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61.
62.
L(+)-lactate transport in perfused rat skeletal muscle: kinetic characteristics and sensitivity to pH and transport inhibitors 总被引:1,自引:0,他引:1
P W Watt P A MacLennan H S Hundal C M Kuret M J Rennie 《Biochimica et biophysica acta》1988,944(2):213-222
We have examined lactate uptake (as the rate of net muscle lactate accumulation) and unidirectional inward transport (measured by a paired-tracer dilution method) in muscle of the perfused skinned rat hindlimb. Inhibition of tracer influx (fractional uptake at 1 mM L(+)-lactate, 43.3 +/- 3.1% but only 32.9 +/- 1.8% at 50 mM lactate) suggested some competition between tracer and native forms of the carboxylate for transport. D(-)-lactate (50 mM) did not inhibit uptake of tracer L(+)-lactate. Pyruvate (25 mM), but none of five other monocarboxylates, inhibited uptake of tracer lactate, by 22% (P less than 0.01). Altering perfusate pH from 7.4 to 6.8 caused a 36% increase (P less than 0.001) in the unidirectional L(+)-lactate transport at 1 mM L(+)-lactate, whereas increasing pH to 7.7 reduced transport by 18% (P less than 0.01). Tracer lactate influx was inhibited by 500 microM 4-acetamido-4'-isothiocyanostilbene (SITS) (19%), 5 mM alpha-cyano-4-hydroxycinnamic acid (CIN) (20-30%), 1 mM amiloride (27%) and by a thiol group reagent p-chloromercuribenzenesulphonic acid (pCMBS) (26%). Overall the results indicate that at least two processes are involved in the transfer of lactate: one, saturable, with a Vmax of 0.84 mumol.min-1.g-1 and an apparent Km of 21 mM was sensitive to SITS, CIN, and a thiol group reagent; the other was non-saturable and insensitive to SITS and CIN with an apparent rate constant of 0.1 min-1. 相似文献
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Dreissenid mussels (Dreissena polymorpha and D. bugensis) have re-engineered Great Lakes ecosystems since their introduction in the late 1980s. Dreissenids can have major indirect
impacts on profundal habitats by redirecting nutrients and energy away from pelagic production (which supplies profundal production)
and depositing nutrients and energy in the nearshore zones that they occupy. However, strong empirical evidence for the effects
of this redirection of resources on fish populations is currently lacking. Here, we report significant shifts in isotopic
signatures, depth distribution and diets of a coldwater profundal fish population that are all consistent with a greater reliance
on nearshore resources after the establishment of dreissenid mussels in South Bay, Lake Huron. Isotopic signatures of scales
collected from 5-year-old lake whitefish (Coregonus clupeaformis) demonstrated remarkable stability over the 50-year period prior to the establishment of dreissenids (1947–1997) and a sudden
and significant change in isotopic signatures (3‰ enrichment in δ13C and 1‰ depletion in δ15N) after their establishment (2001–2005). These dramatic shifts in isotopic signatures were accompanied by a coincident shift
in the mean depth of capture of lake whitefish towards the nearshore. A comparison of previously unpublished pre-invasion
diets of lake whitefish from South Bay with contemporary diets collected between 2002 and 2005 also indicate a greater reliance
on nearshore prey after the invasion of dreissenid mussels. This study is the first to report changes in the carbon source
available to lake whitefish associated with restructured benthic communities after the appearance of dreissenid mussels. Further,
this study contributes to a growing body of work that demonstrates the ecological insights that can be gained through isotopic
analysis of archived fish bony tissues in ecosystems that have experienced significant levels of disturbance.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
67.
D. M. Kirby‡ K. J. Rennie T. K. Smulders-Srinivasan R. Acin-Perez§¶ M. Whittington† J.-A. Enriquez§ A. J. Trevelyan D. M. Turnbull† R. N. Lightowlers† 《Cell proliferation》2009,42(4):413-424
Objectives: Defects of the mitochondrial genome (mtDNA) cause a series of rare, mainly neurological disorders. In addition, they have been implicated in more common forms of movement disorders, dementia and the ageing process. In order to try to model neuronal dysfunction associated with mitochondrial disease, we have attempted to establish a series of trans mitochondrial mouse embryonic stem cells harbouring pathogenic mtDNA mutations.
Materials and methods: Trans mitochondrial embryonic stem cell cybrids were generated by fusion of cytoplasts carrying a variety of mtDNA mutations, into embryonic stem cells that had been pretreated with rhodamine 6G, to prevent transmission of endogenous mtDNA. Cybrids were differentiated into neurons and assessed for efficiency of differentiation and electrophysiological function.
Results: Neuronal differentiation could occur, as indicated by expression of neuronal markers. Differentiation was impaired in embryonic stem cells carrying mtDNA mutations that caused severe biochemical deficiency. Electrophysiological tests showed evidence of synaptic activity in differentiated neurons carrying non-pathogenic mtDNA mutations or in those that caused a mild defect of respiratory activity. Again, however, neurons carrying mtDNA mutations that resulted in severe biochemical deficiency had marked reduction in post-synaptic events.
