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1.
Autonomic regulation of a chloride current in heart 总被引：33，自引：0，他引：33
In isolated heart cells, beta-adrenergic receptor stimulation induced a background current that was suppressed by simultaneous muscarinic receptor stimulation. Direct activation of adenylate cyclase with forskolin also elicited this current, suggesting regulation by adenosine 3',5'-monophosphate (cAMP). This current could be recorded when sodium, calcium, and potassium currents were eliminated by channel antagonists or by ion substitution. Alteration of the chloride equilibrium potential produced changes in the reversal potential expected for a chloride current. Activation of this chloride current modulated action potential duration and altered the resting membrane potential in a chloride gradient-dependent manner. 相似文献
2.
Glycolysis preferentially inhibits ATP-sensitive K+ channels in isolated guinea pig cardiac myocytes 总被引：22，自引：0，他引：22
In heart, glycolysis may be a preferential source of adenosine triphosphate (ATP) for membrane functions. In this study the patch-clamp technique was used to study potassium channels sensitive to intracellular ATP levels in permeabilized ventricular myocytes. Activation of these K+ channels has been implicated in marked cellular K+ loss leading to electrophysiological abnormalities and arrhythmias during myocardial ischemia. The results showed that glycolysis was more effective than oxidative phosphorylation in preventing ATP-sensitive K+ channels from opening. Experiments in excised inside-out patches suggested that key glycolytic enzymes located in the membrane or adjacent cytoskeleton near the channels may account for their preference for glycolytic ATP. 相似文献
3.
[目的]为烤烟施用硫酸钾镁肥和优质栽培技术的推广提供依据。[方法]采用田间小区试验,设4种钾肥处理,研究了硫酸钾镁肥对烤烟主要生物学、经济性状及产量、产值的影响。[结果]各处理烤烟生育期基本一致。施用复合肥处理的株高、茎粗、各部位叶片长宽和单叶重均优于硫酸钾和硫酸钾镁肥处理;施用硫酸钾镁肥处理的上等烟比例均优于施用硫酸钾和复合肥的处理。施用硫酸钾镁肥与硫酸钾相比,增产97.4~162.3 kg/hm2,增产率4.4%~7.2%,差异显著。在4种钾肥处理中,施用硫酸钾镁肥1 643 kg/hm2产值居第1位,为27 555.2元/hm2,比对照增收3 750.0元/hm2,增收15.7%,差异极显著。施用硫酸钾镁肥处理与对照相比,纯收入增加1 241.0~1 565.0元/hm2,增收7.8%~9.9%。[结论]施用硫酸钾镁肥能改善烤烟生物学性状,具有显著的增产增收效果。 相似文献
4.
[目的]研究镁钾配施对寒地水稻(Oryza sativa L.)产量的影响,以确定适宜的镁钾配比量。[方法]以空育131为材料,按照随机区组设计,研究镁肥、钾肥对水稻产量的影响,并探明镁肥、钾肥最佳施用比例。[结果]在高中低施钾区,按照七水硫酸镁与氧化钾1∶1(钾肥165.0 kg/hm2,镁肥100.5 kg/hm2)或者1∶2(钾肥276.0 kg/hm2,镁肥100.5 kg/hm2)的重量比配施,能够在水稻关键生育时期合理增加水稻叶片氮含量;按照七水硫酸镁与氧化钾1∶2的重量比配施,能够保持群体叶面积指数趋于合理,不发生早衰和贪青现象;按照七水硫酸镁配施比例与氧化钾2∶1(钾肥165.0 kg/hm2,镁肥201.0 kg/hm2)的重量比配施,能够通过增加穗数和结实率提高产量,产量为9 660 kg/hm2。[结论]该研究对于保持土壤养分平衡,进一步增加水稻产量和改善稻米品质,促进水稻产业可持续发展具有深远意义。 相似文献
5.
