Background:Residual force enhancement(rFE),defined as increased isometric force following active lengthening compared to a fixed-end isometric contraction at the same muscle length and level of activation,is present a...Background:Residual force enhancement(rFE),defined as increased isometric force following active lengthening compared to a fixed-end isometric contraction at the same muscle length and level of activation,is present across all scales of muscle.While rFE is always present at the cellular level,often rFE"non-re sponders"are observed during joint-level voluntary contractions.Methods:We compared rFE between the joint level and single fiber level(vastus lateralis biopsies)in 16 young males.In vivo voluntary kneeextensor rFE was measured by comparing steady-state isometric torque between a stretch-hold(maximal activation at 150°,stretch to 70°,hold)and a fixed-end isometric contraction,with ultrasonographic recording of vastus lateralis fascicle length(FL).Fixed-end contractions were performed at 67.5°,70.0°,72.5°,and 75.0°;the joint angle that most closely matched FL of the stretch-hold contraction's isometric steady-state was used to calculate rFE.The starting and ending FLs of the stretch-hold contraction were expressed as%optimal FL,determined via torqueangle relationship.Resu lts:In single fiber experiments,the starting and ending fiber lengths were matched relative to optimal length determined from in vivo testing,yielding an average sarcomere excursion of~2.2-3.4μm.There was a greater magnitude of rFE at the single fiber(~20%)than joint level(~5%)(p=0.004),with"non-re sponders"only observed at the joint level.Conclusion:By comparing rFE across scales within the same participants,we show the development of the rFE non-responder phenomenon is upstream of rFE's cellular mechanisms,with rFE only lost rather than gained when scaling from single fibers to the joint level.展开更多
BACKGROUND:Heterotopic ossification of skeletal muscle is a clinically serious complication.For heterotopic ossification of skeletal muscles,the cells involved in the process of heterotopic ossification remain unclear...BACKGROUND:Heterotopic ossification of skeletal muscle is a clinically serious complication.For heterotopic ossification of skeletal muscles,the cells involved in the process of heterotopic ossification remain unclear.OBJECTIVE:To investigate the involvement of myocytes,fascia cells,and endothelial cells in the process of heterotopic ossification in skeletal muscle and to observe the cell origin of heterotopic ossification in skeletal muscle induced by bone morphogenetic protein 4.METHODS:Both C2C12 cells and the myotubes formed by the C2C12 cells in the induction medium were cultured,and 500 ng/mL bone morphogenetic protein 4 was added to the medium respectively,and whether the C2C12 cells and myotubes continued to proliferate within 10 days under the treatment were observed under a microscope.Myogenic cells(L6,derived from rats)and fibroblast-derived cells(derived from human)were co-cultured.After treatment with 500 ng/mL bone morphogenetic protein 4 and 10 ng/mL transforming growth factor-β,osteogenic and chondrogenic differentiation potential within 21 days were observed using Safranine O staining and Alcian blue staining.Using transgenic animal FVB/N-TgN(TIE2-LacZ)182Sato mice,15μL of adeno-associated virus-bone morphogenetic protein 4(5×1010 PFU/mL)were implanted in the thigh muscle space of genetic mice for 10 and 14 days.X-gal staining was used to observe the formation of new blood vessel endothelium in the differentiated bone.RESULTS AND CONCLUSION:(1)Bone morphogenetic protein 4 caused myotube breakdown and increased C2C12 cell proliferation.Compared with other groups,the pure fibroblast-derived cell group had a higher area of positive alcian blue and safarin O staining(P<0.05)and a lower area of alkaline phosphatase staining(P<0.05),while the pure L6 group had a bigger area of alkaline phosphatase staining(P<0.05)but a smaller area of positive alcian blue and safarin O staining(P<0.05).(2)Transplantation of adeno-associated virus-bone morphogenetic protein 4-adsorbed gelatin sponge into FVB/N-TgN(TIE2-LacZ)182Sato mice resulted in heterotopic ossification.(3)X-gal staining results demonstrated that there was no obvious staining in chondrocytes and differentiated bones and Tie2+endothelial cells did not participate in the formation of the alienated bone.(4)These findings verify that fibroblasts are the primary source of osteoblasts during the adeno-associated virus-bone morphogenetic protein 4-induced ectopic endochondral ossification in skeletal muscle,but myogenic cells are the main source of osteoblasts.Tie2+endothelial cells might not be the cell source for cartilage and bone.展开更多
