人HCN2 真核表达载体的构建及在HEK293 细胞中的表达

目的:构建含有人HCN2基因的真核表达载体,并观察在人胚胎肾细胞(HEK293)中的表达情况。方法:对人HCN2基因全序列进行分析,进行oligo设计,通过PCR,扩增HCN2全长cDNA,通过双酶切(XhoI和BamHI)装入真核表达载体pIRES2-EGFP中,脂质体法转染入HEK293细胞中,利用真核表达载体中带有绿色荧光蛋白GFP报告基因,对转染效率进行监测,采用反转录-聚合酶链反应检测HCN2 mRNA表达,全细胞膜片钳技术检测HCN2通道电流。结果:测序及酶切结果表明HCN2基因正确,荧光显微镜下,转染细胞观察到绿色荧光,反转录-聚合酶链反应检测到HCN2 mRNA表达,膜片钳检测到hHCN2基因编码的通道电流。结论:成功地构建了HCN2真核表达载体并进行了起搏通道HCN2基因的异源性表达。     

人HCN2真核表达载体的构建及在HEK293细胞中的表达

目的：构建含有人HCN2基因的真核表达载体,并观察在人胚胎肾细胞（HEK293）中的表达情况。方法：对人HCN2基因全序列进行分析,进行oligo设计,通过PCR,扩增HCN2全长cDNA,通过双酶切（XhoI和BamHI）装入真核表达载体pIRES2-EGFP中,脂质体法转染入HEK293细胞中,利用真核表达载体中带有绿色荧光蛋白GFP报告基因,对转染效率进行监测,采用反转录-聚合酶链反应检测HCN2 mRNA表达,全细胞膜片钳技术检测HCN2通道电流。结果：测序及酶切结果表明HCN2基因正确,荧光显微镜下,转染细胞观察到绿色荧光,反转录-聚合酶链反应检测到HCN2 mRNA表达,膜片钳检测到hHCN2基因编码的通道电流。结论：成功地构建了HCN2真核表达载体并进行了起搏通道HCN2基因的异源性表达。     

人HCN4通道的滞后现象:影响窦房结起搏的潜在决定因素(英文)

超极化活化环核苷酸门控(hyperpolarization-activated cyclic-nucleotide-gated,HCN)通道参与调制心脏跳动的节律和速率。与HCN1和HCN2有所不同,慢通道HCN4可能不存在电压依赖的滞后现象。本研究采用单细胞膜片钳方法,在稳定转染hHCN4的HEK293细胞上进行电生理记录,观察hHCN4通道是否存在滞后现象,以及cAMP对其的调制作用;同时采用实时定量RT-PCR方法检测窦房结和心房组织中HCNs的表达。电压钳实验结果显示hHCN4电流(Ih)激活随着保持电位超极化的变化而向去极化方向移动。三角电位变化钳(triangular ramp)和动作电位钳的结果也显示了hHCN4的滞后现象。cAMP增加Ih电流幅度,且使电流激活向去极化方向移动,从而改变内源性hHCN4滞后行为。RT-PCR结果显示,人窦房结组织主要表达HCN4,占75%,HCN1占21%,HCN2占3%,HCN3占0.7%。以上结果提示,人窦房结组织主要表达HCN4亚型,hHCN4的Ih存在电压依赖性的滞后现象,且受cAMP调制。由此推断,hHCN4通道的滞后现象可能在窦房结起搏活动中起到了关键作用。     

幼鼠和成年大鼠心室肌细胞起搏电流的改变

目的:运用膜片钳全细胞技术和实时定量聚合酶链式反应(PCR),探讨幼鼠和成年大鼠心室肌细胞起搏电流(If)及超极化激活的环核苷酸门控通道(HCN)亚型的改变。方法:分离3d的幼鼠和成年大鼠的心室肌细胞;测定HCN1、HCN2、HCN3和HCN4 mRNA的表达;记录If并研究其特性。结果:在新生大鼠心室肌细胞记录到If并得到电流密度-电压曲线,其激活电压约为-75mV;实时定量PCR检测HCN1、HCN2、HCN3和HCN4 mRNA在总HCN mRNA的表达中所占比例分别为0.23%±0.01%、83.58%±0.04%、0.79%±0.01%和15.44%±0.01%。在成年大鼠心室肌细胞也记录到超极化激活、并可以被4mmol/LCsCl阻断的If,其激活电压约为-115mV;HCN1、HCN2、HCN3和HCN4 mRNA在总HCN mRNA中所占比例分别为0.72%±0.02%、91.58%±0.08%、0.27%±0.02%和7.12%±0.02%。HCN2∶HCN4为(13.06±0.21)∶1。结论:随着年龄的增长,大鼠心室肌细胞HCN2所占比例增加;If值减小,激活电压变负。     

