趙璐 綜述 蘇立 審校
(重慶醫(yī)科大學(xué)附屬第二醫(yī)院心血管內(nèi)科 重慶市心律失常治療中心,重慶400010)
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心房顫動與離子通道重構(gòu)研究進(jìn)展
趙璐 綜述 蘇立 審校
(重慶醫(yī)科大學(xué)附屬第二醫(yī)院心血管內(nèi)科 重慶市心律失常治療中心,重慶400010)
心房顫動是臨床上最常見的持續(xù)性快速性心律失常之一,可導(dǎo)致心力衰竭、腦栓塞、認(rèn)知功能障礙等嚴(yán)重并發(fā)癥,是中國老年人發(fā)病率、致殘致死率較高的一種疾病。心房顫動的發(fā)生機(jī)制較為復(fù)雜,大量研究表明,心臟離子通道重構(gòu)在心房顫動的發(fā)生和維持中發(fā)揮極其重要的作用。作用于離子通道的藥物已廣泛應(yīng)用于臨床,但其療效欠佳,并發(fā)癥較多。因此探索有效的離子通道藥物,對預(yù)防心房顫動的發(fā)生,延緩心房顫動的進(jìn)程,提高患者生活質(zhì)量,延長患者壽命具有重大意義。
心房顫動;心房電重構(gòu);離子通道重構(gòu);離子通道藥物
心房顫動是臨床上最常見的威脅人類健康的持續(xù)性心律失常之一,它能夠顯著增加老年人心力衰竭、腦栓塞和認(rèn)知功能障礙的風(fēng)險,且治療效果欠佳[1-2]。其發(fā)生的病理生理學(xué)機(jī)制非常復(fù)雜,可能與多通道改變導(dǎo)致心臟電重構(gòu)有關(guān)。目前認(rèn)為,與心房顫動有關(guān)的離子通道改變主要包括:鉀離子通道、鈣離子通道、鈉離子通道以及起搏離子通道等。其中,瞬時外向鉀電流(transient outward K+current,Ito)、超快延遲整流鉀電流(ultrarapid delayed rectifier K+current,IKur)與L型鈣電流(L-type Ca2+current,ICa-L)的表達(dá)異常與心房顫動電重構(gòu)的發(fā)生密切相關(guān)?,F(xiàn)就離子通道重構(gòu)與心房顫動電重構(gòu)的發(fā)病機(jī)制與治療進(jìn)展做一綜述。
心房顫動發(fā)病機(jī)制較為復(fù)雜,目前認(rèn)為心房顫動的發(fā)生機(jī)制主要包括四個方面:心房電重構(gòu)、心房結(jié)構(gòu)重構(gòu)、自主神經(jīng)功能紊亂以及鈣離子穩(wěn)態(tài)失調(diào)(圖1)。它們的變化均可由心血管疾病引起,并最終導(dǎo)致心房顫動[3]。近年的研究表明心房電重構(gòu)在心房顫動的發(fā)生與維持中起重要作用。Wijffels等[4]于1995年通過羊慢性心房顫動模擬實驗提出“心房電重構(gòu)”和“心房顫動致心房顫動”理論,并提出心房有效不應(yīng)期(atrial effective refractory period, AERP)和動作電位時程(action potential duration, APD)縮短是電重構(gòu)的主要電生理基礎(chǔ)。心房顫動反復(fù)發(fā)作或連續(xù)心房刺激會導(dǎo)致AERP和APD進(jìn)行性縮短,心房肌不應(yīng)期離散度增加以及動作電位傳導(dǎo)速度減慢等心房電生理學(xué)改變,從而有利于心房顫動的發(fā)生和維持,而離子通道重構(gòu)是心房電重構(gòu)時AERP和ADP改變的基礎(chǔ)。
注:局灶激動學(xué)說(focal ectopic firing)和折返基質(zhì)(reentry substrate)共同構(gòu)成了心房顫動發(fā)生和維持的電生理機(jī)制。局灶激動學(xué)說是由于延遲后除極達(dá)到閾值而引起自發(fā)的動作電位的產(chǎn)生。折返基質(zhì)主要是由于AERP縮短導(dǎo)致折返波長減小和/或傳導(dǎo)異常[3]。
圖1 心房顫動的主要病理生理學(xué)機(jī)制
