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Vol. 294, Issue 1, 339-346, July 2000
Department of Pharmacology II, Faculty of Medicine & Graduate
School of Medicine, Osaka University (Y.Ka., A.F., Y.Ku.); Department
of Cardiovascular Medicine, Okayama University Medical School (Y.Ka.,
T.O.); Department of Veterinary Pharmacology, Faculty of Agriculture,
Osaka Prefectural University, Osaka, Japan (A.F.); and Centre National
de la Recherche Scientifique Unité Mixte de Recherche, Faculty of
Science, University of Tours, Tours, France (I.F.)
Vesnarinone, a phosphodiesterase inhibitor, prolongs cardiac action
potential duration by inhibiting the delayed rectifier K+
current, IK. We examined the effect of this
agent on human ether-a-go-go related gene (HERG) and
KvLQT1/minK K+ channels heterologously expressed in human
embryonic kidney 293T cells with the whole-cell patch-clamp technique.
HERG channel current was inhibited by vesnarinone in a
concentration-dependent manner, whereas KvLQT1/minK current was hardly
affected by the drug. The inhibition of HERG current by vesnarinone
became more prominent and faster as the membrane potential was more
depolarized. The properties of inhibition could be described by a first
order reaction between the drug and the channel that was apparently independent of HERG channel gating. Although the unbinding rate constant of the drug was constant, the apparent binding rate constant increased as the membrane was more depolarized and the drug
concentration was raised. This model also could explain the fast
recovery from the drug's effect at hyperpolarized potentials and its
rate-dependent inhibition of HERG. Therefore, the effect of vesnarinone
on the HERG-K+ current could be adequately described by a
simple kinetic model of drug-channel interaction.
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