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Cardiovasc Res. 2013 Apr 1;98(1):136-44. doi: 10.1093/cvr/cvt007. Epub 2013 Jan 22.

Atrial selectivity in Na+channel blockade by acute amiodarone.

Author information

1
Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8401, Japan. tsuzuki@riem.nagoya-u.ac.jp

Abstract

AIMS:

Na(+) channel blockers are often used to treat atrial fibrillation (AF), but may sometimes cause ventricular contractile dysfunction. However, amiodarone, a multi-channel blocker with Na(+) channel block, causes less contractile dysfunction. In this study, we tested the hypothesis that Na(+) channel block by amiodarone is selective in atrial myocytes (AM) compared with ventricular myocytes (VM).

METHODS AND RESULTS:

Na(+) currents (INa) were measured using whole-cell patch-clamp technique in isolated rabbit AM and VM. Amiodarone inhibited INa in AM (IC50: 1.8 ± 1.1 μM; n = 8) much more than in VM (40.4 ± 11.9 μM; n = 7, P < 0.01). Amiodarone at 10 μM shifted the steady-state inactivation relationship in AM (-16.2 ± 1.7 mV shift, n = 12) compared with VM (-5.9 ± 0.7 mV shift; n = 13; P < 0.01). For mexiletine, the inhibition of INa and inactivation curve shifts were comparable for AM and VM. The effects of amiodarone and mexiletine on conduction velocity (CV) in Langendorff-perfused rabbit hearts were evaluated using an optical mapping system. The decrease of CV by 3 μM amiodarone was significantly larger in the atrium (-18.9 ± 3.8% change; n = 5) compared with the ventricle (-3.7 ± 3.7%; n = 5; P < 0.01). In contrast, mexiletine reduced CV equally in the atrium and the ventricle.

CONCLUSION:

Amiodarone preferentially inhibits INa of AM compared with VM. Atrial selective Na(+) channel block by amiodarone may contribute to treating AF with less effect on ventricular contractility than other Na(+) channel blockers.

PMID:
23341577
DOI:
10.1093/cvr/cvt007
[Indexed for MEDLINE]
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