HCN 通道在神经系统中的分布及功能

超极化激活的环核苷酸门控的阳离子通道(hyperpolarization activated cyclic nucleotide gated channels,HCN),分为四个亚型:HCN1、HCN2、HCN3和HCN4。关于其在神经系统中作用的研究有很多,但是有些研究的结果似乎是矛盾的,这些矛盾的结果可能与其分布特点有关。在神经系统中,HCN通道的各个亚型的分布具有差异,这决定了其作用的差异性,因此在不同区域有其特定的生理功能。本文从不同脑区、脊髓及外周DRG等方面综述了HCN通道4个亚型在神经系统的分布,并且针对具体组织、核团分析其作用和生理功能。     

超极化激活的环核苷酸门控性阳离子通道（HCN）与疾病的相关性

超极化激活的环核苷酸门控的阳离子通道(hyperpolarization-activated cyclic nucleotide-gate cation channel,HCN)是一种特殊的阳离子通道,存在于神经细胞、小肠间质细胞、窦房结细胞或心脏细胞等具有自律性的细胞膜上,是产生过度激活正离子电流的结构基础,被认为是起搏细胞的重要特征。HCN离子蛋白通道不但与细胞凋亡以及电流传导有着密切关系,而且还与多种生命活动过程密切相关,近年来,已涉及到疼痛、癫痫、心律失常、消化道系统等许多疾病,特别是有关神经系统方面的疾病,下面将超极化激活的环核苷酸门控性阳离子通道(HCN)与疾病的关系综述如下。     

心源性猝死者窦房结病理学观察和HCN4、CX45的表达及其意义

目的:研究心源性猝死者窦房结病理学改变和超级化激活环核苷酸门控阳离子通道基因4(HCN4)、缝隙连接蛋白45(Cx45)的表达.方法:实验组为21例心源性猝死者,对照组18例(交通事故损伤致死9例,心脏破裂4例,肝破裂3例,脾破裂2例).经HE染色观察窦房结的形态学变化;应用免疫组化检测HCN4和Cx45在窦房结的表达.结果:心源性猝死组HCN4的表达高于对照组(P＜0.05),心源性猝死者窦房结Cx45的表达明显低于对照组(P＜0.01).结论:窦房结病理改变是引起心源性猝死的重要原因之一,HCN4表达的增高和Cx45表达的减少与心源性猝死的发生有一定的相关性.     

HCN通道:生物学特性及疼痛相关作用

脊椎动物的超极化激活环核苷酸门控通道(hyperpolarization-activated cyclic nucleotide-gated channels,HCN通道)具有反向电压依赖性,其开放依赖细胞表面的超极化。HCN在机体各组织的分布和数量及开放状态存在差异。HCN通道的开放受到cAMP及其它物质或信号传导通路直接或者间接的调控。HCN及其介导的Ih/If电流可以影响细胞膜静息电位,控制神经元兴奋性、突触电位和突触传递并在调节心律等方面起到重要作用,并且参与了疼痛等生理或病理过程的调控。部分药物可以通过对HCN通道的作用治疗疼痛等相关疾病。本文将从HCN通道的结构、分布、调控、在疼痛及其它相关疾病中起到的作用等方面对近年来HCN通道研究的新发现进行回顾和综述。     

妊娠期高血压疾病大鼠肾脏中蛋白激酶C-a亚型蛋白表达和转录水平的变化

目的:通过研究PKC-a蛋白及mRNA转录表达水平在妊娠期高血压疾病大鼠肾脏中的变化,以探讨妊娠期高血压疾病肾脏病理生理变化发生的机制.方法:注射L-NAME方法制备妊娠期高血压疾病动物模型并应用Westem印迹杂交及RT-PCR半定量方法检测15例妊娠期高血压疾病大鼠、正常妊娠大鼠、健康孕龄大鼠肾脏组织PKC-α亚型的表达情况.结果:妊娠期高血压疾病大鼠肾脏组织中PKC-α的蛋白及mRNA表达水平显著高于正常妊娠组(P<0.01),正常妊娠大鼠肾脏PKC-α的蛋白及mRNA表达水平明显低于对照组大鼠(P<0.01).结论:妊娠期高血压疾病大鼠肾脏组织中存在PKC-α的蛋白及mRNA的过度表达,它可能参与妊娠期高血压疾病肾脏病理生理变化.     

