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Effects of anorexinogen agents on cloned voltage-gated K(+) channel hKv1.5
L Perchenet1, L Hilfiger, J Mizrahi
1Preclinical Research, F. Hoffmann-La-Roche Ltd., Basel, Switzerland.
Abstract:
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 K(D) of inhibition greater than to 300 microM and are not potent inhibitors of hKv1.5. Sibutramine and fluoxetine inhibited hKv1.5 current with lower K(D) values of 41 and 21 microM, 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.
Insights
Appetite suppressants like sibutramine and fluoxetine inhibit hKv1.5 channels, which are linked to pulmonary hypertension. These drugs block the channels when open, but their potency doesn't correlate with causing pulmonary hypertension.
Area of Science:
- Pharmacology
- Cardiovascular Physiology
- Molecular Biology
Background:
- Appetite suppressants are linked to primary pulmonary hypertension (PPH).
- Dysfunctional voltage-gated potassium channels, specifically hKv1.5, are implicated in PPH.
- Reduced hKv1.5 gene transcription and mRNA instability are observed in pulmonary artery cells of PPH patients.
Purpose of the Study:
- To compare the effects of various anorexinogen agents on hKv1.5 channels.
- To determine the potency and mechanism of action of these agents on hKv1.5 channels.
Main Methods:
- Stable expression of hKv1.5 channels in a mammalian cell line.
- Electrophysiological recordings to measure hKv1.5 current inhibition.
- Dose-response analysis to determine inhibition constants (K(D)).
- Single-channel recordings to assess open probability and duration.
Main Results:
- Aminorex, phentermine, and dexfenfluramine showed weak inhibition of hKv1.5 (K(D) > 300 microM).
- Sibutramine and fluoxetine potently inhibited hKv1.5 current (K(D) = 41 microM and 21 microM, respectively).
- Sibutramine and fluoxetine demonstrated an open channel block mechanism, reducing hKv1.5 open probability and duration.
Conclusions:
- Sibutramine and fluoxetine are potent inhibitors of hKv1.5 channels, preferentially blocking them in the open state.
- The inhibitory effects of sibutramine and fluoxetine on hKv1.5 channels do not correlate with their propensity to cause PPH or their therapeutic plasma concentrations.