孙海英, 肖国胜, 王焱, 李贵荣
心肌细胞兴奋性是维持正常的心脏活动的一个重要生理因素。本研究旨在使用全细胞膜片技术探讨豚鼠心房和心室肌细胞不同兴奋性的离子机理。结果显示，心室肌细胞兴奋性比心房肌细胞低。虽然豚鼠心室肌细胞的电压门控快Na+电流(INa)密度较低，但与其兴奋性较低并不相关，因为其在阀电位附近的可用度比率比心房肌细胞高。经典内向整流钾电流(IK1)在心室肌细胞比在心房肌细胞更大，这可能是心室肌细胞兴奋性较低的部分原因。此外，去极化引起的有内向整流特性的瞬时外向钾电流(Itoir)在心室肌细胞较大，并可能是其兴奋性较低的主要原因。在心室肌细胞，5 μmol/L Ba2+显著抑制Itoir，增强细胞兴奋性，并使INa激活的阈电位更负，其作用独立于对INa的影响。本研究结果证明，除经典的IK1外，Itoir在豚鼠心房肌和心室肌细胞的兴奋性差异形成和心肌兴奋性维持中起着主要作用。然而，Itoir增加是否会通过降低兴奋性以保护心脏，还需要进一步研究。
关键词： 心脏电生理学; 全细胞膜片钳技术; 兴奋性; 内向整流性瞬时外向钾电流; 内向整流钾电流; 电压门控钠离子电流
Ionic mechanism underlying distinctive excitability in atrium and ventricle of the heart
Hai-Ying Sun, Guo-Sheng Xiao, Yan Wang, Gui-Rong Li
Departments of Physiology and Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China； Xiamen Heart Center, Zhongshan Hospital, Medical School of Xiamen University, Xiamen 361004, China
Cellular excitability is an important physiological factor in maintaining normal cardiac activity. The present study was designed to investigate the ionic mechanism underlying different excitability in atrial and ventricular myocytes of guinea pig heart using a whole-cell patch configuration. We found that excitability is lower in ventricular myocytes than that in atrial myocytes. Although the density of voltage-gated fast Na+ current (INa) was lower in ventricular myocytes, it would not correlate to the lower excitability since its availability was greater than that in atrial myocytes around threshold potential. Classical inward rectifier K+ current (IK1) was greater in ventricular myocytes than that in atrial myocytes, which might contribute in part to the lower excitability. In addition, the transient outward K+ current with inward rectification (Itoir) elicited by depolarization was greater in ventricular myocytes than that in atrial myocytes and might contribute to the lower excitability. In ventricular myocytes, Ba2+ at 5 µmol/L significantly inhibited Itoir, enhanced excitability, and shifted the threshold potential of INa activation to more negative, and the effect was independent of affecting INa. Our results demonstrate the novel information that in addition to classical IK1, Itoir plays a major role in determining the distinctive excitability in guinea pig atrial and ventricular myocytes and maintaining cardiac excitability. More effort is required to investigate whether increase of Itoir would be protective via reducing excitability.
Key words: cardiac electrophysiology; whole-cell patch clamp; excitability; transient outward K+ current with inward rectification; inward rectifier K+ current; voltage-gated Na+ current
孙海英, 肖国胜, 王焱, 李贵荣. 心房与心室肌细胞兴奋性不同的离子机理研究[J]. 生理学报 2014; 66 (1): 85-95.
Hai-Ying Sun, Guo-Sheng Xiao, Yan Wang, Gui-Rong Li. Ionic mechanism underlying distinctive excitability in atrium and ventricle of the heart. Acta Physiol Sin 2014; 66 (1): 85-95 (in Chinese with English abstract).