Slowed growth of cultured fibroblasts from human radiation wounds

To study radiation effect separate from the microcirculation, fibroblasts were cultured from four patients with radiation wounds. Cells could be grown from irradiated tissue near the ulcer and from control normal tissue, but no cells could be cultured from the ulcers. The ability of radiation-treated fibroblasts to attach to the substrate and form colonies was less than that of unirradiated cells. Irradiated skin fibroblasts from the four patients had significantly longer mean generation times than did control cells. During log-phase growth (1 to 9 days), the population doublings of damaged cells were significantly reduced compared to colonies from normal cells. These data suggest a permanent intrinsic radiation effect on fibroblasts or a selective ablation of faster-growing fibroblast subpopulations that is not dependent on decreased blood supply.     

Biochemical adaptation of mitochondria,muscle, and whole-animal respiration to endurance training

The experimental intervention of exercise training has been used to study mitochondrial biosynthesis, and the physiologic integration of subcellular, cellular, and whole-animal energetics. Gross mitochondrial composition was unchanged in rat muscle by a 10-week program of endurance treadmill running. The mitochondrial concentration of iron-sulfur clusters, cytochromes, flavoprotein, dehydrogenases, oxidases, and membrane protein and lipid, as well as the ratios of each component to the others, maintained constant proportions. The mitochondrial content of muscle, however, increased by approximately 100% as did absolute tissue oxidative capacity. The soluble portions of mitochondria maintained a constant total protein content and mass, relative to the membrane fraction, despite adaptive changes in the specific activities of some citric acid-cycle enzymes. Mitochondria from endurance-trained muscles generated normal transmembrane potentials, ADP/O ratios, and respiratory control ratios. Muscle oxidase activity was highly correlated (r = 0.92) with endurance capacity, which increased 403%. Whole-animal maximal O₂ consumption (), however, increased only 14% and was a relatively poor predictor of endurance. Thus, mitochondrial factors, rather than , must play an important role in dictating the limits of endurance activity. Conversely, was strongly related to the maximal intensity of work which could be attained aerobically (r = 0.82). Comparison of O₂ consumption at the mitochondrial, muscle, and whole-animal levels revealed that maximal muscle oxidase activity was not an absolute limitation to : It is concluded that other factors intervene to control the percentage of muscle O₂ consumption capacity which may be utilized during exercise.     

Slowed diffusion in tumors revealed by microfiberoptic epifluorescence photobleaching

It has not been possible to measure diffusion deep in solid tissues such as tumors because of the limited light penetration of conventional optical techniques. Here we report a microfiberoptic epifluorescence photobleaching (MFEP) method in which photobleaching is done by laser epi-illumination through a multimode fiberoptic whose micron-sized tip can be introduced deep into tissues. We applied MFEP to measure the diffusion of fluorescent macromolecules in tumors in living mice, at depths well beyond those accessible by surface optical measurements. Macromolecule diffusion was slowed about twofold within 200 microm of the surface of a solid tumor, but was slowed greater than tenfold beyond 500 microm. Our results reveal a remarkable and previously unrecognized slowing of diffusion deep in tumors, which correlated with the differing tissue architectures of tumor periphery versus core, and with altered tumor vasculature produced by aquaporin-1 deletion. MFEP should have wide applications for measuring diffusion in organs, solid tumors and other light-inaccessible tissue masses.     

Slowed decomposition is biotically mediated in an ectomycorrhizal, tropical rain forest

Bacteria and fungi drive the cycling of plant litter in forests, but little is known about their role in tropical rain forest nutrient cycling, despite the high rates of litter decay observed in these ecosystems. However, litter decay rates are not uniform across tropical rain forests. For example, decomposition can differ dramatically over small spatial scales between low-diversity, monodominant rain forests, and species-rich, mixed forests. Because the climatic patterns and soil parent material are identical in co-occurring mixed and monodominant forests, differences in forest floor accumulation, litter production, and decomposition between these forests may be biotically mediated. To test this hypothesis, we conducted field and laboratory studies in a monodominant rain forest in which the ectomycorrhizal tree Dicymbe corymbosa forms >80% of the canopy, and a diverse, mixed forest dominated by arbuscular mycorrhizal trees. After 2 years, decomposition was significantly slower in the monodominant forest (P < 0.001), but litter production was significantly greater in the mixed forest (P < 0.001). In the laboratory, we found microbial community biomass was greater in the mixed forest (P = 0.02), and the composition of fungal communities was distinct between the two rain forest types (P = 0.001). Sequencing of fungal rDNA revealed a significantly lower richness of saprotrophic fungi in the monodominant forest (19 species) relative to the species-rich forest (84 species); moreover, only 4% percent of fungal sequences occurred in both forests. These results show that nutrient cycling patterns in tropical forests can vary dramatically over small spatial scales, and that changes in microbial community structure likely drive the observed differences in decomposition.     

