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91.
Biological response could not be predicted based on chemical concentration of the sediment contaminants. Bioassays integrate the response of test organisms to contaminants and nutrients. Comparative results of five acute bioassays indicated that Neubauer phytoassay was the most sensitive. The microbial biomass and algal growth tests indicated a response to the availability of contaminants and nutrients. These results suggest the usefulness of a diversity of bioassays in toxicity testing of sediment contamination. 相似文献
92.
V A Markevich L L Voronin V N Mats U Tsippel' 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》1983,33(3):535-542
In experiments with stimulation of emotiogenic zones (lateral and medial hypothalamus, raphe nuclei), as a conditioning agent, a study was made of summary responses of the pyramidal tract to electrical stimulation of the sensorimotor cortex in immobilized and freely moving rats. The responses exhibited a positive early direct P-component (mean latency 0.8 +/- 0.3 ms) and a late synaptic N-component (mean latency 1.8 +/- 0.5). Reduction of the N-component amplitude was observed during stimulation of the lateral hypothalamus, and its enhancement during stimulation of the medial hypothalamus. Stimulation of the raphe nuclei produced variable, statistically non-significant changes. The experiments have shown that the identified pyramidal neurones tend to reciprocal reactions during stimulation of positive and negative emotiogenic structures. Inhibitory and excitatory influences of the respectively positive and negative emotiogenic structures on pyramidal neurones are due to indirect modulating actions on presynaptic structures. 相似文献
93.
Yu. M. Kokoz A. S. Grichenko A. F. Korystova D. A. Lankina N. I. Markevich 《Bioscience reports》1999,19(1):17-25
The perforated patch clamp method was used to study the effect of the agonist of beta-adrenoreceptors isoproterenol on L-type Ca2+ current in cardiocytes of rats and ground squirrels in two states: active and hibernating. It is shown that isoproterenol exerts a dual effect on Ca2+ currents of rats and ground squirrels in the active state: at V
h = –50 mV, the current increases, whereas at V
h = –30 mV, it decreases. In hibernating ground squirrels, the dual effect of isoproterenol is not observed: isoproterenol increases Ca2+ current at any V
h values. The hypothesis is put forward that, during the entrance of ground squirrels into hibernation, the phosphorylation of one of the sites (not cAMP-dependent) of L-type Ca2+ channels is blocked. 相似文献
94.
Kolomiĭtseva IK Kulagina TP Markevich LN Potekhina NI Slozhenikina LV Fialkovskaia LA 《Biofizika》2002,47(6):1106-1115
Changes in the activity of ornithindecarboxylase in various tissues and in the amount of catecholamine in rat hypothalamus by the action of acute and chronic ionizing radiation were studied. A nonmonotonous relationship between the metabolic parameters of animal tissues and cells and the radiation dose was revealed. It was assumed that the nonmonotonous character of the dose-response dependence results from the nonmonotonous time course of the metabolic response to irradiation. It was also assumed that living systems have the property of responding to stress agents by nonmonotonous changes in metabolism. In the case of acute irradiation, this response manifests itself as oscillations of metabolic parameters about the control. The oscillations occur with a particular amplitude and periods, which vary with radiation dose, and damp out with time. As a result, in a fixed time interval, the dose-response curve may be nonmonotonous. Reverse dose-response relationships are also possible. In the case of chronic irradiation, the metabolic and functional parameters oscillate throughout irradiation time, and a modification of the response occurs. A prolong exposure to ionizing radiation causes strong changes in the metabolism of lipids of cell membranes, organelles and chromatin, as well as in the functional properties of some mammalian cells and tissues. The necessity of constructing quantitative models for explaining the nonmonotonous dose-response dependence is discussed. 相似文献
95.
A systems biology approach is applied to gain a quantitative understanding of the integration of signalling by the small GTPase Ras. The Ras protein acts as a critical switch in response to signals that determine the cell's fate. In unstimulated cells, Ras switching between an inactive GDP-binding and active GTP-binding state is controlled by the intrinsic catalytic activities of Ras. The calculated high sensitivity of the basal Ras-GTP fraction to changes in the rate constant of GTP-hydrolysis by Ras can account for the carcinogenic potential of Ras mutants with decreased GTPase activities. Extracelluar stimuli initiate Ras interactions with GDP/GTP exchange factors such as SOS, and GTP-hydrolysis activating proteins such as RasGAP. Our data on freshly isolated hepatocytes stimulated with epidermal growth factor (EGF) show transient SOS activation and sustained Ras-GTP patterns. We demonstrate that these dose-response data can only be explained by transient RasGAP activitation, and not by merely switching off the SOS signal, e.g. by inhibitory phosphorylation of SOS. A transient RasGAP activity can be brought about by a number of mechanisms. A comprehensive kinetic model of the EGF receptor (EGFR) network was developed to explore feasible molecular scenarios, including the receptor-mediated recruitment of SOS and RasGAP to the plasma membrane, phosphorylation of RasGAP and p190 RhoGAP by soluble tyrosine kinases, and RasGAP interactions with phosphoinositides and p190 RhoGAP. We show that a transient RasGAP association with EGFR followed by the capture of RasGAP through the formation of complexes with p190 RhoGAP can account for data on hepatocytes. In summary, our results demonstrate that a combination of experimental monitoring and integrated dynamic analysis is capable of dissecting regulatory mechanisms that govern cellular signal transduction. 相似文献
96.
