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人HCN4 通道的滞后现象：影响窦房结起搏的潜在决定因素

萧永福^*, Natalie Chandler, Halina Dobrzynski, Eric S. Richardson, Erica M. TenBroek, Joshua J. Wilhelm, Vinod Sharma, Anthony Varghese, Mark R. Boyett, Paul A. Iaizzo, Daniel C. Sigg 萧永福, Daniel C. Sigg

美敦力公司心脏节律疾病管理部，明尼苏达州Mounds View 55112，美国；曼彻斯特大学医学院，曼彻斯特 M13 9NT，英国；明尼苏达州大学 外科学系； 整合生物学与生理学系，明尼阿波利斯 MN 55432，美国； 美敦力公司 科学技术部，明尼阿波利斯 MN55432，美国；威斯康辛大学雷河分校计算机系，雷河WI 54022，美国

摘要

超极化活化环核苷酸门控(hyperpolarization-activated cyclic-nucleotide-gated, HCN)通道参与调制心脏跳动的节律和速率。与HCN1 和HCN2 有所不同，慢通道HCN4 可能不存在电压依赖的滞后现象。本研究采用单细胞膜片钳方法，在稳定转染hHCN4 的HEK293 细胞上进行电生理记录，观察hHCN4 通道是否存在滞后现象，以及cAMP 对其的调制作用；同时采用实时定量RT-PCR 方法检测窦房结和心房组织中HCNs 的表达。电压钳实验结果显示hHCN4 电流(I_h)激活随着保持电位超极化的变化而向去极化方向移动。三角电位变化钳(triangular ramp)和动作电位钳的结果也显示了hHCN4 的滞后现象。cAMP 增加Ih电流幅度，且使电流激活向去极化方向移动，从而改变内源性hHCN4 滞后行为。RT-PCR 结果显示，人窦房结组织主要表达HCN4，占75%，HCN1 占21%，HCN2 占3%，HCN3 占0.7%。以上结果提示，人窦房结组织主要表达HCN4 亚型，hHCN4 的Ih 存在电压依赖性的滞后现象，且受cAMP 调制。由此推断，hHCN4 通道的滞后现象可能在窦房结起搏活动中起到了关键作用。

关键词： HCN4 通道; 滞后; 窦房结; cAMP

分类号：R541

Hysteresis in human HCN4 channels: A crucial feature potentially affecting sinoatrial node pacemaking

Yong-Fu Xiao^*, Natalie Chandler, Halina Dobrzynski, Eric S. Richardson, Erica M. TenBroek, Joshua J. Wilhelm, Vinod Sharma, Anthony Varghese, Mark R. Boyett, Paul A. Iaizzo, Daniel C. Sigg

Cardiac Rhythm Disease Management, Medtronic Inc., Mounds View, MN 55112, USA； 2School of Medicine, University of Manchester, Manchester M13 9NT, UK； 3Department of Surgery and 4Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, MN 55455, USA； 5Corporate Science and Technology, Medtronic Inc., Minneapolis, MN 55432, USA； 6Computer Science Department, University of Wisconsin-River Falls, WI 54022, USA

Abstract

The hyperpolarization-activated cyclic nucleotide-gated (HCN) channels modulate and regulate cardiac rhythm and rate. Ithas been suggested that, unlike the HCN1 and HCN2 channels, the slower HCN4 channel may not exhibit voltage-dependent hysteresis.We studied the electrophysiological properties of human HCN4 (hHCN4) channels and its modulation by cAMP to determine whetherhHCN4 exhibits hysteresis, by using single-cell patch-clamp in HEK293 cells stably transfected with hHCN4. Quantitative real-timeRT-PCR was also used to determine levels of expression of HCNs in human cardiac tissue. Voltage-clamp analysis revealed that hHCN4current (Ih) activation shifted in the depolarizing direction with more hyperpolarized holding potentials. Triangular ramp and actionpotential clamp protocols also revealed hHCN4 hysteresis. cAMP enhanced Ih and shifted activation in the depolarizing direction, thusmodifying the intrinsic hHCN4 hysteresis behavior. Quantitative PCR analysis of human sinoatrial node (SAN) tissue showed thatHCN4 accounts for 75% of the HCNs in human SAN while HCN1 (21%), HCN2 (3%), and HCN3 (0.7%) constitute the remainder.Our data suggest that HCN4 is the predominant HCN subtype in the human SAN and that Ih exhibits voltage-dependent hysteresisbehavior that can be modified by cAMP. Therefore, hHCN4 hysteresis potentially plays a crucial role in human SAN pacemaking activity.

Key words: HCN4 channel; hysteresis; sinoatrial node; cAMP

收稿日期：2009-11-14　　录用日期：2010-01-19

通讯作者：萧永福　　E-mail: yong-fu.xiao@medtronic.com

引用本文：

萧永福, Natalie Chandler, Halina Dobrzynski, Eric S. Richardson, Erica M. TenBroek, Joshua J. Wilhelm, Vinod Sharma, Anthony Varghese, Mark R. Boyett, Paul A. Iaizzo, Daniel C. Sigg 萧永福, Daniel C. Sigg . 人HCN4 通道的滞后现象：影响窦房结起搏的潜在决定因素[J]. 生理学报 2010; 62 (1): 1-13.

Yong-Fu Xiao, Natalie Chandler, Halina Dobrzynski, Eric S. Richardson, Erica M. TenBroek, Joshua J. Wilhelm, Vinod Sharma, Anthony Varghese, Mark R. Boyett, Paul A. Iaizzo, Daniel C. Sigg. Hysteresis in human HCN4 channels: A crucial feature potentially affecting sinoatrial node pacemaking. Acta Physiol Sin 2010; 62 (1): 1-13 (in Chinese with English abstract).