共查询到20条相似文献,搜索用时 31 毫秒
1.
van Beek J.H.G.M. Tian X. Zuurbier C.J. de Groot B. van Echteld C.J.A. Eijgelshoven M.H.J. Hak J.B. 《Molecular and cellular biochemistry》1998,184(1-2):321-344
Although usually steady-state fluxes and metabolite levels are assessed for the study of metabolic regulation, much can be learned from studying the transient response during quick changes of an input to the system. To this end we study the transient response of O2 consumption in the heart during steps in heart rate. The time course is characterized by the mean response time of O2 consumption which is the first statistical moment of the impulse response function of the system (for mono-exponential responses equal to the time constant). The time course of O2 uptake during quick changes is measured with O2 electrodes in the arterial perfusate and venous effluent of the heart, but the venous signal is delayed with respect to O2 consumption in the mitochondria due to O2 diffusion and vascular transport. We correct for this transport delay by using the mass balance of O2, with all terms (e.g. O2 consumption and vascular O2 transport) taken as function of time. Integration of this mass balance over the duration of the response yields a relation between the mean transit time for O2 and changes in cardiac O2 content. Experimental data on the response times of venous [O2] during step changes in arterial [O2] or in perfusion flow are used to calculate the transport time between mitochondria and the venous O2 electrode. By subtracting the transport time from the response time measured in the venous outflow the mean response time of mitochondrial O2 consumption (tmito) to the step in heart rate is obtained.In isolated rabbit heart we found that tmito to heart rate steps is 4-12 s at 37°C. This means that oxidative phosphorylation responds to changing ATP hydrolysis with some delay, so that the phosphocreatine levels in the heart must be decreased, at least in the early stages after an increase in cardiac ATP hydrolysis. Changes in ADP and inorganic phosphate (Pi) thus play a role in regulating the dynamic adaptation of oxidative phosphorylation, although most steady state NMR measurements in the heart had suggested that ADP and Pi do not change. Indeed, we found with 31P-NMR spectroscopy that phosphocreatine (PCr) and Pi change in the first seconds after a quick change in ATP hydrolysis, but remarkably they do this significantly faster (time constant ~2.5 s) than mitochondrial O2 consumption (time constant 12 s). Although it is quite likely that other factors besides ADP and Pi regulate cardiac oxidative phosphorylation, a fascinating alternative explanation is that the first changes in PCr measured with NMR spectroscopy took exclusively place in or near the myofibrils, and that a metabolic wave must then travel with some delay to the mitochondria to stimulate oxidative phosphorylation. The tmito slows with falling temperature, intracellular acidosis, and sometimes also during reperfusion following ischemia and with decreased mitochondrial aerobic capacity. In conclusion, the study of the dynamic adaptation of cardiac oxidative phosphorylation to demand using the mean response time of cardiac mitochondrial O2 consumption is a very valuable tool to investigate the regulation of cardiac mitochondrial energy metabolism in health and disease. 相似文献
2.
The binding of polyamine as a function of concentration to normal and sickling rcc'. blood cells is analyzed by Langmuir type binding isotherms, based on the Gouy-Chapman model for an electrical double Iayer, where the zeta potential is a function of only the normal distance coordinate. For normal erythrocytes, the apparent exotropic binding constants are found to be 103, 110, and 130 dl/g at normal distance coordinates of 4, 5, and 6 Å, iezpectively. The esotropic binding constant is determined to be 420 dl/g at a distance of 7 Å. For sickling red blood cells, the apparent exotropic binding constants are 3.3, 3.8, 4.6, and 6-7 dl/g at a distance of 4 to 7 Å. The esotropic binding constant at a distance of 8 Å is found to be 12-9 dl/g. The apparent binding affinity of polyamines to the normal red blood cell. therefore, is approximately 30 times greater than to the sickling erythrocyte.The Praxis pulse nuclear magnetic resonance spectrometer is used to determine the spin-lattice relaxation time (T1) for water in the presence of normal and sickling red blood cells. The spin-lattice relaxation time is found to be 540 ms for normal erythrocytes and 445 ms for sickling red blood cells in the oxy state. Differences in the spin-spin relaxation time (T2) for the two types of erythrocyte are negligible, being within the range of normal experimental error. 相似文献
3.
