提出了一种电压钳位零电压开关(zero voltage switch,ZVS)型推挽式高频环节DC/AC变换器,首先给出了所提出高频环节DC/AC变换器的推衍过程,针对所推衍出的拓扑结构给出了其开关控制策略。重点叙述了其稳态工作原理,并采用状态空间法建立...提出了一种电压钳位零电压开关(zero voltage switch,ZVS)型推挽式高频环节DC/AC变换器,首先给出了所提出高频环节DC/AC变换器的推衍过程,针对所推衍出的拓扑结构给出了其开关控制策略。重点叙述了其稳态工作原理,并采用状态空间法建立了变换器的输入输出平均模型,然后分析了该变换器的主要特性。通过对比分析发现,所提出的DC/AC变换器与移相全桥式DC/AC变换器具有相类似的特性,变压器原边功率管S_1、S_2很容易实现ZVS开通,功率管S_3在漏感能量足够的条件下实现ZVS开通,且其两端电压可被钳位于输入电压,变压器副边的周波变换器则很容易实现ZVS换流。此外,相比传统推挽式DC/AC变换器,所提出变换器解决了其硬开关、损耗大的问题。最后,设计了一台功率为500VA,输入输出为48VDC/110V 50Hz AC原理样机,实验结果验证了所提出变换器的工作原理及理论分析的正确性,变换器效率可达91.5%以上。展开更多
目的:探讨中药复方制剂参松养心胶囊对KV1.4钾通道C型(KV1.4△N)失活的影响。方法:将Kv1.4ΔNmRNA注射入非洲爪蟾卵母细胞中,使用双电极钳制法(Two electrodes voltage clamp TEV)观察参松养心胶囊对KV1.4ΔN电生理特性的影响。结果:参...目的:探讨中药复方制剂参松养心胶囊对KV1.4钾通道C型(KV1.4△N)失活的影响。方法:将Kv1.4ΔNmRNA注射入非洲爪蟾卵母细胞中,使用双电极钳制法(Two electrodes voltage clamp TEV)观察参松养心胶囊对KV1.4ΔN电生理特性的影响。结果:参松养心胶囊对Kv1.4ΔN通道的峰电流有抑制作用,这种阻滞作用具有电压依赖性,随电位的升高而作用加强,符合单指数和线性关系。参松养心胶囊可加速KV1.4ΔN钾通道电流的失活过程,同时可使KV1.4ΔN通道失活后的恢复减慢。结论:参松养心胶囊能显著抑制KV1.4钾通道电流,这可能是其抗心律失常作用的机制之一。展开更多
High-resolution microscopy opens the door for detailed single-cell studies with fluorescent reporter dyes and proteins. We used a confocal spinning disc microscope to monitor fluorescent dyes and the fluorescent prote...High-resolution microscopy opens the door for detailed single-cell studies with fluorescent reporter dyes and proteins. We used a confocal spinning disc microscope to monitor fluorescent dyes and the fluorescent protein Venus in tobacco and Arabidopsis guard cells. Multi-barreled microelectrodes were used to inject dyes and apply voltage pulses, which provoke transient rises in the cytosolic Ca^2＋ level. Voltage pulses also caused changes in the distribution of Lucifer Yellow and Venus, which pointed to a reversible increase of guard cell cytosolic volume. The dynamic cytosolic volume changes turned out to be provoked by current injection of ions. A reduction of the clamp current, by blocking K^＋ uptake channels with Cs^＋, strongly suppressed the cytosolic volume changes. Cs^＋ not only inhibited the expansion of the cytosol, but also inhibited hyperpolarization-induced elevations of the cytosolic Ca^2＋ concentration. A complete loss of voltage-induced Ca^2＋ signals occurred when Ca^2＋-permeable plasma membrane channels were simultaneously blocked with La^3＋. This shows that two mechanisms cause hyperpolarization-induced elevation of the cytosolic Ca^2＋-concentration： （i） activation of voltage-dependent Ca^2＋-permeable channels, （ii） osmotically induced expansion of the cytosol, which leads to a release of Ca^2＋ from intracellular stores.展开更多
The Na+/Ca2+ exchanger plays an important role in regulation of airway smooth muscle contraction by regulating intracellular calcium, and is a potential target for treatment of asthma. To test modulation of exchanger ...The Na+/Ca2+ exchanger plays an important role in regulation of airway smooth muscle contraction by regulating intracellular calcium, and is a potential target for treatment of asthma. To test modulation of exchanger activity, we used Xenopus oocytes as model system. Na+/Ca2+ exchanger was expressed in the cells by microinjection of cRNA of the exchanger isoform NCX1. The activity of NCX1 was determined as Ni2+-sensitive current under voltage clamp in low Cl– medium and in the presence of the Cl–-channel inhibitor niflumic acid. Only this composition of solution allowed determining NCX1-mediated current with sufficient accuracy. Among a few tested Chinese herbal drugs, glycyrrhizic acid turned out to be a potent inhibitor of NCX1 with an apparent IC50 value of 40 μM. Previous work had revealed elevated cyclophylin A concentration in serum of asthmatic rats after receiving acupuncture treatment. Extracellular incubation of the oocytes in cyclophylin A for one day led to significant inhibition with an apparent IC50 value of about 1 μM. We suggest that effects of acupuncture and application of glycyrrhizic acid as an active constituent of Chinese medicine for treatment of asthma symptoms may partially be attributed to inhibition of the reversed mode of NCX1 and that these compounds may stimulate the search for new anti-asthmatic drugs.展开更多
