L-甲状腺素诱导心肌肥厚模型下电压依赖性钾通道信使核糖核酸的表达

目的 :探讨心肌肥厚易致心律失常的机制。　　方法 :SD大鼠实验组 9只 ,对照组 7只 ,用 L -甲状腺素诱导法制备大鼠心肌肥厚模型 ,用逆转录多聚酶链反应方法(RT- PCR)半定量分析肥厚心肌内电压依赖性 K 通道信使核糖核酸 (m RNA)水平。　　结果 :实验组与对照组相比 ,实验组即肥厚心肌内电压依赖性 K 通道 m RNA的表达水平显著下降 (P<0 .0 5 )。　　结论 :电压依赖性 K 通道是心肌电活动的主要离子通道 ,心肌肥厚时电压依赖性 K 通道基因表达水平下降 ,可能会导致动作电位复极化时间延长 ,与易诱发心律失常有关     

Molecular Biology of the Voltage-Gated Potassium Channels of the Cardiovascular System

Cardiovascular K⁺ Channel Molecular Biology. K⁺ channels represent the most diverse class of voltage-gated ion channels in terms of function and structure. Voltage-gated K⁺ channels in the heart establish the resting membrane K permeability, modulate the frequency and duration of action potentials, and are targets of several antiarrhythmic drugs. Consequently, an understanding of K⁺ channel structure-function relationships and pharmacology is of great practical interest. However, the presence of multiple overlapping currents in native cardiac myocytes complicates the study of basic K⁺ channel function and drug-channel interactions in these cells. The application of molecular cloning technology to cardiovascular K⁺ channels has identified the primary structure of these proteins, and heterologous expression systems have allowed a detailed analysis of channel function and pharmacology without contaminating currents. To date six different K⁺ channels have been cloned from rat and human heart, and all have been functionally characterized in either Xenopus oocytes or mammalian tissue culture systems. This initial research is an important step toward understanding the molecular basis of the action potential in the heart. An important challenge for the future is to determine the cell-specific expression and relative contribution of these cloned channels to cardiac excitability.     

Toward an Understanding of the Molecular Mechanisms of Ventricular Fibrillation

A major goal of basic research in cardiac electrophysiology is to understand the mechanisms responsible for ventricular fibrillation (VF). Here we review recent experimental and numerical results, from the ion channel to the organ level, which might lead to a better understanding of the cellular and molecular mechanisms of VF. The discussion centers on data derived from a model of stable VF in the Langendorff-perfused guinea pig heart that demonstrate distinct patterns of organization in the left (LV) and right (RV) ventricles. Analysis of optical mapping data reveals that VF excitation frequencies are distributed throughout the ventricles in clearly demarcated domains. The highest frequency domains are usually found on the anterior wall of the LV, demonstrating that a high frequency reentrant source (a rotor) that remains stationary in the LV is the mechanism that sustains VF in this model. Computer simulations predict that the inward rectifying potassium current (I _K1) is an essential determinant of rotor stability and rotation frequency, and patch-clamp results strongly suggest that the outward component of the background current (presumably I _K1) of cells in the LV is significantly larger in the LV than in the RV. These data have opened a new and potentially exciting avenue of research on the possible role played by inward rectifier channels in the mechanism of VF and may lead us toward an understanding of its molecular basis and hopefully lead to new preventative approaches.     

Autonomic Regulation of Voltage-Gated Cardiac Ion Channels

Altering voltage-gated ion channel currents, by changing channel number or voltage-dependent kinetics, regulates the propagation of action potentials along the plasma membrane of individual cells and from one cell to its neighbors. Functional increases in the number of cardiac sodium channels (Na_V1.5) at the myocardial sarcolemma are accomplished by the regulation of caveolae by β adrenergically stimulated G-proteins. We demonstrate that Na_V1.5, Ca_V1.2a, and K_V1.5 channels specifically localize to isolated caveolar membranes, and to punctate regions of the sarcolemma labeled with caveolin-3. In addition, we show that Na_V1.5, Ca_V1.2a, and K_V1.5 channel antibodies label the same subpopulation of isolated caveolae. Plasma membrane sheet assays demonstrate that Na_V1.5, Ca_V1.2a, and K_V1.5 cluster with caveolin-3. This may have interesting implications for the way in which adrenergic pathways alter the cardiac action potential morphology and the velocity of the excitatory wave.     