The architectural development of Acacia karroo conforms to Troll’s model. Growth of the branches is modular and sympodial with heteroblastic leaves on all long shoots of the tree, including the seedling. Axillary bud...The architectural development of Acacia karroo conforms to Troll’s model. Growth of the branches is modular and sympodial with heteroblastic leaves on all long shoots of the tree, including the seedling. Axillary buds tend to proliferate especially on flowering shoots where they form fascicles consisting of up to 10 inflorescences arranged in two parallel serial rows per leaf axil. Most axillary buds are sylleptic and basal buds which give rise to short shoots, each producing two to five cataphylls each season, but no flowers. Inflorescences are only produced on long shoots (modules) of the current season. After flowering the terminal part of the module aborts, trees are usually andromonoecious with capitate inflorescences containing 40 to 100 flowers each, with some male and some hermaphrodite. Some trees produce only male flowers. Anthesis in the same inflorescence, the same tree as well as amongst trees of the same community are synchronised and occur at intermittent intervals, each lasting three or more days at a time. Flowers are protogynous and pollen is produced in polyads, each consisting of 16 pollen grains. Ovaries contain 10 to 14 ovules each. The concave stigma has space for only one polyad which can fertilise all ovules in the ovary after a single pollination event. Fruit set is low with 0 to 10 fruits (pods) per inflorescence.展开更多
Mosquitoes are exceptional in their ability to pierce into human skin with a natural ultimate painless microneedle, named fascicle. Here the structure of the Aedes albopictus mosquito fascicle is obtained using a Scan...Mosquitoes are exceptional in their ability to pierce into human skin with a natural ultimate painless microneedle, named fascicle. Here the structure of the Aedes albopictus mosquito fascicle is obtained using a Scanning Electron Microscope (SEM), and the whole process of the fascicle inserting into human skin is observed using a high-speed video imaging technique. Direct measurements of the insertion force for mosquito fascicle to penetrate into human skin are reported. Results show that the mosquito uses a very low force (average 18 μN) to penetrate into the skin. This force is at least three orders of magnitude smaller than the reported lowest insertion force for an artificial microneedle with an ultra sharp tip to insert into the human skin. In order to understand the piercing mechanism of mosquito fascicle tip into human multilayer skin tissue, a numerical simulation is conducted to analyze the insertion process using a nonlinear finite element method. A good agreement occurs between the numerical results and the experimental measurements.展开更多
基金supported by the Natural Sciences and Engineering Research Council of Canada(NSERC,Grant No.RGPIN-2024-03782).
文摘Background:Residual force enhancement(rFE),defined as increased isometric force following active lengthening compared to a fixed-end isometric contraction at the same muscle length and level of activation,is present across all scales of muscle.While rFE is always present at the cellular level,often rFE"non-re sponders"are observed during joint-level voluntary contractions.Methods:We compared rFE between the joint level and single fiber level(vastus lateralis biopsies)in 16 young males.In vivo voluntary kneeextensor rFE was measured by comparing steady-state isometric torque between a stretch-hold(maximal activation at 150°,stretch to 70°,hold)and a fixed-end isometric contraction,with ultrasonographic recording of vastus lateralis fascicle length(FL).Fixed-end contractions were performed at 67.5°,70.0°,72.5°,and 75.0°;the joint angle that most closely matched FL of the stretch-hold contraction's isometric steady-state was used to calculate rFE.The starting and ending FLs of the stretch-hold contraction were expressed as%optimal FL,determined via torqueangle relationship.Resu lts:In single fiber experiments,the starting and ending fiber lengths were matched relative to optimal length determined from in vivo testing,yielding an average sarcomere excursion of~2.2-3.4μm.There was a greater magnitude of rFE at the single fiber(~20%)than joint level(~5%)(p=0.004),with"non-re sponders"only observed at the joint level.Conclusion:By comparing rFE across scales within the same participants,we show the development of the rFE non-responder phenomenon is upstream of rFE's cellular mechanisms,with rFE only lost rather than gained when scaling from single fibers to the joint level.