Guanine nucleotide binding (G) proteins (subunit composition alpha beta gamma) dissociate on activation with guanosine triphosphate (GTP) analogs and magnesium to give alpha-guanine nucleotide complexes and free beta gamma subunits. Whether the opening of potassium channels by the recently described Gk in isolated membrane patches from mammalian atrial myocytes was mediated by the alpha k subunit or beta gamma dimer was tested. The alpha k subunit was found to be active, while the beta gamma dimer was inactive in stimulating potassium channel activity. Thus, Gk resembles Gs, the stimulatory regulatory component of adenylyl cyclase, and transducin, the regulatory component of the visual system, in that it regulates its effector function--the activity of the ligand-gated potassium channel--through its guanine nucleotide binding subunit. 相似文献
6.
Energized configurations of heart mitochondria in situ 总被引：3，自引：0，他引：3
R A Harris C H Williams M Caldwell D E Green E Valdivia 《Science (New York, N.Y.)》1969,165(894):700-703
Changes in the configurational state of the cristal membranes of rat heart mitochondria within the living cell can be induced by imposing energizing conditions. An exact correlation has been established between the configurational states of the cristal membrane and the energy states of the mitochondrion. The configurational changes observed in mitochondria in situ are comparable to those established for beef heart mitochondria in vitro and are consistent with the postulate of the conformational basis of energy transductions in membrane systems. The formation of paracrystalline arrays is one of the noteworthy features of configurational changes of mitochondria in situ. 相似文献
7.
Atrotoxin: a specific agonist for calcium currents in heart 总被引：5，自引：0，他引：5
S L Hamilton A Yatani M J Hawkes K Redding A M Brown 《Science (New York, N.Y.)》1985,229(4709):182-184
A specific label for voltage-dependent calcium channels is essential for the isolation and purification of the membrane protein that constitutes the calcium channel and for a better understanding of its function. A fraction of Crotalus atrox that increases voltage-dependent calcium currents in single, dispersed guinea pig ventricular cells was isolated. In the doses used, neither sodium nor potassium currents were changed. The fraction was active in the absence of detectable phospholipase or protease activity, and the active component, designated atrotoxin, produced its effect rapidly and reversibly. The effect was produced by extracellular but not intracellular application of the agent. The increase in Ca2+ current was blocked by the Ca2+ channel blockers cobalt and nitrendipine. The active fraction completely blocked specific [3H]nitrendipine binding to guinea pig ventricular membrane preparations. The inhibition of nitrendipine binding by atrotoxin was apparently via an allosteric mechanism. Thus atrotoxin was shown to bind to the Ca2+ channel and to act as a specific Ca2+ channel agonist. 相似文献
8.
Ma D Zerangue N Lin YF Collins A Yu M Jan YN Jan LY 《Science (New York, N.Y.)》2001,291(5502):316-319
Little is known about the identity of endoplasmic reticulum (ER) export signals and how they are used to regulate the number of proteins on the cell surface. Here, we describe two ER export signals that profoundly altered the steady-state distribution of potassium channels and were required for channel localization to the plasma membrane. When transferred to other potassium channels or a G protein-coupled receptor, these ER export signals increased the number of functional proteins on the cell surface. Thus, ER export of membrane proteins is not necessarily limited by folding or assembly, but may be under the control of specific export signals. 相似文献
9.
[目的]在云南省曲靖市植烟土壤交换性钙镁比超过20的缺镁烟区,通过土壤镁肥施用和叶面喷施进行钙镁比调控,了解其对烤烟钾、钙、镁吸收的影响,为曲靖市缺镁烟区烤烟的平衡施肥技术提供理论依据和生产指导。[方法]通过田间小区试验,采用完全随机区组设计,以不施镁肥作为对照,分别设3个叶面喷施硫酸钾镁肥处理和2个根层施镁＋叶面喷施处理。采集根、茎、上部叶、中部叶和下部叶5个部位进行烘干称重,并且粉碎制样,测定钾、钙、镁含量;每个小区从初烤烟叶中选取上部（B2F）、中部（C3F）、下部（X2F）样品,分析烟叶全钾、钙、镁含量。[结果]从不同部位来看,叶面喷施及土壤施用和叶面喷施配合调控钙镁比提高了中、下部烟叶对镁、钾的吸收以及下部烟叶对钙的吸收,但降低了上部烟叶对镁、钾、钙的吸收以及中部烟叶对钙的吸收。烟叶不同部位镁、钾、钙的累积分配量比较表现为中部叶〉下部叶〉上部叶;从不同部位来看,中、上部烟叶钙镁比、钾镁比降低,下部烟叶钙镁比增加,而下部烟叶钾镁比处理之间没有差异。[结论]叶面喷施及土壤施用和叶面喷施配合调控对烟叶钙镁比、钾镁比的影响,主要是通过影响镁的吸收。 相似文献
10.