Cardiovascular Ion Channels as a Molecular Target of Flavonoids

Flavonoids are a class of naturally occurring polyphenols abundant in edibles and beverages of plant origin. Epidemiological studies consistently associate high flavonoid intake with a reduced risk for the development of cardiovascular diseases. So far these beneficial effects have been mainly attributed to nonspecific antioxidant and antiinflammatory properties. However, there is an increasing body of evidence that flavonoids specifically target molecular structures including cardiovascular ion channels. Playing a pivotal role in the regulation of vascular tone and cardiac electric activity, ion channels represent a major target for the induction of antihypertensive and cardioprotective effects. Thus, pharmacological properties of flavonoids on cardiovascular ion channels, ion currents and tissue preparations are being increasingly addressed in experimental studies. Whereas it has become clear that cardiovascular ion channels represent an important molecular target of flavonoids, the published data have not yet been systematically reviewed.     

高血压的治疗与离子通道相关性研究进展

高血压是一种多因素相互作用的常见慢性疾病,严重危害人类健康,常引起心、脑、肾等重要器官的病变,降压是治疗高血压的首要目标。目前,抗高血压药物有很多,其作用靶点也各不一致,其中作用于离子通道的药物是人们关注的热点。现将高血压的治疗与离子通道之间的相关性综述如下。     

Domain organization and function in GluK2 subtype kainate receptors

Glutamate receptor ion channels (iGluRs) are excitatory neurotransmitter receptors with a unique molecular architecture in which the extracellular domains assemble as a dimer of dimers. The structure of individual dimer assemblies has been established previously for both the isolated ligand-binding domain (LBD) and more recently for the larger amino terminal domain (ATD). How these dimers pack to form tetrameric assemblies in intact iGluRs has remained controversial. Using recently solved crystal structures for the GluK2 kainate receptor ATD as a guide, we performed cysteine mutant cross-linking experiments in full-length tetrameric GluK2 to establish how the ATD packs in a dimer of dimers assembly. A similar approach, using a full-length AMPA receptor GluA2 crystal structure as a guide, was used to design cysteine mutant cross-links for the GluK2 LBD dimer of dimers assembly. The formation of cross-linked tetramers in full-length GluK2 by combinations of ATD and LBD mutants which individually produce only cross-linked dimers suggests that subunits in the ATD and LBD layers swap dimer partners. Functional studies reveal that cross-linking either the ATD or the LBD inhibits activation of GluK2 and that, in the LBD, cross-links within and between dimers have different effects. These results establish that kainate and AMPA receptors have a conserved extracellular architecture and provide insight into the role of individual dimer assemblies in activation of ion channel gating.     

线粒体ATP敏感性钾通道与心肌保护的研究进展

缺血预处理对心肌的保护作用强大,但其机制复杂,涉及许多信号转导途径。目前认为线粒体ATP敏感性钾通道是其终末效应器。是细胞的一种重要离子通道,其结构复杂,功能多样,在细胞的生理、病理生理过程中起着重要作用。线粒体ATP敏感性钾通道的心肌保护机制主要涉及减轻缺血细胞钙超载,减轻自由基损伤,减少细胞凋亡及减轻远期心室重构。就线粒体ATP敏感性钾通道的结构及其心肌保护机制作一综述。     

Vascular ATP-Dependent Potassium Channels, Nitric Oxide, and Human Forearm Reactive Hyperemia

Vascular ATP-dependent potassium (K⁺ _ATP) channels open and contribute to reactive hyperemia (RH) in animals. The contribution of K⁺ _ATP channels to ischemic vasolidation during RH and interactions with endothelium-derived nitric oxide have not been well characterized in human subjects. RH blood flow responses (mL/dL) following 5 minutes of cuff occlusion were measured using strain-gauge plethysmography in 22 normal human subjects age 42 ± 2 years. Measurements were obtained at baseline and following intra-arterial administration of the K⁺ _ATP channel closer glibenclamide, the nitric oxide synthase inhibitor L-N-monomethyl arginine (L-NMMA), or both drugs simultaneously. Glibenclamide (100 µg/min) did not change basal flow (2.7 ± 0.3 to 2.7 ± 0.3 mL/min/dL), but L-NMMA (8 µmol/min) and combined glibenclamide and L-NMMA significantly (p < 0.05) decreased basal flow (3.0 ± 0.5 to 2.0 ± 0.2 and 3.3 ± 0.5 to 2.5 ± 0.3, respectively). Glibenclamide significantly (p < 0.01) decreased RH flow (18.2 ± 1.3 to 14.8 ± 1.3) and excess flow (5.3 ± 1.2 to 1.3 ± 1.3). L-NMMA significantly (p < 0.05) decreased RH flow (21.2 ± 1.8 to 18.9 ± 1.9) and tended to decrease excess flow (6.1 ± 2.2 to 3.9 ± 2.5). Combined drug infusion significantly (p < 0.1) decreased RH flow (21.6 ± 2.2 to 18.0 ± 2.4) and excess flow (6.3 ± 1.6 to 1.6 ± 1.6), with reductions in RH and excess flow similar to those following glibenclamide infusion alone. We conclude that forearm vascular K⁺ _ATP channels are closed at baseline. They open and contribute to RH vasodilation. The addition of nitric oxide inhibition to K⁺ _ATP channel blockade does not result in additive or synergistic inhibition of RH.     