妊娠期高血压疾病大鼠肾脏中蛋白激酶C-а亚型蛋白表达和转录水平的变化

目的：通过研究PKC-α蛋白及mRNA转录表达水平在妊娠期高血压疾病大鼠肾脏中的变化,以探讨妊娠期高血压疾病肾脏病理生理变化发生的机制。方法：注射L-NAME方法制备妊娠期高血压疾病动物模型并应用Western印迹杂交及RT-PCR半定量方法检测15例妊娠期高血压疾病大鼠、正常妊娠大鼠、健康孕龄大鼠肾脏组织PKC-α亚型的表达情况。结果：妊娠期高血压疾病大鼠肾脏组织中PKC-α的蛋白及mRNA表达水平显著高于正常妊娠组（P〈0.01）,正常妊娠大鼠肾脏PKC-α的蛋白及mR-NA表达水平明显低于对照组大鼠（P〈0.01）。结论：妊娠期高血压疾病大鼠肾脏组织中存在PKC-α的蛋白及mRNA的过度表达,它可能参与妊娠期高血压疾病肾脏病理生理变化。     

Properties of hyperpolarization-activated pacemaker current defined by coassembly of HCN1 and HCN2 subunits and basal modulation by cyclic nucleotide

Members of the HCN channel family generate hyperpolarization-activated cation currents (Ih) that are directly regulated by cAMP and contribute to pacemaker activity in heart and brain. The four HCN isoforms show distinct but overlapping patterns of expression in different tissues. Here, we report that HCN1 and HCN2, isoforms coexpressed in neocortex and hippocampus that differ markedly in their biophysical properties, coassemble to generate heteromultimeric channels with novel properties. When expressed in Xenopus oocytes, HCN1 channels activate 5-10-fold more rapidly than HCN2 channels. HCN1 channels also activate at voltages that are 10-20 mV more positive than those required to activate HCN2. In cell-free patches, the steady-state activation curve of HCN1 channels shows a minimal shift in response to cAMP (+4 mV), whereas that of HCN2 channels shows a pronounced shift (+17 mV). Coexpression of HCN1 and HCN2 yields Ih currents that activate with kinetics and a voltage dependence that tend to be intermediate between those of HCN1 and HCN2 homomers, although the coexpressed channels do show a relatively large shift by cAMP (+14 mV). Neither the kinetics, steady-state voltage dependence, nor cAMP dose-response curve for the coexpressed Ih can be reproduced by the linear sum of independent populations of HCN1 and HCN2 homomers. These results are most simply explained by the formation of heteromeric channels with novel properties. The properties of these heteromeric channels closely resemble the properties of I(h) in hippocampal CA1 pyramidal neurons, cells that coexpress HCN1 and HCN2. Finally, differences in Ih channel properties recorded in cell-free patches versus intact oocytes are shown to be due, in part, to modulation of Ih by basal levels of cAMP in intact cells.     

Pacemaker channels produce an instantaneous current.

Spontaneous rhythmic activity in mammalian heart and brain depends on pacemaker currents (I(h)), which are produced by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Here, we report that the mouse HCN2 pacemaker channel isoform also produced a large instantaneous current (I(inst(HCN2))) in addition to the well characterized, slowly activating I(h). I(inst(HCN2)) was specific to expression of HCN2 on the plasma membrane and its amplitude was correlated with that of I(h). The two currents had similar reversal potentials, and both were modulated by changes in intracellular Cl(-) and cAMP. A mutation in the S4 domain of HCN2 (S306Q) decreased I(h) but did not alter I(inst(HCN2)), and instantaneous currents in cells expressing either wild type HCN2 or mutant S306Q channels were insensitive to block by Cs(+). Co-expression of HCN2 with the accessory subunit, MiRP1, decreased I(h) and increased I(inst(HCN2)), suggesting a mechanism for modulation of both currents in vivo. These data suggest that expression of HCN channels may be accompanied by a background conductance in native tissues and are consistent with at least two open states of HCN channels: I(inst(HCN2)) is produced by a Cs(+)-open state; hyperpolarization produces an additional Cs(+)-sensitive open state, which results in I(h).     