1990: annus mirabilis of potassium channels 总被引：17，自引：0，他引：17
C Miller 《Science (New York, N.Y.)》1991,252(5010):1092-1096
Voltage-gated potassium channels make up a large molecular family of integral membrane proteins that are fundamentally involved in the generation of bioelectric signals such as nerve impulses. These proteins span the cell membrane, forming potassium-selective pores that are rapidly switched open or closed by changes in membrane voltage. After the cloning of the first potassium channel over 3 years ago, recombinant DNA manipulation of potassium channel genes is now leading to a molecular understanding of potassium channel behavior. During the past year, functional domains responsible for channel gating and potassium selectivity have been identified, and detailed structural pictures underlying these functions are beginning to emerge. 相似文献
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12.
Adenohypophysial transmembrane potentials: polarity reversal by elevated external potassium ion concentration 总被引：4，自引：0，他引：4
Incubation of rat adenohypophyses in potassium ion of sufficient concentration to provoke the release of several of the adenohypophysial trophic hormones produces a reversed, positive transmembrane potential in more than half the cells. This finding is consistent with a process of "stimulus-secretion coupling" in which hypothalamic releasing factors act by selective depolarization of their "target" cells. The positive potentials may be due to a prolonged preferential permeability to calcium ions triggered by an initial depolarization of the cell membrane to a threshold value by increased external potassium ion. 相似文献
13.
A rat kidney messenger RNA that induces a slowly activating, voltage-dependent potassium current on its expression in Xenopus oocytes was identified by combining molecular cloning with an electrophysiological assay. The cloned complementary DNA encodes a novel membrane protein that consists of 130 amino acids with a single putative transmembrane domain. This protein differs from the known ion channel proteins but is involved in the induction of selective permeation of potassium ions by membrane depolarization. 相似文献
14.
为明确植烟酸化土壤施用调理剂后土壤pH值的动态变化,及其对烤烟根系特性的影响,以云南省保山市昌宁县、腾冲市的植烟酸化土壤为研究对象,采用盆栽试验,研究了石灰、木本泥炭基腐殖酸钾(腐殖酸钾)+水热法矿物钾肥(矿物钾肥)、腐殖酸钾+钙镁磷肥3种土壤调理剂组合,及硫酸钾施用对土壤pH值和烤烟根系特性的影响。结果表明:添加腐殖酸钾+矿物钾肥、腐殖酸钾+钙镁磷肥后60 d内,土壤pH值表现为先下降后逐步回升的趋势;短期内施用石灰对提高土壤pH值的效果最好,但长期来看有复酸风险。施用腐殖酸钾+矿物钾肥、腐殖酸钾+钙镁磷肥可显著(P<0.05)提高根际土壤有机酸含量、烤烟根系活力、根系ATP酶活性与地上部干物质量。在腾冲市供试土壤上,施用腐殖酸钾+矿物钾肥、腐殖酸钾+钙镁磷肥处理的烟株根系生物量较空白对照分别显著(P<0.05)增加46.09%、83.70%。结果表明,腐殖酸钾+矿物钾肥或腐殖酸钾+钙镁磷肥的土壤调理剂组合,能够减缓植烟酸化土壤继续酸化,且有利于烟株的生长发育。 相似文献
15.
