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851.
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Amitabha Bose Jorge Golowasch Yinzheng Guan Farzan Nadim 《Journal of computational neuroscience》2014,37(2):229-242
Neuronal oscillatory activity is generated by a combination of ionic currents, including at least one inward regenerative current that brings the cell towards depolarized voltages and one outward current that repolarizes the cell. Such currents have traditionally been assumed to require voltage-dependence. Here we test the hypothesis that the voltage dependence of the regenerative inward current is not necessary for generating oscillations. Instead, a current I NL that is linear in the biological voltage range and has negative conductance is sufficient to produce regenerative activity. The current I NL can be considered a linear approximation to the negative-conductance region of the current–voltage relationship of a regenerative inward current. Using a simple conductance-based model, we show that I NL , in conjunction with a voltage-gated, non-inactivating outward current, can generate oscillatory activity. We use phase-plane and bifurcation analyses to uncover a rich variety of behaviors as the conductance of I NL is varied, and show that oscillations emerge as a result of destabilization of the resting state of the model neuron. The model shows the need for well-defined relationships between the inward and outward current conductances, as well as their reversal potentials, in order to produce stable oscillatory activity. Our analysis predicts that a hyperpolarization-activated inward current can play a role in stabilizing oscillatory activity by preventing swings to very negative voltages, which is consistent with what is recorded in biological neurons in general. We confirm this prediction of the model experimentally in neurons from the crab stomatogastric ganglion. 相似文献
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856.
Peptides from a mycobacillin-synthesizing cell-free system 总被引:5,自引:4,他引:1
In a cell-free system from Bacillus subtilis B(3), ATP-P(i) exchange was catalysed by l-proline at a pH optimum of 7.2. Further stimulation by component amino acids of mycobacillin was inhibited by deprivation from the synthesizing system of even a single amino acid occurring at any point of the cyclic peptide. This inhibition, however, decreased with the distance in the molecule of the given amino acid from l-proline. Peptides containing respectively two, three, four, five and six amino acids were isolated from the mycobacillin-synthesizing system by an amino acid-deprivation technique. The amino acid composition of these peptides and also their N- and C-terminal amino acid residues were the same as those of peptides that would be obtained if mycobacillin synthesis occurred starting from l-proline and was interrupted at various points along the polypeptide chain. 相似文献
857.
Exposure of the red alga Porphyra
perforata or leaves of Phytolacca
americana and Echinodorus sp. to white light equivalent to full sunlight for short periods induced large decreases of variable fluorescence measured at 695 nm at 77K. This change was not produced by photoinhibition but rather appeared to result from an inorease in the rate constant of radiationless transition in the reaction centers of photosystem II. It is proposed that this increase is related to the formation of the high energy state which serves as a photoprotective mechanism in plants. 相似文献
858.
Li X.; Eschun G.; Bose D.; Jacobs H.; Yang J. J.; Light R. B.; Mink S. N. 《Journal of applied physiology》1998,85(5):1693-1701
In the heart,histamine (H3) receptors mayfunction as inhibitory presynaptic receptors that decrease adrenergicnorepinephrine release in conditions of enhanced sympathetic neuralactivity. We hypothesized thatH3-receptor blockade might improvecardiovascular function in sepsis. In a canine model ofEscherichia coli sepsis, we found thatH3-receptor blockade increasedcardiac output (3.6 to 5.3 l/min, P < 0.05), systemic blood pressure (mean 76 to 96 mmHg,P < 0.05), and left ventricularcontractility compared with pretreatment values. Plasma histamineconcentrations increased modestly in theH3-blocker-sepsis groupcompared with values obtained in a nonsepsis-time-control group.In an in vitro preparation, histamineH3 activation could be identifiedunder conditions of septic plasma. We conclude that activation ofH3 receptors may contribute tocardiovascular collapse in sepsis. 相似文献
859.
J K Saha L V Hryshko R A Bouchard T Chau D Bose 《Canadian journal of physiology and pharmacology》1989,67(7):788-794
Contraction of canine ventricular trabeculae were recorded stimulation at a frequency of 0.5 Hz and after rest periods of 2 and 8 min to analyze the effect of the Ca channel agonist BAY k 8644, on sarcoplasmic reticular function. Short periods of rest interposed between steady trains of stimuli caused a potentiation of the postrest beat. This is believed to be due to the mobilization of activator Ca from the sarcoplasmic reticulum (SR). Racemic BAY k 8644 and its Ca channel agonist enantiomer, (-) BAY k 8644, both produced an increase in contraction in response to a steady train of stimuli but converted rest potentiation into rest depression. This has been interpreted as increased loss of Ca from the SR during diastole. Addition of Ca channel antagonists, (+) BAY k 8644, nitrendipine, or nifedipine, to reverse the agonistic effect of (-) and racemic BAY k 8644 on the Ca channel did not convert the rest depression into rest potentiation. In the presence of stimuli but converted rest potentiation into rest depression. This has been interpreted as increased loss of Ca from the SR during diastole.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
860.
An adenylate-rich segment in the virion RNA of Sindbis virus 总被引:12,自引:0,他引:12