小電導鈣激活鉀通道和心房顫動的關連

Abstract

直到過去幾年，有越來越多的流行病學的證據顯示，心房顫動（atrial fibrillation）是可以遺傳的。在2010年，一個以歐洲人為對象的全基因組關聯研究（genome-wide association study）指出，染色體1q21上的KCNN3基因的單核苷酸多型性（single nucleotide polymorphism）rs13376333與心房顫動風險有顯著的關聯。KCNN3基因編碼小電導鈣離子激活鉀離子通道（small conductance Ca2+-activated K+ channels）（也被稱為SK3通道）。直到最近才有報告指出，SK通道與心肌細胞，主要是心房細胞，的動作電位持續期間的再極化有關，研究顯示，SK通道的抑制與心房顫動的抑制與產生可能都有關係，雖然這些研究的結果有衝突，卻也指出SK通道在心房顫動產生的機制上可能扮演重要的角色，其詳細的機轉仍待進一步釐清。 我們的研究有兩部分。首先，我們試圖探討在台灣人身上，KCNN3基因的單核苷酸多型性rs13376333和心房顫動之間有無顯著關聯。 我們在214位孤立性心房顫動病人與214對照組病人，和322位結構性心房顫動病人與322對照組病人身上，進行了一個病例對照關聯研究 我們的研究顯示，在台灣人，單核苷酸多型性rs13376333和心房顫動（包括孤立性與結構性）亦有顯著關聯。我們發現在結構性心房顫動病人，單核苷酸多型性rs13376333的風險對偶基因T的頻率是6.5％，對照組病人是3.1％ [對偶基因（allele）P= 0.004，勝算比= 2.18，95％信賴區間：1.23-3.96;基因型（genotype）P=0.012]。在孤立性心房顫動病人，單核苷酸多型性rs13376333的風險對偶基因T的頻率是8.6％，對照組病人是3.0％（對偶基因P< 0.001，勝算比= 3.02，95％信賴區間：1.54-6.29;基因型P= 0.001）。 第二部分，我們試圖探討以藥物活化SK通道對心臟電氣生理的影響。 我們以大鼠做體內（in vivo）心臟電氣生理實驗，包括計劃性的電生理刺激（programmed electrophysiological pacing）和心房顫動的誘發，藉由施打SK通道的活化劑-SKA-31，評估心房電氣生理的變化，並研究SK通道功能的活化是否會影響心房顫動或導致其他心律不整的產生。 我們的實驗發現，施打SK通道的活化劑-SKA-31會明顯縮短心房的動作電位持續期（action potential duration）（74.6 ms ± 2.8 ms VS. 70.8 ms ± 2.2 ms，P= 0.02)，但此效果只是短暫的，心房的有效不反應（effective refractory period）則無顯著改變（73.5 ms ± 1.9 ms VS. 71.4 ms ± 2.4 ms，P= 0.1)。施打SK通道的活化劑-SKA-31後，心房顫動維持的時間會延長（1.8 s ± 0.5 s VS. 2.9 s ± 1.2 s，P= 0.035)。另外，我們也並未觀察到有任何心室的律不整的產生。

During the last few years a growing number of epidemiologic evidence has indicated that atrial fibrillation（AF）is heritable. In 2010, a genome-wide association study in individuals of European ancestry demonstrated a significant association of the single nucleotide polymorphism（SNP）rs13376333 in KCNN3 on chromosome 1q21 with AF. The KCNN3 gene codes for voltage-independent small conductance Ca2+-activated K+ channels（also known as SK3）. Recently, several reports have shown that SK channels are associated with action potential duration of cardiomyocytes, especially atrial myocytes. Some studies demonstrated that pharmacological inhibition or blockade of SK channels is associated with inhibition or promotion of atrial fibrillation. Although these results are conflicting, they reveal that SK channels may play an important role on the mechanism of atrial fibrillation. Our study has two parts. First, we plan to investigate whether this association between SNP rs13376333 and AF also exists in Taiwanese subjects. We performed a case-control association study of 214 subjects with lone AF vs. 214 controls, and 322 subjects with structural AF vs. 322 controls for SNP rs13376333 on chromosome 1q21. We found significant allele and genotype associations between SNP rs13376333 and both structural and lone AF. In patients with structural AF, the frequency of the risk allele T of SNP rs13376333 was 6.5% compared with 3.1% in unaffected controls（allele P= 0.004, OR, 2.18, 95%CI: 1.23–3.96; genotype P= 0.012）. In the lone AF group, the frequency of the risk allele T of SNP rs13376333 was 8.6% compared with 3.0% in unaffected controls（allele P< 0.001, OR, 3.02; 95%CI: 1.54–6.29; genotype P= 0.001）. Second, we planed to assess the effect of pharmacological activation of SK channels on cardiac electrophysiology. In rat in vivo model, we performed electrophysiological studies, including programmed electrophysiological pacing and AF induction. After administrations of SK channels activaotor-SKA-31, we evaluated the changes of atrial action potential duration（APD）and atrial effective refractory period（ERP）and studied whether pharmacological activation of SK channels had effect on AF duration and induced ventricular arrhythmias. After injections of SKA-31, we found that atrial APD shortened significantly（74.6 ms ± 2.8 ms VS. 70.8 ms ± 2.2 ms，P= 0.02), but this effect was only transient, and atrial ERP didn’t change significantly（73.5 ms ± 1.9 ms VS. 71.4 ms ± 2.4 ms，P= 0.1). The duration of AF increased significantly after SKA-31 injections（1.8 s ± 0.5 s VS. 2.9 s ± 1.2 s，P= 0.035). Besides, we didn’t observe any ventricular arrhythmias after SKA-31 injections.