For making it clear whether GABAA-like receptor is in cells or rat testis and how itsgene expresses in tissue cells, the mRNA of rat testis was microinjected into Xenopusoocyte. The membrane electrobiological results ...For making it clear whether GABAA-like receptor is in cells or rat testis and how itsgene expresses in tissue cells, the mRNA of rat testis was microinjected into Xenopusoocyte. The membrane electrobiological results showed that an inward 30 nA micro-currentwas elicited, under two-electrode voltageclamped configuration, by extracellular GABA(500 μmol/L), and both Bicuculline and Picrotoxin could inhibit this effect. It is an indication that the mRNA of rat testis can express GABA receptor in the membrane of Xenonpus oocyte. Using Muscimol as a excitant of GABA receptor type A, the micro--currentwas also elicited to generate; however, using Baclofen as a excitant of GABA receptortype B, the micro-current could not be induced. These results indicate that GABA receptorexpressed in Xenopus oocyte membrane is not type B but for type A. On the basis of the research result above, 24-mer oligonucleotides to be complementary to the high conservativeregion of the cDNAs of neur-GABA receptors were synthesized as probes to hybridize respectively with the RNAs Of brain and testis of adult rat, and of rat testes of the variousages. The dot hybridizations showed that the hybrid signal of rat testis was stronger thanthat of rat brain, meaning that, compared with rat brain, the RNA of rat testis has morehomologous regions with probes, and also implying that the GABA receptor from theRNA Of rat testis may be similar to neural-GABA receptor. This receptor therefore iscalled as GABA_A-like receptor. The dot blot analysis above also showed the testis GABA_Alike receptor. The dot blot analysis above also showed testis GABA_A like receptor mRNAcontent changed with the develOPmental age of rats. There is a very low level of gene expression in the rat testis on day 5 postnatal; there is the highest expression of GABA_A-likereceptor gene in rat testes on day 30to 100 after birth; the expression begins to drop on day200 after birth.展开更多
文摘提出了一种电压钳位零电压开关(zero voltage switch,ZVS)型推挽式高频环节DC/AC变换器,首先给出了所提出高频环节DC/AC变换器的推衍过程,针对所推衍出的拓扑结构给出了其开关控制策略。重点叙述了其稳态工作原理,并采用状态空间法建立了变换器的输入输出平均模型,然后分析了该变换器的主要特性。通过对比分析发现,所提出的DC/AC变换器与移相全桥式DC/AC变换器具有相类似的特性,变压器原边功率管S_1、S_2很容易实现ZVS开通,功率管S_3在漏感能量足够的条件下实现ZVS开通,且其两端电压可被钳位于输入电压,变压器副边的周波变换器则很容易实现ZVS换流。此外,相比传统推挽式DC/AC变换器,所提出变换器解决了其硬开关、损耗大的问题。最后,设计了一台功率为500VA,输入输出为48VDC/110V 50Hz AC原理样机,实验结果验证了所提出变换器的工作原理及理论分析的正确性,变换器效率可达91.5%以上。
文摘目的:探讨中药复方制剂参松养心胶囊对KV1.4钾通道C型(KV1.4△N)失活的影响。方法:将Kv1.4ΔNmRNA注射入非洲爪蟾卵母细胞中,使用双电极钳制法(Two electrodes voltage clamp TEV)观察参松养心胶囊对KV1.4ΔN电生理特性的影响。结果:参松养心胶囊对Kv1.4ΔN通道的峰电流有抑制作用,这种阻滞作用具有电压依赖性,随电位的升高而作用加强,符合单指数和线性关系。参松养心胶囊可加速KV1.4ΔN钾通道电流的失活过程,同时可使KV1.4ΔN通道失活后的恢复减慢。结论:参松养心胶囊能显著抑制KV1.4钾通道电流,这可能是其抗心律失常作用的机制之一。
文摘High-resolution microscopy opens the door for detailed single-cell studies with fluorescent reporter dyes and proteins. We used a confocal spinning disc microscope to monitor fluorescent dyes and the fluorescent protein Venus in tobacco and Arabidopsis guard cells. Multi-barreled microelectrodes were used to inject dyes and apply voltage pulses, which provoke transient rises in the cytosolic Ca^2＋ level. Voltage pulses also caused changes in the distribution of Lucifer Yellow and Venus, which pointed to a reversible increase of guard cell cytosolic volume. The dynamic cytosolic volume changes turned out to be provoked by current injection of ions. A reduction of the clamp current, by blocking K^＋ uptake channels with Cs^＋, strongly suppressed the