The changes in several parameters of the candicidin fermentation (total, mycelium-associated, and extracellular product formation; growth rate; DNA content; glucose utilization; dissolved oxygen in the broth; and oxygen uptake rate) during the trophophase-idiophase transition are compared with previously reported data for the polyene macrolides, candidin and candihexin. The maturation time, tm, and the productformation rate constant, kp, have been calculated for each of the three polyene macrolides using a simple mathematical model. Slow-feeding of glucose, which resulted in candidin and candihexin overproduction has been shown to increase the polyene formation rate constant and toretard trophophase to idiophase transition (longer maturation time). The opposite effect is achieved by repeated feeding of soybean meal. The values of the maturation times and polyene formation rates obtained were used to predict the production of polyene macrolide antibiotics in batch cultures. 相似文献
4.
Evaluating regional ecological environmental quality (EEQ) using remote sensing is important for achieving sustainable development. The remote sensing ecological index (RSEI) is a typical EEQ evaluation model used to comprehensively reflect regional ecological quality. However, owing to its complete dependence on remote sensing image information, the RSEI also has inherent issues, including unstable time series and inconsistent resolutions of its four sub-indices. To address these problems, this study used the Google Earth Engine (GEE) to propose an optimisation notion for the harmonic analysis of time series (HANTS) coupled random forest (RF) model and determined the accuracy and image quality of the optimised RSEI (RSEIo) for the Yangtze River Basin (YRB). Based on the findings, HANTS could fill the gaps in the images, effectively reducing the noise and discrete degrees of the four indices and thereby improving the stability of the RSEI. The correlation coefficient (R) between the RSEI and RSEIo was 0.93, with a root mean square error (RMSE) of 0.13, indicating that RSEIo is reliable. The image quality assessment (based on contrast and information entropy) indicates that HANTS combined with the RF model can produce RSEIo images with higher definitions and richer information at a constant spatial resolution. Further, the pixel-by-pixel coefficient of variation evaluation indicates that the RSEIo image was highly stabilised, yielding higher numbers of effective RSEIo images without changing the temporal resolution. Compared with traditional RSEI calculations, the optimisation proposal herein could highlight ecological differences caused by topographic changes in the YRB, which would produce an RSEI closer to actual surface conditions. Further, this proposed method could be used to obtain more detailed ecological information at a constant spatiotemporal resolution, thereby meeting the needs of long-term ecological monitoring in large-scale regions. 相似文献
5.
《Biorheology》1996,33(6):489-503
Red blood cell (RBC) shape change under shear is generally reversible, with the time course of shape recovery a function of the elastic and viscous properties of the RBC membrane. RBC shape recovery can be investigated, using several different techniques, to provide information about the membrane material properties that are not directly accessible by frequently used methods to assess RBC deformability (e.g., micropore filtration). In the present study, RBC shape recovery was studied in a Couette system after abrupt cessation of shear, either by analyzing the time course of laser light reflection or by serial measurements of elongation indexes from laser diffraction patterns. The time course of shape recovery monitored with both techniques can be described with an exponential equation. Calculated time constants for normal human RBC were 119 ± 17 msec and 97 ± 15 msec as measured by light reflection and ektacytometry, respectively. Treatment of RBC with glutaraldehyde resulted in dose-dependent decreases in the shape recovery time constant. Heat treatment (48 ° C, 20 min), which is known to increase mainly the shear elastic modulus of the membrane, decreased the time constant by 65%. In contrast, wheat germ agglutinin treatment increased the shape recovery time constant by 22%, presumably by increasing membrane surface viscosity. Our results indicate that the shape recovery time constant of RBC can be measured easily and accurately by computerized light reflection analysis. 相似文献
6.
Adrián Ponce-Alvarez Bjørg Elisabeth Kilavik Alexa Riehle 《Journal of computational neuroscience》2010,29(1-2):351-365
Spike time irregularity can be measured by the coefficient of variation. However, it overestimates the irregularity in the case of pronounced firing rate changes. Several alternative measures that are local in time and therefore relatively rate-independent were proposed. Here we compared four such measures: CV2, LV, IR and SI. First, we asked which measure is the most efficient for time-resolved analyses of experimental data. Analytical results show that CV2 has the less variable estimates. Second, we derived useful properties of CV2 for gamma processes. Third, we applied CV2 on recordings from the motor cortex of a monkey performing a delayed motor task to characterize the irregularity, that can be modulated or not, and decoupled or not from firing rate. Neurons with a CV2-rate decoupling have a rather constant CV2 and discharge mainly irregularly. Neurons with a CV2-rate coupling can modulate their CV2 and explore a larger range of CV2 values. 相似文献
7.
