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Resting State (resting + state)
Selected AbstractsUnusual Allylpalladium Carboxylate Complexes: Identification of the Resting State of Catalytic Enantioselective Decarboxylative Allylic Alkylation Reactions of Ketones,ANGEWANDTE CHEMIE, Issue 37 2009Nathaniel Prickelnd! Die enantioselektive palladiumkatalysierte decarboxylierende Alkylierung von Ketonenolaten verläuft über ,1 -,-Allylpalladium-Carboxylat-Komplexe wie 1 (Pd,gelb, O,rot, N,blau, P,violett) durch langsamen CO2 -Verlust. An Brausepulver erinnert das Verhalten unreiner Proben von 1, die im festen Zustand ein Gas (vermutlich CO2) ausstoßen und in Lösung aufschäumen. [source] Anisotropic contraction in forisomes: Simple models won't fitCYTOSKELETON, Issue 5 2008Winfried S. Peters Abstract Forisomes are ATP-independent, Ca2+ -driven contractile protein bodies acting as reversible valves in the phloem of plants of the legume family. Forisome contraction is anisotropic, as shrinkage in length is associated with radial expansion and vice versa. To test the hypothesis that changes in length and width are causally related, we monitored Ca2+ - and pH-dependent deformations in the exceptionally large forisomes of Canavalia gladiata by high-speed photography, and computed time-courses of derived geometric parameters (including volume and surface area). Soybean forisomes, which in the resting state resemble those of Canavalia geometrically but have less than 2% of the volume, were also studied to identify size effects. Calcium induced sixfold volume increases in forisomes of both species; in soybean, responses were completed in 0.15 s, compared to about 0.5 s required for a rapid response in Canavalia followed by slow swelling for several minutes. This size-dependent behavior supports the idea that forisome contractility might rest on similar mechanisms as those of polyelectrolyte gels, a class of artificial "smart" materials. In both species, time-courses of forisome length and diameter were variable and lacked correlation, arguing against a simple causal relationship between changes in length and width. Moreover, changes in the geometry of soybean forisomes differed qualitatively between Ca2+ - and pH-responses, suggesting that divalent cations and protons target different sites on the forisome proteins. Cell Motil. Cytoskeleton 2008. © 2008 Wiley-Liss, Inc. [source] A comparison of five fMRI protocols for mapping speech comprehension systemsEPILEPSIA, Issue 12 2008Jeffrey R. Binder Summary Aims:, Many fMRI protocols for localizing speech comprehension have been described, but there has been little quantitative comparison of these methods. We compared five such protocols in terms of areas activated, extent of activation, and lateralization. Methods:, fMRI BOLD signals were measured in 26 healthy adults during passive listening and active tasks using words and tones. Contrasts were designed to identify speech perception and semantic processing systems. Activation extent and lateralization were quantified by counting activated voxels in each hemisphere for each participant. Results:, Passive listening to words produced bilateral superior temporal activation. After controlling for prelinguistic auditory processing, only a small area in the left superior temporal sulcus responded selectively to speech. Active tasks engaged an extensive, bilateral attention, and executive processing network. Optimal results (consistent activation and strongly lateralized pattern) were obtained by contrasting an active semantic decision task with a tone decision task. There was striking similarity between the network of brain regions activated by the semantic task and the network of brain regions that showed task-induced deactivation, suggesting that semantic processing occurs during the resting state. Conclusions:, fMRI protocols for mapping speech comprehension systems differ dramatically in pattern, extent, and lateralization of activation. Brain regions involved in semantic processing were identified only when an active, nonlinguistic task was used as a baseline, supporting the notion that semantic processing occurs whenever attentional resources are not controlled. Identification of these lexical-semantic regions is particularly important for predicting language outcome in patients undergoing temporal lobe surgery. [source] Inhibitory Effect of Lamotrigine on A-type Potassium Current in Hippocampal Neuron,Derived H19-7 CellsEPILEPSIA, Issue 7 2004Chin-Wei Huang Summary:,Purpose: We investigated the effects of lamotrigine (LTG) on the rapidly inactivating A-type K+ current (IA) in embryonal hippocampal neurons. Methods: The whole-cell configuration of the patch-clamp technique was applied to investigate the ion currents in cultured hippocampal neuron,derived H19-7 cells in the presence of LTG. Effects of various related compounds on IA in H19-7 cells were compared. Results: LTG (30 ,M,3 mM) caused a reversible reduction in the amplitude of IA. The median inhibitory concentration (IC50) value required for the inhibition of IA by LTG was 160 ,M. 4-Aminopyridine (1 mM), quinidine (30 ,M), and capsaicin (30 ,M) were effective in suppressing the amplitude of IA, whereas tetraethylammonium chloride (1 mM) and gabapentin (100 ,M) had no effect on it. The time course for the inactivation of IA was changed to the biexponential process during cell exposure to LTG (100 ,M). LTG (300 ,M) could shift the steady-state inactivation of IA to a more negative membrane potential by approximately ,10 mV, although it had no effect on the slope of the inactivation curve. Moreover, LTG (100 ,M) produced a significant prolongation in the recovery of IA inactivation. Therefore in addition to the inhibition of voltage-dependent Na+ channels, LTG could interact with the A-type K+ channels to suppress the amplitude of IA. The blockade of IA by LTG does not simply reduce current magnitude, but alters current kinetics, suggesting a