鉀離子通道是心臟電活動中最重要的離子通道之一,鉀離子流是心肌細(xì)胞動作電位復(fù)極的主要外向電流,其亞型繁多復(fù)雜,影響表達(dá)因素最多。主要存在于人心房肌細(xì)胞中的鉀離子電流為:延遲整流鉀電流(delayed rectifier K+current,IK)、Ito、內(nèi)向整流鉀電流(inward rectifier K+current,IK1)、乙酰膽堿激活鉀電流(acetylcholine-activated K+current,IK-Ach)和ATP依賴鉀電流(ATP-activated K+current,IK-ATP)。細(xì)胞內(nèi)K+濃度的變化主要依賴于細(xì)胞內(nèi)的K+外流,其中,Ito和Ikur參與心肌動作電位1相復(fù)極過程;IK的三種亞型[緩慢激活延遲整流鉀電流(slow delayed rectifier K+current,IKs)、快速激活延遲整流鉀電流(rapid delayed rectifier K+current,IKr)、IKur]參與心肌動作電位2相和3相復(fù)極過程。研究發(fā)現(xiàn),在心房顫動患者和實驗動物模型中多種鉀通道m(xù)RNA和蛋白的表達(dá)均降低[5-6],表明鉀離子通道m(xù)RNA與相關(guān)蛋白表達(dá)的改變與心房顫動電重構(gòu)的發(fā)生密切相關(guān)。
2.1IK與Kv1.5通道
IK是一種無失活過程的離子流,它激活較緩慢,是心肌細(xì)胞動作電位復(fù)極過程的主要離子流。IK由3種亞型組成,即IKs、IKr和IKur。它們中的任何一種離子流受到阻滯,均可使細(xì)胞復(fù)極延長。其中IKur是一種在人心房肌細(xì)胞特異性表達(dá),而心室肌不表達(dá)或低表達(dá)的復(fù)極化鉀離子電流。它的特點是在去極化激活時,幾乎立即出現(xiàn)外向電流,主要參與心房肌細(xì)胞復(fù)極的1相和2相。IKur通過影響APD和AERP而影響心房的正常節(jié)律,從而引起心房顫動并參與心房顫動的維持。研究者們主要發(fā)現(xiàn)了4組重要的克隆K+通道,分別是Kv1、Kv2、Kv3和Kv4。與IKur相關(guān)鉀通道主要包括Kv1.5、Kv1.2和Kv3.2等。在人心房肌IKur,其電生理特性與Kv1.5相似。Kv1.5鉀通道是Kv1鉀通道的一個亞型,是IKur的分子基礎(chǔ),由KCNA5基因編碼。
近年來有關(guān)IKur的研究頗多,且取得了突破性的進(jìn)展。一方面,Kv1.5通道轉(zhuǎn)錄和翻譯水平下調(diào)可能是IKur降低的分子基礎(chǔ)。研究發(fā)現(xiàn)[7-8],在慢性心房顫動患者中,Kv1.5 mRNA及相應(yīng)蛋白的表達(dá)下調(diào)減弱IKur,并延長AERP和APD。IKur減弱引起APD和AERP延長,進(jìn)而易發(fā)生早期后除極,增加心房對應(yīng)激誘發(fā)的觸發(fā)活動的易損性;增大心房復(fù)極離散度,促進(jìn)各向異性傳導(dǎo),引發(fā)并維持心房顫動。但是,Lu等[9]在通過血管緊張素Ⅱ誘導(dǎo)的新生大鼠心房肌細(xì)胞中發(fā)現(xiàn),Kv1.5 mRNA和蛋白表達(dá)水平在誘導(dǎo)后12 h增加,且持續(xù)到誘導(dǎo)后24 h。Hu等[10]也發(fā)現(xiàn),在甲狀腺功能亢進(jìn)的小鼠心房肌細(xì)胞中,心房肌細(xì)胞Kv1.5和Kv2.1 mRNA含量和蛋白質(zhì)的表達(dá)水平增加,APD縮短,且在右房更加明顯。有學(xué)者認(rèn)為,造成這種現(xiàn)象的原因可能與病程的長短、種屬的差異有關(guān)。另一方面,KCNA5基因表達(dá)差異可能是心房顫動電重構(gòu)的重要環(huán)節(jié)。KCNA5基因突變可使患者對心房顫動的易感性增加,該突變是家族性孤立性心房顫動的一種基因型[11]。Christophersen等[12]通過對307例孤立性心房顫動患者KCNA5基因編碼序列的測序也證明了KCNA5基因突變增加心房顫動的易感性。
2.2Ito與Kv4.3鉀通道
Ito是復(fù)極早期的主要電流,決定動作電位平臺期起始的電位高度,影響平臺期其他電流的激活,在心房顫動的發(fā)生發(fā)展過程中扮演非常重要的角色。Ito包含兩種成分:Ito1與Ito2。它們的發(fā)生機(jī)制不同,Ito1對4-氨基吡啶敏感(屬SH族),Ito2可能是Ca依賴性的氯通道(屬SLO族)。Ito2情況復(fù)雜,研究較少,一般就將Ito1稱為Ito。Ito是在去極化的條件下才被激活的,它屬于有失活過程的鉀離子流。Ito相關(guān)鉀通道主要有Kv1.4、Kv4.2和Kv4.3。在人心房肌中Kv4.3對Ito形成起主要作用,而Kv1.4僅少量表達(dá)。
