Molecular and functional remodeling of Ito by angiotensin II in the mouse left ventricle

The transient outward potassium current (I_to) in cardiac myocytes is mainly mediated by members of the Kv4 subfamily of voltage-gated potassium channels. Several in vitro studies have shown that angiotensin II (Ang II), which plays an important role in the development of cardiac hypertrophy, rapidly downregulates Kv4.3 mRNA expression. However, it is not clear whether Ang II regulates I_toin vivo and whether this regulation may depend on alterations in Kv4.3 gene expression. To address this question, we determined the effects of acute (24 h) and chronic (14 days) exogenous infusions of Ang II on I_to and the expression of its channel subunits in the mouse left ventricle. Ang II rapidly increased blood pressure and reduced Kv4.2 but not Kv4.3 mRNA levels in the absence of cardiac hypertrophy. In response to chronically elevated Ang II levels cardiac hypertrophy developed, which was associated with a downregulation of Kv4.2 and Kv4.3 mRNA levels, and an upregulation of Kv1.4 mRNA levels. In contrast, neither KChIP2 mRNA levels nor amplitude or macroscopic inactivation kinetics of I_to were affected by the acute or chronic Ang II treatments. Consistent with the unchanged I_to amplitude, Kv4.2, Kv4.3, and KChIP protein expression levels were similar after chronic Ang II and sham treatment. Our findings demonstrate that elevations of Ang II concentrations that induce hypertension and cardiac hypertrophy do not alter the amplitude of I_to in the mouse left ventricle. Furthermore, they suggest that functional expression of cardiac I_to in mice is stabilized by KChIP2.     

Delayed endosome-dependent CamKII and p38 kinase signaling in cardiomyocytes destabilizes Kv4.3 mRNA

The Kv4.3 transient outward current (I(to)) channel, which produces early repolarization in human cardiomyocytes, is downregulated with cardiac pathology. This is evident in cultured neonatal rat cardiomyocytes in which Angiotensin II (Ang II) acts via p38 mitogen-activated protein kinase (p38K) to increase apoptosis and induce Kv4.3 mRNA destabilization to downregulate the channel protein. However, it is not understood how p38K activation, which is activated transiently for minutes, induces downstream effects hours later. Here we show that there is a second phase of p38K activation. Inhibiting this delayed p38K activation eliminated Kv4.3 mRNA destabilization. Furthermore, inhibiting endosome generation left the transient activation of p38K intact, but blocked delayed p38K activation and the Kv4.3 effect. CamKII was also found to be required for delayed p38K activation and Kv4.3 mRNA destabilization. Finally, CamKII methionine oxidation and activation are biphasic, with the delayed phase requiring endosomes. Hence, in addition to participating in channel traffic, cardiomyocyte endosomes control channel mRNA expression by mediating delayed oxidative CamKII-p38K signaling.     

AUF1 is upregulated by angiotensin II to destabilize cardiac Kv4.3 channel mRNA

Expression of cardiac myocyte Kv4 channels (Kv4.3 for human, Kv4.2 and Kv4.3 for rodents) is downregulated with hypertrophy in vivo leading to a decrease in the transient outward current (Ito). This effect is recapitulated in vitro with rat neonatal cardiac myocytes treated with angiotensin II (Ang II), which acts via AT₁ receptors, NADPH oxidase and p38 MAP kinase to destabilize the 3′ untranslated region (3′UTR) of the Kv4.3 channel messenger RNA (mRNA). Here deletion analysis and mutagenesis identify an AU-rich element (ARE) in the Kv4.3 3′UTR that is required for Ang II-induced destabilization. Overexpression of AUF1 (ARE/poly-(U)-binding/degradation factor 1), an RNA destabilizing protein, mimics and occludes the Ang II effect, while RNA interference targeted against AUF1 blocks the Ang II effect on the Kv4.3 3′UTR. Ang II upregulates AUF1 by activating AT₁ receptors, NADPH oxidase and p38 MAP kinase. Finally, pull-down assays establish that Ang II increases AUF1 binding to the ARE required for destabilization, while binding of the mRNA stabilizing protein HuR is unaffected. Hence, Ang II acts via AT₁ receptors, NADPH oxidase and p38 MAP kinase to upregulate AUF1, which in turn binds to an ARE in the Kv4.3 3′UTR to destabilize the channel mRNA.     