state-dependent blockade. LTG might have a higher affinity to the inactivated state than to the resting state of the IA channel. Conclusions: This study suggests that in hippocampal neurons, during exposure to LTG, the LTG-mediated inhibition of these K+ channels could be one of the ionic mechanisms underlying the increased neuronal excitability. [source] The calpain 1,,-actinin interactionFEBS JOURNAL, Issue 23 2003Resting complex between the calcium-dependant protease, its target in cytoskeleton Calpain 1 behaviour toward cytoskeletal targets was investigated using two ,-actinin isoforms from smooth and skeletal muscles. These two isoforms which are, respectively, sensitive and resistant to calpain cleavage, interact with the protease when using in vitro binding assays. The stability of the complexes in EGTA [Kd(,Ca2+) = 0.5 ± 0.1 µm] was improved in the presence of 1 mm calcium ions [Kd(+Ca2+) = 0.05 ± 0.01 µm]. Location of the binding structures shows that the C-terminal domain of ,-actinin and each calpain subunit, 28 and 80 kDa, participates in the interaction. In particular, the autolysed calpain form (76/18) affords a similar binding compared to the 80/28 intact enzyme, with an identified binding site in the catalytic subunit, located in the C-terminal region of the chain (domain III,IV). The in vivo colocalization of calpain 1 and ,-actinin was shown to be likely in the presence of calcium, when permeabilized muscle fibres were supplemented by exogenous calpain 1 and the presence of calpain 1 in Z-line cores was shown by gold-labelled antibodies. The demonstration of such a colocalization was brought by coimmunoprecipitation experiments of calpain 1 and ,-actinin from C2.7 myogenic cells. We propose that calpain 1 interacts in a resting state with cytoskeletal targets, and that this binding is strengthened in pathological conditions, such as ischaemia and dystrophies, associated with high calcium concentrations. [source] Complementation of NADPH oxidase in p67-phox-deficient CGD patientsFEBS JOURNAL, Issue 4 2000p67-phox/p40-phox interaction Chronic granulomatous disease (CGD) is due to a functional defect of the O2, generating NADPH oxidase of phagocytes. Epstein,Barr-virus-immortalized B lymphocytes express all the constituents of oxidase with activity 100 times less than that of neutrophils. As in neutrophils, oxidase activity of Epstein,Barr-virus-immortalized B lymphocytes was shown to be defective in the different forms of CGD; these cells were used as a model for the complementation studies of two p67-phox-deficient CGD patients. Reconstitution of oxidase activity was performed in vitro by using a heterologous cell-free assay consisting of membrane-suspended or solubilized and purified cytochrome b558 that was associated with cytosol or with the isolated cytosolic-activating factors (p67-phox, p47-phox, p40-phox) from healthy or CGD patients. In p67-phox-deficient CGD patients, two cytosolic factors are deficient or missing: p67-phox and p40-phox. Not more than 20% of oxidase activity was recovered by complementing the cytosol of p67-phox-deficient patients with recombinant p67-phox. On the contrary, a complete restoration of oxidase activity was observed when, instead of cytosol, the cytosolic factors were added in the cell-free assay after isolation in combination with cytochrome b558 purified from neutrophil membrane. Moreover, the simultaneous addition of recombinant p67-phox and recombinant p40-phox reversed the previous complementation in a p40-phox dose-dependent process. These results suggest that in the reconstitution of oxidase activity, p67-phox is the limiting factor; the efficiency of complementation depends on the membrane tissue and the cytosolic environment. In vitro, the transition from the resting to the activated state of oxidase, which results from assembling, requires the dissociation of p40-phox from p67-phox for efficient oxidase activity. In the process, p40-phox could function as a negative regulatory factor and stabilize the resting state. [source] Reliving lifelong episodic autobiographical memories via the hippocampus: A correlative resting PET study in healthy middle-aged subjectsHIPPOCAMPUS, Issue 5 2008Pascale Piolino Abstract We aimed at identifying the cerebral structures whose synaptic function subserves the recollection of lifetime's episodic autobiographical memory (AM) via autonoetic consciousness. Twelve healthy middle-aged subjects (mean age: 59 years ± 2.5) underwent a specially designed cognitive test to assess the ability to relive richly detailed episodic autobiographical memories from five time periods using the Remember/Know procedure. We computed an index of episodicity (number of Remember responses justified by the recall of specific events and details) and an index of retrieval spontaneity, and additionally an index of semanticized memories (number of Know responses). The regional cerebral blood flow (rCBF) was measured in the resting state, with H2O15 as part of an activation PET study. The indexes were correlated with blood flow using volumes of interest in frontotemporal regions, including hippocampus and voxel-wise analyses in SPM. With both analyses, significant correlations were mainly found between the index of episodicity and rCBF in the medial temporal lobe, including hippocampus, across the five time periods (unlike the index of semanticized memories) and between the spontaneity index and rCBF in the prefrontal areas. These results highlight, in healthy subjects, the distinct role of these two structures in AM retrieval and support the view that the hippocampus is needed for reexperiencing detailed episodic memories no matter how old they are. © 2008 Wiley-Liss, Inc. [source] Resting state sensorimotor functional connectivity in multiple sclerosis inversely correlates with transcallosal motor pathway transverse diffusivityHUMAN BRAIN MAPPING, Issue 7 2008Mark J. Lowe Abstract Recent studies indicate that functional connectivity