Conclusions: Differentiated neurons carrying severely pathogenic mtDNA defects can provide a useful model for understanding how such mutations can cause neuronal dysfunction. 相似文献
Materials and methods: Trans mitochondrial embryonic stem cell cybrids were generated by fusion of cytoplasts carrying a variety of mtDNA mutations, into embryonic stem cells that had been pretreated with rhodamine 6G, to prevent transmission of endogenous mtDNA. Cybrids were differentiated into neurons and assessed for efficiency of differentiation and electrophysiological function.
Results: Neuronal differentiation could occur, as indicated by expression of neuronal markers. Differentiation was impaired in embryonic stem cells carrying mtDNA mutations that caused severe biochemical deficiency. Electrophysiological tests showed evidence of synaptic activity in differentiated neurons carrying non-pathogenic mtDNA mutations or in those that caused a mild defect of respiratory activity. Again, however, neurons carrying mtDNA mutations that resulted in severe biochemical deficiency had marked reduction in post-synaptic events.
Conclusions: Differentiated neurons carrying severely pathogenic mtDNA defects can provide a useful model for understanding how such mutations can cause neuronal dysfunction. 相似文献
68.
KASSO DAÏNOU JEAN‐PHILIPPE BIZOUX JEAN‐LOUIS DOUCET GRÉGORY MAHY OLIVIER J. HARDY MYRIAM HEUERTZ 《Molecular ecology》2010,19(20):4462-4477
The impact of the Pleistocene climate oscillations on the structure of biodiversity in tropical regions remains poorly understood. In this study, the forest refuge theory is examined at the molecular level in Milicia excelsa, a dioecious tree with a continuous range throughout tropical Africa. Eight nuclear microsatellites (nSSRs) and two sequences and one microsatellite from chloroplast DNA (cpDNA) showed a deep divide between samples from Benin and those from Lower Guinea. This suggests that these populations were isolated in separate geographical regions, probably for several glacial cycles of the Pleistocene, and that the nuclear gene pools were not homogenized despite M. excelsa’s wind‐pollination syndrome. The divide could also be related to seed dispersal patterns, which should be largely determined by the migration behaviour of M. excelsa’s main seed disperser, the frugivorous bat Eidolon helvum. Within Lower Guinea, a north–south divide, observed with both marker types despite weak genetic structure (nSSRs: FST = 0.035, cpDNA: GST = 0.506), suggested the existence of separate Pleistocene refugia in Cameroon and the Gabon/Congo region. We inferred a pollen‐to‐seed dispersal distance ratio of c. 1.8, consistent with wide‐ranging gene dispersal by both wind and bats. Simulations in an Approximate Bayesian Computation framework suggested low nSSR and cpDNA mutation rates, but imprecise estimates of other demographic parameters, probably due to a substantial gene flow between the Lower Guinean gene pools. The decline of genetic diversity detected in some Gabonese populations could be a consequence of the relatively recent establishment of a closed canopy forest, which could negatively affect M. excelsa’s reproductive system. 相似文献
69.
Nicholas A. Burd Daniel W. D. West Aaron W. Staples Philip J. Atherton Jeff M. Baker Daniel R. Moore Andrew M. Holwerda Gianni Parise Michael J. Rennie Steven K. Baker Stuart M. Phillips 《PloS one》2010,5(8)
Background
We aimed to determine the effect of resistance exercise intensity (% 1 repetition maximum—1RM) and volume on muscle protein synthesis, anabolic signaling, and myogenic gene expression.Methodology/Principal Findings
Fifteen men (21±1 years; BMI = 24.1±0.8 kg/m2) performed 4 sets of unilateral leg extension exercise at different exercise loads and/or volumes: 90% of repetition maximum (1RM) until volitional failure (90FAIL), 30% 1RM work-matched to 90%FAIL (30WM), or 30% 1RM performed until volitional failure (30FAIL). Infusion of [ring-13C6] phenylalanine with biopsies was used to measure rates of mixed (MIX), myofibrillar (MYO), and sarcoplasmic (SARC) protein synthesis at rest, and 4 h and 24 h after exercise. Exercise at 30WM induced a significant increase above rest in MIX (121%) and MYO (87%) protein synthesis at 4 h post-exercise and but at 24 h in the MIX only. The increase in the rate of protein synthesis in MIX and MYO at 4 h post-exercise with 90FAIL and 30FAIL was greater than 30WM, with no difference between these conditions; however, MYO remained elevated (199%) above rest at 24 h only in 30FAIL. There was a significant increase in AktSer473 at 24h in all conditions (P = 0.023) and mTORSer2448 phosphorylation at 4 h post-exercise (P = 0.025). Phosporylation of Erk1/2Tyr202/204, p70S6KThr389, and 4E-BP1Thr37/46 increased significantly (P<0.05) only in the 30FAIL condition at 4 h post-exercise, whereas, 4E-BP1Thr37/46 phosphorylation was greater 24 h after exercise than at rest in both 90FAIL (237%) and 30FAIL (312%) conditions. Pax7 mRNA expression increased at 24 h post-exercise (P = 0.02) regardless of condition. The mRNA expression of MyoD and myogenin were consistently elevated in the 30FAIL condition.Conclusions/Significance
These results suggest that low-load high volume resistance exercise is more effective in inducing acute muscle anabolism than high-load low volume or work matched resistance exercise modes. 相似文献70.