微机控制的韧带动态力学特性测试系统

本系统是为自动测试人体韧带或类似组织的动态力学特性试验而研制的。在试验时,受控的加载过程和数据采集过程同时进行。系统向韧带试件提供一个快速的匀速可控的拉伸载荷,模拟人体剧烈运动的实况,同时实时采集力和变形的数据。系统还提供对所采集数据的分析手段,从而得到力、变形、应力、应变、弹性模量和变形能等参数之间的关系,并可以图形和文字形式输出。系统亦可将各数据文件转换为其它应用软件包可接受的形式,以便利用标准商品软件包的数据和图象处理能力。系统采用菜单提示的人机对话方式进行监控。     

Hepatic gluconeogenesis and Krebs cycle fluxes in a CCl4 model of acute liver failure

Acute liver failure was induced in rats by CCl4 administration and its effects on the hepatic Krebs cycle and gluconeogenic fluxes were evaluated in situ by 13C NMR isotopomer analysis of hepatic glucose following infusion of [U-13C]propionate. In fed animals, CCl4 injury caused a significant increase in relative gluconeogenic flux from 0.80+/-0.10 to 1.34 +/-0.24 times the flux through citrate synthase (p<0.01). In 24-h fasted animals, CCl4-injury also significantly increased relative gluconeogenic flux from 1.36+/-0.16 to 1.80+/-0.22 times the flux through citrate synthase (p<0.01). Recycling of PEP via pyruvate and oxaloacetate was extensive under all conditions and was not significantly altered by CCl4 injury. CCl4 injury significantly reduced hepatic glucose output by 26% (42.8+/-7.3 vs 58.1+/-2.4 micromol/kg/min, p=0.005), which was attributed to a 26% decrease in absolute gluconeogenic flux from PEP (85.6+/-14.6 vs 116+/-4.8 micromol/kg/min, p<0.01). These changes were accompanied by a 47% reduction in absolute citrate synthase flux (90.6+/-8.0 to 47.6+/-8.0 micromol/kg/min, p<0.005), indicating that oxidative Krebs cycle flux was more susceptible to CCl4 injury. The reduction in absolute fluxes indicate a significant loss of hepatic metabolic capacity, while the significant increases in relative gluconeogenic fluxes suggest a reorganization of metabolic activity towards preserving hepatic glucose output.     

Ca2+ permeability of the plasma membrane induced by rotavirus infection in cultured cells is inhibited by tunicamycin and brefeldin A

Rotavirus infection of cultured cells induces a progressive increase in plasma membrane permeability to Ca2+. The viral product responsible for this effect is not known. We have used tunicamycin and brefeldin A to prevent glycosylation and membrane traffic and study the involvement of viral glycoproteins, NSP4 and/or VP7, in rotavirus-infected HT29 and MA104 cells. In infected cells, we observed an increase of plasma membrane Ca2+ permeability and a progressive depletion of agonist-releasable ER pools measured with fura 2 and an enhancement of total Ca2+ content measured as 45Ca2+ uptake. Tunicamycin inhibited the increase in membrane Ca2+ permeability, induced a depletion of agonist-releasable and 45Ca2+-sequestered pools. Brefeldin A inhibited the increase of Ca2+ permeability and the increase in 45Ca2+ uptake induced by infection. We propose that the glycosylated viral product NSP4 (and/or VP7) travels to the plasma membrane to form a Ca2+ channel and hence elevate Ca2+ permeability.     

