Korean J Physiol Pharmacol.  2016 Jan;20(1):75-82. 10.4196/kjpp.2016.20.1.75.

Blockade of Kv1.5 by paroxetine, an antidepressant drug

• Lee HM
• Hahn SJ
• Choi BH

• KMID: 2150476
• DOI: http://doi.org/10.4196/kjpp.2016.20.1.75

Abstract

Paroxetine, a selective serotonin reuptake inhibitor (SSRI), has been reported to have an effect on several ion channels including human ether-a-go-go-related gene in a SSRI-independent manner. These results suggest that paroxetine may cause side effects on cardiac system. In this study, we investigated the effect of paroxetine on Kv1.5, which is one of cardiac ion channels. The action of paroxetine on the cloned neuronal rat Kv1.5 channels stably expressed in Chinese hamster ovary cells was investigated using the whole-cell patch-clamp technique. Paroxetine reduced Kv1.5 whole-cell currents in a reversible concentration-dependent manner, with an IC50 value and a Hill coefficient of 4.11 microM and 0.98, respectively. Paroxetine accelerated the decay rate of inactivation of Kv1.5 currents without modifying the kinetics of current activation. The inhibition increased steeply between -30 and 0 mV, which corresponded with the voltage range for channel opening. In the voltage range positive to 0 mV, inhibition displayed a weak voltage dependence, consistent with an electrical distance delta of 0.32. The binding (k(+1)) and unbinding (k(-1)) rate constants for paroxetine-induced block of Kv1.5 were 4.9 microM(-1)s(-1) and 16.1 s-1, respectively. The theoretical K(D) value derived by k(-1)/k(+1) yielded 3.3 microM. Paroxetine slowed the deactivation time course, resulting in a tail crossover phenomenon when the tail currents, recorded in the presence and absence of paroxetine, were superimposed. Inhibition of Kv1.5 by paroxetine was use-dependent. The present results suggest that paroxetine acts on Kv1.5 currents as an open-channel blocker.

Keyword

Kv1.5; Open channel block; Paroxetine; Selective serotonin reuptake inhibitor; Shaker-type K+ channel

MeSH Terms

Animals
Clone Cells
Cricetinae
Cricetulus
Female
Humans
Inhibitory Concentration 50
Ion Channels
Kinetics
Neurons
Ovary
Paroxetine*
Patch-Clamp Techniques
Rats
Serotonin
Tail
Ion Channels
Paroxetine
Serotonin

Figure

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  Fig. 1 Structure of paroxetine.

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  Fig. 2 Concentration-dependent and reversible inhibition of Kv1.5 by paroxetine.(A) Superimposed current traces were produced by applying 250-ms depolarizing pulses from a holding potential of -80 to +50 mV followed by a 250-ms repolarizing pulse to -40 mV every 10 s in the absence and presence of 1, 3, 10, and 30 µM paroxetine, as indicated. The dotted line represents zero current. (B) Concentration-dependent curve of inhibition by paroxetine. Current amplitudes of Kv1.5 measured at the end of the depolarizing pulses (closed circle) and peak current (open square) were used and the respective percentage inhibitions were plotted against various concentrations of paroxetine. The solid line is fitted to the data points by the Hill equation. Data are expressed as mean±S.E.M. (C) Representative time course for inhibition in the presence of 10 µM paroxetine. The current amplitudes were measured at the end of a 250-ms depolarizing pulses from a holding potential of -80 to +50 mV every 10 s in the presence of 10 mM paroxetine and normalized to the first current amplitude and the normalized data were plotted as a function of time.

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  Fig. 3 Voltage dependence of paroxetine-induced inhibition of Kv1.5 currents.The Kv1.5 currents were produced by applying 250-ms pulses between -60 and +50 mV in 10-mV increments followed by a 250-ms repolarizing pulse to -40 mV every 10 s, from a holding potential of -80 mV under control conditions (A), and after the addition of 10 µM paroxetine (B). The dotted lines in (A) and (B) represent zero current. (C) Resultant I~V relationships taken at the end of the test pulses in the absence (open circle) and presence (closed circle) of 10 µM paroxetine. (D) Percentage current inhibition (closed square) from data in (C) was plotted against the membrane potential. For potentials positive to 0 mV, the data of percentage current inhibition was recalculated by using ln{(IControl-IParoxetine)/IParoxetine} (closed triangle) and replotted against membrane potential. The voltage dependence was linear fitted with equation 7 (see MATERIALS AND METHODS), shown by the solid line with the indicated values for the equivalent electrical distance (δ=0.32±0.07, n=5). The dotted line represents the activation curve of Kv1.5 under control conditions, which was obtained from a deactivating tail current amplitude at -40 mV after 250-ms depolarizing pulses to potentials between -60 to +50 mV in steps of 10 mV from a holding potentials of -80 mV and thereafter normalization using equation 2 (see MATERIALS AND METHODS).

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  Fig. 4 Concentration-dependent kinetics of Kv1.5 inhibition by paroxetine.(A) Superimposed Kv1.5 current traces were elicited by applying 250-ms depolarizing pulses from a holding potential of -80 to +50 mV every 10 s in the presence of paroxetine (1, 3, 10, and 30 µM). The dotted line represents zero current. (B) The drug-induced time constants (τD) were obtained by a selection of the fast time constant from a double exponential fitting to the decaying traces of Kv1.5 currents. The inverse of τD obtained at +50 mV was plotted versus paroxetine concentrations. The solid line represents the least-squares fit of the data to the relation 1/τD=k+1[D]+k-1. A binding rate constant (k+1) and an unbinding rate constant (k-1) were obtained from the slope and intercept values of the fitted line. Data are expressed as mean±S.E.M.

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  Fig. 5 Effects of paroxetine on deactivation kinetics of Kv1.5.(A) Tail currents were induced at a 250-ms repolarizing pulses of -40 mV after a 250-ms depolarizing pulse of +50 mV from a holding potential of -80 mV in the absence and presence of 10 µM paroxetine. The dotted lines represent a zero current. Tail crossover phenomenon (indicated by the arrow) observed by superimposing the two tail currents. (B) Deactivation time constants (τ) obtained from (A). The deactivation time constants (τ) were obtained from a single exponential fitting to the decaying traces of Kv1.5 currents. The symbol * indicates a statistically significant difference (n=4, p<0.05 versus control data). Data are expressed as mean±S.E.M.

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  Fig. 6 Effects of repetitive depolarization on paroxetine-induced inhibition of Kv1.5 currents.(A) Original current traces under control conditions and in the presence of 10 µM paroxetine obtained by applying 20 repetitive 125-ms depolarizing pulses of +50 mV from a holding potential of -80 mV at 1 and 2 Hz. The dotted lines represent a zero current. (B) Plot of normalized current at 1 and 2 Hz under control conditions (open circle and open triangle, n=4) and in the presence of 10 µM paroxetine (closed circle and closed triangle, n=4) as a function of the number of pulses. Peak amplitudes of the current from every pulse were normalized to the peak amplitudes of current obtained from the first pulse. (C) Relative current (IParoxetine/IControl) plotted at 1 (open square) and 2 Hz (closed square) from (B) as a function of the number of pulses. Data are expressed as mean±S.E.M.

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