cytosolic volume changes. Cs^＋ not only inhibited the expansion of the cytosol, but also inhibited hyperpolarization-induced elevations of the cytosolic Ca^2＋ concentration. A complete loss of voltage-induced Ca^2＋ signals occurred when Ca^2＋-permeable plasma membrane channels were simultaneously blocked with La^3＋. This shows that two mechanisms cause hyperpolarization-induced elevation of the cytosolic Ca^2＋-concentration： （i） activation of voltage-dependent Ca^2＋-permeable channels, （ii） osmotically induced expansion of the cytosol, which leads to a release of Ca^2＋ from intracellular stores.
文摘The Na+/Ca2+ exchanger plays an important role in regulation of airway smooth muscle contraction by regulating intracellular calcium, and is a potential target for treatment of asthma. To test modulation of exchanger activity, we used Xenopus oocytes as model system. Na+/Ca2+ exchanger was expressed in the cells by microinjection of cRNA of the exchanger isoform NCX1. The activity of NCX1 was determined as Ni2+-sensitive current under voltage clamp in low Cl– medium and in the presence of the Cl–-channel inhibitor niflumic acid. Only this composition of solution allowed determining NCX1-mediated current with sufficient accuracy. Among a few tested Chinese herbal drugs, glycyrrhizic acid turned out to be a potent inhibitor of NCX1 with an apparent IC50 value of 40 μM. Previous work had revealed elevated cyclophylin A concentration in serum of asthmatic rats after receiving acupuncture treatment. Extracellular incubation of the oocytes in cyclophylin A for one day led to significant inhibition with an apparent IC50 value of about 1 μM. We suggest that effects of acupuncture and application of glycyrrhizic acid as an active constituent of Chinese medicine for treatment of asthma symptoms may partially be attributed to inhibition of the reversed mode of NCX1 and that these compounds may stimulate the search for new anti-asthmatic drugs.
文摘For making it clear whether GABAA-like receptor is in cells or rat testis and how itsgene expresses in tissue cells, the mRNA of rat testis was microinjected into Xenopusoocyte. The membrane electrobiological results showed that an inward 30 nA micro-currentwas elicited, under two-electrode voltageclamped configuration, by extracellular GABA(500 μmol/L), and both Bicuculline and Picrotoxin could inhibit this effect. It is an indication that the mRNA of rat testis can express GABA receptor in the membrane of Xenonpus oocyte. Using Muscimol as a excitant of GABA receptor type A, the micro--currentwas also elicited to generate; however, using Baclofen as a excitant of GABA receptortype B, the micro-current could not be induced. These results indicate that GABA receptorexpressed in Xenopus oocyte membrane is not type B but for type A. On the basis of the research result above, 24-mer oligonucleotides to be complementary to the high conservativeregion of the cDNAs of neur-GABA receptors were synthesized as probes to hybridize respectively with the RNAs Of brain and testis of adult rat, and of rat testes of the variousages. The dot hybridizations showed that the hybrid signal of rat testis was stronger thanthat of rat brain, meaning that, compared with rat brain, the RNA of rat testis has morehomologous regions with probes, and also implying that the GABA receptor from theRNA Of rat testis may be similar to neural-GABA receptor. This receptor therefore iscalled as GABA_A-like receptor. The dot blot analysis above also showed the testis GABA_Alike receptor. The dot blot analysis above also showed testis GABA_A like receptor mRNAcontent changed with the develOPmental age of rats. There is a very low level of gene expression in the rat testis on day 5 postnatal; there is the highest expression of GABA_A-likereceptor gene in rat testes on day 30to 100 after birth; the expression begins to drop on day200 after birth.