Supra-maximal cycling efficiency assessed in humans by using a new protocol

This study proposed a non-invasive method to determine the gross (GE, no baseline correction), net (NE, resting metabolism as the baseline correction) and work (WE, unloaded cycling as the baseline correction) efficiencies during cycling at an intensity higher than the maximal aerobic power (MAP). Twelve male subjects performed two exercises consisting of 4 min at 50% MAP followed either by 8 min at 63% MAP or by 8 sequences of 60 s divided into 10 s at 130% MAP and 50 s at 50% MAP (i.e., 63% MAP on average). Oxygen uptake was continuously measured to calculate GE, NE and WE at 50%, 63% and 130% MAP, and the data presented as the means and standard deviations. The GE values were 18.2%, 19.1%, 22.7%, the NE values were 22.4%, 22.8%, 24.3% and the WE values were 34.2%, 31.4% and 27.2% at 50%, 63% and 130% MAP, respectively. The GE and NE increased (P<0.001) whereas the WE decreased (P<0.001) with each increment in power output. The GE was lower than the NE (P<0.001) at 50% and 63% MAP and than the WE (P<0.001) at all intensities. The NE was lower (P<0.001) than the WE at 50% and 63% MAP. These results showed that (1) efficiency index values obtained during supra-maximal exercise were consistent with previous proposals and (2) the efficiency-power output relationships were not limited to sub-maximal intensity levels but were confirmed at higher power output.     

Effects of muscle blood flow on muscle energy metabolism and contractility

Energy metabolism and contractility of rat’s femoral triceps muscles were investigated by varying blood flow levels with ligation of the femoral artery. The triceps were stimulated electrically to produce equivalent conditions as exercise loading, and phosphorus nuclear magnetic resonance (³¹P-NMR) spectra and muscle tension levels were monitored. The ratio of inorganic phosphate (Pi) to ‘Pi+phosphocreatine (PCr)’, i.e. Pi/(Pi+PCr), was obtained from ³¹P-NMR spectra. This ratio was related to the reduction of blood flow ratio (BFR) during and after the stimulation period, whereas before starting the stimulation, there was no significant correlation. These findings indicate: (i) muscle energy metabolism during decreased blood flow is influenced by the stimulation (loading) given to the muscle; and (ii) changes of muscle energy metabolism due to decreased muscle blood flow during the loading is evaluable by measuring ³¹P-NMR spectra. Muscle tension reached the plateau 8 min after starting the stimulation, regardless of BFR, but muscle tension ratio decreased as BFR became lower. This indicates that decreased blood flow diminishes muscle contractility, and then lowers muscle function levels. Our findings indicate that muscle blood flow plays an important role in muscle function, and blood flow and muscle function levels are evaluable by measuring ³¹P-NMR spectra of the muscle.     

Effect of a Water‐Soluble Polymer on Polymer Interdiffusion in P(MMA‐co‐BA) Latex Films

We describe non‐radiative energy‐transfer experiments to measure the rates of polymer interdiffusion in P(MMA‐co‐BA) latex films formed in the presence of poly(vinyl alcohol) (PVOH). PVOH had relatively little effect on the initial efficiency of energy transfer, even when the amount of PVOH was large enough to form the continuous phase. Since Φ_ET(0) is a measure of the interfacial area between D‐ and A‐labeled cells in the film, we conclude that under these circumstances the dispersed P(MMA‐co‐BA) copolymer is in the form of clusters with many contacts between particles containing D and A labels. These large amounts of PVOH also reduce the amount of polymer diffusion that takes place when the films are annealed. When smaller amounts of PVOH are present, the effects are measurable but much smaller. In the presence of 2 to 17 wt.‐% PVOH, the polymer diffusion rate is retarded. The magnitude of the effect increases with the amount of PVOH present, and the effect is larger at 45 °C than at 63 °C. We show that the PVOH has its largest influence at the very early stages of polymer diffusion.

Schematic representation of an energy transfer experiment, which monitors polymer interdiffusion in a latex film.     

Angular homeostasis IX. Polygonal orbits with a moving target: Implications for anomalous numbers of digits in congenital heart disease

This paper explores properties of discrete processes in which a pursuer seeks a target that is moving at constant velocity r that is a fixed proportion of the speed of the pursuer. The pursuer is subjected to proportional angular homeostasis, so chosen that the number of steps per circuit is small. The orbits relative to the target may assume any of four forms: polygons that reverse their sense an infinite number of times; or polygons that after a finite number of reversals ultimately come to have an integer numbers of sides; or have a rational numbers of sides; or have an irrational number of sides that densely fill an annulus. None of the polygons is regular. In the parameter space, the boundary line between the first of these sets and the other three has a somewhat bizarre pattern and may possibly be fractal, but no proof is forthcoming. Unlike the pattern with a stationary target, there may be a set or catchment of diverse values of the speed ratio, r, and the correction coefficient, b that all result in figures of some specified number, n, of sides (although with vertices in differing locations). Catchments have been found for only those polygons that have the winding number of 1. The implications are discussed that this property has for the genetic coding of biological traits that are countable. Some attention is also paid to the relevance of polygons with few sides to ontogenic growth when the correction coefficient is cyclically arc- or time-dependent. © 1993 Wiley-Liss, Inc.     

