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Heart Rhythm. 2012 Jun;9(6):953-60. doi: 10.1016/j.hrthm.2012.01.010. Epub 2012 Jan 11.

Ranolazine stabilizes cardiac ryanodine receptors: a novel mechanism for the suppression of early afterdepolarization and torsades de pointes in long QT type 2.

Author information

1
Department of Bioengineering, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA.

Abstract

BACKGROUND:

Ranolazine (Ran) is known to inhibit multiple targets, including the late Na(+)current, the rapid delayed rectifying K(+)current, the L-type Ca(2+)current, and fatty acid metabolism. Functionally, Ran suppresses early afterdepolarization (EADs) and torsades de pointes (TdP) in drug-induced long QT type 2 (LQT2) presumably by decreasing intracellular [Na(+)](i) and Ca(2+)overload. However, simulations of EADs in LQT2 failed to predict their suppression by Ran.

OBJECTIVE:

To elucidate the mechanism(s) whereby Ran alters cardiac action potentials (APs) and cytosolic Ca(2+)transients and suppresses EADs and TdP in LQT2.

METHODS:

The known effects of Ran were included in simulations (Shannon and Mahajan models) of rabbit ventricular APs and Ca(2+)transients in control and LQT2 models and compared with experimental optical mapping data from Langendorff rabbit hearts treated with E4031 (0.5 μM) to block the rapid delayed rectifying K(+)current. Direct effects of Ran on cardiac ryanodine receptors (RyR2) were investigated in single channels and changes in Ca(2+)-dependent high-affinity ryanodine binding.

RESULTS:

Ran (10 μM) alone prolonged action potential durations (206 ± 4.6 to 240 ± 7.8 ms; P <0.05); E4031 prolonged action potential durations (204 ± 6 to 546 ± 35 ms; P <0.05) and elicited EADs and TdP that were suppressed by Ran (10 μM; n = 7 of 7 hearts). Simulations (Shannon but not Mahajan model) closely reproduced experimental data except for EAD suppression by Ran. Ran reduced open probability (P(o)) of RyR2 (half maximal inhibitory concentration = 10 ± 3 μM; n = 7) in bilayers and shifted half maximal effective concentration for Ca(2+)-dependent ryanodine binding from 0.42 ± 0.02 to 0.64 ± 0.02 μM with 30 μM Ran.

CONCLUSIONS:

Ran reduces P(o) of RyR2, desensitizes Ca(2+)-dependent RyR2 activation, and inhibits Ca(i) oscillations, which represents a novel mechanism for its suppression of EADs and TdP.

PMID:
22245792
PMCID:
PMC3335957
DOI:
10.1016/j.hrthm.2012.01.010
[Indexed for MEDLINE]
Free PMC Article

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