using low-frequency BOLD fluctuations (LFBFs) is reduced between the bilateral primary sensorimotor regions in multiple sclerosis. In addition, it has been shown that pathway-dependent measures of the transverse diffusivity of water in white matter correlate with related clinical measures of functional deficit in multiple sclerosis. Taken together, these methods suggest that MRI methods can be used to probe both functional connectivity and anatomic connectivity in subjects with known white matter impairment. We report the results of a study comparing anatomic connectivity of the transcallosal motor pathway, as measured with diffusion tensor imaging (DTI) and functional connectivity of the bilateral primary sensorimotor cortices (SMC), as measured with LFBFs in the resting state. High angular resolution diffusion imaging was combined with functional MRI to define the transcallosal white matter pathway connecting the bilateral primary SMC. Maps were generated from the probabilistic tracking employed and these maps were used to calculate the mean pathway diffusion measures fractional anisotropy ,FA,, mean diffusivity ,MD,, longitudinal diffusivity ,,1,, and transverse diffusivity ,,2,. These were compared with LFBF-based functional connectivity measures (Fc) obtained at rest in a cohort of 11 multiple sclerosis patients and ,10 age- and gender-matched control subjects. The correlation between ,FA, and Fc for MS patients was r = ,0.63, P < 0.04. The correlation between all subjects ,,2, and Fc was r = 0.42, P < 0.05. The correlation between all subjects ,,2, and Fc was r = ,0.50, P < 0.02. None of the control subject correlations were significant, nor were ,FA,, ,,1,, or ,MD, significantly correlated with Fc for MS patients. This constitutes the first in vivo observation of a correlation between measures of anatomic connectivity and functional connectivity using spontaneous LFBFs. Hum Brain Mapp, 2008. © 2008 Wiley-Liss, Inc. [source] Negative BOLD responses to epileptic spikesHUMAN BRAIN MAPPING, Issue 6 2006Eliane Kobayashi Abstract Simultaneous electroencephalogram/functional magnetic resonance imaging (EEG-fMRI) during interictal epileptiform discharges can result in positive (activation) and negative (deactivation) changes in the blood oxygenation level-dependent (BOLD) signal. Activation probably reflects increased neuronal activity and energy demand, but deactivation is more difficult to explain. Our objective was to evaluate the occurrence and significance of deactivations related to epileptiform discharges in epilepsy. We reviewed all EEG-fMRI studies from our database, identified those with robust responses (P = 0.01, with ,5 contiguous voxels with a |t| > 3.1, including ,1 voxel at |t| > 5.0), and divided them into three groups: activation (A = 8), deactivation (D = 9), and both responses (AD = 43). We correlated responses with discharge type and location and evaluated their spatial relationship with regions involved in the "default" brain state (Raichle et al. [2001]: Proc Natl Acad Sci 98:676,682]. Deactivations were seen in 52/60 studies (AD+D): 26 related to focal discharges, 12 bilateral, and 14 generalized. Deactivations were usually distant from anatomical areas related to the discharges and more frequently related to polyspike- and spike-and-slow waves than to spikes. The "default" pattern occurred in 10/43 AD studies, often associated with bursts of generalized discharges. In conclusion, deactivations are frequent, mostly with concomitant activation, for focal and generalized discharges. Discharges followed by a slow wave are more likely to result in deactivation, suggesting neuronal inhibition as the underlying phenomenon. Involvement of the "default" areas, related to bursts of generalized discharges, provides evidence of a subclinical effect of the discharges, temporarily suspending normal brain function in the resting state. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc. [source] Differential interictal activity of the precuneus/posterior cingulate cortex revealed by resting state functional MRI at 3T in generalized vs.JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2008Partial seizure Abstract Purpose To characterize, using functional MRI (fMRI), the pattern of active brain regions in the resting state in patients with epilepsy. Materials and Methods We studied 28 patients with epilepsy, divided into a partial seizure (PS; N = 9) and a generalized seizure group (GS; N = 19), and 34 control subjects. Resting state fMRI was performed using a GE 3T scanner by collecting 200 volumes of echo-planar imaging (EPI) images with subjects relaxed, eyes closed. Data were processed using a modification of the method of Fransson (Hum Brain Mapp 2005;26:15,29), which reveals information on regional low-frequency Blood Oxygenation Level Dependent (BOLD) signal oscillations in the resting state without any a priori hypothesis. The significant active areas in brain were identified with both individual and group analysis. Results Controls showed active regions in the precuneus/posterior cingulate cortex (PCC) and medial prefrontal cortex (MPFC)/ventral anterior cingulate cortex (vACC), theregions associated with the brain "default mode." Similar active regions were observed in PS, whereas GS showed no significant activation of precuneus/PCC. Conclusion In GS, the lack of activation in precuneus/PCC may partly account for their more severe interictal deficits, compared to PS, in cognitive functions such as concentration and memory. J. Magn. Reson. Imaging 2008;27:1214,1220. © 2008 Wiley-Liss, Inc. [source] Improved artifact correction for combined electroencephalography/functional MRI by means of synchronization and use of vectorcardiogram recordingsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2008Karen J. Mullinger BSc Abstract Purpose To demonstrate that two methodological developments (synchronization of the MR scanner and electroencephalography [EEG] clocks and use of