role in mathematics, some ideas from functional linguistics are applied to explain to what extent mathematical notations are to be considered abstract. Finally, abstraction is examined from the perspective of mathematics education, to show that the teaching ideas resulting from one-dimensional interpretations of abstraction have proved utterly unsuccessful.     

Tandemly duplicated Arabidopsis genes that encode polygalacturonase-inhibiting proteins are regulated coordinately by different signal transduction pathways in response to fungal infection

Polygalacturonase-inhibiting proteins (PGIPs) are plant proteins that counteract fungal polygalacturonases, which are important virulence factors. Like many other plant defense proteins, PGIPs are encoded by gene families, but the roles of individual genes in these families are poorly understood. Here, we show that in Arabidopsis, two tandemly duplicated PGIP genes are upregulated coordinately in response to Botrytis cinerea infection, but through separate signal transduction pathways. AtPGIP2 expression is mediated by jasmonate and requires COI1 and JAR1, whereas AtPGIP1 expression is upregulated strongly by oligogalacturonides but is unaffected by salicylic acid, jasmonate, or ethylene. Both AtPGIP1 and AtPGIP2 encode functional inhibitors of polygalacturonase from Botrytis, and their overexpression in Arabidopsis significantly reduces Botrytis disease symptoms. Therefore, gene duplication followed by the divergence of promoter regions may result in different modes of regulation of similar defensive proteins, thereby enhancing the likelihood of defense gene activation during pathogen infection.