Received March 14, 2006
Revised April 18, 2006
Accepted after revision April 28, 2006
Heart/Cardiac Muscle [240]
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Rapid Electrical Stimulation Induces Early Activation of Kinase Signal Transduction Pathways and Apoptosis in Adult Rat Ventricular Myocytes
Yukio Kuramochi 1,
Xinxin Guo 1,
Douglas B Sawyer 1,
Chee Chew Lim 1*
1 Boston University Medical Center
* To whom correspondence should be addressed. E-mail: cheelim{at}bu.edu.
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Abstract |
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Chronic tachycardia in patients and rapid pacing in animal models induces myocardial dysfunction and initiates a cascade of compensatory adaptations that are ultimately unsustainable, leading to ventricular enlargement and failure. The molecular pathogenesis during the early stages of tachycardia-induced cardiomyopathy, however, remain unclear. We utilized our previously reported cell culture pacing system to directly assess PI3K/Akt and MAPK signaling of adult rat ventricular myocytes (ARVM) in response to rapid electrical stimulation. Freshly isolated ARVMs were maintained quiescent (0 Hz), or continuously stimulated at 5 Hz (normofrequency) and 8 Hz (rapid frequency). Pacing resulted in an increase in mitochondrial respiration, assessed by mitochondrial uptake of MTT, at 48 hours. Rapid pacing at 8 Hz significantly increased cell injury and death as assessed by trypan blue uptake, creatine phosphokinase release, and Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick End Labeling (TUNEL) assay. Pacing at 5 Hz induced early, but weak, activation of Akt and p38. Rapid pacing further augmented the early activation of Akt and p38, and induced Erk, and JNK activation. ARVM incubation with PI3K inhibitor, LY294002, resulted in a 2-fold increase of TUNEL positive cells under all pacing conditions examined. In conclusion, rapid pacing has immediate and detrimental consequences for cardiomyocyte survival, with pro-apoptotic pathways (e.g. JNK, p38) able to overwhelm anti-apoptotic signaling (PI3K/Akt, ERK). The rapid pacing methodology described in this report will be particularly useful in determination of cell signaling pathways associated with tachycardia-induced cardiomyopathy.
Key Words:
Cardiac arrhythmia, Cardiac cell, Cell signalling
