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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

Abstract

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

Received: 　　Accepted:

Corresponding author: 李贵荣　　E-mail:

Citing This Article：

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).