Background
The rate-limiting step that determines the dominant time constant (τD) of mammalian rod photoresponse recovery is the deactivation of the active phosphodiesterase (PDE6). Physiologically relevant Ca2+-dependent mechanisms that would affect the PDE inactivation have not been identified. However, recently it has been shown that τD is modulated by background light in mouse rods.Methodology/Principal Findings
We used ex vivo ERG technique to record pharmacologically isolated photoreceptor responses (fast PIII component). We show a novel static effect of calcium on mouse rod phototransduction: Ca2+ shortens the dominant time constant (τD) of saturated photoresponse recovery, i.e., when extracellular free Ca2+ is decreased from 1 mM to ∼25 nM, the τD is reversibly increased ∼1.5–2-fold.Conclusions
We conclude that the increase in τD during low Ca2+ treatment is not due to increased [cGMP], increased [Na+] or decreased [ATP] in rod outer segment (ROS). Also it cannot be due to protein translocation mechanisms. We suggest that a Ca2+-dependent mechanism controls the life time of active PDE. 相似文献8.
9.
The time constant of movement detectors in the fly visual system has been proposed to adapt in response to moving stimuli (de Ruyter van Steveninck et al. 1986). The objective of the present study is to analyse, whether this adaptation can be induced as well, if the luminance of a stationary uniform field is modulated in time. The experiments were done on motion-sensitive wide-field neurones of the lobula plate, the posterior part of the third visual ganglion of the blowfly, calliphora erythrocephala. These cells are assumed to receive input from large retinotopic arrays of movement detectors. In order to demonstrate that our results concern the properties of the movement detectors rather than those of a particular wide-field cell we recorded from two different types of them, the H1- and the HSE-cell. Both cell types respond to a brief movement stimulus in their preferred direction with a transient excitation. This response decays about exponentially. The time constant of this decay reflects, in a first approximation, the time constant of the presynaptic movement detectors. It was determined after prestimulation of the cell by the following stimuli: (a) periodic stationary grating; (b) uniform field, the intensity of which was modulated sinusoidally in time (flicker stimulation); (c) periodic grating moving front-to-back; (d) periodic grating moving back-to-front. The decay of the response is significantly faster not only after movement but also after flicker stimulation as compared with pre-stimulation with a stationary stimulus. This is interpreted as an adaptation of the movement detector's time constant. The finding that flicker stimulation also leads to an adaptation shows that movement is not necessary for this process. Instead the adaptation of the time constant appears to be governed mainly by the temporal modulation (i.e., contrast frequency) of the signal in each visual channel. 相似文献
10.
Rates of embryogenesis and of development and growth in several nematodes are linearly related to temperature over a considerable range. On this basis, published data on the thermal time requirements are compared for a tropical and a temperate species of plant parasitic nematode Meloidogyne javanica and M. hapla respectively, the two being closely related and morphologically and biologically similar. M. hapla has a lower base temperature (Tb) and a higher thermal constant (S) than M. javanica with the relative values being almost inversed. Consequently, above their respective Tb values the slope of the relationship between rate of development and temperature was greater for the tropical species than that for the temperate species. A mathematical exploration of the relationship between Tb and S was made assuming that, over a narrow range, Tb×S was a constant. With this assumption, for any given average environmental temperature (Te) the optimum base temperature for minimum developmental duration was Te/2, and the temperature at which the duration of development was equal for the otherwise identical species was shown to be the sum of their base temperatures. The practical effect of the differences in Tb and S was to give M. hapla, the temperate species, a shorter life cycle and hence a competitive advantage at temperatures below 21ÅC and M. javanica, the tropical species, the advantage above that temperature. It is argued that a negative correlation between Tb and S is likely to be widespread, and provides a mechanism for regulating the distributions of related, competing organisms. Support for the hypothesis that the value of S tends to decrease as Tb increases is derived from data on the embryogenesis of an animal parasitic nematode Haemonchus contortus and from seed germination studies. Contrary results and exceptions are also briefly discussed. The observed interaction between Tb and S may be fundamental to many poikilothermic organisms and plants and provides an explanation for tropical species generally having higher Tb values than temperate ones. The ecological implications of different values of Tb and of S, including their relationship with organisms which are “r” or “K” strategists are briefly discussed. 相似文献
11.
Asymptotic properties are established for estimators of time dependent intensities in Markov branching processes with varying and random environments. For the varying environment model, the estimators are shown to be uniformly strongly consistent on bounded intervals as the initial population size X0 → ∞, and, when considered as empirical stochastic processes, to converge weakly to Gaussian processes with independent increments. For random environments, the estimators are shown to be asymptotically normal as t → ∞, where t is the time parameter. 相似文献
12.