文摘BACKGROUND:Heterotopic ossification of skeletal muscle is a clinically serious complication.For heterotopic ossification of skeletal muscles,the cells involved in the process of heterotopic ossification remain unclear.OBJECTIVE:To investigate the involvement of myocytes,fascia cells,and endothelial cells in the process of heterotopic ossification in skeletal muscle and to observe the cell origin of heterotopic ossification in skeletal muscle induced by bone morphogenetic protein 4.METHODS:Both C2C12 cells and the myotubes formed by the C2C12 cells in the induction medium were cultured,and 500 ng/mL bone morphogenetic protein 4 was added to the medium respectively,and whether the C2C12 cells and myotubes continued to proliferate within 10 days under the treatment were observed under a microscope.Myogenic cells(L6,derived from rats)and fibroblast-derived cells(derived from human)were co-cultured.After treatment with 500 ng/mL bone morphogenetic protein 4 and 10 ng/mL transforming growth factor-β,osteogenic and chondrogenic differentiation potential within 21 days were observed using Safranine O staining and Alcian blue staining.Using transgenic animal FVB/N-TgN(TIE2-LacZ)182Sato mice,15μL of adeno-associated virus-bone morphogenetic protein 4(5×1010 PFU/mL)were implanted in the thigh muscle space of genetic mice for 10 and 14 days.X-gal staining was used to observe the formation of new blood vessel endothelium in the differentiated bone.RESULTS AND CONCLUSION:(1)Bone morphogenetic protein 4 caused myotube breakdown and increased C2C12 cell proliferation.Compared with other groups,the pure fibroblast-derived cell group had a higher area of positive alcian blue and safarin O staining(P<0.05)and a lower area of alkaline phosphatase staining(P<0.05),while the pure L6 group had a bigger area of alkaline phosphatase staining(P<0.05)but a smaller area of positive alcian blue and safarin O staining(P<0.05).(2)Transplantation of adeno-associated virus-bone morphogenetic protein 4-adsorbed gelatin sponge into FVB/N-TgN(TIE2-LacZ)182Sato mice resulted in heterotopic ossification.(3)X-gal staining results demonstrated that there was no obvious staining in chondrocytes and differentiated bones and Tie2+endothelial cells did not participate in the formation of the alienated bone.(4)These findings verify that fibroblasts are the primary source of osteoblasts during the adeno-associated virus-bone morphogenetic protein 4-induced ectopic endochondral ossification in skeletal muscle,but myogenic cells are the main source of osteoblasts.Tie2+endothelial cells might not be the cell source for cartilage and bone.
文摘The architectural development of Acacia karroo conforms to Troll’s model. Growth of the branches is modular and sympodial with heteroblastic leaves on all long shoots of the tree, including the seedling. Axillary buds tend to proliferate especially on flowering shoots where they form fascicles consisting of up to 10 inflorescences arranged in two parallel serial rows per leaf axil. Most axillary buds are sylleptic and basal buds which give rise to short shoots, each producing two to five cataphylls each season, but no flowers. Inflorescences are only produced on long shoots (modules) of the current season. After flowering the terminal part of the module aborts, trees are usually andromonoecious with capitate inflorescences containing 40 to 100 flowers each, with some male and some hermaphrodite. Some trees produce only male flowers. Anthesis in the same inflorescence, the same tree as well as amongst trees of the same community are synchronised and occur at intermittent intervals, each lasting three or more days at a time. Flowers are protogynous and pollen is produced in polyads, each consisting of 16 pollen grains. Ovaries contain 10 to 14 ovules each. The concave stigma has space for only one polyad which can fertilise all ovules in the ovary after a single pollination event. Fruit set is low with 0 to 10 fruits (pods) per inflorescence.
基金supported by the National Natural Science Foundation of China (No.10672035,No.90816025,No.10721062)SRFDP (No.20060141007)
文摘Mosquitoes are exceptional in their ability to pierce into human skin with a natural ultimate painless microneedle, named fascicle. Here the structure of the Aedes albopictus mosquito fascicle is obtained using a Scanning Electron Microscope (SEM), and the whole process of the fascicle inserting into human skin is observed using a high-speed video imaging technique. Direct measurements of the insertion force for mosquito fascicle to penetrate into human skin are reported. Results show that the mosquito uses a very low force (average 18 μN) to penetrate into the skin. This force is at least three orders of magnitude smaller than the reported lowest insertion force for an artificial microneedle with an ultra sharp tip to insert into the human skin. In order to understand the piercing mechanism of mosquito fascicle tip into human multilayer skin tissue, a numerical simulation is conducted to analyze the insertion process using a nonlinear finite element method. A good agreement occurs between the numerical results and the experimental measurements.