Homo- and heteromeric assembly of TRP channel subunits

Mammalian homologues of the Drosophila melanogaster transient receptor potential (TRP) channels are the second largest cation channel family within the superfamily of hexahelical cation channels. Most mammalian TRP channels function as homooligomers and mediate mono- or divalent cation entry upon activation by a variety of stimuli. Because native TRP channels may be multimeric proteins of possibly complex composition, it is difficult to compare cation conductances in native tissues to those of clearly defined homomeric TRP channel complexes in living cells. Therefore, the possibility of heteromeric TRP channel assembly has been investigated in recent years by several groups. As a major conclusion of these studies, most heteromeric TRP channel complexes appear to consist of subunit combinations only within relatively narrow confines of phylogenetic subfamilies. Although the general capability of heteromer formation between closely related TRP channel subunits is now clearly established, we are only beginning to understand whether these heteromeric complexes are of physiological significance. This review summarizes the current knowledge on the promiscuity and specificity of the assembly of channel complexes composed of TRPC-, TRPV- and TRPM-subunits of mammalian TRP channels.     

Faster gastric emptying for glucose-polymer and fructose solutions than for glucose in humans

Summary This study examined the rates of gastric emptying for water and 13 different carbohydrate-containing solutions in seven subjects, using conventional gastric intubation techniques. The rates of gastric emptying for water and a 10% glucose-polymer solution were also measured during 90 min of treadmill running at 75% of each subject's maximum oxygen consumption . At rest, 15% glucose-polymer (P) and fructose (F) solutions emptied more rapidly from the stomach and provided a faster rate of carbohydrate delivery than did a 15% glucose (G) solution (p<0.05). The G solutions showed a constant energy delivery rate of 3.3 kcal · min^–1; energy delivery from P and F solutions rose with increasing solution concentrations. The osmolality of the gastric aspirate predicted the rate of gastric emptying for all solutions (p<0.05) but overestimated rates of emptying for 10% and 15% P solutions and underestimated emptying rates for 10% and 15% F solutions. Exercise at 75% decreased the rate of gastric emptying of water but not of 10% P solutions. Thus the different rates of gastric emptying for different carbohydrate-containing solutions were not entirely explained by differences in osmolality. Furthermore, exercise may have different effects on the gastric emptying rates of water and carbohydrate solutions.     

NEAT – non‐exercise activity thermogenesis – egocentric & geocentric environmental factors vs. biological regulation

Non‐exercise activity thermogenesis (NEAT) is the energy expenditure of all physical activities other than volitional sporting‐like exercise. NEAT includes all those activities that render us vibrant, unique and independent beings such as going to work, playing guitar, toe‐tapping and dancing. The factors that account for the 2000 kcal day^?1 variability of NEAT can be categorized as environmental or biological. The environmental determinants of NEAT can be view using one of two models. In the egocentric model we consider a single person as the focus, e.g. ‘my job’. In the geocentric model we consider the ‘environment’ as the focus, e.g. well‐lit and safe walk ways. These models provide us with a theoretical framework to understand NEAT and how best to intervene to promote NEAT. As well as environmental effectors of NEAT, there are also biological regulatory mechanisms that enable us to account for three‐quarters of the biological variance in susceptibility and resistance to fat gain with human over‐feeding. NEAT is likely to be regulated through a central mechanism that integrates NEAT with energy intake and energy stores so that NEAT is activated with over‐feeding and suppressed with under‐feeding. In conclusion, NEAT is likely to serve as a crucial thermoregulatory switch between energy storage and dissipation that is biologically regulated and influenced, and perhaps over‐ridden, by environment. Deciphering the role of NEAT may lead to a better understanding of the pathogenesis, prevention and treatment of obesity.