肌浆网/内质网钙调控在心血管疾病中的研究进展

肌浆网/内质网(SR/ER)是细胞内重要的钙储库及调控系统,主要通过Ca2+释放通道雷尼丁受体(RyR)和1,4,5-三磷酸肌醇受体(IP3R),以及Ca2+摄取蛋白肌浆网Ca2+-ATP酶(SERCA)和基质交感分子1(STIM1)等调节钙信号,维持细胞内钙稳态。研究发现,SR/ER钙平衡对细胞正常生理功能的发挥和信息传递非常重要,SR/ER钙稳态失调与缺血性心脏病、心肌肥厚、高血压及心力衰竭等心血管疾病的发生发展密切相关。本文就SR/ER钙调控在心血管疾病中的研究进展作一概述,重点阐述SR/ER钙离子通道和相关调控蛋白对细胞内钙信号的调节机制,以期为临床心血管疾病的治疗提供重要策略和潜在靶点。     

IP3R在心血管疾病中的作用研究进展

l，4，5三磷酸肌醇受体是存在于内质网、肌浆网及核膜上的一种配体门控Ca2 释放通道蛋白，精确地调控胞浆内Ca2 浓度的变化，从而通过钙信号对细胞内许多生理过程如细胞分裂、增殖、生长、凋亡、功能发挥调节作用。人类近期应用激光共聚焦显微镜、放射配基受体等实验对IP3R的结构、功能及其调节因素进行了研究，表明其在多种心血管疾病的病理生理机制中发挥了重要作用。     

病理性钙信号与急性胰腺炎

胰腺腺泡细胞异常钙信号是AP最早期的细胞内事件,在AP的发生和发展过程中起关键作用。腺泡细胞内钙信号的转导受细胞内钙信号元件严格调控,主要包括细胞内钙库上表达的钙释放通道如三磷酸肌醇受体和兰尼碱受体、细胞膜上的钙库操纵型钙内流通道以及参与回补胞内钙库的肌质网膜钙ATP酶和参与钙外排的胞膜钙ATP酶等。目前研究提示这些钙...     

钙调神经磷酸酶对钙化细胞Ⅰ型三磷酸肌醇受体表达的影响

目的探讨大鼠血管平滑肌细胞钙化过程中钙调神经磷酸酶对Ⅰ型三磷酸肌醇受体蛋白和mRNA表达的影响。方法大鼠胸主动脉血管平滑肌细胞经传代培养后随机分为对照组、钙化组和环孢素A组,采用磷酸二氢钠诱导大鼠动脉血管平滑肌细胞钙化。应用免疫印迹法及实时荧光定量RT-PCR法测定钙调神经磷酸酶B亚基、Ⅰ型三磷酸肌醇受体的表达变化,同时测定Ca2+浓度及碱性磷酸酶、钙调神经磷酸酶活性。结果与对照组比较,钙化组钙调神经磷酸酶B亚基、Ⅰ型三磷酸肌醇受体蛋白和mRNA表达显著增加(P<0.01);与钙化组比较,环孢素A组钙调神经磷酸酶B亚基、Ⅰ型三磷酸肌醇受体蛋白和mRNA表达显著降低(P<0.01)。钙化组Ca2+浓度、钙调神经磷酸酶活性、碱性磷酸酶活性较对照组显著增高(P<0.01);环孢素A组碱性磷酸酶活性、Ca2+浓度较钙化组显著增加(P<0.05或P<0.01),钙调神经磷酸酶活性较钙化组显著降低(P<0.01)。结论钙调神经磷酸酶能够增强钙化细胞中Ⅰ型三磷酸肌醇受体mRNA和蛋白的表达。     

钙池操纵的Ca2+通道的激活机制研究进展

钙池操纵的Ca~(2 )通道(store-operated Ca~(2 ) channels,SOC)是非兴奋细胞Ca~(2 )内流的主要通道之一,参与多种病理和生理过程,在钙信号通路的研究中,SOC的激活机制一直是人们关注的焦点之一,迄今为止,钙内流因子模型(Ca~(2 ) innux factor model,CIF model)和构象耦联模型fconformational coupling model)受到广泛关注.部分学者已经从很多不同类型的细胞中提取出CIF,并证实钙非依赖性的磷脂酶A_2(Ca~(2 )-independent phospholipase A_2,iPLA_2)作为CIF的底物,在某些类型细胞的SOC激活过程中发挥重要作用,并进一步提出了ER- CIF-iPLA_2-CaM-LysoPLs-SOC通路模型.瞬时受体电位(transient receptor potential,TRP)通道蛋白与1.4,5-磷酸肌醇受体(inositol 1,4,5 trisphosphate receptor,IP_3R)的结构连接作为构象耦联模型的基础已被广泛证实,随着对IP_3R,Ryanodine受体、肌动蛋白等在钙信号通路中所发挥作用的深入研究,构象耦联模型将得到不断补充和完善.SOC激活机制的破解,将对进一步完善非兴奋细胞的钙通道特性及其调节机制理论带来重大突破.     

