Kjølbye Anne Louise, Dikshteyn Maria, Eloff Benjamin C, Deschênes Isabelle, Rosenbaum David S
MetroHealth Campus, Case Western Reserve University, 2500 MetroHealth Drive, Cleveland, OH 44109-1998, USA.
Am J Physiol Heart Circ Physiol. 2008 Jan;294(1):H41-9. doi: 10.1152/ajpheart.01089.2006. Epub 2007 Nov 2.
Discordant action potential alternans creates large gradients of refractoriness, which are thought to be the mechanisms linking T-wave alternans to cardiac arrhythmogenesis. Since intercellular coupling acts to maintain synchronization of repolarization between cells, we hypothesized that intercellular uncoupling, such as during ischemia, would initiate discordant alternans and that restoration of intercellular coupling by the gap junction opener rotigaptide may provide a novel approach for suppressing arrhythmogenic discordant alternans. Optical mapping was used to record action potentials from ventricular epicardium of Langendorff-perfused guinea pig hearts. Threshold for spatially synchronized (i.e., concordant) alternans and discordant alternans was determined by increasing heart rate step-wise during 1) baseline, 2) treatment with rotigaptide or vehicle, and 3) global low-flow ischemia + rotigaptide or vehicle. Ischemia reduced the threshold for concordant alternans in both groups from 362 +/- 8 to 305 +/- 9 beats/min (P < 0.01) and for discordant alternans from 423 +/- 6 to 381 +/- 7 beats/min (P < 0.01). Interestingly, rotigaptide also increased the threshold for discordant alternans relative to vehicle both before (438 +/- 7 vs. 407 +/- 8 beats/min, P < 0.05) and during (394 +/- 7 vs. 364 +/- 9 beats/min, P < 0.05) ischemia. Rotigaptide increased conduction velocity and prevented conduction slowing and dispersion of repolarization during ischemia. Confocal immunofluorescence revealed that total connexin43 quantity and cellular distribution were unchanged before or after low-flow ischemia, with and without rotigaptide. However, connexin43 dephosphorylation in response to low-flow ischemia was significantly prevented by rotigaptide (15.9 +/- 7.0 vs. 0.3 +/- 6.4%, P < 0.001). These data suggest that intercellular uncoupling plays an important role in the transition from concordant to discordant alternans. By suppressing discordant alternans, repolarization gradients, and connexinx43 dephosphorylation, rotigaptide may protect against ischemia-induced arrhythmias. Drugs that selectively open gap junctions offer a novel strategy for antiarrhythmic therapy.
不一致的动作电位交替变化会产生较大的不应期梯度，这被认为是将T波交替变化与心律失常发生联系起来的机制。由于细胞间耦联作用可维持细胞间复极化的同步性，我们推测细胞间去耦联，如在缺血期间，会引发不一致的交替变化，并且通过缝隙连接开放剂罗替戈汀恢复细胞间耦联可能为抑制致心律失常的不一致交替变化提供一种新方法。采用光学标测技术记录Langendorff灌注豚鼠心脏心室心外膜的动作电位。通过在以下三个阶段逐步增加心率来确定空间同步（即一致）交替变化和不一致交替变化的阈值：1）基线期；2）用罗替戈汀或赋形剂处理时；3）整体低流量缺血 + 罗替戈汀或赋形剂。缺血使两组一致交替变化的阈值从362±8次/分钟降至305±9次/分钟（P<0.01），使不一致交替变化的阈值从423±6次/分钟降至381±7次/分钟（P<0.01）。有趣的是，无论是在缺血前（438±7次/分钟对407±8次/分钟，P<0.05）还是缺血期间（394±7次/分钟对364±9次/分钟，P<0.05），与赋形剂相比，罗替戈汀也提高了不一致交替变化的阈值。罗替戈汀增加了传导速度，并在缺血期间防止了传导减慢和复极化离散。共聚焦免疫荧光显示，无论有无罗替戈汀，在低流量缺血前后，总的连接蛋白43数量和细胞分布均未改变。然而，罗替戈汀显著阻止了低流量缺血引起的连接蛋白43去磷酸化（15.9±7.0%对0.3±6.4%，P<0.001）。这些数据表明，细胞间去耦联在从一致交替变化向不一致交替变化的转变中起重要作用。通过抑制不一致交替变化、复极化梯度和连接蛋白43去磷酸化，罗替戈汀可能预防缺血诱导的心律失常。选择性开放缝隙连接的药物为抗心律失常治疗提供了一种新策略。
