Xiao Yong-Fu, Chandler Natalie, Dobrzynski Halina, Richardson Eric S, Tenbroek Erica M, Wilhelm Joshua J, Sharma Vinod, Varghese Anthony, Boyett Mark R, Iaizzo Paul A, Sigg Daniel C
Cardiac Rhythm Disease Management, Medtronic Inc., Mounds View, MN 55112, USA.
Sheng Li Xue Bao. 2010 Feb 25;62(1):1-13.
The hyperpolarization-activated cyclic nucleotide-gated (HCN) channels modulate and regulate cardiac rhythm and rate. It has 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 whether hHCN4 exhibits hysteresis, by using single-cell patch-clamp in HEK293 cells stably transfected with hHCN4. Quantitative real-time RT-PCR was also used to determine levels of expression of HCNs in human cardiac tissue. Voltage-clamp analysis revealed that hHCN4 current (I(h)) activation shifted in the depolarizing direction with more hyperpolarized holding potentials. Triangular ramp and action potential clamp protocols also revealed hHCN4 hysteresis. cAMP enhanced I(h) and shifted activation in the depolarizing direction, thus modifying the intrinsic hHCN4 hysteresis behavior. Quantitative PCR analysis of human sinoatrial node (SAN) tissue showed that HCN4 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 I(h) exhibits voltage-dependent hysteresis behavior that can be modified by cAMP. Therefore, hHCN4 hysteresis potentially plays a crucial role in human SAN pacemaking activity.
超极化激活的环核苷酸门控（HCN）通道可调节和调控心律及心率。有人提出，与HCN1和HCN2通道不同，较慢的HCN4通道可能不表现出电压依赖性滞后现象。我们通过在稳定转染hHCN4的HEK293细胞中使用单细胞膜片钳技术，研究了人类HCN4（hHCN4）通道的电生理特性及其受cAMP的调节情况，以确定hHCN4是否表现出滞后现象。还使用定量实时RT-PCR来确定人类心脏组织中HCNs的表达水平。电压钳分析显示，hHCN4电流（I(h)）激活在去极化方向上随着更超极化的钳制电位而发生偏移。三角波斜坡和动作电位钳制方案也显示出hHCN4的滞后现象。cAMP增强了I(h)并使激活在去极化方向上发生偏移，从而改变了hHCN4的内在滞后行为。对人类窦房结（SAN）组织的定量PCR分析表明，HCN4占人类SAN中HCNs的75%，而HCN1（21%）、HCN2（3%）和HCN3（0.7%）构成其余部分。我们的数据表明，HCN4是人类SAN中主要的HCN亚型，并且I(h)表现出可被cAMP改变的电压依赖性滞后行为。因此，hHCN4滞后现象可能在人类SAN起搏活动中起关键作用。