心肌细胞钙瞬变信号的研究进展

心肌细胞钙瞬变信号是指细胞动作电位或其他原因引起心肌细胞内游离Ca2+浓度迅速波动的现象,包括钙火花、钙波、钙震荡、钙星、钙空穴等.钙瞬变信号的幅度及时程受细胞膜L型钙通道、肌浆网膜钙释放通道、钙-ATP酶、瞬时受体电位蛋白、连接素等的影响.钙瞬变信号与心肌细胞的收缩性及传导性相关,并参与了心肌肥厚、心力衰竭等疾病发生发展过程.     

SK通道在心血管疾病中的作用研究进展

小电导钙离子激活钾通道（Small conductance Ca2+-activated K+ channel,SK）是一种表达于全身多组织细胞的Ca2+敏感性钾通道,对细胞的电位变化及功能起着重要的作用。研究表明,SK通道参与了多种心血管疾病的发生与发展,本文综述近几年SK通道在心血管疾病中的研究进展。     

U50488对大鼠离体心心律及心肌细胞内游离钙的影响

观察选择性Kappa(κ)阿片受体激动剂U50488对大鼠离体心心律及心肌细胞内游离钙([Ca2+]i)的作用.结果显示:U50488可诱发心律失常并增加静息心肌细胞[Ca2+]i,U50488诱发心律失常及增加心肌细胞[Ca2+]i的作用可被选择性κ阿片受体拮抗剂Nor-binaltorphimine(Nor-BNI)及选择性磷酯酶C抑制剂U73122、新霉素及链霉素所阻断.表明心脏κ阿片受体激活所致的心律失常是由于磷酸肌醇信号传导通路激活引起心肌细胞[Ca2+]i增多所致.     

血管内皮细胞瞬时受体势通道的研究进展

血管内皮细胞上的瞬时受体势（transient receptor potential,TRP）通道参与血管张力等多种功能的调节,如TRPC1、TRPC4、TRPC6和TRPV1参与血管通透性的调节,TRPC4、TRPV1和TRPV4参与血管张力的调节,TRPC4参与了低氧诱导的血管重构,TRPC3、TRPC4和TRPM2则参与氧化应激诱导的应答。各种TRP通道的激活和调节模式存在很大差异,不同的TRP通道可能由特定的刺激激活,如血管活性物质、氧化应激、机械刺激和加热。TRP通道可能将这些刺激转换成胞内Ca2＋的变化,进而引起不同的血管反应。TRP通道功能失调可引起多种心血管系统疾病。阐明调节内皮TRP通道的机制,开发以不同亚型的TRP通道为靶点的特异性药物,有望为心血管疾病的治疗开辟新的前景。     

应用RNA阵列技术检测自发性高血压大鼠肌浆网钙释放通道基因表达变化

目的 探讨肌浆网Ca2 释放通道在原发性高血压发病机制中的变化特点。方法 提取2、4、6、8、10、12周龄各组雄性自发性高血压大鼠(spontaneously hypertensive rats,SHR)和正常血压大鼠(Wistar-kyoto rats,WKY)心室肌、血管平滑肌、肝脏和肾脏组织的总RNA,共294个样品,利用高通量RNA阵列技术检测肌浆网兰尼碱受体2(ryanodine receptor,RyR2)和1,4,5-三磷酸肌醇受体1(inositol 1,4,5-triphosphate receptors,IP3R1)在不同周龄SHR中mRNA的表达谱改变。结果 与同周龄WKY相比较,SHR在6、8、10、12周龄血压出现显著性升高(P均<0.01),10、12周龄心室肌重量/体重比出现显著增加(P均<0.01),心肌中RyR2基因表达在4、6、8、10、12周龄出现显著性升高(P<0.05或P<0.01),IP3R1基因表达在6、8、10、12周龄出现显著性升高(P<0.05或P<0.01)。血管平滑肌组织中RyR2基因表达在4、6、8、10、12周龄出现显著性升高(P<0.05),IP3R1基因表达在4、6、8、10、12周龄出现显著性升高(P<0.05或P<0.01)。肝脏和肾脏组织中未见上述基因的明显表达。结论 肌浆网Ca2 释放通道受体蛋白RyR2和IP3R1 mRNA表达变化是实验性高血压发生和发展过程中重要的分子生物学机制。     

Immunophilin FK506 binding protein associated with inositol 1,4,5-trisphosphate receptor modulates calcium flux.

