ToxSci Advance Access published online on September 8, 2008
Toxicological Sciences, doi:10.1093/toxsci/kfn189
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Time-Dependent Block of Ultra-Rapid Delayed Rectifier K+ Currents by Aconitine, a Potent Cardiotoxin, in Heart-Derived H9c2 Myoblasts and in Neonatal Rat Ventricular Myocytes
a Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan, Taiwan b Department of Anesthesiology, Buddhist Dalin Tzu Chi General Hospital, Chiayi County, Taiwan c Department of Physiology, National Cheng Kung University Medical College, Tainan, Taiwan d Department of Life Sciences, National Central University, Taoyuan county, Taiwan
* Address correspondence to: Dr. Sheng-Nan Wu, Department of Physiology, National Cheng Kung University Medical College, No. 1, University Road, Tainan 70101, Taiwan. Tel: 886-6-2353535-5334; Fax: 886-6-2362780; e-mail: snwu{at}mail.ncku.edu.tw.
Received April 28, 2008; revision received August 16, 2008; accepted August 22, 2008
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Abstract |
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Aconitine (ACO), a highly toxic diterpenoid alkaloid, is recognized to have effects on cardiac voltage-gated Na+ channels. However, it remains unknown whether it has any effects on K+ currents. The effects of ACO on ion currents in differentiated clonal cardiac (H9c2) cells and in cultured neonatal rat ventricular myocytes were investigated in this study. In H9c2 cells, ACO suppressed ultra-rapid delayed rectifier K+ current (IKur) in a time- and concentration-dependent fashion. The IC50 value for ACO-induced inhibition of IKur was 1.4 µM. ACO could accelerate the inactivation of IKur with no change in the activation time constant of this current. Steady-state inactivation curve of IKur during exposure to ACO could be demonstrated. Recovery from block by ACO was fitted by a single-exponential function. The inhibition of IKur by ACO could still be observed in H9c2 cells preincubated with ruthenium red (30 µM). Intracellular dialysis with ACO (30 µM) had no effects on IKur. IKur elicited by simulated action potential waveforms was sensitive to block by ACO. Single-cell Ca2+ imaging revealed that ACO (10 µM) alone did not affect intracellular Ca2+ in H9c2 cells. In cultured neonatal rat ventricular myocytes, ACO also blocked IKur and prolonged action potential along with appearance of early-after depolarizations. Mulit-electrode recordings on neonatal rat ventricular tissues also suggested that ACO-induced electrocardiographic changes could be associated with inhibition of IKur. This study provides the evidence that ACO can produce a depressant action on IKur in cardiac myocytes.
Key Words: aconitine; ultra-rapid delayed rectifier K+ current; action potential; H9c2 cell; neonatal rat ventricular myocyte; multi-electrode array recording.