| 19371335 |
Kang L, Zheng MQ, Morishima M, Wang Y, Kaku T, Ono K: Bepridil up-regulates cardiac Na+ channels as a long-term effect by blunting proteasome signals through inhibition of calmodulin activity. Br J Pharmacol. 2009 Jun;157(3):404-14. Epub 2009 Apr 9.
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 micromol.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 Ca2+/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-le ucinamide]. 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 alpha-subunit, which in turn increased Na+ current. |
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