the scanner's vectorcardiogram [VCG]) improve the quality of EEG data recorded in combined EEG/functional MRI experiments in vivo. Materials and Methods EEG data were recorded using a 32-channel system, during simultaneous multislice EPI acquisition carried out on a 3 Tesla scanner. Recordings were made on three subjects in the resting state and on five subjects using a block paradigm involving visual stimulation with a 10-Hz flashing checkerboard. Results Gradient artifacts were significantly reduced in the EEG data recorded in vivo when synchronization and a TR equal to a multiple of the EEG clock period were used. This was evident from the greater attenuation of the signal at multiples of the slice acquisition frequency. Pulse artifact correction based on R-peak markers derived from the VCG was shown to offer a robust alternative to the conventionally used ECG-based method. Driven EEG responses at frequencies of up to 60 Hz due to the visual stimulus could be more readily detected in data recorded with EEG and MR scanner clock synchronization. Conclusion Synchronization of the scanner and EEG clocks, along with VCG-based R-peak detection is advantageous in removing gradient and pulse artifacts in combined EEG/fMRI recordings. This approach is shown to allow the robust detection of high frequency driven activity in the EEG data. J. Magn. Reson. Imaging 2008;27:607,616. © 2008 Wiley-Liss, Inc. [source] Blunted Pituitary-Adrenocortical Stress Response in Adult Rats Following Neonatal Dexamethasone TreatmentJOURNAL OF NEUROENDOCRINOLOGY, Issue 10 2000K. Felszeghy Abstract Glucocorticoids have a prominent impact on the maturation of the stress-related neuroendocrine system and on the postnatal establishment of adaptive behaviour. The present study aimed at investigating the stress responsiveness of the hypothalamo-pituitary-adrenocortical (HPA) axis in young and adult rats after neonatal treatment with the synthetic glucocorticoid agonist, dexamethasone. Newborn male Wistar rats were injected s.c. with 1 µg/g dexamethasone on postnatal days 1, 3 and 5. Circulating adrenocorticotropic hormone (ACTH) and corticosterone concentrations were measured in the resting state and following a 30-min cold stress at the age of 10 days, as well as after a 30-min restraint stress at the age of 14 weeks. Also in adults, pituitary and adrenocortical hormone responsiveness was evaluated after i.v. administration of 2 µg/kg corticotropin releasing hormone (CRH). In addition, glucocorticoid (GR) and mineralocorticoid receptor (MR) binding capacities were assessed in the pituitaries of adult rats. The results showed that at day 10 basal ACTH concentration was elevated while the cold stress-evoked ACTH response was attenuated in the dexamethasone-treated rats. As adults, treated rats showed a suppressed elevation of both ACTH and corticosterone plasma cncentrations in response to restraint, while basal hormonal concentrations were not altered. There was no difference in the magnitude of the CRH-induced elevation of ACTH and corticosterone concentrations initially; however, the dexamethasone-treated animals showed a prolonged secretion of both hormones. These animals also showed a selective decrease in pituitary GR binding capacity. Neonatal dexamethasone treatment strongly suppressed body weight gain, and adrenal and thymus weights in the early phase of postnatal development. By adulthood, the body and adrenal weights were normalized while thymus weight was greater than in controls. These findings indicate that neonatal dexamethasone treatment permanently alters HPA axis activity by reducing stress responses to cold and restraint probably through supra-pituitary actions, and by decreasing the effectiveness of feedback through a diminished GR binding in the pituitary. [source] Platelet integrin ,IIb,3: activation mechanismsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 7 2007Y.-Q. MA Summary., Integrin ,IIb,3 plays a critical role in platelet aggregation, a central response in hemostasis and thrombosis. This function of ,IIb,3 depends upon a transition from a resting to an activated state such that it acquires the capacity to bind soluble ligands. Diverse platelet agonists alter the cytoplasmic domain of ,IIb,3 and initiate a conformational change that traverses the transmembrane region and ultimately triggers rearrangements in the extracellular domain to permit ligand binding. The membrane-proximal regions of ,IIb and ,3 cytoplasmic tails, together with the transmembrane segments of the subunits, contact each other to form a complex which restrains the integrin in the resting state. It is unclasping of this complex that induces integrin activation. This clasping/unclasping process is influenced by multiple cytoplasmic tail binding partners. Among them, talin appears to be a critical trigger of ,IIb,3 activation, but other binding partners, which function as activators or suppressors, are likely to act as co-regulators of integrin activation. [source] The P2Y1 receptor plays an essential role in the platelet shape change induced by collagen when TxA2 formation is preventedJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 6 2004P. Mangin Summary., ADP and TxA2 are secondary agonists which play an important role as cofactors when platelets are activated by agonists such as collagen or thrombin. The aim of the present study was to characterize the role of the ADP receptor P2Y1 in collagen-induced activation of washed platelets. Inhibition of P2Y1 alone with the selective antagonist MRS2179 prolonged the lag phase preceding aggregation in response to low or high concentrations of fibrillar collagen, without affecting the maximum amplitude of aggregation or secretion. A combination of MRS2179 and aspirin resulted in complete inhibition of platelet shape change at low and high collagen concentrations, together with a profound decrease in aggregation and secretion. Scanning electron microscopy showed that these