臨床及動物實驗等多項研究提示,Ito電流密度下降以及Kv4.3通道m(xù)RNA及其蛋白的表達(dá)降低,是通過某種機(jī)制調(diào)節(jié)轉(zhuǎn)錄及翻譯過程使Kv4.3鉀通道m(xù)RNA及其蛋白的表達(dá)下調(diào),從而使Ito、APD和AERP降低。因此,Kv4.3通道m(xù)RNA及其蛋白表達(dá)下調(diào)可能是Ito密度減少的分子基礎(chǔ)。慢性持續(xù)性心房顫動患者的心房肌細(xì)胞上Ito密度明顯降低,且伴有通道m(xù)RNA和蛋白表達(dá)的下調(diào)[18]。Ji等[19]在心房快速起搏大鼠模型中觀察到,Kv4.3 mRNA的表達(dá)在起搏6 h內(nèi)無明顯變化,但起搏12 h后表達(dá)明顯降低,此后則保持穩(wěn)定不變。他們利用全細(xì)胞膜片鉗技術(shù)檢測到APD50在刺激后明顯縮短。Giudicessi等[20]在研究編碼Kv4.3的KCND3基因突變與Brugada綜合征的關(guān)系時發(fā)現(xiàn),兩個BrS1-8基因型陰性病例存在新的Kv4.3錯義基因突變。Kv4.3-L450F和Kv4.3-G600R表現(xiàn)為功能增強的表型,Ito峰電流密度分別增加146.2%(P<0.05)和50.4%(P<0.05)。該發(fā)現(xiàn)表明KCND3基因突變在Brugada綜合征發(fā)病和表型表達(dá)中起重要作用,KCND3基因突變所致Ito電流梯度增強可能會觸發(fā)致命性心律失常。
臨床常用的多種抗心律失常藥如奎尼丁、普羅帕酮均被證實可抑制Ito,延長APD及AERP。維納卡蘭(vernakalant)作為新型的治療心房顫動藥物,具有顯著的Ito阻滯作用, 在心率加快的時候, 此藥物的Ito阻滯作用會隨之加強[21]。omega-3多聚不飽和脂肪酸作為心房顫動的治療藥物于2010年被寫入ESC心房顫動指南,在動物實驗中,omega-3多聚不飽和脂肪酸通過濃度依賴的方式抑制Ito,有直接抗心律失常作用,且能降低外科手術(shù)尤其是冠狀動脈搭橋術(shù)后心房顫動的發(fā)生,但其并不適用于無器質(zhì)性心臟病的心房顫動人群[22-24]。
鈣離子流是維持心肌動作電位上一個較長平臺的主要內(nèi)向電流。由于這個較長的去極化水平,從而為其他離子流的活動提供合適的電位條件,同時也為心肌細(xì)胞動作電位有較長的不應(yīng)期提供電位條件。心肌細(xì)胞主要存在兩種類型的鈣離子通道:L型鈣通道(L-type Ca2+channel, LTCC)和T型鈣通道(T-type Ca2+channel, TTCC)。其中LTCC的開放激活電壓要明顯高于TTCC,且失活較慢,開放持續(xù)時間較長,在維持心房肌細(xì)胞動作電位平臺期和介導(dǎo)心率依賴的動作電位變化中起著重要作用。ICa-L相關(guān)鈣通道主要有Cav1.2和Cav2.3。
目前認(rèn)為,細(xì)胞內(nèi)鈣超載是心房顫動發(fā)生和維持的主要機(jī)制之一,占心房電重構(gòu)的中心環(huán)節(jié)。由于在每一個動作電位時都會有Ca2+進(jìn)入心房肌細(xì)胞,因此快速心房節(jié)律可增加鈣超載,并同時開啟自我保護(hù)機(jī)制來減少Ca2+的進(jìn)入,Ca2+電流失活和ICa-L的下調(diào)通過縮短APD減少鈣超載,從而減少心房顫動的易感性和持續(xù)性[25]。研究發(fā)現(xiàn)[26],通過依賴鈣/鈣調(diào)蛋白依賴性蛋白激酶Ⅱ的Ryanodine受體過度磷酸化促進(jìn)肌漿網(wǎng)Ca2+釋放與Na+/Ca2+交換,導(dǎo)致肌漿網(wǎng)內(nèi)Ca2+減少和舒張期Ca2+內(nèi)流,誘發(fā)早期后除極、增強觸發(fā)活動,從而促進(jìn)心房顫動的發(fā)生。心房快速起搏大鼠模型中觀察到,LTCC mRNA和蛋白的表達(dá)在起搏6 h后明顯降低,并隨著起搏的延續(xù)而降低[15],故ICa-L下調(diào)可能與心房顫動的發(fā)生和維持密切相關(guān)。Liu等[27]認(rèn)為,在SD大鼠心肌細(xì)胞中,KCNE2基因的高表達(dá)可減少ICa-L電流,而通過RNA干擾KCNE2表達(dá)可升高ICa-L電流,說明KCNE2基因突變可能通過抑制ICa-L來導(dǎo)致長QT綜合征2型和家族性心房顫動。綜上所述,LTCC組成蛋白基因表達(dá)的下調(diào)和其基因突變是導(dǎo)致ICa-L密度下降,心房動作電位和AERP改變的主要原因。