Markevich NI Korystova AF Grichenko AS Lankina DA Kokoz YM 《Membrane & cell biology》2000,14(1):109-127
The regulation of L-type Ca2+ current in isolated rat cardiac cells was studied using the perforated patch-clamp technique. A dual effect of the cAMP-dependent phosphorylation activator, isoproterenol, at different holding potentials (V(h)) was shown. The currents increased at V(h) = -50 mV and decreased at V(h) = -30 mV. A dihydropyridine agonist, BAY K 8644, and isoproterenol had an additive effect on the activation of Ca2+ channels at holding potentials close to the resting potential. The additivity was disturbed at more positive V(h). The activating effect of BAY K 8644 did not virtually change in the presence of a protein kinase blocker, H8, and a phosphatase activator, acetylcholine. The results were interpreted within the framework of a two-site phosphorylation model with two independent pathways of Ca2+ current regulation. 相似文献
97.
Evgeny V. Esin Alyona I. Nikiforova Elena V. Shulgina Ksenia V. Metal’nikova Alexandra V. Novosadova Dmitry V. Zlenko Grigorii N. Markevich Vsevolod N. Leman 《Hydrobiologia》2018,806(1):237-250
Knowledge of larval dispersal and connectivity in coral reef species is crucial for understanding population dynamics, resilience, and evolution of species. Here, we use ten microsatellites and one mitochondrial marker (cytochrome b) to investigate the genetic population structure, genetic diversity, and historical demography of the powder-blue tang Acanthurus leucosternon across more than 1000 km of the scarcely studied Eastern African region. The global AMOVA results based on microsatellites reveal a low but significant F ST value (F ST = 0.00252 P < 0.001; D EST = 0.025 P = 0.0018) for the 336 specimens sampled at ten sample sites, while no significant differentiation could be found in the mitochondrial cytochrome b dataset. On the other hand, pairwise F ST, PCOA, and hierarchical analysis failed to identify any genetic breaks among the Eastern African populations, supporting the hypothesis of genetic homogeneity. The observed genetic homogeneity among Eastern African sample sites can be explained by the lengthy post-larval stage of A. leucosternon, which can potentiate long-distance dispersal. Tests of neutrality and mismatch distribution signal a population expansion during the mid-Pleistocene period. 相似文献
98.
Typical preparation of seed samples for infrared (IR) microspectroscopy involves imbibition of the seed for varying time periods followed by cryosectioning. Imbibition, however, may initiate germination even at 4° C with associated changes in the chemistry of the sample. We have found that it is possible to section seeds that are sufficiently hard, such as soybeans, on a standard laboratory microtome without imbibition. The use of dry sectioning of unimbibed seeds is reported here, as well as a comparison of different mounting media and modes of analysis. Glycerol, Tissue-Tek, and ethanol were used as mounting media, and the quality of the resulting spectra was assessed. Ethanol was the preferred mountant, because it dried quickly with no residue and thus did not interfere with the spectrum of interest. Analysis in transmission mode using barium fluoride windows to hold the samples was compared with transmission-reflection analysis with sections mounted on special infrared-reflecting slides. The two modes of analysis performed well in different regions of the spectrum. The mode of analysis (transmission vs. transmission-reflection) should be based on the components of greatest interest in the sample. 相似文献
99.
Zosimovskiĭ VA Korshunov VA Markevich VA 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》2007,57(2):210-220
Schaffer collateral stimulation with a single current impulse can evoke a double response in hippocampal field CA1 of freely moving rats. The late response appears as a population excitatory postsynaptic potential with a preceding short-term potential (frequently biphasic) only after the early population spike and is time-locked to it. The wave shape and polarity of the late response, its latency with respect to the peak of the early population spike suggest that the excitation wave produced in the CA1 field by the stimulation of Schaffer collaterals passes across the entorhinal cortex and returns to the CA1 directly via the perforant path fibers. In waking rat, the medium-intensity stimulation of Schaffer collaterals (able to evoke in the CA1 an early population spike of sufficiently high amplitude) usually does not result in the appearance of the late response. However, similar stimulation becomes efficient after the tetanization of Schaffer collaterals, under conditions of the long-term potentiation of the early population spike. Moreover, the late response occurrence is facilitated in a rat falling asleep after the development in the CA1 of high-amplitude low-frequency EEG oscillations typical for the slow-wave sleep and in a sleeping rat independently of the EEG pattern. 相似文献