Role of subunit heteromerization and N-linked glycosylation in the formation of functional hyperpolarization-activated cyclic nucleotide-gated channels

The coassembly of homologous subunits to heteromeric complexes serves as an important mechanism in generating ion channel diversity. Here, we have studied heteromerization in the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel family. Using a combination of fluorescence confocal microscopy, coimmunoprecipitation, and electrophysiology we found that upon coexpression in HEK293 cells almost all dimeric combinations of HCN channel subunits give rise to the formation of stable channel complexes in the plasma membrane. We also identified HCN1/HCN2 heteromers in mouse brain indicating that heteromeric channels exist in vivo. Surprisingly, HCN2 and HCN3 did not coassemble to heteromeric channels. This finding indicates that heteromerization requires specific structural determinants that are not present in all HCN channel combinations. Using N-glycosidase F we show that native as well as recombinant HCN channels are glycosylated resulting in a 10-20-kDa shift in the molecular weight. Tunicamycin, an inhibitor of N-linked glycosylation, blocked surface membrane expression of HCN2. Similarly, a mutant HCN2 channel in which the putative N-glycosylation site in the loop between S5 and the pore helix was replaced by glutamine (HCN2N380Q) was not inserted into the plasma membrane and did not yield detectable whole-cell currents. These results indicate that N-linked glycosylation is required for cell surface trafficking of HCN channels. Cotransfection of HCN2N380Q with HCN4, but not with HCN3, rescued cell surface expression of HCN2N380Q. Immunoprecipitation revealed that this rescue was due to the formation of a HCN2N380Q/HCN4 heteromeric channel. Taken together our results indicate that subunit heteromerization and glycosylation are important determinants of the formation of native HCN channels.     

Hyperpolarization-activated cyclic nucleotide-gated channel 1 is a molecular determinant of the cardiac pacemaker current I(f)

The pacemaker current I(f) of the sinoatrial node (SAN) is a major determinant of cardiac diastolic depolarization and plays a key role in controlling heart rate and its modulation by neurotransmitters. Substantial expression of two different mRNAs (HCN4, HCN1) of the family of pacemaker channels (HCN) is found in rabbit SAN, suggesting that the native channels may be formed by different isoforms. Here we report the cloning and heterologous expression of HCN1 from rabbit SAN and its specific localization in pacemaker myocytes. rbHCN1 is an 822-amino acid protein that, in human embryonic kidney 293 cells, displayed electrophysiological properties similar to those of I(f), suggesting that HCN1 can form a pacemaker channel. The presence of HCN1 in the SAN myocytes but not in nearby heart regions, and the electrophysiological properties of the channels formed by it, suggest that HCN1 plays a central and specific role in the formation of SAN pacemaker currents.     

Aldosterone modulates I(f) current through gene expression in cultured neonatal rat ventricular myocytes

Mineralocorticoid receptor (MR) antagonists decrease the incidence of sudden cardiac death in patients with heart failure, as has been reported in two clinical trials (Randomized Aldactone Evaluation Study and Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study). Aldosterone has been shown to increase the propensity to arrhythmias by changing the expression or function of various ion channels. In this study, we investigate the effect of aldosterone on the expression of hyperpolarization-activated current (I(f)) channels in cultured neonatal rat ventricular myocytes, using the whole cell patch-clamp technique, real-time PCR, and Western blotting. Incubation with 10 nM aldosterone for 17-24 h significantly accelerates the rate of spontaneous beating by increasing diastolic depolarization. I(f) current elicited by hyperpolarization from -50 to -130 mV significantly increases aldosterone by 10 nM (by 1.9-fold). Exposure to aldosterone for 1.5 h increases hyperpolarization-activated cyclic nucleotide-gated (HCN) 2 mRNA by 26.3% and HCN4 mRNA by 47.2%, whereas HCN1 mRNA expression remains unaffected. Aldosterone (24-h incubation) increases the expression of HCN2 protein (by 60.0%) and HCN4 protein (by 84.8%), but not HCN1 protein. MR antagonists (1 microM eplerenone or 0.1 microM spironolactone) abolish the increase of I(f) channel expression (currents, mRNA, and protein levels) by 10 nM aldosterone. In contrast, 1 microM aldosterone downregulated I(f) channel gene expression. Glucocorticoid receptor antagonist (100 nM RU-38486) did not affect the increase of I(f) current by 10 nM aldosterone. These findings suggest that aldosterone in physiological concentrations upregulates I(f) channel gene expression by MR activation in cardiac myocytes and may increase excitability, which may have a potential proarrhythmic bearing under pathophysiological conditions.