Are transitions in human gait determined by mechanical, kinetic or energetic factors?

It is currently unclear whether it is the need to maintain metabolic efficiency, the need to keep skeletal loading below critical force levels, or simple mechanical factors that drive the walk-to-run (W R) and run-to-walk (R-W) transitions in human gait. Eighteen adults (9 males and 9 females) locomoted on an instrumented treadmill using their preferred gait. Each completed 2 ascending (W-R) and 2 descending (R-W) series of trials under three levels of loading (0%, 15% and 30% body weight). For each trial, participants locomoted for 60 s at each of 9 different speeds -4 speeds both above and below their preferred transition speed (PTS) plus their PTS. Evidence was sought for critical levels of key kinetic (maximum vertical force, impulse, first peak force, time to first peak force and maximum loading rate), energetic (oxygen consumption, transport cost) and mechanical variables (limb lengths, strength) predictive of the gait transition. Analyses suggested the kinetic variables of time to first peak force and loading rate as the most likely determinants of the W-R and R-W transitions. (C) 2003 Elsevier Science B.V. All rights reserved.

Balancing acts: Respiratory sensations, motor control and human posture

1. The present brief review covers some novel aspects of integration between respiration and movement of the body. 2. There are potent viscerosomatic reflexes in animals involving small-diameter pulmonary afferents that, when excited, would limit exercise. However, recent studies using lobeline injections to excite pulmonary afferents in awake humans suggest that there is no evoked reflex motoneuronal inhibition. Instead, the noxious respiratory sensations generated by the vagal afferents may be crucial in the decision to stop exercise. 3. While respiratory movements may affect limb movements, the control of the trunk and limbs can involve interaction (and even interference) with key respiratory muscles, such as the diaphragm. Recent studies have revealed that not only does the diaphragm receive feed-forward drive prior to some limb movements, but that it also contracts both phasically and tonically during repetitive limb movements. 4. Thus, challenges to posture can indirectly challenge ventilation, while coordinated diaphragm contraction may contribute to control of the trunk.

In vivo DNA electrotransfer

The use of electrotransfer for DNA delivery to prokaryotic cells, and eukaryotic cells in vitro, has been well known and widely used for many years. However, it is only recently that electric fields have been used to enhance DNA transfer to animal cells in vivo, and this is known as DNA electrotransfer or in vivo DNA electroporation. Some of the advantages of this method of somatic cell gene transfer are that it is a simple method that can be used to transfer almost any DNA construct to animal cells and tissues in vivo; multiple constructs can be co-transfected; it is equally applicable to dividing and nondividing cells; the DNA of interest does not need to be subeloned into a specific viral transfer vector and there is no need for the production of high titre viral stocks; and, as no viral genes are expressed there is less chance of an adverse immunologic reaction to vector sequences. The ease with which efficient in vivo gene transfer can be achieved with in vivo DNA electrotransfer is now allowing genetic analysis to be applied to a number of classic animal model systems where transgenic and embryonic stem cell techniques are not well developed, but for which a wealth of detailed descriptive embryological information is available, or surgical manipulation is much more feasible. As well as exciting applications in developmental biology, in vivo DNA electrotransfer is also being used to transfer genes to skeletal muscle and drive expression of therapeutically active proteins, and to examine exogenous gene and protein function in normal adult cells situated within the complex environment of a tissue and organ system in vivo. Thus, in effect providing the in vivo equivalent of the in vitro transient transfection assay. As the widespread use of in vivo electroporation has really only just begun, it is likely that the future will hold many more applications for this technology in basic research, biotechnology and clinical research areas.