Modulation of action potential duration on myocyte hypertrophic pathways

Prolongation of the action potential duration (APD) has consistently been observed in experimental models of cardiac hypertrophy and failure as well as in humans and is partially attributed to a reduction of a hyperpolarizing current provided by the calcium-independent transient outward K(+) channel (I(to)). In the present study, we examined the effects of manipulating ion channel currents (I(to) and sodium/calcium exchanger (NCX)) and the associated alterations in action potential duration on cardiomyocyte hypertrophy and signaling induced by angiotensin II (AngII). Our aim was to examined whether distinct patterns of intracellular calcium manipulation could generate distinct patterns of MAPkinase activation and cellular hypertrophy. Cultured neonatal rat ventricular myocytes (NRVMs) were infected with Ad. beta-gal/GFP, Ad.Kv4.3, Ad.Kv4.3 antisense or Ad.NCX adenoviruses and hypertrophy induced by incubation with AngII. Overexpression of Kv4.3 increased I(to) density, shortened APD, decreased Ca(2+) influx and inhibited AngII-induced (3)H-leucine incorporation and ANF and beta-MHC expression. These hypertrophic changes were also paralleled by blockade of ERK MAP kinases activation as well as calcineurin expression. These electrical and hypertrophic changes produced by overexpression of Kv4.3 were completely and significantly reversed by Kv4.3 antisense and NCX gene transfer. Our findings indicate that AngII-mediated hypertrophy response in NRVMs can be abrogated by an enhancement of I(to) function through overexpression of Kv4.3 and that modulation of action potential duration can be important in the development of cardiac hypertrophy.     

Mechanical stretch and angiotensin II differentially upregulate the renin-angiotensin system in cardiac myocytes In vitro.

Pressure overload in vivo results in left ventricular hypertrophy and activation of the renin-angiotensin system in the heart. Mechanical stretch of neonatal rat cardiac myocytes in vitro causes secretion of angiotensin II (Ang II), which in turn plays a pivotal role in mechanical stretch-induced hypertrophy. Although in vivo data suggest that the stimulus of hemodynamic overload serves as an important modulator of cardiac renin-angiotensin system (RAS) activity, it is not clear whether observed upregulation of RAS genes is a direct effect of hemodynamic stress or is secondary to neurohumoral effects in response to hemodynamic overload. Moreover, it is unclear whether activation of the local RAS in response to hemodynamic overload predominantly occurs in cardiac myocytes or fibroblasts or both. In the present study, we examined the effect of mechanical stretch on expression of angiotensinogen, renin, angiotensin-converting enzyme (ACE), and Ang II receptor (AT(1A), AT(1B), and AT(2)) genes in neonatal rat cardiac myocytes and cardiac fibroblasts in vitro. The level of expression of angiotensinogen, renin, ACE, and AT(1A) genes was low in unstretched cardiac myocytes, but stretch upregulated expression of these genes at 8 to 24 hours. Stimulation of cardiac myocytes with Ang II also upregulated expression of angiotensinogen, renin, and ACE genes, whereas it downregulated AT(1A) and did not affect AT(1B) gene expression. Although losartan, a specific AT(1) antagonist, completely inhibited Ang II-induced upregulation of angiotensinogen, renin, and ACE genes, as well as stretch-induced upregulation of AT(1A) expression, it did not block upregulation of angiotensinogen, renin, and ACE genes by stretch. Western blot analyses showed increased expression of angiotensinogen and renin protein at 16 to 24 hours of stretch. The ACE-like activity was also significantly elevated at 24 hours after stretch. Radioligand binding assays revealed that stretch significantly upregulated the AT(1) density on cardiac myocytes. Interestingly, stretch of cardiac fibroblasts did not result in any discernible increases in the expression of RAS genes. Our results indicate that mechanical stretch in vitro upregulates both mRNA and protein expression of RAS components specifically in cardiac myocytes. Furthermore, components of the cardiac RAS are independently and differentially regulated by mechanical stretch and Ang II in neonatal rat cardiac myocytes.     