Tetrameric assembly of KvLm K+ channels with defined numbers of voltage sensors

Voltage-gated K⁺ (Kv) channels are tetrameric assemblies in which each modular subunit consists of a voltage sensor and a pore domain. KvLm, the voltage-gated K⁺ channel from Listeria monocytogenes, differs from other Kv channels in that its voltage sensor contains only three out of the eight charged residues previously implicated in voltage gating. Here, we ask how many sensors are required to produce a functional Kv channel by investigating heterotetramers comprising combinations of full-length KvLm (FL) and its sensorless pore module. KvLm heterotetramers were produced by cell-free expression, purified by electrophoresis, and shown to yield functional channels after reconstitution in droplet interface bilayers. We studied the properties of KvLm channels with zero, one, two, three, and four voltage sensors. Three sensors suffice to promote channel opening with FL₄-like voltage dependence at depolarizing potentials, but all four sensors are required to keep the channel closed during membrane hyperpolarization.     

心肌肽素对豚鼠心室肌细胞内向整流钾电流的影响

目的研究心肌肽素对豚鼠心室肌细胞内向整流钾电流(IK1)的影响,探讨心肌肽素抗心律失常的作用机制。方法用急性酶解法分离豚鼠心室肌细胞,用标准的全细胞膜片钳技术,观察不同浓度的心肌肽素对内向整流钾电流的影响。结果在测试电压100mV的条件下,观察豚鼠心室肌细胞IK1内向电流对心肌肽素的影响。10μg/ml心肌肽素使IK1从给药前21.0±6.3pA/pF降低到给药后18.4±5.4pA/pF(P<0.05),抑制率为(20±3)%。50μg/ml心肌肽素使IK1从给药前22.8±5.5pA/pF降低到给药后16.0±3.8pA/pF(P<0.01),抑制率为(32±6)%。50μg/ml心肌肽素没有改变IK1的电流密度电压曲线形态。结论心肌肽素抑制豚鼠心室肌细胞IK1,可能是其抗心律失常作用的机理之一。     

Block of HERG Potassium Channels by the Antihistamine Astemizole and its Metabolites Desmethylastemizole and Norastemizole

INTRODUCTION: The selective H1-receptor antagonist astemizole (Hismanal) causes acquired long QT syndrome. Astemizole blocks the rapidly activating delayed rectifier K+ current I(Kr) and the human ether-a go-go-related gene (HERG) K+ channels that underlie it. Astemizole also is rapidly metabolized. The principal metabolite is desmethylastemizole, which retains H1-receptor antagonist properties, has a long elimination time of 9 to 13 days, and its steady-state serum concentration exceeds that of astemizole by more than 30-fold. A second metabolite is norastemizole, which appears in serum in low concentrations following astemizole ingestion and has undergone development as a new antihistamine drug. Our objective in the present work was to study the effects of desmethylastemizole, norastemizole, and astemizole on HERG K+ channels. METHODS AND RESULTS: HERG channels were expressed in a mammalian (HEK 293) cell line and studied using the patch clamp technique. Desmethylastemizole and astemizole blocked HERG current with similar concentration dependence (half-maximal block of 1.0 and 0.9 nM, respectively) and block was use dependent. Norastemizole also blocked HERG current; however, block was incomplete and required higher drug concentrations (half-maximal block of 27.7 nM). CONCLUSIONS: Desmethylastemizole and astemizole cause equipotent block of HERG channels, and these are among the most potent HERG channel antagonists yet studied. Because desmethylastemizole becomes the dominant compound in serum, these findings support the postulate that it becomes the principal cause of long QT syndrome observed in patients following astemizole ingestion. Norastemizole block of HERG channels is weaker; thus, the risk of producing ventricular arrhythmias may be lower. These findings underscore the potential roles of some H1-receptor antagonist metabolites as K+ channel antagonists.     