platelets had conserved the discoid morphology typical of the resting state. A lack of shape change was also observed in aspirin-treated P2Y1 - and G,q -deficient mouse platelets and in ,-storage pool-deficient platelets from Fawn Hooded rats. In contrast, when the second ADP receptor P2Y12 was inhibited with AR-C69931MX, aspirin-treated platelets were still able to change shape and displayed only a moderate decrease in aggregation and secretion. In conclusion, this study provides evidence that collagen requires not only the TxA2 receptor Tp,, but also P2Y1, to induce platelet shape change. [source] Quantitative analysis of first-pass contrast-enhanced myocardial perfusion MRI using a patlak plot method and blood saturation correctionMAGNETIC RESONANCE IN MEDICINE, Issue 2 2009Takashi Ichihara Abstract The objectives of this study were to develop a method for quantifying myocardial K1 and blood flow (MBF) with minimal operator interaction by using a Patlak plot method and to compare the MBF obtained by perfusion MRI with that from coronary sinus blood flow in the resting state. A method that can correct for the nonlinearity of the blood time,signal intensity curve on perfusion MR images was developed. Myocardial perfusion MR images were acquired with a saturation-recovery balanced turbo field-echo sequence in 10 patients. Coronary sinus blood flow was determined by phase-contrast cine MRI, and the average MBF was calculated as coronary sinus blood flow divided by left ventricular (LV) mass obtained by cine MRI. Patlak plot analysis was performed using the saturation-corrected blood time,signal intensity curve as an input function and the regional myocardial time,signal intensity curve as an output function. The mean MBF obtained by perfusion MRI was 86 ± 25 ml/min/100 g, showing good agreement with MBF calculated from coronary sinus blood flow (89 ± 30 ml/min/100 g, r = 0.74). The mean coefficient of variation for measuring regional MBF in 16 LV myocardial segments was 0.11. The current method using Patlak plot permits quantification of MBF with operator interaction limited to tracing the LV wall contours, registration, and time delays. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Functional perfusion imaging using continuous arterial spin labeling with separate labeling and imaging coils at 3 TMAGNETIC RESONANCE IN MEDICINE, Issue 5 2003Toralf Mildner Abstract Functional perfusion imaging with a separate labeling coil located above the common carotid artery was demonstrated in human volunteers at 3 T. A helmet resonator and a spin-echo echo-planar imaging (EPI) sequence were used for imaging, and a circular surface coil of 6 cm i.d. was employed for labeling. The subjects performed a finger-tapping task. Signal differences between the condition of finger tapping and the resting state were between ,0.5% and ,1.1 % among the subjects. The imaging protocol included a long post-label delay (PLD) to reduce transit time effects. Labeling was applied for all repetitions of the functional run to reduce the sampling interval. Magn Reson Med 49:791,795, 2003. © 2003 Wiley-Liss, Inc. [source] Phosphatidylserine exposure and other apoptotic-like events in Bernard-Soulier syndrome platelets,AMERICAN JOURNAL OF HEMATOLOGY, Issue 8 2010Margaret L. Rand In the Bernard-Soulier syndrome (BSS), the giant platelets are said to have increased phosphatidylserine (PS) surface exposure in the resting state and shortened survival in the circulation. When normal platelets are activated, they undergo many biochemical and morphological changes, some of which are apoptotic. Herein, we investigated apoptotic-like events in BSS platelets upon activation, specifically, PS exposure, microparticle (MP) formation, cell shrinkage, and loss of mitochondrial inner membrane potential (,,m). Platelets from two unrelated BSS patients were examined in whole blood; agonists used were collagen, thrombin, PAR1- or PAR4-activating peptides (APs), or combinations of collagen with thrombin, and the PAR-APs. Flow cytometry was used to measure PS exposure (annexin A5 binding), platelet-derived MPs (forward scatter; events <0.75 ,m size), and ,,m (TMRM fluorescence). PS exposure was increased on resting and activated BSS platelets, and this was independent of the platelet size. MP formation by BSS platelets was generally enhanced. Cell shrinkage occurred on activation to form smaller, PS-exposing platelets in BSS and controls. A proportion of PS-exposing BSS and control platelets exhibited ,,m loss, but unlike controls, there was also loss of ,,m in the BSS platelets not exposing PS. Thus, BSS platelets undergo apoptotic-like events upon activation, with PS exposure and MP formation being enhanced. These events may play a role in the shortened survival in BSS, as well as affecting thrombin generation. Am. J. Hematol. 85:584,592, 2010. © 2010 Wiley-Liss, Inc. [source] Menstrual cycle variability and the perimenopauseAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2001Kathleen A. O'Connor Menopause, the final cessation of menstrual cycling, occurs when the pool of ovarian follicles is depleted. The one to five years just prior to the menopause are usually marked by increasing variability in menstrual cycle length, frequency of ovulation, and levels of reproductive hormones. Little is known about the mechanisms that account for these characteristics of ovarian cycles as the menopause approaches. Some evidence suggests that the dwindling pool of follicles itself is responsible for cycle characteristics during the perimenopausal transition. Another hypothesis is that the increased variability reflects "slippage" of the hypothalamus, which loses the ability to regulate menstrual cycles at older reproductive ages. This paper examines the underlying cause of the increasing variability in menstrual cycle length prior to the menopause. A model of ovarian cycles is developed, based on the process of follicular growth and depletion. Under this