Peroxisome proliferator-activated receptor beta/delta activation improves angiotensin II-induced cardiac hypertrophy in vitro

Agonists of the peroxisome proliferator-activated receptor alpha (PPARalpha) and gamma (gamma) exert anti-proliferative and anti-inflammatory effects that led to the testing of these drugs in experimental cardiac hypertrophy. However, the effect of PPAR beta/delta (beta/delta) agonists in hypertrophy is not yet known. In this paper, an experiment was conducted to explore whether PPARbeta/delta activation has an effect on cardiac hypertrophy. An in vitro cardiomyocyte hypertrophy from neonatal rats was induced with Angiotensin II (Ang II1micromol x L(-1)) stimulation. For the examination of PPAR beta/delta effect, the cultured rat cardiac myocytes were pretreated with GW0742 (10 micromol.L(-1)), an agonist of PPARbeta/delta, for 48h before Ang II stimulation. The following parameters in the cultured cells were determined: surface areas of myocytes were measured by the NIH Image Software; (3)H-leucine incorporation into myocytes was counted by liquid scintillometer; mRNA expression of PPARbeta/delta, ANP, BNP, MMP9, MMP2, and IL-1beta was detected by RT-PCR; PPARbeta/delta protein expression was evaluated with immunofluorescence staining; GW0742 could ameliorate Ang II-induced cardiomyocyte hypertrophy, as indicated by its inhibitory effects on the surface area of myocytes, and ANP and BNP mRNA expressions in myocytes and (3)H-leucine incorporation into myocytes. Meanwhile, GW0742 pretreatment exerted inhibition on mRNA expression augmentation of such cytokines as MMP9, MMP2, and IL-1beta in hypertrophic myocytes. In addition, the down-regulated expression of PPARbeta/delta mRNA and protein in hypertrophic myocytes was also significantly reversed by GW0742. We demonstrate for the first time that GW0742 exerts a beneficial effect on Ang II-induced cardiac hypertrophy and the relation to inflammation response.     

G1 cyclins are involved in the mechanism of cardiac myocyte hypertrophy induced by angiotensin II

The importance of the cell cycle in proliferating cells is well known, but little is known about the role of cell cycle regulatory proteins in cardiac myocytes, which are fully differentiated cells. The present study determined, in vitro, the effect of angiotensin II (Ang II) treatment of neonatal rat cardiac myocytes on protein levels of cyclins and retinoblastoma gene product (pRb) phosphorylation. The role of G1 cyclin/cdk in Ang II-induced cardiac myocyte hypertrophy by overexpressing cdk inhibitor p21Cip1/Waf1 or p16INK4a was also examined using recombinant adenoviral vectors encoding these genes. Western blot analysis revealed that Ang II stimulated cyclin D1, D2, D3 and A protein levels in cardiac myocytes. Moreover, Ang II phosphorylated pRb on serine 780, which is known to occur in mitotic cells during cell cycle progression. Cultured cardiac myocytes treated with Ang II and infected with either control or recombinant adenovirus indicated that expression of p21 and p16 inhibited Ang II-induced cardiac myocyte hypertrophy, [3H]leucine incorporation into total cellular proteins, and skeletal alpha-actin (SK-A) and atrial natriuretic peptide (ANP) mRNA accumulation. Control virus had no effects on these parameters. These results suggest that G1 cyclins play an important role in cardiac myocyte hypertrophy stimulated by Ang II.     