Cardiac Arrhythmias and Antiarrhythmic Drugs: Recent Advances in Our Understanding of Mechanism

Cardiac Arrhythmia Therapy. The purpose of this review is to consider our understanding of the mechanisms of action of cardiac antiarrhythmic drugs, as well as the status of our comprehension of arrhythmias and their therapy. The approach will be to review the basis for normal electrical activity of the heart, the mechanisms for cardiac arrhythmias, and our understanding of the mechanisms of drug action, and to distill from these strategies for the future. Immediate strategies in the prevention and treatment of life-threatening arrhythmias will most likely continue to make use of catheter and electrically based therapy, but the longterm treatment of large populations of individuals will still require the search for, and testing and administration of, pharmacologic therapy. It is emphasized that simplistic approaches to the solution of the complex problem of arrhythmias and their management will probably continue to cause problems, and that only by mastering the complexities of pathophysiology may success be best assured.     

Recent Advances in Understanding the Molecular Mechanisms of the Long QT Syndrome

Long QT Syndrome. Competing theories to explain the congenital long QT syndrome have included an imbalance in sympathetic innervation of the heart or a defect in repolarizing ion currents. Recent studies have identified at least four chromosomal loci at which mutations cause the congenital long QT syndrome in different families. The specific genes mutated in affected individuals have been identified at two of these loci, and both encode cardiac ion channels. The affected genes are SCN5A, the cardiac sodium channel gene, and HERG, whose protein product likely underlies I_Kr, the rapidly activating delayed rectifier. Thus, currently available evidence indicates that the congenital long QT syndrome is a primary disease of cardiac ion channels. Abnormalities in either inward or outward currents can cause the disease. Ongoing studies are evaluating the function of the mutant ion channels and the relationship between individual mutations and the clinical manifestations of the syndrome.     

The Role of Potassium Channels in Relaxant Effect of Levosimendan in Rat Small Mesenteric Arteries

Summary We investigated both the effect of levosimendan and the role of various potassium channels in KCl-precontracted rat small mesenteric arteries. Levosimendan (10⁻⁶−10⁻³ M) or cromakalim (CRO, 10⁻⁷−10⁻⁴ M) produced concentration-dependent relaxation responses in small mesenteric arteries precontracted by 30 mM KCl. The relaxant responses to levosimendan in KCl-precontracted arteries did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of rat small mesenteric arterial segments with ATP-dependent potassium channel (KATP) blocker glibenclamide (GLI, 10⁻⁶ M) for 30 min significantly inhibited the relaxant responses to both levosimendan and CRO. Neither the Ca²⁺-activated potassium channel (KCa) blocker iberiotoxin (10⁻⁷ M) nor the voltage-dependent potassium channel (KV) blocker 4-aminopyridine (5 mM) incubation for 30 min caused significant alterations in relaxant responses to levosimendan in KCl-precontracted small mesenteric arteries. These findings suggested that levosimendan-induced relaxation responses in isolated rat small mesenteric arteries were neither depended on endothelium nor inhibited by the blockers of KV or KCa but, they rather seem to depend on the activation of KATP.     

Unitary Current Analysis of L-type Ca2+ Channels in Human Fetal Ventricular Myocytes

INTRODUCTION: L-type calcium channels were studied in cell-attached patches from ventricular cell membranes of human fetal heart. METHODS AND RESULTS: Experiments were performed in the presence of 70 mM Ba2+ as the charge carrier at 22 degrees C to 24 degrees C. Unitary current sweeps were evoked by 300-msec depolarizing pulses to 0 mV from a holding potential of -50 mV at 0.5 Hz. Recorded currents were blocked by nisoldipine (1 microM) and stimulated by (-)Bay K 8644 (1 microM). During control, channel activity was seen in 13.9%+/-4.2% of the total 200 sweeps. Ensemble average current amplitude was 0.03+/-0.01 pA (n = 6) and average conductance was 20.4+/-0.2 pS (n = 5). Analysis of single channel kinetics showed open time and closed time histograms were best fit by one and two exponentials, respectively. Mean open time was tau(o) = 0.99+/-0.05 msec (n = 6). Mean closed time fast (tau(cf)) and slow (tau(cs)) component values were tau(cf) = 0.85+/-0.09 msec and tau(cs) = 8.0+/-0.94 msec (n = 6), respectively. With intrapipette (-)Bay K 8644 (1 microM), mean open time was best fit by two exponentials, tau(of) = 0.9+/-0.2 msec (n = 10) and tau(os) = 13.4+/-2.6 msec (n = 10); mean close time values were tau(cf) = 0.6+/-0.1 msec (n = 10) and tau(cs) = 9.8+/-1.9 msec (n = 10), respectively. With (-)Bay K 8644, channel activity was 66.5%+/-7.4%, the ensemble average current was 0.52+/-0.04 pA (n = 10) and the conductance 20.7+/-0.5 pS (n = 5). CONCLUSION: (1) the data establishes the characteristics of L-type Ca channels of human fetal hearts and their modulation by dihydropyridines; (2) the open time kinetics differ from those of avian embryonic and rat fetal hearts; and (3) the findings provide new and relevant information for understanding the physiologic behavior of unitary Ca2+ channels in the developing human heart and the baseline comparison for diseases that implicate Ca2+ channels in their etiology, such as autoimmune-associated congenital heart block.     