在甘蔗伸长盛期,SCMV—A侵染的蔗株叶片中蔗糖含量明显低于健株,还原糖含量则相反;不同钾、镁肥施用水平下,SCMV—A侵染的蔗株均比对照健株显著矮化,蔗茎和蔗糖含量均显著降低.而蔗茎锤度、蔗糖和还原糖含量则因钾、镁肥施用量的不同或高或低于其相应健株;适量施钾可增加健株的蔗茎及蔗糖产量,又可部分减少由SCMV—A年致的产量损失.施镁肥也有部分减少由SCMV—A引致产量损失的效果. 相似文献
16.
Puromycin dihydrochloride neutralized with bases of potassium, lithium, calcium, or magnesium fails to block expression of memory of maze learning in mice, unlike puromycin neutralized with NaOH. This failure may be due to cationic binding at anionic membrane sites with a resultant exclusion of sufficient peptidyl-puromycin to make it ineffective in blocking memory. 相似文献
17.
The effects of calcium removal on the voltage-dependent potassium channels of isolated squid neurons were studied with whole cell patch-clamp techniques. When the calcium ion concentration was lowered from 10 to 0 millimolar (that is, no added calcium), potassium channel activity, identified from its characteristic time course, disappeared within a few seconds and there was a parallel increase in resting membrane conductance and in the holding current. The close temporal correlation of the changes in the three parameters suggests that potassium channels lose their ability to close in the absence of calcium and simultaneously lose their selectivity. If potassium channels were blocked by barium ion before calcium ion was removed, the increases in membrane conductance and holding current were delayed or prevented. Thus calcium is an essential cofactor in the gating of potassium channels in squid neurons. 相似文献
18.
Bachmaier K Neu N de la Maza LM Pal S Hessel A Penninger JM 《Science (New York, N.Y.)》1999,283(5406):1335-1339
Chlamydia infections are epidemiologically linked to human heart disease. A peptide from the murine heart muscle-specific alpha myosin heavy chain that has sequence homology to the 60-kilodalton cysteine-rich outer membrane proteins of Chlamydia pneumoniae, C. psittaci, and C. trachomatis was shown to induce autoimmune inflammatory heart disease in mice. Injection of the homologous Chlamydia peptides into mice also induced perivascular inflammation, fibrotic changes, and blood vessel occlusion in the heart, as well as triggering T and B cell reactivity to the homologous endogenous heart muscle-specific peptide. Chlamydia DNA functioned as an adjuvant in the triggering of peptide-induced inflammatory heart disease. Infection with C. trachomatis led to the production of autoantibodies to heart muscle-specific epitopes. Thus, Chlamydia-mediated heart disease is induced by antigenic mimicry of a heart muscle-specific protein. 相似文献
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20.
麻沙泥田增施钙镁肥对烤烟生长和产量的影响 总被引：3，自引：1，他引：3
通过田间试验研究麻沙泥田上钙镁肥对烤烟生长和产量的影响。结果表明:在施钙肥条件下,施镁15 kg/hm2的产量最高,高达2709 kg/hm2,比不施镁肥处理增产3.6%。足量施入镁肥或镁肥与钙肥混施具有提高烟苗株高和叶片数,促进其生长的效果,烟叶产量和烤烟等级均表现为随施镁量的增加先增加后降低的趋势。适量施入镁肥具有提高烤烟产量、上等烟叶比例、上中等烟叶比例和产值的作用。施镁可提高烤烟叶片中镁含量,钙肥对镁的吸收具有显著的抑制作用。不施钙时,施入镁肥显著提高烤烟中钾、镁含量,而施入钙肥会对钾镁养分的吸收起到抑制作用,施钙条件下增加镁的施入可大幅度提高烟叶的钾、镁养分含量。在土壤中不施钙肥条件下,施入镁肥对钙的吸收会起副作用,而在施入大量钙肥情况下,施入适量镁肥显著提高烟叶的钙含量。 相似文献