Hiroyuki Suga 《Bulletin of mathematical biology》1979,41(2):139-150
Oxygen consumption of the left ventricle (MVO
2) was evaluated theoretically under the condition that the ventricle pumps a constant stroke volume against a constant arterial
pressure, hence producing a constant external mechanical stroke work, with a widely varied contractility.MVO
2 was calculated by an empirical equation which had been inferred previously. Theoretical results indicated that the ventricle
has a contractility at whichMVO
2 is minimal in spite of constant external work and therefore the mechanical efficiency as a pump is maximal. Such a contractility
can be considered to be optimal from a standpoint of metabolic economy. The optimal contractility fell within the physiological
range of contractility which had been observed experimentally. The result suggests a possibility that the contractility of
a normal heart might be physiologically adapted to such an optimal level. 相似文献
13.
Flowering phenology and allozyme variation were studied to test the existence of positive assortative mating for flowering time in a natural population of Primula sieboldii E. Morren, a heterostylous perennial herb, consisting of approximately 180 genets in a deciduous forest. There was significant variation in flowering date among genets, but not between heterostylous morphs. The temporal order of the flowering time of genets was fairly constant for the two years of the study. The spatial heterogeneity of light availability at the study site was small during the flowering season of the species. In order to analyze the extent of genetic differentiation between early- and late-flowering genet groups, allozyme diversities were analyzed with 10 loci. The GST between the early- and late-flowering groups was not significantly different from zero. Evidence of positive assortative mating for flowering time was not detected. Prolongation of flowering duration due to pollen limitation may be one important factor preventing the genetic differentiation of early- and late-flowering groups by enhancing the overlap of flowering time among genets. 相似文献
14.
In the determination of the rates of oxygen consumption with a Clark-type oxygen electrode, and experimental error is caused by finite response time of the oxygen electrode for a rapid oxidation reaction. A theoretical equation between the observed pseudo first-order rate constant (kobs) and the true rate constant (k) where T is a time constant for a first-order response of the oxygen electrode, was derived and found to hold up to k = 23 min?1 in oxidation of hydroquinone at pH 7.60–8.63. 相似文献
15.
Clustered interval‐censored data commonly arise in many studies of biomedical research where the failure time of interest is subject to interval‐censoring and subjects are correlated for being in the same cluster. A new semiparametric frailty probit regression model is proposed to study covariate effects on the failure time by accounting for the intracluster dependence. Under the proposed normal frailty probit model, the marginal distribution of the failure time is a semiparametric probit model, the regression parameters can be interpreted as both the conditional covariate effects given frailty and the marginal covariate effects up to a multiplicative constant, and the intracluster association can be summarized by two nonparametric measures in simple and explicit form. A fully Bayesian estimation approach is developed based on the use of monotone splines for the unknown nondecreasing function and a data augmentation using normal latent variables. The proposed Gibbs sampler is straightforward to implement since all unknowns have standard form in their full conditional distributions. The proposed method performs very well in estimating the regression parameters as well as the intracluster association, and the method is robust to frailty distribution misspecifications as shown in our simulation studies. Two real‐life data sets are analyzed for illustration. 相似文献
16.
A new model for predicting time course toxicity of heavy metals based on Biotic Ligand Model (BLM) 总被引:1,自引:0,他引:1
Ayumi Hatano Ryo Shoji 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2010,151(1):25-32
A new model for predicting time course toxicity of heavy metals was developed by extending the effective ratio of biotic ligand binding with toxic heavy metals to the total biotic ligand for 50% of test organisms (f50) derived by the Biotic Ligand Model (BLM). BLM has been well-known as a useful model for prediction of heavy metal toxicity. BLM can consider the effect of exposure conditions such as pH and Ca2+ on heavy metal toxicity. In addition to the exposure conditions, heavy metal toxicity is strongly dependent on exposure time. In this study, BLM is extended to predict time dependency of heavy metal toxicity by connecting with the concept of primary reaction. The model developed in this study also generates the estimation of the 50% effect concentration (EC50) for toxicologically unknown organisms and heavy metals. Two toxicological and kinetic constants, f50,0 and k, were derived from the initial value of f50 (f50,0) and a time constant (k) independent of time. The model developed in this study enables us to acquire information on the toxicity of heavy metals such as Cu, Cd and Co easily. 相似文献
17.
