1 Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada; and 2 Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada
Submitted 25 May 2007
; ...accepted in final form 3 October 2007
The aim of the present study was to test whether titin is a calcium-dependent spring and whether it is the source of the passive force enhancement observed in muscle and single fiber preparations. We measured passive force enhancement in troponin C (TnC)-depleted myofibrils in which active force production was completely eliminated. The TnC-depleted construct allowed for the investigation of the effect of calcium concentration on passive force, without the confounding effects of actin-myosin cross-bridge formation and active force production. Passive forces in TnC-depleted myofibrils ( n = 6) were 35.0 ± 2.9 nN/ µm 2 when stretched to an average sarcomere length of 3.4 µm in a solution with low calcium concentration (pCa 8.0). Passive forces in the same myofibrils increased by 25% to 30% when stretches were performed in a solution with high calcium concentration (pCa 3.5). Since it is well accepted that titin is the primary source for passive force in rabbit psoas myofibrils and since the increase in passive force in TnC-depleted myofibrils was abolished after trypsin treatment, our results suggest that increasing calcium concentration is associated with increased titin stiffness. However, this calcium-induced titin stiffness accounted for only 25% of the passive force enhancement observed in intact myofibrils. Therefore, 75% of the normally occurring passive force enhancement remains unexplained. The findings of the present study suggest that passive force enhancement is partly caused by a calcium-induced increase in titin stiffness but also requires cross-bridge formation and/or active force production for full manifestation.
myofibrils; residual force enhancement; titin; stiffness; calcium
Address for reprint requests and other correspondence: W. Herzog, Faculty of Kinesiology, Univ. of Calgary, Calgary, AB, Canada T2N 1N4 (e-mail: walter{at}kin.ucalgary.ca )
We investigated force enhancement following stretching in the in situ cat soleus muscle on the ascending and descending limb of the force-length relationship by varying the amount and speed of ...stretching and the frequency of activation (5 Hz, 30 Hz). There was a small but consistent (P<0.05) amount of force enhancement following muscle stretching on the ascending limb of the force-length relationship for both stimulation frequencies. The steady-state active isometric forces following stretches of 9 mm on the descending limb of the force-length relationship were always equal to or greater than the corresponding forces from the purely isometric contractions at the length at which the stretch was started. Therefore, force production for these trials showed positive stiffness and was associated with stable behavior. Following active stretching of cat soleus on the descending limb of the force-length relationship, the passive forces at the end of the test were significantly greater than the corresponding passive forces for purely isometric contractions, or the passive forces following stretching of the passive muscle. This passive force enhancement following active stretching increased with increasing magnitude of stretch, was not associated with structural damage, and only disappeared once the muscle was shortened. For stretches of 6 mm and 9 mm, the passive force enhancement accounted for more than 50 % of the total force enhancement, reaching a peak contribution of 83.7 % for the stretches of 9 mm at a speed of 3 mm s(-1). The results of this study suggest that a passive structural element provides a great part of the force enhancement on the descending limb of the force-length relationship of the cat soleus. Furthermore, the results indicate that mechanisms other than sarcomere length non-uniformity alone are operative.
Residual force enhancement in myofibrils and sarcomeres Joumaa, V; Leonard, T.R; Herzog, W
Proceedings - Royal Society. Biological sciences/Proceedings - Royal Society. Biological Sciences,
06/2008, Letnik:
275, Številka:
1641
Journal Article
Recenzirano
Odprti dostop
Residual force enhancement has been observed following active stretch of skeletal muscles and single fibres. However, there has been intense debate whether force enhancement is a sarcomeric property, ...or is associated with sarcomere length instability and the associated development of non-uniformities. Here, we studied force enhancement for the first time in isolated myofibrils (n=18) that, owing to the strict in series arrangement, allowed for evaluation of this property in individual sarcomeres (n=79). We found consistent force enhancement following stretch in all myofibrils and each sarcomere, and forces in the enhanced state typically exceeded the isometric forces on the plateau of the force-length relationship. Measurements were made on the plateau and the descending limb of the force-length relationship and revealed gross sarcomere length non-uniformities prior to and following active myofibril stretching, but in contrast to previous accounts, revealed that sarcomere lengths were perfectly stable under these experimental conditions. We conclude that force enhancement is a sarcomeric property that does not depend on sarcomere length instability, that force enhancement varies greatly for different sarcomeres within the same myofibril and that sarcomeres with vastly different amounts of actin-myosin overlap produce the same isometric steady-state forces. This last finding was not explained by differences in the amount of contractile proteins within sarcomeres, vastly different passive properties of individual sarcomeres or (half-) sarcomere length instabilities, suggesting that the basic mechanical properties of muscles, such as force enhancement, force depression and creep, which have traditionally been associated with sarcomere instabilities and the corresponding dynamic redistribution of sarcomere lengths, are not caused by such instabilities, but rather seem to be inherent properties of the mechanisms of contraction.
