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Vol. 298, Issue 3, 1108-1119, September 2001
Preclinical Research, F. Hoffmann-La-Roche Ltd., Basel, Switzerland
Appetite suppressants have been associated with primary pulmonary
hypertension (PPH), inhibition of voltage-gated potassium channels,
membrane depolarization, and calcium entry in pulmonary artery smooth
muscle cells. In cells taken from pulmonary arteries of primary
pulmonary hypertensive patients, voltage-gated potassium channels
appear to be dysfunctional and in particular, reduced hKv1.5 gene
transcription and hKv1.5 mRNA instability have been shown. We have
compared the effects of anorexinogen agents on hKv1.5 channels stably
expressed in mammalian cell line. We found that aminorex, phentermine,
dexfenfluramine, sibutramine, and fluoxetine cause a dose-dependent
inhibition of hKv1.5 current. Aminorex, phentermine, and
dexfenfluramine had a KD of inhibition greater than to 300 µM and are not potent inhibitors of hKv1.5. Sibutramine and fluoxetine inhibited hKv1.5 current with lower KD values of 41 and 21 µM, respectively.
Block by both drugs increased rapidly between
20 and +10 mV,
coincident with channel opening and suggested an open channel block
mechanism. This was confirmed by a slower deactivation time course
resulting in a "crossover" phenomenon when tail currents recorded
under control conditions and in the presence of either drug were
superimposed. Single channel experiments demonstrated that open
probability and open duration of hKv1.5 were decreased by fluoxetine
and sibutramine. These results indicate that among the anorexinogen
agents tested, sibutramine and fluoxetine are the most potent toward
hKv1.5 channel, which they preferentially block in the open state.
Nevertheless, their inhibitory effects do not correlate with their
ability to produce PPH neither with their previously reported
therapeutic plasma concentrations.
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