血管紧张素Ⅱ及其受体拮抗剂对心肌细胞肥大的影响

目的观察血管紧张素Ⅱ（AngⅡ）、AT1受体拮抗剂氯沙坦和AT2受体拮抗剂PD123177对心肌细胞蛋白质合成速率和AT1受体mRNA表达的影响。方法采用3H-亮氨酸掺入法测定培养的心肌细胞蛋白质合成速率,RT-PCR方法检测心肌细胞AT1受体mRNA表达。结果在培养的心肌细胞中加入AngⅡ可明显增加心肌细胞3H-亮氨酸的掺入量,并呈剂量依赖性,氯沙坦可显著抑制AngⅡ引起的蛋白质合成增加,而PD123177对其无影响;AngⅡ上调AT1受体基因表达,氯沙坦抑制其上调,PD123177无影响。结论AngⅡ可通过上调AT1受体引起心肌细胞肥大,氯沙坦下调AT1受体,抑制心肌细胞肥大。     

Early down-regulation of K+ channel genes and currents in the postinfarction heart

INTRODUCTION: Down-regulation of key K+ channel subunit gene expression and K+ currents is a universal response to cardiac hypertrophy, whatever the cause, including the postmyocardial infarction (post-MI) remodeled heart. METHODS AND RESULTS: We investigated the hypothesis that down-regulation of K+ channel genes and currents post-MI occurs early and before significant remodeled hypertrophy of the noninfarcted myocardium could be detected. We investigated (1) the incidence of induced ventricular tachyarrhythmias (VT) in 3-day post-MI rat heart; (2) action potential (AP) characteristics of isolated left ventricular (LV) myocytes from sham-operated and 3-day post-MI heart; (3) time course of changes in outward K+ currents Ito-fast(f) and I(K) in isolated myocytes from 3-day and 4-week post-MI noninfarcted LV and compared the changes with sham-operated animals; and (4) changes in the messenger and protein levels of Kv2.1, Kv4.2, and Kv4.3 in the LV and right ventricle of 3-day post-MI heart. Sustained VT was induced in 6 of 10 3-day post-MI rats and in none of 8 sham rats. The membrane capacitance of myocytes isolated from 3-day post-MI noninfarcted LV was not significantly different from control, whereas membrane capacitance 4-week post-MI was significantly higher, reflecting the development of hypertrophy. AP duration was increased and the density of Ito-f and I(K) were significantly decreased in 3-day post-MI LV myocytes compared with sham. The reduced density of Ito did not significantly differ in 4-week post-MI LV myocytes, whereas the density of I(K) was decreased further at 4 weeks post-MI. The changes in Ito-f and I(K) correlated with decreased messenger and protein levels of Kv4.2/Kv4.3 and Kv2.1, respectively. CONCLUSION: These results support the hypothesis that down-regulation of K+ channel gene expression and current in the post-MI LV occurs early and may be dissociated from the slower time course of post-MI remodeled hypertrophy. These changes may contribute to early arrhythmogenesis of the post-MI heart.     