The mechanisms for chaos terrain formation on Europa have long been a source of debate in the scientific community. There exist numerous theoretical and numerical models for chaos formation, but to ...date there has been a lack of quantifiable observations that can be used to constrain models and permit comparison to the outputs of these chaos models. Here, we use mapping and statistical analysis to develop a quantitative description of chaos terrain and their observed morphologies. For nine chaos features, we map every block, or region of pre‐existing terrain within disrupted matrix. We demonstrate that chaos terrains follow a continuous spectrum of morphologies between two endmembers, platy and knobby. We find that any given chaos terrain's morphology can be quantified by means of the linearized exponential slope of its cumulative block area distribution. This quantitative metric provides a new diagnostic parameter in future studies of chaos terrain formation and comparison.
Plain Language Summary
Europa, a moon of Jupiter, exhibits a tantalizingly young icy surface and a subsurface liquid water ocean. The formation of chaos terrains—consisting of blocks of preexisting terrain and hummocky matrix material—on Europa is of particular interest to the astrobiological community. However, there exists no consensus on how chaos terrains form, nor any quantitative way to compare the outputs of formation models to the actual observations of chaos. Here, we map all of the blocks within nine representative chaos terrains that have a variety of appearances. We find that the cumulative area of blocks of a given chaos terrain is statistically correlated to its appearance. This correlation is important because it gives us way to quantitatively describe each chaos terrain, which can be used as a comparison to formation models.
Key Points
We use mapping and statistical analysis to develop a quantitative description of chaos terrains on Europa
Chaos terrains follow a continuous spectrum of morphologies between two endmembers, platy and knobby
Chaos morphology can be quantified by the cumulative block area distribution and used as a tool in evaluating chaos formation models
Abstract
The hyperdiverse shrew genus Crocidura is one of few small mammal genera distributed across Sundaland and all of its boundaries. This represents a rare opportunity to study the geological ...history of this region through the evolutionary history of these shrews. We generate a phylogeny of all recognized species of Sundaland Crocidura and show that most speciation events took place during the Pleistocene, prior to the inundation of the Sunda Shelf around 400 000 years ago. We find east–west differentiation within two separate lineages on Borneo, and that the current taxonomy of its two endemic species does not reflect evolutionary history, but ecophenotypic variation of plastic traits related to elevation. Sulawesi shrews are monophyletic, with a single notable exception: the black-footed shrew (C. nigripes). We show that the black-footed shrew diverged from its relatives on Borneo recently, suggesting a human-assisted breach of Wallace’s line. Overall, the number of Crocidura species, especially on Borneo, probably remains an underestimate.
Abstract
We here present a comprehensive integrative taxonomic review of the genus Hylomys, using molecular (mitochondrial genomes and up to five nuclear loci) and morphological data from museum ...specimens across its distribution, resulting in the description of two new species and the elevation of three subspecies to specific status. This revision significantly increases the known diversity of Hylomys from two to seven extant species, challenging the traditional view of species-level diversity within gymnures. We discuss the implications of the taxonomic findings for conservation, particularly in relation to the restricted distribution ranges of several species that may be threatened by habitat loss and/or climate change. Our research emphasizes the importance of scientific collections and underscores the potential of museum genomics and additional field sampling to identify new species and improve our understanding of species diversity in poorly studied regions. Speciation events within Hylomys occurred during the Late Miocene and Early Pliocene, possibly driven by shifting climate conditions such as the strengthening of the Indian monsoon and the expansion of seasonally dry conditions. This study supports northern Sumatra and the southern Annamites as centres of localized endemicity and suggests the need for additional small mammal surveys across Sumatra’s Barisan Range.
The Indonesian island of Sulawesi has a complex geological history. It is composed of several landmasses that have arrived at a near modern configuration only in the past few million years. It is the ...largest island in the biodiversity hotspot of Wallacea-an area demarcated by the biogeographic breaks between Wallace's and Lydekker's lines. The mammal fauna of Sulawesi is transitional between Asian and Australian faunas. Sulawesi's three genera of squirrels, all endemic (subfamily Nannosciurinae: Hyosciurus, Rubrisciurus and Prosciurillus), are of Asian origin and have evolved a variety of phenotypes that allow a range of ecological niche specializations. Here we present a molecular phylogeny of this radiation using data from museum specimens. High throughput sequencing technology was used to generate whole mitochondrial genomes and a panel of nuclear ultraconserved elements providing a large genome-wide dataset for inferring phylogenetic relationships.