Slowed conduction and ventricular tachycardia after targeted disruption of the cardiac sodium channel gene Scn5a

Voltage-gated sodium channels drive the initial depolarization phase of the cardiac action potential and therefore critically determine conduction of excitation through the heart. In patients, deletions or loss-of-function mutations of the cardiac sodium channel gene, SCN5A, have been associated with a wide range of arrhythmias including bradycardia (heart rate slowing), atrioventricular conduction delay, and ventricular fibrillation. The pathophysiological basis of these clinical conditions is unresolved. Here we show that disruption of the mouse cardiac sodium channel gene, Scn5a, causes intrauterine lethality in homozygotes with severe defects in ventricular morphogenesis whereas heterozygotes show normal survival. Whole-cell patch clamp analyses of isolated ventricular myocytes from adult Scn5a(+/-) mice demonstrate a approximate to50% reduction in sodium conductance. Scn5a(+/-) hearts have several defects including impaired atrioventricular conduction, delayed intramyocardial conduction, increased ventricular refractoriness, and ventricular tachycardia with characteristics of reentrant excitation. These findings reconcile reduced activity of the cardiac sodium channel leading to slowed conduction with several apparently diverse clinical phenotypes, providing a model for the detailed analysis of the pathophysiology of arrhythmias.

Contribution of cholinergic systems to state-dependent modulation of respiratory control

Respiration is altered during different stages of the sleep-wake cycle. We review the contribution of cholinergic systems to this alteration, with particular reference to the role of muscarinic acetylcholine receptors (MAchRs) during rapid eye movement (REM) sleep. Available evidence demonstrates that MAchRs have potent excitatory effects on medullary respiratory neurones and respiratory motoneurones, and are likely to contribute to changes in central chemosensitive drive to the respiratory control system. These effects are likely to be most prominent during REM sleep, when cholinergic brainstem neurones show peak activity levels. It is possible that MAchR dysfunction is involved in sleep-disordered breathing, Such as obstructive sleep apnea. (C) 2002 Elsevier Science B.V. All rights reserved.

A comparative study of carbon gasification with O-2 and CO2 by density functional theory calculations

A comparative study of carbon gasification with O-2 and CO2 was conducted by using density functional theory calculations. It was found that the activation energy and the number of active sites in carbon gasification reactions are significantly affected by both the capacity and manner of gas chemisorption. O-2 has a strong adsorption capacity and the dissociative chemisorption of O-2 is thermodynamically favorable on either bare carbon surface or even isolated edge sites. As a result, a large number of semiquinone and o-quinone oxygen can be formed indicating a significant increase in the number of active sites. Moreover, the weaker o-quinone C-C bonds can also drive the reaction forward at (ca. 30%) lower activation energy. Epoxy oxygen forms under relatively high O-2 pressure, and it can only increase the number of active sites, not further reduce the activation energy. CO2 has a lower adsorption capacity. Dissociative chemisorption of CO2 can only occur on two consecutive edge sites and o-quinone oxygen formed from CO2 chemisorption is negligible, let alone epoxy oxygen. Therefore, CO2-carbon reaction needs (ca 30%) higher activation energy. Furthermore, the effective active sites are also reduced by the manner Of CO2 chemisorption. A combination of the higher activation energy and the fewer active sites leads to the much lower reaction rate Of CO2-carbon.

Cadherin-directed actin assembly: E-cadherin physically associates with the Arp2/3 complex to direct actin assembly in nascent adhesive contacts

Cadherin cell adhesion molecules are major determinants of tissue patterning which function in cooperation with the actin cytoskeleton [1-4]. In the context of stable adhesion [1], cadherin/catenin complexes are often envisaged to passively scaffold onto cortical actin filaments. However, cadherins also form dynamic adhesive contacts during wound healing and morphogenesis [2]. Here actin polymerization has been proposed to drive cell surfaces together [5], although F-actin reorganization also occurs as cell contacts mature [6]. The interaction between cadherins and actin is therefore likely to depend on the functional state of adhesion. We sought to analyze the relationship between cadherin homophilic binding and cytoskeletal activity during early cadherin adhesive contacts. Dissecting the specific effect of cadherin ligation alone on actin regulation is difficult in native cell-cell contacts, due to the range of juxtacrine signals that can arise when two cell surfaces adhere [7]. We therefore activated homophilic ligation using a specific functional recombinant protein. We report the first evidence that E-cadherin associates with the Arp2/3 complex actin nucleator and demonstrate that cadherin binding can exert an active, instructive influence on cells to mark sites for actin assembly at the cell surface.