心房顫動的發(fā)生和維持是一個極為復(fù)雜的病理生理過程,目前的研究顯示離子通道重構(gòu)在心房顫動電重構(gòu)中起到重要作用,且心房顫動電重構(gòu)的離子通道問題是近年的研究熱點,但其發(fā)生機(jī)制尚不完全清楚。心房顫動的藥物治療策略主要包括控制節(jié)律與心率。目前最常用的離子通道阻滯劑為Ⅰ、Ⅲ類離子通道阻滯劑,主要應(yīng)用于轉(zhuǎn)復(fù)和維持竇性心律,但長期有效性欠佳。其中經(jīng)典的Ⅲ類藥物胺碘酮在臨床中應(yīng)用廣泛,是最為有效的藥物,但其不良反應(yīng)較多。新Ⅲ類藥物決奈達(dá)隆對陣發(fā)性或持續(xù)性心房顫動、心房撲動治療有效,較之胺碘酮以其較少的心外不良反應(yīng)而備受關(guān)注[30]。其他抗心律失常藥物,如血管緊張素轉(zhuǎn)換酶抑制劑、血管緊張素受體阻滯劑、他汀類、omega-3多聚不飽和脂肪酸等,在動物實驗中均能抑制心房的電重構(gòu)或結(jié)構(gòu)重構(gòu),可降低心房顫動的發(fā)生,但上述藥物的臨床研究結(jié)果仍存在爭議[31- 32]。因此探索有效的離子通道阻滯劑在心房顫動電重構(gòu)中的作用和表達(dá),可有效地預(yù)防和控制心房顫動的發(fā)生,且為心房顫動的治療提供新的思路和新的作用靶點。
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Research Progress of Atrial Fibrillation and Ion Channel Remodeling
ZHAO Lu, SU Li
(Department of Cardiology,The Second Affiliated Hospital of Chongqing Medical University,The Arrhythmia Therapeutic Center of Chongqing,Chongqing 400010,China)
Atrial fibrillation is one of the most common clinical sustained tachyarrhythmia, which can cause serious complications like heart failure, cerebral embolism and cognitive impairment. It has a high morbidity,mortality and disability rate disease in seniors. The mechanism of atrial fibrillation is complex, and a large number of studies have shown that cardiac ion channel remodeling plays an extremely important role in the occurrence and persistence of atrial fibrillation. The drugs located in ion channel targets have been used in atrial fibrillation, which are still ineffective and cause further complications. This study explores the effective ion channel drugs that can prevent the occurrence of atrial fibrillation, delay the development of atrial fibrillation, improve the quality of life and prolong the life span in patients.
atrial fibrillation; atrial electrical remodeling; ion channel remodeling; ion channel drugs
趙璐(1991—),在讀碩士,主要從事心律失?;A(chǔ)與臨床研究。Email: zhaoluhc@126.com
蘇立(1970—),副主任醫(yī)師,博士,主要從事心律失常及心臟電生理研究。Email: sulicq@163.com
R
A
10.3969/j.issn.1004-3934.2015.05.014
2015-04-02