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Bepridil up‐regulates cardiac Na + channels as a long‐term effect by blunting proteasome signals through inhibition of calmodulin activity
Author(s) -
Kang L,
Zheng MQ,
Morishima M,
Wang Y,
Kaku T,
Ono K
Publication year - 2009
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2009.00174.x
Subject(s) - bepridil , cycloheximide , calmodulin , chemistry , channel blocker , biophysics , mg132 , pharmacology , microbiology and biotechnology , proteasome inhibitor , biochemistry , calcium , biology , protein biosynthesis , apoptosis , verapamil , enzyme , organic chemistry
Background and purpose: Bepridil is an anti‐arrhythmic agent with anti‐electrical remodelling effects that target many cardiac ion channels, including the voltage‐gated Na + channel. However, long‐term effects of bepridil on the Na + channel remain unclear. We explored the long‐term effect of bepridil on the Na + channel in isolated neonatal rat cardiomyocytes and in a heterologous expression system of human Na v 1.5 channel. Experimental approach: Na + currents were recorded by whole‐cell voltage‐clamp technique. Na + channel message and protein were evaluated by real‐time RT‐PCR and Western blot analysis. Key results: Treatment of cardiomyocytes with 10 µmol·L −1 bepridil for 24 h augmented Na + channel current ( I Na ) in a dose‐ and time‐dependent manner. This long‐term effect of bepridil was mimicked or masked by application of W‐7, a calmodulin inhibitor, but not KN93 [2‐[N‐(2‐hydroxyethyl)‐N‐(4‐methoxy benzenesulphonyl)]‐amino‐N‐(4‐chlorocinnamyl)‐N‐methylbenzylamine], a Ca 2+ /calmodulin‐dependent kinase inhibitor. During inhibition of protein synthesis by cycloheximide, the I Na increase due to bepridil was larger than the increase without cycloheximide. Bepridil and W‐7 significantly slowed the time course of Na v 1.5 protein degradation in neonatal cardiomyocytes, although the mRNA levels of Na v 1.5 were not modified. Bepridil and W‐7 did not increase I Na any further in the presence of the proteasome inhibitor MG132 [N‐[(phenylmethoxy)carbonyl]‐L‐leucyl‐N‐[(1S)‐1‐formyl‐3‐methylbutyl]‐L‐leucinamide]. Bepridil, W‐7 and MG132 but not KN93 significantly decreased 20S proteasome activity in a concentration‐dependent manner. Conclusions and implications: We conclude that long‐term exposure of cardiomyocytes to bepridil at therapeutic concentrations inhibits calmodulin action, which decreased degradation of the Na v 1.5 α‐subunit, which in turn increased Na + current.