Decreased expression of the Id3 gene at 1p36.1 in ovarian adenocarcinomas

The molecular events that drive the initiation and progression of ovarian adenocarcinoma are not well defined. We have investigated changes in gene expression in ovarian cancer cell lines compared to an immortalized human ovarian surface epithelial cell line (HOSE) using a cDNA array. We identified 17 genes that were under-expressed and 10 genes that were over-expressed in the cell lines compared to the HOSE cells. One of the genes under-expressed in the ovarian cancer cell lines, Id3, a transcriptional inactivator, was selected for further investigation. Id3 mRNA was expressed at reduced levels in 6 out of 9 ovarian cancer cell lines compared to the HOSE cells while at the protein level, all 7 ovarian cancer cell lines examined expressed the Id3 protein at greatly reduced levels. Expression of Id3 mRNA was also examined in primary ovarian tumours and was found in only 12/38 (32%) cases. A search was conducted far mutations of Id3 in primary ovarian cancers using single stranded conformation polymorphism (SSCP) analysis. Only one nucleotide substitution, present also in the corresponding constitutional DNA, was found in 94 ovarian tumours. Furthermore no association was found between LOH at 1p36 and lack of expression of Id3. These data suggest that Id3 is not the target of LOH at 1p36. (C) 2001 Cancer Research Campaign.

Provision of 4-1BB ligand enhances effector and memory CTL responses generated by immunization with dendritic cells expressing a human tumor-associated antigen

Up-regulation of receptor-ligand pairs during interaction of an MHC-presented epitope on dendritic cells (DCs) with cognate TCR may amplify, sustain, and drive diversity in the ensuing T cell immune response. Members of the TNF ligand superfamily and the TNFR superfamily contribute to this costimulatory molecule signaling. In this study, we used replication deficient adenoviruses to introduce a model tumor-associated Ag (the E7 oncoprotein of human papillomavirus 16) and the T cell costimulatory molecule 4-IBBL into murine DCs, and monitored the ability of these recombinant DO to elicit E7-directed T cell responses following immunization. Splenocytes from mice immunized with DCs expressing E7 alone elicited E7-directed effector and memory CTL responses. Coexpression of 4-1BBL in these E7-expressing DO increased effector and memory CTL responses when they were used for immunization. 4-1BBL expression up-regulated CD80 and CD86 second signaling molecules in DO. We also report an additive effect of 4-IBBL and receptor activator of NF-kappaB/receptor activator of NF-kappaB ligand coexpression in E7-transduced DC inummogens on E7-directed effector and memory CTL responses and on MHC class II and CD80/86 expression in DCs. Additionally, expression of 4-1BBL in E7-transduced DCs reduced nonspecific T cell activation characteristic of adenovirus vector-associated immunization. The results have generic implications for improved or tumor Ag-expressing DC vaccines by incorporation of exogenous 4-1BBL. There are also specific implications for an improved DC-based vaccine for human papillomavirus 16-associated cervical carcinoma.

Numerical simulations of wind and temperature structure within an Alpine lake basin, Lake Tekapo, New Zealand

High-resolution numerical model simulations have been used to study the local and mesoscale thermal circulations in an Alpine lake basin. The lake (87 km(2)) is situated in the Southern Alps, New Zealand and is located in a glacially excavated rock basin surrounded by mountain ranges that reach 3000 m in height. The mesoscale model used (RAMS) is a three-dimensional non-hydrostatic model with a level 2.5 turbulence closure scheme. The model demonstrates that thermal forcing at local (within the basin) and regional (coast-to-basin inflow) scales drive the observed boundary-layer airflow in the lake basin during clear anticyclonic summertime conditions. The results show that the lake can modify (perturb) both the local and regional wind systems. Following sunrise, local thermal circulations dominate, including a lake breeze component that becomes embedded within the background valley wind system. This results in a more divergent flow in the basin extending across the lake shoreline. However, a closed lake breeze circulation is neither observed nor modelled. Modelling results indicate that in the latter part of the day when the mesoscale (coast-to-basin) inflow occurs, the relatively cold pool of lake air in the basin can cause the intrusion to decouple from the surface. Measured data provide qualitative and quantitative support for the model results.