Department of Cardiology, Minhang Central Hospital, Shanghai, China.
PLoS One. 2014 Jan 27;9(1):e72181. doi: 10.1371/journal.pone.0072181. eCollection 2014.
HERG K(+) channel, the genetic counterpart of rapid delayed rectifier K(+) current in cardiac cells, is responsible for many cases of inherited and drug-induced long QT syndromes. HERG has unusual biophysical properties distinct from those of other K(+) channels. While the conventional pulse protocols in patch-clamp studies have helped us elucidate these properties, their limitations in assessing HERG function have also been progressively noticed. We employed AP-clamp techniques using physiological action potential waveforms recorded from various regions of canine heart to study HERG function in HEK293 cells and identified several novel aspects of HERG function. We showed that under AP-clamp IHERG increased gradually with membrane repolarization, peaked at potentials around 20-30 mV more negative than revealed by pulse protocols and at action potential duration (APD) to 60%-70% full repolarization, and fell rapidly at the terminal phase of repolarization. We found that the rising phase of IHERG was conferred by removal of inactivation and the decaying phase resulted from a fall in driving force, which were all determined by the rate of membrane repolarization. We identified regional heterogeneity and transmural gradient of IHERG when quantified with the area covered by IHERG trace. In addition, we observed regional and transmural differences of IHERG in response to dofetilide blockade. Finally, we characterized the influence of HERG function by selective inhibition of other ion currents. Based on our results, we conclude that the distinct biophysical properties of HERG reported by AP-clamp confer its unique function in cardiac repolarization thereby in antiarrhythmia and arrhythmogenesis.
HERG K(+) 通道是心脏细胞中快速延迟整流钾 (K(+)) 电流的遗传对应物，负责许多遗传性和药物诱导的长 QT 综合征。HERG 具有与其他 K(+) 通道不同的异常生理特性。虽然膜片钳研究中的传统脉冲方案有助于我们阐明这些特性，但它们在评估 HERG 功能方面的局限性也逐渐被注意到。我们使用生理动作电位波形的 AP 钳位技术从犬心脏的不同区域记录，研究 HEK293 细胞中的 HERG 功能，并确定了 HERG 功能的几个新方面。我们表明，在 AP 钳位下，IHERG 随着膜复极化逐渐增加，在比脉冲方案揭示的更负 20-30 mV 的电位处达到峰值，在动作电位持续时间 (APD) 达到 60%-70%的完全复极化，然后在复极化的终末阶段迅速下降。我们发现，IHERG 的上升相是由失活的消除引起的，下降相是由驱动力的下降引起的，这两者都是由膜复极化的速度决定的。当用 IHERG 轨迹覆盖的面积来量化时，我们发现 IHERG 具有区域性异质性和穿壁梯度。此外，我们观察到在应对多非利特阻断时 IHERG 的区域性和穿壁差异。最后，我们通过选择性抑制其他离子电流来表征 HERG 功能的影响。基于我们的结果，我们得出结论，AP 钳位报告的 HERG 的独特生理特性赋予了其在心脏复极化中的独特功能，从而影响抗心律失常和心律失常发生。