Linlin Yi 《Behavioural processes》2009,81(2):274-279
This study examined two possible psychophysical time scales, a logarithmic representation of time with constant variability and a linear representation of time with scalar variability. Twenty-four rats were tested on a modified temporal bisection procedure in which multiple responses could occur in a 10-s time window after the termination of a stimulus. The number of “long” or “short” responses was used as a measure of the rats’ certainty of the duration of the presented interval. Data were analyzed with signal detection theory, and straight lines were fit to the zROC curves with the assumptions of a logarithmic representation of time with constant variability and a linear representation of time with scalar variability. The logarithmic representation of time with constant variability provided a better fit to the data than the linear representation of time with scalar variability. 相似文献
18.
S. Doganlar S. D. Tanksley M. A. Mutschler 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,100(2):249-255
Using RAPD marker analysis, two quantitative trait loci (QTLs) associated with earliness due to reduced fruit-ripening time
(days from anthesis to ripening = DTR) were identified and mapped in an F2 population derived from a cross between Lycopersicon esculentum’E6203’ (normal ripening) and Lycopersicon esculentum’Early Cherry’ (early ripening). One QTL, on chromosome 5, was associated with a reduction in both ripening time (5 days)
and fruit weight (29.3%) and explained 15.8 and 13% of the total phenotypic variation for DTR and fruit weight, respectively.
The other QTL, on chromosome 12, was primarily associated with a reduction only in ripening time (7 days) and explained 12.3%
of the total phenotypic variation for DTR. The gene action at this QTL was found to be partially dominant (d/a=0.41). Together,
these two QTLs explained 25.1% of the total phenotypic variation for DTR. Additionally, two QTLs associated with fruit weight
were identified in the same F2 population and mapped to chromosomes 4 and 6, respectively. Together, these two QTLs explained 30.9% of the total phenotypc
variation for fruit weight. For all QTLs, the ’Early Cherry’ alleles caused reductions in both ripening time and fruit weight.
The polymorphic band for the most significant RAPD marker (OPAB-06), linked to the reduced ripening time QTL on chromosome
12, was converted to a cleaved amplified polymorphism (CAP) assay for marker-aided selection and further introgression of
early ripening time (DTR) into cultivated tomato.
Received: 15 March 1999 / Accepted: 29 April 1999 相似文献
19.
Residence time and kinetic efficiency analysis of extracellular signal-regulated kinase 2 inhibitors
Darin Vanderpool Charles E. Grimshaw J. David Lawson Jacques Ermolieff 《Analytical biochemistry》2015
The RAS/RAF/MEK/ERK signal transduction cascade plays an important role in the regulation of critical cellular processes such as cell proliferation, migration, and differentiation. The up-regulation of this pathway can negatively affect cell homeostasis and is responsible for the development of various forms of cancer and inflammation processes. Therefore, there is a strong interest in pursuing drug programs targeting some of the enzymes involved in this pathway. In addition to the determination of Ki, Kd, IC50, and/or EC50, a more thorough kinetic analysis can provide useful information for the selection of the best lead series during the early stage of the drug discovery process. This study describes a medium-throughput fluorescent probe displacement assay for the rapid determination of the koff constant, residence time, and kinetic efficiency for ERK (extracellular signal-regulated kinase) inhibitors. Using this method, we have identified several inhibitors that we have subjected to further kinetic analysis by comparing koff constants determined for these time-dependent inhibitors using either the active or inactive form of ERK2. 相似文献
20.
Brian S. Scott 《Journal of cellular physiology》1977,91(2):305-316
The effect of potassium (K+) on the time course of neuron survival has been investigated by counting neurons over a 24-day period in live cultures of dissociated dorsal root ganglia from embryonic chick, fetal and newborn mouse, and fetal human material. In both normal K (6 mM) and in elevated K (20 mM mouse and human, 40 mM chick) there was initially a rapid exponential decrease in neuron survival. However, the magnitude of this decrease was less in the elevated K. In normal K neuron number decreased monotonically; the rate of degeneration itself decreased with time so that after 24 days neuron survival became relatively constant. In contrast, in elevated K the neuron number actually increased over a limited time interval before attaining a stable long-term value much greater than that in normal K. Thus, elevated K enhanced long-term survival by causing a lower rate of degeneration and also by causing an increase in neuron number during a limited period of the time in culture. From these observations and other evidence, it is argued that K can substitute to some extent for the trophic action normally exerted by the peripheral field of innervation of the DRG. It is further argued that K acts through its depolarizing effect on the membrane potential and that modification of intracellular ionic concentrations seems less likely to be involved. 相似文献