We have studied the role of external current stimuli in a four-dimensional Hodgkin-Huxley-type model of cold receptor in this paper. Firstly, we researched its firing patterns from direct current (DC) and alternating current (AC) stimuli. Under different values of DC stimulus intensity, interspike intervals (ISIs) with period-doubling bifurcation phenomena appeared. Second, research has shown that neurons are extremely sensitive to changes in the frequency and amplitude of the current used to stimulate them. As the stimulus frequency increased, discharge rhythms emerged ranging from burst firing to chaotic firing and spiking firing. Meanwhile, various phase-locking patterns have been studied in this paper, such as p : 1 (p > 1), 1 : q (q > 1), 2 : q (q > 1) and p : q (p; q > 1), etc. Finally, based on the fast-slow dynamics analysis, codimension-two bifurcation analysis of the fast subsystem was performed in the parameter (asr;B)-plane. We mainly investigated cusp bifurcation, fold-Hopf bifurcation, Bogdanov-Takens bifurcation and generalized Hopf bifurcation. These results revealed the effect of external current stimuli on the neuronal discharge rhythm and were instructive for further understanding the dynamical properties and mechanisms of the Huber-Braun model.
Ca2+ is an important factor mediating many biotic and abiotic stress responses in plants. In this study, we measured the chlorophyll (Chl) fluorescence of transgenic rice with increased or decreased expression of a calcium-sensing receptor (OsCaS) gene during water deficit caused by polyethylene glycol to prove our hypothesis that increased Ca2+ in combination with increased OsCaS could enhance the drought resistance of transgenic rice. Transcript abundance (evaluated by RT-PCR) was significantly lower in OsCaS antisense line 766 (AS766) than that in the wild type, while the overexpression line 777 (O777) showed four times higher amount than that in the wild type. Chl fluorescence showed that the photochemical quantum yield of PSII in the light increased due to addition of Ca2+ in the O777, but dropped in the AS766. Nonphotochemical quenching increased under stress in both transgenic lines and in the wild type, but less in the O777. Nonregulatory quantum yield of energy dissipation showed no significant change under drought stress. Photochemical quenching was significantly higher in the O777 than those in the AS766 and in the wild type after the Ca2+ treatment. In the absence of stress, the electron transport rate (ETR) was significantly higher in the O777 than in both the AS766 and the wild type. In contrast, the ETR of the wild type and both transgenic lines decreased under drought stress, while the effect of polyethylene glycol was partially alleviated by Ca2+ addition in the O777. In summary, excitation energy conversion and dissipation by PSII were regulated by Ca2+ in the O777. It might partially alleviate the effect of drought stress, whereas addition of Ca2+ had no effect in the wild type and the AS766., R. Wei, Y. Liu, Y. Sui, M. Xu, S. Liu, X. Zhao., and Obsahuje seznam literatury
As a novel gasotrans mitter, h ydrogen sulfide (H 2 S) has vasodilating and antihypertensive effects in cardiovascular system. Thus, we hypothesized that H 2 S might have beneficial effects on thoracic endothelial function in two -kidney one -clip (2K1C) rats, a model of renovascular hypertension. Sodium hydrosulfide (NaHS , 56 μmol/kg /day ) was administrated intra - peritoneally from the third day after the 2K1C operation. Along with the development of hypertension, t he systolic blood pressure (SBP) was measured before the operation and each week thereafter. The oxidative stress wa s determined by measurement of malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity and protein expression of oxidative stress -related proteins (AT 1 R, NADPH oxidase subunits). Acetylcholine (ACh) -induced vasorelaxation and angiotensin I I (Ang II) -induced vasocontraction were performed on isolated thoracic aorta. The SBP w as significantly increased from the first week after operation , and was lowered by NaHS. NaHS supplementation ameliorated endothelial dysfunction. The protein expression of oxidative stress -related proteins were downregulated, while SOD activity upregulated. In conclusion, improvement of endothelial function is involved in the antihypertensive mechanism of H 2 S. The protective effect of H 2 S is attributable to suppression o f vascular oxidative stress that involves inhibition of Ang II -AT 1 R action, downregulation of oxidases, as well as upregulation of antioxidant enzyme., H. Xue, S. Zhou, L. Xiao, Q. Guo, S. Liu, Y. Wu., and Obsahuje bibliografii
The peptide surfactants are amphiphilic peptides which have a hydrophobic tail and a hydrophilic head, and have been reported to stabilize and protect some membrane proteins more effectively than conventional surfactants. The effects of a class of peptide surfactants on the structure and thermal stability of the photosynthetic membrane protein lightharvesting complex II (LHCII) in aqueous media have been investigated. After treatment with the cationic peptide surfactants A6K, V6K2, I5K2 and I5R2, the absorption at 436 nm and 470 nm decreased and the absorption at 500-510 nm and 684-690 nm increased. Moreover, the circular dichroism (CD) signal intensity in the Soret region also decreased significantly, indicating the conformation of some chlorophyll (Chl) a, Chl b, and the xanthophyll molecules distorted upon cationic peptide surfactants treatment. The anionic peptide surfactants A6D and V6D2 had no obvious effect on the absorption and CD spectra. Except for A6D, these peptides all decreased the thermal stability of LHCII, indicating that these peptides may reconstitute protein into a less stable conformation. In addition, the cationic peptide surfactants resulted in LHCII aggregation, as shown by sucrose gradient ultracentrifugation and fluorescence spectra. and S. Liu, Y. Qiu, D.-Y. Yu
Central pattern generators (CPGs) play an important role in controlling rhythmic movements in vivo. Increased insight into mechanisms of CPGs can be obtained by perturbing neuron activities so as to study a range of behaviors. By applying this method, a series of simulations were performed to research different transition modes between firing patterns in a pacemaker neuron model of stomatogastric ganglion (STG). Firstly, with the perturbation of parameters in model, such as external stimulus, parameters in compartments and connection between compartments, different firing patterns and bifurcation of inter-spike intervals (ISIs) were obtained to exhibit the impact of single parameter on the transions between spiking and bursting. Moreover, perturbing two parameters gCa, Iext simultaneously induced the continuous variation of the bifurcation mode, which implied the crucial role of calcium channel in regulating the rhythm generation. Finally, a two-dimensional parameter space (gCa, Iext) was constructed by spike-counting method to capture the distribution of the firing patterns and different transition mode between them in a comprehensive aspect. In this parameter space, three basic transition modes were concluded: bifurcation ring, period-doubling mode and period-adding mode.