The immunophilin FK506 binding protein 12 (FKBP12) is associated with and modulates the ryanodine receptor calcium release channel of skeletal muscle. Ryanodine receptor has amino acid homology and functional similarity with another intracellular Ca2+ release channel, the inositol 1,4,5-trisphosphate receptor (IP3R). In the present study we show that highly purified preparations of IP3R contain FKBP12. The complex of these two proteins is disrupted by the immunosuppressants FK506 and rapamycin, both of which are known to bind FKBP12 with high affinity. Disrupting the IP3R-FKBP12 interaction increases Ca2+ flux through IP3R, an effect that is reversed by added FKBP12. FKBP12 appears to be physiologically linked to IP3R, regulating its Ca2+ conductance.     

Effect of chronic ethanol exposure on inositol trisphosphate receptors in WB rat liver epithelial cells

BACKGROUND: Enhanced agonist-induced Ca2+ release has been reported in hepatocytes isolated from ethanol-fed rats. Because myo-inositol 1,4,5-trisphosphate receptors (IP3Rs) are involved in the mobilization of Ca2+, we examined the effects of chronic ethanol treatment on IP3R function and levels of IP3R protein by using WB rat liver epithelial cells. METHODS: WB cells were treated with ethanol (50-150 mM) for 24 to 48 hr and were loaded with Fura-2 to measure agonist-induced Ca2+ mobilization or saponin permeabilized to measure myo-inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release. IP3 levels were measured in [3H]-inositol labeled cells. Levels of IP3R protein were quantitated by immunoblotting with antibodies to IP3R isoforms. Lysosomal and proteasomal peptidase activities were assayed in cytosol and membrane fractions using specific fluorogenic peptide substrates. RESULTS: Ethanol treatment enhanced Ca2+ mobilization in response to angiotensin II, vasopressin, and bradykinin. This effect was not due to an increased production of IP3. Chronic ethanol treatment stimulated the mobilization of Ca2+ from saponin-permeabilized cells in response to subsaturating doses of IP3 and increased the basal levels of both type I and type III IP3Rs by 1.8-fold and 1.6-fold, respectively. Ethanol treatment did not prevent angiotensin II-induced IP3R down-regulation or alter lysosomal cathepsin B activity or the trypsin-like and peptidylglutamyl peptidase activities of the proteasome. However, chronic ethanol exposure resulted in a 60% and 41% inhibition of the chymotrypsin-like activity of the proteasome in cytosol and microsomal membranes, respectively. CONCLUSION: We propose that the enhanced agonist-mediated Ca2+ mobilization observed in chronic ethanol-treated WB liver epithelial cells results from increased IP3R expression caused by an inhibition of IP3R degradation pathways by ethanol.     

Agonist-induced Ca2+ entry determined by inositol 1,4,5-trisphosphate recognition

It has been considered that Ca2+ release is the causal trigger for Ca2+ entry after receptor activation. In DT40 B cells devoid of inositol 1,4,5-trisphosphate receptors (IP3R), the lack of Ca2+ entry in response to receptor activation is attributed to the absence of Ca2+ release. We reveal in this article that IP3R recognition of IP3 determines agonist-induced Ca2+ entry (ACE), independent of its Ca2+ release activity. In DT40 IP3R(-/-) cells, endogenous ACE can be rescued with type 1 IP3R mutants (both a DeltaC-terminal truncation mutant and a D2550A pore mutant), which are defective in Ca2+ release channel activity. Thus, in response to B cell receptor activation, ACE is restored in an IP3R-dependent manner without Ca2+ store release. Conversely, ACE cannot be rescued with mutant IP3Rs lacking IP3 binding (both the Delta90-110 and R265Q IP3-binding site mutants). We conclude that an IP3-dependent conformational change in the IP3R, not endoplasmic reticulum Ca2+ pool release, triggers ACE.     