The renin-angiotensin system and experimental heart failure

Experimental studies suggest that the renin-angiotensin system (RAS) and its primary effector peptide, angiotensin II (Ang II), are involved in the pathophysiology of cardiac hypertrophy and failure. All the components required for Ang II production are present in the heart, and cardiac Ang II formation appears to be regulated independent from the circulating RAS. In animal models and in patients with heart failure, the cardiac RAS is activated and, presumably, local Ang II formation is enhanced. Several cardiac cell types express Ang II type 1 (AT1) and/or type 2 (AT2)-receptors and represent potential targets for Ang II-mediated effects. In neonatal cardiac myocytes, Ang II induces a hypertrophic response via the AT1-receptor. Likewise, activation of the AT1-receptor triggers hypertrophy in terminally differentiated cardiac myocytes and in perfused heart preparations. In the neonatal system, Ang II appears to be a major autocrine/paracrine mediator of cardiac myocyte hypertrophy in response to passive mechanical stretch. By contrast, AT1-receptor activation apparently is not required to trigger load-induced hypertrophy in the adult cardiomyocyte. Recent studies suggest that the AT2-receptor opposes AT1-receptor-mediated growth signals in neonatal and in adult cardiac myocytes. Pharmacological studies have established that a blockade of the RAS at the level of the angiotensin-converting enzyme (ACE) or the AT1-receptor ameliorates the remodeling process of the heart and prolongs long-term survival in animal models of cardiac hypertrophy and failure. The therapeutic effects of ACE inhibitors and AT1-receptor antagonists clearly suggest an important role for the ACE-Ang II-AT1-receptor axis in the development of cardiac hypertrophy and failure. It must be kept in mind, however, that these drugs enhance AT2-receptor and B2-kinin receptor-dependent signaling pathways which may contribute significantly to the beneficial effects observed in vivo. Molecular and physiological analyses of transgenic mice with a cardiac-specific overexpression of the AT1 or AT2-receptor confirm that AT1 and AT2-receptor-dependent signaling cascades potently modulate cardiac myocyte function and growth. However, studies in AT1-receptor knockout mice demonstrate that cardiac hypertrophy in response to hemodynamic overload can occur independent from the AT1-receptor. In this paper, we review recent experimental evidence suggesting a critical role for the RAS in cardiac hypertrophy and failure with special emphasis on the putative role of Ang II and Ang II-receptor signaling in cardiac myocytes.     

Diminished Kv4.2/3 but not KChIP2 levels reduce the cardiac transient outward K+ current in spontaneously hypertensive rats

OBJECTIVE: A reduction of the Ca(2+)-independent transient outward potassium current (I(to)) in epicardial but not in endocardial myocytes of the left ventricle has been observed in cardiac hypertrophy and is thought to contribute to the electrical vulnerability associated with this pathology. METHODS: In the present study we investigated the molecular mechanisms underlying regional alterations in I(to) in hypertrophied hearts of spontaneously hypertensive rats (SHR) using the whole-cell patch-clamp technique, quantitative RT-PCR and heterologous expression of underlying ion channel subunits. RESULTS: I(to) was significantly smaller in epicardial myocytes of SHR than in Wistar-Kyoto (WKY) controls (11.1+/-0.9 pA/pF, n=20 vs. 16.8+/-1.7 pA/pF, n=20, p<0.01), but not different in endocardial myocytes from both groups. Quantitative RT-PCR analysis of the genes encoding I(to) revealed significantly lower levels of Kv4.2 and Kv4.3 mRNA in the epicardial region of SHR rats compared to WKY rats. In contrast, mRNA expression levels of all three splice variants of the beta-subunit KChIP2 were significantly higher in both endo- and epicardial myocytes from SHR than from WKY rats. In parallel, inactivation of I(to), which is negatively modulated by KChIP2, was slowed down in SHR while recovery from inactivation remained unchanged. Heterologous co-expression of increasing amounts of KChIP2b together with a fixed amount of Kv4.2 in Xenopus laevis oocytes revealed a hyperbolic relation of recovery from inactivation and inactivation time constant, demonstrating that KChIP2 preferentially affects inactivation, if its expression level is high. CONCLUSION: These results suggest that downregulation of I(to) in the left ventricle of SHR is mediated by a reduced expression of Kv4.2 and Kv4.3 (but not of KChIP2), whereas the slower inactivation of I(to) can be explained by increased expression levels of KChIP2 in SHR.     

