Date Published: July 3, 2014
Publisher: Public Library of Science
Author(s): Xiao-Qiu Tan, Xiu-Li Cheng, Li Zhang, Bo-Wei Wu, Qing-Hua Liu, Jie Meng, Hai-Yan Xu, Ji-Min Cao, Xiongwen Chen.
The potential hazardous effects of multi-walled carbon nanotubes (MWCNTs) on cardiac electrophysiology are seldom evaluated. This study aimed to investigate the impacts of MWCNTs on the Kv4/Ito channel, action potential and heart rhythm and the underlying mechanisms.
HEK293 cells were engineered to express Kv4.2 or Kv4.3 with or without KChIP2 expression. A series of approaches were introduced to analyze the effects of MWCNTs on Kv4/Ito channel kinetics, current densities, expression and trafficking. Transmission electron microscopy was performed to observe the internalization of MWCNTs in HEK293 cells and rat cardiomyocytes. Current clamp was employed to record the action potentials of isolated rat cardiomyocytes. Surface ECG and epicardial monophasic action potentials were recorded to monitor heart rhythm in rats in vivo. Vagal nerve discharge monitoring and H&E staining were also performed.
Induction of MWCNTs into the cytosole through pipette solution soon accelerated the decay of IKv4 in HEK293 cells expressing Kv4.2/4.3 and KChIP2, and promoted the recovery from inactivation when Kv4.2 or Kv4.3 was expressed alone. Longer exposure (6 h) to MWCNTs decreased the IKv4.2 density, Kv4.2/Kv4.3 (but not KChIP2) expression and trafficking towards the plasma membrane in HEK293 cells. In acutely isolated rat ventricular myocytes, pipette MWCNTs also quickly accelerated the decay of IKv4 and prolonged the action potential duration (APD). Intravenous infusion of MWCNTs (2 mg/rat) induced atrioventricular (AV) block and even cardiac asystole. No tachyarrhythmia was observed after MWCNTs administration. MWCNTs did not cause coronary clot but induced myocardial inflammation and increased vagus discharge.
MWCNTs suppress Kv4/Ito channel activities likely at the intracellular side of plasma membrane, delay membrane repolarization and induce bradyarrhythmia. The delayed repolarization, increased vagus output and focal myocardial inflammation may partially underlie the occurrence of bradyarrhythmias induced by MWCNTs. The study warns that MWCNTs are hazardous to cardiac electrophysiology.
Carbon nanotubes (CNTs) have many potential applications in engineering science and medicine because of their controlled composition, electrical conductivity, and great tensile strength . Meanwhile, scientists have been focusing on the biosecurity and toxicity of CNTs, a consideration which is necessary and meaningful for evaluating the reasonability and encouraging widespread application of CNTs in medicine –. One of the potential hazardous effects of CNTs is their impacts on ion channels and cardiac electrophysiology.
The present study focused on the impacts and mechanisms of MWCNTs on Ito channel, action potential and arrhythmogenesis. We first investigated the effects of MWCNTs on the kinetics, current density, expression and trafficking of Kv4.2/4.3 channel in HEK293 cell line with or without KChIP2 expression. We further observed the influences of MWCNTs on the Ito channel and action potential of rat ventricular myocytes and arrhythmogenesis in rats in vivo. The results revealed that MWCNTs did exert some influences on Kv4/Ito channel current, kinetics, trafficking and expression, and prolonged the APD of cardiomyocytes and induced bradyarrhythmias in vivo. These results suggest that MWCNTs could indeed impair the activities of Kv4/Ito channels and the stability of cardiac electrophysiology. The study demonstrated for the first time that MWCNTs are “toxic” to cardiac electrophysiology, just as CNTs being classified “toxic” in terms of nanoecotoxicology .