model, the follicular phase of each menstrual cycle is preceded by an inactive phase, a period of time when no ovarian follicles have left the resting state and begun secreting steroids in response to gonadotropin stimulation. The model makes predictions about the variability in menstrual cycles across the reproductive life span based on the size of the surviving pool of ovarian follicles. We show that the model can explain several characteristics of the perimenopause in humans and macaques and illustrate how the model can be applied to research on the biological and cultural correlates of the timing of menopause. J. Hum. Biol. 13:465,478, 2001. © 2001 Wiley-Liss, Inc. [source] The apo structure of sucrose hydrolase from Xanthomonas campestris pv. campestris shows an open active-site grooveACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2009Elise Champion Glycoside hydrolase family 13 (GH-13) mainly contains starch-degrading or starch-modifying enzymes. Sucrose hydrolases utilize sucrose instead of amylose as the primary glucosyl donor. Here, the catalytic properties and X-ray structure of sucrose hydrolase from Xanthomonas campestris pv. campestris are reported. Sucrose hydrolysis catalyzed by the enzyme follows Michaelis,Menten kinetics, with a Km of 60.7,mM and a kcat of 21.7,s,1. The structure of the enzyme was solved at a resolution of 1.9,Å in the resting state with an empty active site. This represents the first apo structure from subfamily 4 of GH-13. Comparisons with structures of the highly similar sucrose hydrolase from X. axonopodis pv. glycines most notably showed that residues Arg516 and Asp138, which form a salt bridge in the X. axonopodis sucrose complex and define part of the subsite ,1 glucosyl-binding determinants, are not engaged in salt-bridge formation in the resting X. campestris enzyme. In the absence of the salt bridge an opening is created which gives access to subsite ,1 from the `nonreducing' end. Binding of the glucosyl moiety in subsite ,1 is therefore likely to induce changes in the conformation of the active-site cleft of the X. campestris enzyme. These changes lead to salt-bridge formation that shortens the groove. Additionally, this finding has implications for understanding the molecular mechanism of the closely related subfamily 4 glucosyl transferase amylosucrase, as it indicates that sucrose could enter the active site from the `nonreducing' end during the glucan-elongation cycle. [source] Tryptophan as a three-way switch in regulating the function of the secretory signalling glycoprotein (SPS-40) from mammary glands: structure of SPS-40 complexed with 2-methylpentane-2,4-diol at 1.6,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Pradeep Sharma The 40,kDa secretory signalling glycoprotein (SPS-40) is the first example with Trp78 in three functional orientations: (i) a resting state with a pinched conformation, (ii) a stacked conformation when bound to hexasaccharide and (iii) an obstructive conformation when inhibited by 2-methylpentane-2,4-diol (MPD). Trp78 is present in the core of the sugar-binding groove. The hexasaccharide N -acetylglucosamine (GlcNAc6) has been shown to bind to SPS-40. As a result of this, the conformation of Trp78 alters from the native pinched conformation (,1 = ,65.5°, ,2,1 = ,78.8°, ,2,2 = 97.5°) to the stacked conformation (,1 = ,170.0°, ,2,1 = ,114.3°, ,2,2 = 61.6°). Further binding experiments showed that saccharide binding does not occur in the presence of 20% MPD. The crystal structure determination of the complex of SPS-40 with MPD revealed the presence of two MPD molecules in the sugar-binding groove. The very tightly bound MPD molecules at subsites ,2 and ,1 induced an unexpected and a rarely observed conformation of Trp78 (,1 = 55.9°, ,2,1 = 90.2°, ,2,2 = ,88.9°) which is termed an obstructive conformation. The binding of MPD molecules also twisted the side chains of Glu269 and Ile272 considerably. These residues are also part of the sugar-binding groove. The observed obstructive conformation of the side chain of Trp78 in the present structure is the exact opposite of the stacked conformation. This rarely observed conformation is stabilized by a number of hydrogen bonds between Trp78 and Asn79 through water molecules W49, W229, W269, W547 and W557. [source] Refined structure of bovine carboxypeptidase A at 1.25,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2003Alexandra Kilshtain-Vardi The crystal structure of the bovine zinc metalloproteinase carboxypeptidase A (CPA) has been refined to 1.25,Å resolution based on room-temperature X-ray synchrotron data. The significantly improved structure of CPA at this resolution (anisotropic temperature factors, R factor = 10.4%, Rfree = 14.5%) allowed the modelling of conformational disorders of side chains, improved the description of the protein solvent network (375 water molecules) and provided a more accurate picture of the interactions between the active-site zinc and its ligands. The calculation of standard uncertainties in individual atom positions of the refined model of CPA allowed the deduction of the protonation state of some key residues in the active site and confirmed that Glu72 and Glu270 are negatively charged in the resting state of the enzyme at pH 7.5. These results were further validated by theoretical calculations that showed significant reduction of the pKa of these side chains relative to solution values. The distance between the zinc-bound solvent molecule and the metal ion is strongly suggestive of a neutral water molecule and not a hydroxide ion in the resting state of the enzyme. These findings could support both the general acid/general base mechanism, as well as the anhydride mechanism suggested for CPA. [source] Expression, purification, crystallization and preliminary X-ray analysis of calmodulin in complex with the regulatory domain of the plasma-membrane Ca2+ -ATPase ACA8ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2010Henning