Submitted on May 16, 2008
Revised on August 22, 2008
Accepted on September 9, 2008
TRICYCLIC ANTIDEPRESSANT AMITRIPTYLINE ALTERS SARCOPLASMIC RETICULUM CALCIUM HANDLING IN VENTRICULAR MYOCYTES
Aleksey V Zima, Jia Qin, Michael Fill1, and Lothar A Blatter2*
1 Rush Univerity
2 Rush University Chicago
* To whom correspondence should be addressed. E-mail: Lothar_Blatter{at}rush.edu.
Tricyclic antidepressants such as amitriptyline (AMT) have been reported to have adverse side effects on cardiac performance. AMT effects on Ca handling in ventricular myocytes, however, are not well understood. Therefore, we investigated AMT action on sarcoplasmic reticulum (SR) Ca release in ventricular myocytes, ryanodine receptor (RyR) activity and Ca uptake by SR microsomes. In permeabilized myocytes AMT transiently increased free luminal [Ca] followed by marked depletion. AMT (10 µM) caused a rapid and a transient increase of Ca spark frequency, followed by a significant suppression of spark activity. The latter was associated with a decrease of Ca spark amplitude and SR Ca load to 87% and 60%, respectively. AMT (10 µM) completely abolished propagation of spontaneous Ca waves. Higher concentrations of AMT (0.1-1 mM) evoked SR Ca release reminiscent of the effect of caffeine (20 mM) and caused almost complete depletion of SR Ca content. Studies on single calsequestrin-free RyR channels revealed that AMT increased the mean open time and open probability (Po) in a dose dependent fashion (KD = 4.2 µM). High concentrations of AMT (>25 µM) evoked frequent long openings with Po reaching very high levels (>0.70). In studies with cardiac SR microsomes AMT slowed the rate of ATP-dependent Ca uptake. We conclude that AMT affects SR Ca handling in ventricular myocytes by multiple mechanisms including direct stimulation of RyRs and inhibition of SR Ca uptake. These effects could contribute to AMT cardiotoxicity.