Potassium channels in the peripheral microcirculation

Vascular smooth muscle (VSM) cells, endothelial cells (EC), and pericytes that form the walls of vessels in the microcirculation express a diverse array of ion channels that play an important role in the function of these cells and the microcirculation in both health and disease. This brief review focuses on the K+ channels expressed in smooth muscle and endothelial cells in arterioles. Microvascular VSM cells express at least four different classes of K+ channels, including inward-rectifier K+ channels (Kin), ATP-sensitive K+ channels (KATP), voltage-gated K+ channels (Kv), and large conductance Ca2+-activated K+ channels (BKCa). VSM KIR participate in dilation induced by elevated extracellular K+ and may also be activated by C-type natriuretic peptide, a putative endothelium-derived hyperpolarizing factor (EDHF). Vasodilators acting through cAMP or cGMP signaling pathways in VSM may open KATP, Kv, and BKCa, causing membrane hyperpolarization and vasodilation. VSMBKc. may also be activated by epoxides of arachidonic acid (EETs) identified as EDHF in some systems. Conversely, vasoconstrictors may close KATP, Kv, and BKCa through protein kinase C, Rho-kinase, or c-Src pathways and contribute to VSM depolarization and vasoconstriction. At the same time Kv and BKCa act in a negative feedback manner to limit depolarization and prevent vasospasm. Microvascular EC express at least 5 classes of K+ channels, including small (sKCa) and intermediate(IKCa) conductance Ca2+-activated K+ channels, Kin, KATP, and Kv. Both sK and IK are opened by endothelium-dependent vasodilators that increase EC intracellular Ca2+ to cause membrane hyper-polarization that may be conducted through myoendothelial gap junctions to hyperpolarize and relax arteriolar VSM. KIR may serve to amplify sKCa- and IKCa-induced hyperpolarization and allow active transmission of hyperpolarization along EC through gap junctions. EC KIR channels may also be opened by elevated extracellular K+ and participate in K+-induced vasodilation. EC KATP channels may be activated by vasodilators as in VSM. Kv channels may provide a negative feedback mechanism to limit depolarization in some endothelial cells.     

Molecular Basis for Arrhythmias: Role of Two Nonsarcolemmal Ion Channels

Molecular Mechanisms for Arrhythmias. Ventricular tachycardia/fibrillation and sudden cardiac death occur frequently following myocardial ischemia or infarction. The recent Cardiac Arrhythmia Suppression Trial (CAST Study) found that patients treated with the Na-channel antagonists encainide and flecainide suffered increased mortality over placebo. This unexpected result has dampened enthusiasm for treatment of asymptomatic ventricular arrhythmias and more subtly suggests a need for review of current strategies for analysis and treatment of cardiac arrhythmias. This article focuses on two nonsarcolemmal ion channels that may be involved in certain types of ventricular arrhythmias: the gap junction channel and the Ca²⁺-release channel of sarcoplasmic reticulum (SR). Gap junctions enable conduction of the cardiac impulse from cell-to-cell and may be involved in reentrant arrhythmias. SR Ca²⁺-release channels regulate the level of cytosolic Ca²⁺ during initiation of contraction and seem to be the basis for triggered activity. Gap junction and SR Ca²⁺-release channels, though structurally dissimilar molecules, share certain functional and gating characteristics. In different ways, both channels couple the electrical response to the mechanical response. Furthermore, dysfunction of gap junction channels and/or SR Ca²⁺-release channels may underlie the development of arrhythmias in postischemic cells. Classification of arrhythmias on the basis of which channel(s) is principally involved might expedite the development of new drugs targeted at functional regions of the chan-nel(s). Ultimately, pharmacotherapy of arrhythmias directed at the molecules responsible for the electrical dysfunction may replace the empirical approach that dominates current cardiology practice. (J Cardiovasc Electrophysiol, Vol. 1, pp. 464–480, October 1990)