Tidow Plasma-membrane Ca2+ -ATPases (PMCAs) are calcium pumps that expel Ca2+ from eukaryotic cells to maintain overall Ca2+ homoeostasis and to provide local control of intracellular Ca2+ signalling. They are of major physiological importance, with different isoforms being essential, for example, for presynaptic and postsynaptic Ca2+ regulation in neurons, feedback signalling in the heart and sperm motility. In the resting state, PMCAs are autoinhibited by binding of their C-terminal (in mammals) or N-terminal (in plants) tail to two major intracellular loops. Activation requires the binding of calcium-bound calmodulin (Ca2+ -CaM) to this tail and a conformational change that displaces the autoinhibitory tail from the catalytic domain. The complex between calmodulin and the regulatory domain of the plasma-membrane Ca2+ -ATPase ACA8 from Arabidopsis thaliana has been crystallized. The crystals belonged to space group C2, with unit-cell parameters a = 176.8, b = 70.0, c = 69.8,Å, , = 113.2°. A complete data set was collected to 3.0,Å resolution and structure determination is in progress in order to elucidate the mechanism of PMCA activation by calmodulin. [source] The effects of dietary flaxseed on the Fischer 344 rat.CELL BIOCHEMISTRY AND FUNCTION, Issue 6 2005Abstract The hepatotoxic effect of carbon tetrachloride (CCl4) administered by gavage at 0.25,ml CCl4 (1:1 in olive oil) per 100,g body weight was examined 24,h later in regular chow fed (RC) and 10% flax chow fed (FC) male and female Fischer 344 rats. CCl4 -treated RC rats were subdued, lethargic and unkempt. CCl4 -treated FC rats were much less affected. CCl4 treatment resulted in loss of weight in RC and FC rats. In males, the weight loss was 6.7% body mass in RC rats compared to 5.6% body mass in FC rats. In females, the weight loss was 7.5% body mass in both RC and FC rats. While CCl4 treatment increased the level of the liver injury marker plasma alanine aminotransferase (ALT) in RC rats, this CCl4 effect was significantly attenuated in FC rats. In male rats, the ALT increase was 435-fold in RC rats and 119-fold in FC rats, over that of their respective controls. In female rats, the ALT increase was 454-fold in RC rats and 381-fold in FC rats, over that of their respective controls. These results provide evidence that flax consumption protects the liver against injury and that the extent of the protection is sex dependent. CCl4 had no effect on the plasma level of ,-glutamyltranspeptidase (,GT) in RC and FC rats supporting the contention that plasma ,GT is not a useful marker for acute liver injury which is seen in this model. The activity of ,GT was increased in the livers of FC rats compared to RC rats: 2.7-fold in males and 1.5-fold in females. In RC rats, the activity of liver ,GT was decreased by CCl4 treatment: 70% in the male and 25% in the female. However, this CCl4 effect was reversed or abolished by flax consumption. Compared to RC rats: in male FC rats, CCl4 actually increased the activity of liver ,GT 1.28-fold; while in female FC rats, the depressing effect of CCl4 treatment was abolished. The flax-induced preservation of ,GT in the liver in response to injury may be involved in the observed hepatoprotection through generation of GSH. In RC male rats, CCl4 treatment effected a 25% reduction in plasma glucose levels. There was no decrease in CCl4 -treated FC male rats. In female rats, CCl4 treatment effected a 21% decrease in plasma glucose levels in both RC and FC rats. In conclusion, multiple parameters for acute CCl4 -induced injury were attenuated in the FC compared to the RC rat. That flaxseed consumption conferred greater protection against liver injury in the male than in the female suggests an involvement of the estrogenic lignan component of flaxseed. We discuss the possibility that this hepatoprotection is through a flax lignan-induced increase in reduced glutathione related to a flax effect on the activity of liver ,GT in the resting state and the maintenance of its activity in response to injury. Copyright © 2005 John Wiley & Sons, Ltd. [source] 4,-PDD induces Ca2+ influx in human corneal epithelial cells by activating TRPV4 channelsACTA OPHTHALMOLOGICA, Issue 2007S MERGLER Purpose: Transient receptor potential (TRP) isoform expression is evident in human corneal epithelial cells (HCEC-SV40). However, their role in maintaining corneal epithelial homeostasis is not fully understood. We probed for gene and protein expression as well as functional activity of the vanilloid subtype, TRPV4, in immortalized HCEC-SV40 since they elicit Ca2+ dependent regulatory volume decrease (RVD) responses during exposure to a hypotonic challenge. Methods: RT-PCR and Western blotting analyses identified TRPV4 gene and protein expression. Functional activity was assessed based on determining whether the TRPV4 selective agonist, 4,-PDD, induced transients increases in intracellular Ca2+ concentration. Results: Single cell fluorescence imaging results showed that 4,-PDD (3 ,M) increased intracellular Ca2+ concentration. The fura2 fluorescence ratio (f340/f380) was 0.39 ± 0.03578 in the resting state (n = 5). After application of 4,-PDD it increased to 0.904 ± 0.14363 (n = 5; p = 5.72077×10-5). This increase was abolished by the TRP channel blocker ruthenium red or by Ca2+-free Ringer's medium. Conclusions: In conclusion, there is functional TRPV4 expression in HCEC-SV40. TRPV4 expression may provide an osmosensor role to induce RVD behavior during exposure to a hypotonic challenge since this response is mediated through intracellular Ca2+ transients. Supported in part DFG Pl 150/14-1 and NIH, EY04795. CR: none [source] Phosphine Ligands in the Palladium-Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP,NMR Spectroscopic StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2010Verónica de, la Fuente Dipl.