血管紧张素Ⅱ对大鼠心室肌三种离子通道基因表达的效应

目的利用微渗透泵灌注血管紧张素Ⅱ(AngⅡ)大鼠模型,观察AngⅡ对大鼠心室肌三种离子通道基因表达的效应。方法Sprague-Dawley大鼠48只植入微渗透泵,随机分为对照组灌注生理盐水(1μl/h),实验组灌注AngⅡ(200或400ng·kg-1·min-1),持续时间为2w或4w。提取心脏左室RNA,逆转录-聚合酶链反应半定量分析SCN5A、Kv4.3及Cav1.2离子通道基因mRNA的表达量,磷酸甘油醛脱氢酶(GAPDH)为内参。结果SCN5A及Cav1.2基因的mRNA水平则较对照组升高(P<0.05),而Kv4.3基因的mRNA水平较对照组降低(P<0.01),且具有一定剂量及时间依赖性。结论AngⅡ使SCN5A及Cav1.2表达上调,Kv4.3表达下调,且其效应具有剂量及时间依赖性。     

Angiotensin II signaling pathways mediate expression of cardiac T-type calcium channels

Recent studies indicate that cardiac T-type Ca2+ current (ICaT) reappears in hypertrophied ventricular cells. The aim of this study was to investigate the role of angiotensin II (Ang II), a major inducer of cardiac hypertrophy, in the reexpression of T-type channel in left ventricular hypertrophied myocytes. We induced cardiac hypertrophy in rats by abdominal aorta stenosis for 12 weeks and thereafter animals were treated for 2 weeks with losartan (12 mg/kg per day), an antagonist of type 1 Ang II receptors (AT1). In hypertrophied myocytes, we showed that the reexpressed ICaT is generated by the CaV3.1 and CaV3.2 subunits. After losartan treatment, ICaT density decreased from 0.40+/-0.05 pA/pF (n=26) to 0.20+/-0.03 pA/pF (n=27, P<0.01), affecting CaV3.1- and CaV3.2-related currents. The amount of CaV3.1 mRNA increased during hypertrophy and retrieved its nonhypertrophic level after losartan treatment, whereas the amount of CaV3.2 mRNA was unaffected by stenosis. In cultured newborn ventricular cells, chronic Ang II application (0.1 micromol/L) also increased ICaT density and CaV3.1 mRNA amount. UO126, a mitogen-activated protein kinase kinase-1/2 (MEK1/2) inhibitor, reduced Ang II-increased ICaT density and CaV3.1 mRNA amount. Bosentan, an endothelin (ET) receptor antagonist, reduced Ang II-increased ICaT density without affecting the amount of CaV3.1 mRNA. Finally, cotreatment with bosentan and UO126 abolished the Ang II-increased ICaT density. Our results show that AT1-activated MEK pathway and autocrine ET-activated independent MEK pathway upregulate T-type channel expression. Ang II-increased of ICaT density observed in hypertrophied myocytes may play a role in the pathogenesis of Ca2+ overload and arrhythmias seen in cardiac pathology.     

Targeted deletion of Kv4.2 eliminates I(to,f) and results in electrical and molecular remodeling, with no evidence of ventricular hypertrophy or myocardial dysfunction

Previous studies have demonstrated a role for voltage-gated K+ (Kv) channel alpha subunits of the Kv4 subfamily in the generation of rapidly inactivating/recovering cardiac transient outward K+ current, I(to,f), channels. Biochemical studies suggest that mouse ventricular I(to,f) channels reflect the heteromeric assembly of Kv4.2 and Kv4.3 with the accessory subunits, KChIP2 and Kvbeta1, and that Kv4.2 is the primary determinant of regional differences in (mouse ventricular) I(to,f) densities. Interestingly, the phenotypic consequences of manipulating I(to,f) expression in different mouse models are distinct. In the experiments here, the effects of the targeted deletion of Kv4.2 (Kv4.2(-/-)) were examined. Unexpectedly, voltage-clamp recordings from Kv4.2(-/-) ventricular myocytes revealed that I(to,f) is eliminated. In addition, the slow transient outward K+ current, I(to,s), and the Kv1.4 protein (which encodes I(to,s)) are upregulated in Kv4.2(-/-) ventricles. Although Kv4.3 mRNA/protein expression is not measurably affected, KChIP2 expression is markedly reduced in Kv4.2(-/-) ventricles. Similar to Kv4.3, expression of Kvbeta1, as well as Kv1.5 and Kv2.1, is similar in wild-type and Kv4.2(-/-) ventricles. In addition, and in marked contrast to previous findings in mice expressing a truncated Kv4.2 transgene, the elimination I(to,f) in Kv4.2(-/-) mice does not result in ventricular hypertrophy. Taken together, these findings demonstrate not only an essential role for Kv4.2 in the generation of mouse ventricular I(to,f) channels but also that the loss of I(to,f) per se does not have overt pathophysiological consequences.     