Extracellular respiration

Although it has long been known that microbes can generate energy using diverse strategies, only recently has it become clear that a growing number involve electron transfer to or from extracellular substrates. The best-known example of what we will term 'extracellular respiration' is electron transfer between microbes and minerals, such as iron and manganese (hydr)oxides. This makes sense, given that these minerals are sparingly soluble. What is perhaps surprising, however, is that a number of substrates that might typically be classified as 'soluble' are also respired at the cell surface. There are several reasons why this might be the case: the substrate, in its ecological context, might be associated with a solid surface and thus effectively insoluble; the substrate, while soluble, might simply be too large to transport inside the cell; or the substrate, while benign in one redox state, might become toxic after it is metabolized. In this review, we discuss various examples of extracellular respiration, paying particular attention to what is known about the molecular mechanisms underlying these processes. As will become clear, much remains to be learned about the biochemistry, cell biology and regulation of extracellular respiration, making it a rich field of study for molecular microbiologists.     

The amino acid nutrition of respiration deficient and respiration competentSaccharomyces

Respiration deficient variants and normal, respiration competent strains ofSaccharomyces require an exogenous supply of arginine, glutamic acid, leucine, lysine and valine to attain optimal growth. The growth of variant cells, however, is stimulated by these compounds to a far greater proportionate extent than that of normal cells. The petite condition, therefore, exaggerates the limitations in amino acid biosyntheses existent in normal yeasts but does not create new ones. The relative respiratory limitations characteristic of petite and normal cells during growth will account for the qualitative and quantitative aspects of their amino acid requirements.     

Obtaining Specimens with Slowed,Accelerated and Reversed Aging in the Honey Bee Model

Societies of highly social animals feature vast lifespan differences between closely related individuals. Among social insects, the honey bee is the best established model to study how plasticity in lifespan and aging is explained by social factors.The worker caste of honey bees includes nurse bees, which tend the brood, and forager bees, which collect nectar and pollen. Previous work has shown that brain functions and flight performance senesce more rapidly in foragers than in nurses. However, brain functions can recover, when foragers revert back to nursing tasks. Such patterns of accelerated and reversed functional senescence are linked to changed metabolic resource levels, to alterations in protein abundance and to immune function. Vitellogenin, a yolk protein with adapted functions in hormonal control and cellular defense, may serve as a major regulatory element in a network that controls the different aging dynamics in workers.Here we describe how the emergence of nurses and foragers can be monitored, and manipulated, including the reversal from typically short-lived foragers into longer-lived nurses. Our representative results show how individuals with similar chronological age differentiate into foragers and nurse bees under experimental conditions. We exemplify how behavioral reversal from foragers back to nurses can be validated. Last, we show how different cellular senescence can be assessed by measuring the accumulation of lipofuscin, a universal biomarker of senescence.For studying mechanisms that may link social influences and aging plasticity, this protocol provides a standardized tool set to acquire relevant sample material, and to improve data comparability among future studies.     

Self-controlled artificial respiration

We compared respiratory parameters during natural and self-controlled mechanical breathing to investigate mechanisms of respiratory control in alert humans. The self-control of mechanical breathing is realised manually: duration and velocity of air flow are controlled by left and right hands, resp. In this case, the respiratory afferent information is used to control activity of hand muscles but not of breathing muscles. The findings show that lung ventilation during self-controlled mechanical breathing increases by 7.5 l/min. at resting, by 6.3 l/min. during an exercise, as compared with the natural breathing. The increase in the lung ventilation occurs on account of an increase in the tidal volume but the frequency of the self-controlled mechanical breathing tends to be lesser at resting and was statistically significantly lower in exercise that at natural breathing. The exercise increases the lung ventilation by 13.0 l/min. at natural breathing and by 11.8 l/min. during self-controlled mechanical breathing. The findings suggest that the increased lung ventilation during self-controlled mechanical breathing is connected with creation of a new movement skill, and the modified pattern of self-controlled mechanical breathing is caused by a process of cortical transformation of respiratory afferents signals to efferent signals towards the hand muscles.     

论双重呼吸

人教版初中<生物>教材第十一章"鸟纲".对于鸟类"双重呼吸"的概念是这样叙述的:"鸟类每呼吸一次,空气就两次经过肺部,在肺内进行两次气体交换.因此,这种特殊的呼吸方式,叫做"双重呼吸".