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- Liu, Jing-Xia, 1962-
(författare)
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Human muscle spindles : complex morphology and structural organisation
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Muscle spindles are skeletal muscle mechanoreceptors that mediate the stretch reflex and provide axial and limb position information to the central nervous system. They have been proposed to play a major role in the pathophysiology of muscle pain. Knowledge about the normal human muscle spindles is needed in order to understand their role in muscle disease or dysfunction. The aim of this study was to investigate the fiber content and MyHC composition of the muscle spindles in the human biceps brachii (BB) and deep muscles of the neck (DN); to determine whether there are age-related changes in human muscle spindles with respect to structure and MyHC composition; to investigate the distribution of SERCA isoforms and to evaluate whether there is a coordinated expression of SERCA and MyHC isoforms in intrafusal fibers. The myosin heavy chain (MyHC) content correlates to contraction velocity and force and the sarcoplasmic reticulum Ca2+ ATPase (SERCA) is a major determinant of muscle fiber relaxation velocity. Muscle specimens obtained from young and old subjects were serially sectioned and the pattern of distribution of different proteins along the length of the intrafusal fibers was revealed by immunocytochemistry. The MyHC content of single muscle spindles was assessed with SDS-PAGE and immunoblots. There were clear differences between BB and DN with regard to the morphology and MyHC composition of muscle spindles. Virtually each muscle spindle in the BB, but not in the DN, had a unique allotment of numbers of bag1, bag2 and chain fibers. In DN, a number of muscle spindles lacked either bag1 or bag2 fibers. Four major MyHC isoforms (MyHCI, IIa, α-cardiac and intrafusal) were detected by SDS-PAGE. In both BB and DN, immunocytochemistry revealed co-expression of several MyHC isoforms in each intrafusal fiber and regional heterogeneity. Both nuclear bag1 and bag2 fibers contained slow tonic MyHC uniformly and MyHCI, α-cardiac, embryonic and fetal with regional variations. Nuclear chain fibers contained MyHCIIa, embryonic and fetal and in the BB also MyHCIIx. The total number of intrafusal fibers per spindle decreased significantly with aging, due to a significant reduction in the number of nuclear chain fibers. The patterns of MyHC expression were also affected by aging. The bag1 fibers predominantly contained both SERCA isoforms in the encapsulated region. The bag2 fibers were more heterogeneous in their SERCA composition and 16-27% of them lacked both isoforms. Chain fibers contained SERCA1. There was a poor correlation between the MyHC and SERCA isoforms in nuclear bag fibers, whereas a strong correlation existed between MyHCIIa and SERCA1 in the nuclear chain fibers. Human muscle spindles, each being unique, proved to be more complex than anticipated. The clear differences shown between the BB and DN muscle spindles suggest functional specialization in the control of movement among different human muscles. Aging apparently had profound effects on intrafusal fiber content and MyHC composition. The age-related changes in muscle spindle phenotype may reflect deterioration in sensory and motor innervation and are likely to have a detrimental impact on motor control in the elderly.
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| 2. |
- Liu, Shu Ming
(författare)
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Regulation of endothelial transport
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A major role of endothelial cells is to control the influx of solutes into tissues. The aim of the research presented in this thesis was to gain knowledge about the regulation of endothelial transport in relation to the structure of the endothelial cytoskeleton and to elucidate the possible mechanisms of regulation.The transcellular transport of hydrophilic molecules was found to occur viavesicles arranged as chains stretching between the luminal surface and the interior of the cell, and also from the cell interior to the abluminal surface. Intact microtubules were required for this transport, and actin filaments acted as a hinder. In addition, the vesicular transport was stimulated by hydrogen peroxide (H20z) and phorbol myristate acetate (PMA), and the effect of PMA was dependent on reactive oxygen species.The structure of filamentous actin and the permeability were closely associated during stimulation with H20z and PMA. An increase in actin dense peripheral bands (DPBs) was correlated with a decrease in penneability during the first hour of exposure to PMA. For the next 5 h, disruption of DPBs was correlated with an increase in permeability. A low concentration of HzOz (10-5 M) had no effect on either DPBs or permeability, whereas 104 M HzOz disrupted DPBs and increased permeability.Nitric oxide (NO) was involved in the redistribution ofF-actin and the alteration of permeability induced by Hz02 and PMA. Addition of L-arginine, a substrate of NO, increased the number of DPBs and maintained low permeability for up to 6 h in PMAtreated cells. The increase in permeability and disruption of DPBs induced by 10-4 M H202 could be prevented by L-arginine. On the other hand, nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO, disrupted DPBs and caused a direct increase in permeability in PMA-treated cells and in cells treated with both concentrations of Hz02.The involvement of NO in the regulation of endothelial transport by HzOz was cGMP-dependent. An analogue of cGMP, 8-Br-cGMP, prevented the disruption of DPBs and the increase in permeability induced by HzOz even when the production of NO was inhibited by L-NAME.The present findings indicate that the endothelial transport of solutes is associated with the cytoskeleton and that it can be regulated by H20 2 and PMA. The endogenous production of NO appears to be involved in this process via a cGMP-dependent pathway.
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