阿托伐他汀上调过氧化物酶体增殖物活化型受体α、γ表达及抑制心肌细胞肥大的作用

目的探讨阿托伐他汀在体外对血管紧张素Ⅱ（Ang Ⅱ）介导的肥大心肌细胞的作用,分析过氧化物酶体增殖物活化型受体（PPAR）α、γ在其中的可能作用.方法体外培养新生大鼠的心室肌细胞,用Ang Ⅱ诱导建立心肌肥厚模型,在模型中加入不同浓度阿托伐他汀,用软件分析观察心肌细胞表面积,应用3H-亮氨酸掺入实验检测心肌细胞蛋白合成速率及使用RT-PCR半定量测定心钠素、脑钠素、基质金属蛋白酶9、基质金属蛋白酶2、白介素1β和PPARα、γ mRNA的表达变化.结果 Ang Ⅱ可使体外培养的心肌细胞表面积和3H-亮氨酸的掺入增加,升高心钠素、脑钠素、基质金属蛋白酶9、基质金属蛋白酶2和白介素1β的表达,PPARα、γ表达下降;阿托伐他汀可逆转上述变化并呈剂量依赖性,而作为溶剂的DMSO对心肌肥厚无影响.结论阿托伐他汀具有抑制Ang Ⅱ介导的体外心肌细胞肥大的作用,PPARα及PPARγ很可能参与该过程.     

快速起搏大鼠心房肌细胞L-型钙通道及钾通道Kv4.3的表达变化

目的 利用原代培养的心房肌细胞建立快速起搏模型,研究L-型钙通道及钾通道Kv4.3在快速起搏早期的表达变化.方法 原代培养大鼠心房肌细胞,并建立快速起搏细胞模型,利用RT-PCR以及Western-blot方法检测L-型钙通道α1c及钾通道Kv4.3在快速起搏3、6、12、24 h后mRNA和蛋白的表达变化.结果 快速起搏6 h后L-型钙通道α1c的mRNA和蛋白表达较起搏前持续降低,并于24 h时达到最低值;而钾通道Kv4.3 mRNA和蛋白的表达在快速起搏12 h后降低,并且在其后保持相对稳定的水平.结论 快速起搏早期,原代培养心房肌细胞L-型钙通道α1c及钾通道Kv4.3的mRNA和蛋白表达均出现不同程度的降低,提示其发生了离子通道重构,并且可能是电重构的分子基础.     

硫酸奎尼丁对乳大鼠心室肌细胞Kv4．3基因mRNA水平表达的影响

目的探讨硫酸奎尼丁对乳大鼠心室肌细胞Kv4．3基因mRNA水平表达的影响及其治疗Brugada综合征的分子机制。方法将乳大鼠心室肌细胞随机分为对照组及硫酸奎尼丁干预组,培养至24、48、72h,应用半定量逆转录一聚合酶链反应（RT-PCR）技术检测Kv4．3基因mRNA表达的变化。结果于预至24h对Kv4．3基因mRNA水平表达无明显影响;至48h,各干预组较对照组显著降低（P〈0．05）,且5与10μmol／L组较1μmol／L组下调作用更为显著（P〈0．05）;至72h,各干预组较对照组显著降低（P〈0．05）,而各干预组间差异无统计学意义。结论硫酸奎尼丁可显著下调Kv4-3基因mRNA水平表达,且较长时间干预时低浓度与较高浓度下调的幅度相近。