Domain organization of the type 1 inositol 1,4,5-trisphosphate receptor as revealed by single-particle analysis

The inositol 1,4,5-trisphosphate receptor (IP(3)R) is a tetrameric intracellular Ca(2+) channel, which mediates the release of Ca(2+) from the endoplasmic reticulum in response to many different extracellular stimuli. We present a 3D structure of the type 1 IP(3)R obtained by electron microscopy and single-particle analysis that reveals its domain organization. The IP(3)R has a flower-like appearance with fourfold symmetry and is made up of three distinct domains connected by slender links. By relating the organization of the structural domains to secondary-structure predictions and biochemical data we develop a model in which structural domains are mapped onto the amino acid sequence to deduce the location of the channel region and the cytoplasmic inositol 1,4,5-trisphosphate-binding and modulatory subdomains. The structure of the IP(3)R is compared with that of other tetrameric cation channels. The channel domain is similar in size and shape to its counterparts in the ryanodine receptor and the Shaker voltage-gated K(+) channel.     

Ryanodine receptors/calcium release channels in heart failure and sudden cardiac death

Calcium (Ca2+) ions are second messengers in signaling pathways in all types of cells. They regulate muscle contraction, electrical signals which determine the cardiac rhythm and cell growth pathways in the heart. In the past decade cDNA cloning has provided clues as to the molecular structure of the intracellular Ca2+ release channels (ryanodine receptors, RyR, and inositol 1,4,5-trisphosphate receptors, IP3R) on the sarcoplasmic and endoplasmic reticulum (SR/ER) and an understanding of how these molecules regulate Ca2+ homeostasis in the heart is beginning to emerge. The intracellular Ca2+ release channels form a distinct class of ion channels distinguished by their structure, size, and function. Both RyRs and IP3Rs have gigantic cytoplasmic domains that serve as scaffolds for modulatory proteins that regulate the channel pore located in the carboxy terminal 10% of the channel sequence. The channels are tetramers comprised of four RyR or IP3R subunits. RyR2 is required for excitation-contraction (EC) coupling in the heart. Using co-sedimentation and co-immunoprecipitation we have defined a macromolecular complex comprised of RyR2, FKBP12.6, PKA, the protein phosphatases PP1 and PP2A, and an anchoring protein mAKAP. We have shown that protein kinase A (PKA) phosphorylation of RyR2 dissociates FKBP12.6 and regulates the channel open probability (P(o)). In failing human hearts RyR2 is PKA hyperphosphorylated resulting in defective channel function due to increased sensitivity to Ca2+-induced activation.     

Norepinephrine-induced inositol 1,4,5-trisphosphate formation in atrial myocytes is regulated by extracellular calcium,protein kinase C,and calmodulin

We investigated whether alteration of extracellular and intracellular Ca2+ concentrations, protein kinase C, and calmodulin modulate norepinephrine (NE)-induced inositol 1,4,5-trisphosphate (IP3) formation in neonatal rat atrial myocytes. NE-induced IP3 production in atrial myocytes was stimulated by elevation of extracellular Ca2+ in a dose-dependent manner. However, TMB-8 (an intracellular calcium antagonist) and A23187 (an intracellular calcium agonist) did not significantly affect NE-induced IP3 production. PMA (a protein kinase C agonist) significantly decreased and staurosporine (a protein kinase C antagonist) significantly stimulated NE-induced IP3 production. W7 (a calmodulin antagonist) significantly increased the NE-induced IP3. In conclusion, elevation of extracellular Ca2+ concentrations affects NE-induced IP3 formation in atrial myocytes. Protein kinase C and calmodulin may control the IP3 response to NE by a negative feedback mechanism.     

Multiple stores of calcium are released in the sea urchin egg during fertilization.

Fertilization initiates a transient increase in intracellular Ca2+ principally by Ca2+ release from intracellular stores. Possible multiple Ca2+ stores and multiple receptor regulation of the same store have been reported. Here we report the presence of at least two independent intracellular Ca2+ stores in the sea urchin egg, which are released during fertilization. Ca2+ release from one store is mediated by inositol 1,4,5-trisphosphate (IP3) and is sensitive to low molecular weight heparin. The other store is heparin insensitive and independent of IP3 regulation, but the regulatory factor remains unidentified. A transient increase in Ca2+ in heparin-loaded eggs is observed during fertilization, which suggests that IP3-independent Ca2+ release mediates the production of IP3 and release of the IP3-dependent store. Experiments presented here do not support the idea of sperm receptor coupling to inositol phospholipid hydrolysis through a GTP-binding protein mediating the fertilization response.