Our analysis confirmed monophyly of the Sulawesi taxa with deep divergences between the three endemic genera, which predate the amalgamation of the current island of Sulawesi. This suggests lineages may have evolved in allopatry after crossing Wallace's line. Nuclear and mitochondrial analyses were largely congruent and well supported, except for the placement of Prosciurillus murinus. Mitochondrial analysis revealed paraphyly for Prosciurillus, with P. murinus between or outside of Hyosciurus and Rubrisciurus, separate from other species of Prosciurillus. A deep but monophyletic history for the four included species of Prosciurillus was recovered with the nuclear data.
The divergence of the Sulawesi squirrels from their closest relatives dated to ~9.7-12.5 million years ago (MYA), pushing back the age estimate of this ancient adaptive radiation prior to the formation of the current conformation of Sulawesi. Generic level diversification took place around 9.7 MYA, opening the possibility that the genera represent allopatric lineages that evolved in isolation in an ancient proto-Sulawesian archipelago. We propose that incongruence between phylogenies based on nuclear and mitochondrial sequences may have resulted from biogeographic discordance, when two allopatric lineages come into secondary contact, with complete replacement of the mitochondria in one species.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Three emergent subfossil reef flats from the inshore Keppel Islands, Great Barrier Reef (GBR), Australia, were used to reconstruct relative sea level (RSL). Forty-two high-precision uranium–thorium ...(U–Th) dates obtained from coral microatolls and coral colonies (2σ age errors from ±8 to 37 yr) in conjunction with elevation surveys provide evidence in support of a nonlinear RSL regression throughout the Holocene. RSL was as least 0.75 m above present from ~6500 to 5500 yr before present (yr BP; where “present” is 1950). Following this highstand, two sites indicated a coeval lowering of RSL of at least 0.4 m from 5500 to 5300 yr BP which was maintained for ~200 yr. After the lowstand, RSL returned to higher levels before a 2000-yr hiatus in reef flat corals after 4600 yr BP at all three sites. A second possible RSL lowering event of ~0.3 m from ~2800 to 1600 yr BP was detected before RSL stabilised ~0.2 m above present levels by 900 yr BP. While the mechanism of the RSL instability is still uncertain, the alignment with previously reported RSL oscillations, rapid global climate changes and mid-Holocene reef “turn-off” on the GBR are discussed.
Janzen's influential “mountain passes are higher in the tropics” hypothesis predicts restricted gene flow and genetic isolation among populations spanning elevational gradients in the tropics. Few ...studies have tested this prediction, and studies that focus on population genetic structure in Southeast Asia are particularly underrepresented in the literature. Here, we test the hypothesis that mountain treeshrews (Tupaia montana) exhibit limited dispersal across their broad elevational range which spans ~2,300 m on two peaks in Kinabalu National Park (KNP) in Borneo: Mt Tambuyukon (MT) and Mt Kinabalu (MK). We sampled 83 individuals across elevations on both peaks and performed population genomics analyses on mitogenomes and single nucleotide polymorphisms from 4,106 ultraconserved element loci. We detected weak genetic structure and infer gene flow both across elevations and between peaks. We found higher genetic differentiation on MT than MK despite its lower elevation and associated environmental variation. This implies that, contrary to our hypothesis, genetic structure in this system is not primarily shaped by elevation. We propose that this pattern may instead be the result of historical processes and limited upslope gene flow on MT. Importantly, our results serve as a foundational estimate of genetic diversity and population structure from which to track potential future effects of climate change on mountain treeshrews in KNP, an important conservation stronghold for the mountain treeshrew and other montane species.
Serositis is a rare manifestation of chronic GvHD (cGvHD). No risk factors or laboratory changes associated with this syndrome have been recognized to date, and outcomes have not been described in a ...large series. We searched our institutional database for patients undergoing allogeneic hematopoietic cell transplant identified as having serositis or pericarditis. Laboratory studies from prior to diagnosis, at diagnosis and post diagnosis of serositis, as well as outcomes from invasive procedures were included. Twenty patients met criteria for cGvHD-associated serositis, and all but three patients had a prior diagnosis of cGvHD. Fifteen were male, and the complication occurred in the setting of immunosuppressant taper in 12 cases. Ten patients required invasive interventions, including pericardial window or stripping. A significant increase in blood monocytes and decrease in serum albumin were identified at diagnosis compared with pre-diagnosis. Out of 20 patients, 17 were treated with steroids, with 12 demonstrating a complete response. These data suggest that cGvHD-associated serositis occurs mainly in the setting of treated as opposed to de novo cGvHD and biomarkers associated with the syndrome include a decrease in albumin and an increase in absolute monocyte count. Outcome data from larger series are required to better understand the optimal management of this rare complication.
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