-Chem. Abstract Novel cis -1,2-bis(di- tert -butyl-phosphinomethyl) carbocyclic ligands 6,9 have been prepared and the corresponding palladium complexes [Pd(O3SCH3)(L-L)][O3SCH3] (L- L=diphosphine) 32,35 synthesised and characterised by NMR spectroscopy and X-ray diffraction. These diphosphine ligands give very active catalysts for the palladium-catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9, containing four- and six-membered ring backbones giving more active systems. The acid used as co-catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex [Pd(O3SCH3)(L- L)][O3SCH3], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism. [source] Origin of Diastereoselectivity in the Organolanthanide-Mediated Intramolecular Hydroamination/Cyclisation of Aminodienes: A Computational Exploration of Constrained Geometry CGC,Ln Catalysts,CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2007Sven Tobisch Dr. Abstract The regulation of ring-substituent diastereoselectivity in the intramolecular hydroamination/cyclisation (IHC) of ,-substituted aminodienes by constrained geometry CGC,lanthanide catalysts (CGC=[Me2Si(,5 -Me4C5)(tBuN)]2,) has been elucidated by means of a reliable DFT method. The first survey of relevant elementary steps for the 1-methyl-(4E,6)-heptadienylamine substrate (1) and the [{Me2Si(,5 -Me4C5)(tBuN)}Sm{N(TMS)2}] starting material (2) identified the following general mechanistic aspects of Ln-catalysed aminodiene IHC. The substrate-adduct 3 -S of the active CGC,Ln,amidodiene compound represents the catalyst's resting state, but the substrate-free form 3, with a chelating amidodiene functionality is the direct precursor for cyclisation. This step proceeds with almost complete regioselectivity through exocyclic ring closure by means of a frontal trajectory, giving rise to the CGC,Ln,azacycle intermediate 4. Subsequent protonolysis of 4 is turnover limiting, whilst the ring-substituent diastereoselectivity is dictated by exocyclic ring closure. Unfavourable close interatomic contacts between the substrate's ,-substituent and the catalyst backbone have been shown to largely govern the trans/cis selectivity. Substituents of sufficient bulk in the ,-position of the substrate have been identified as being vital for stereochemical induction. The present study has indicated that the diastereoselectivity of ring closure can be considerably modulated. The variation of the lanthanide's ionic radius and introduction of extra steric pressure at the substrate's ,-position and/or the CGC N centre have been identified as effective handles for tuning the selectivity. The quantification of these factors reported herein represents the first step toward the rational design of improved CGC,Ln catalyst architectures and will thus aid this process. [source] The Reaction of o -Alkynylarene and Heteroarene Carboxaldehyde Derivatives with Iodonium Ions and Nucleophiles: A Versatile and Regioselective Synthesis of 1H -Isochromene, Naphthalene, Indole, Benzofuran, and Benzothiophene CompoundsCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2006José Barluenga Prof. Dr. Abstract The reaction of o -alkynylbenzaldehydes 1 with different alcohols, silylated nucleophiles 5, electron-rich arenes 10, and heteroarenes 12 in the presence of the reagent IPy2BF4, at room temperature, gave functionalized 4-iodo-1H -isochromenes 2, 6, 11, and 13 in a regioselective manner. When alkynes 16 and alkenes 19 and 20 were used as nucleophiles, a regioselective benzannulation reaction took place to form 1-iodonaphthalenes 17 and 1-naphthyl ketones 18, respectively. Moreover, the latter process has been adapted to accomplish the synthesis of indole, benzofuran, and benzothiophene derivatives (23, 27, and 28, respectively). The three patterns of reactivity observed for the o -alkynylbenzaldehyde derivatives with IPy2BF4 stem from a common iodinated isobenzopyrylium ion intermediate, A, that evolves in a different way depending on the nucleophile present in the reaction medium. A mechanism is proposed and the different reaction pathways observed as a function of the type of nucleophile are discussed. Furthermore, the reaction of the o -hexynylbenzaldehyde 1,b with styrene was monitored by NMR spectroscopy. Compound III, a resting state for the common intermediate in the absence of acid, has been isolated. Its evolution in acid media has been also tested, thereby providing support to the proposed mechanism. [source] Mechanism and exo -Regioselectivity of Organolanthanide-Mediated Intramolecular Hydroamination/Cyclization of 1,3-Disubstituted Aminoallenes: A Computational StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2006Sven Tobisch Priv.-Doz. Abstract The complete catalytic reaction course for the organolanthanide-assisted intramolecular hydroamination/cyclization (IHC) of 4,5-heptadien-1-ylamine by a prototypical [(,5 -Me5C5)2LuCH(SiMe3)2] precatalyst has been critically scrutinized by employing a reliable DFT method. A computationally verified mechanistic scenario for the IHC of 1,3-disubstituted aminoallene substrates has been proposed that is consistent with the empirical rate law determined by experiment and accounts for crucial experimental observations. It involves kinetically rapid substrate association and dissociation equilibria, facile and reversible intramolecular allenic CC insertion into the LnN bond, and turnover-limiting protonation of the azacycle's tether functionality, with the amine-amidoalleneLn adduct complex representing the catalyst's resting state. This mechanistic scenario bears resemblance to the mechanism that has been recently proposed in a computational exploration of aminodiene IHC. The unique features of the IHC of the two substrate classes are discussed. Furthermore, the thermodynamic and kinetic factors that control the regio- and stereoselectivity of aminoallene IHC have been elucidated. These achievements have provided a deeper insight into the catalytic structure,reactivity relationships in organolanthanide-assisted cyclohydroamination of unsaturated CC functionalities. [source] | ||||||||||||||||