Korean J Physiol Pharmacol.  2018 Jan;22(1):71-80. 10.4196/kjpp.2018.22.1.71.

Antidepressant drug paroxetine blocks the open pore of Kv3.1 potassium channel

• Lee HM
• Chai OH
• Hahn SJ
• Choi BH

• KMID: 2398557
• DOI: http://doi.org/10.4196/kjpp.2018.22.1.71

Abstract

In patients with epilepsy, depression is a common comorbidity but difficult to be treated because many antidepressants cause pro-convulsive effects. Thus, it is important to identify the risk of seizures associated with antidepressants. To determine whether paroxetine, a very potent selective serotonin reuptake inhibitor (SSRI), interacts with ion channels that modulate neuronal excitability, we examined the effects of paroxetine on Kv3.1 potassium channels, which contribute to highfrequency firing of interneurons, using the whole-cell patch-clamp technique. Kv3.1 channels were cloned from rat neurons and expressed in Chinese hamster ovary cells. Paroxetine reversibly reduced the amplitude of Kv3.1 current, with an ICâ‚…â‚€ value of 9.43 µM and a Hill coefficient of 1.43, and also accelerated the decay of Kv3.1 current. The paroxetine-induced inhibition of Kv3.1 channels was voltage-dependent even when the channels were fully open. The binding (k₊₁) and unbinding (k₋₁) rate constants for the paroxetine effect were 4.5 µM⁻¹s⁻¹ and 35.8 s⁻¹, respectively, yielding a calculated K(D) value of 7.9 µM. The analyses of Kv3.1 tail current indicated that paroxetine did not affect ion selectivity and slowed its deactivation time course, resulting in a tail crossover phenomenon. Paroxetine inhibited Kv3.1 channels in a usedependent manner. Taken together, these results suggest that paroxetine blocks the open state of Kv3.1 channels. Given the role of Kv3.1 in fast spiking of interneurons, our data imply that the blockade of Kv3.1 by paroxetine might elevate epileptic activity of neural networks by interfering with repetitive firing of inhibitory neurons.

Keyword

Kv3.1; Open channel block; Paroxetine; Selective serotonin reuptake inhibitor; Shaw-type K⁺ channel

MeSH Terms

Animals
Antidepressive Agents
Clone Cells
Comorbidity
Cricetinae
Cricetulus
Depression
Epilepsy
Female
Fires
Humans
Interneurons
Ion Channels
Neurons
Ovary
Paroxetine*
Patch-Clamp Techniques
Rats
Seizures
Serotonin
Shaw Potassium Channels*
Tail
Antidepressive Agents
Ion Channels
Paroxetine
Serotonin
Shaw Potassium Channels

Figure

• 

  Fig. 1 The structure of paroxetine.

• 

  Fig. 2 Paroxetine inhibits Kv3.1 channels in a concentration-dependent manner.(A) Potassium currents were generated by depolarizing Kv3.1-expressing CHO cells to +40 mV for 300 ms from a holding potential of −80 mV every 10 s. Paroxetine was applied to the bath solution at 3, 10, 30, and 100 µM; current traces obtained with indicated concentrations were superimposed. The dotted line represents the zero current. (B) Group data show the concentration dependence of paroxetine-induced suppression of Kv3.1 current. The amplitudes of Kv3.1 currents were measured at the end of the depolarizing pulses at various concentrations of paroxetine. Solid line, the data points were fitted with the Hill equation. Data are expressed as means±SEM. (C) The time course of paroxetine-mediated inhibition of Kv3.1 current, which was activated by a depolarizing pulse (+40 mV for 300 ms) every 10 s. The amplitudes were measured at the end of the 300-ms depolarizing pulses. Paroxetine (30 µM) was applied to the extracellular solution. The data are from a representative cell.

• 

  Fig. 3 The paroxetine-induced inhibition of Kv3.1 currents is dependent on membrane potential.(A) Kv3.1 currents were produced by applying 300-ms pulses between −50 and +70 mV in 10 mV increments every 10 s, from a holding potential of −80 mV. (B) Kv3.1 currents were recorded from the cell shown in (A) in the presence of 30 µM paroxetine. The dotted lines in (A) and (B) represent the zero current. (C) The I–V relationships measured at the end of the test pulses in the absence (open circle) and presence (closed circle) of 30 µM paroxetine. (D) Percent inhibition of Kv3.1 current was plotted against the membrane potential (closed square). The degree of current reduction was recalculated with the equation of ln{(Icontrol−Iparoxetine)/Iparoxetine} and plotted against the membrane potential (closed triangle). From the linear fit of the voltage dependence data (solid line for closed triangles), the equivalent electrical distance (δ) was estimated to be 0.5±0.02.

• 

  Fig. 4 Paroxetine accelerates the decay of Kv3.1 current.(A) Kv3.1 currents were elicited by +40 mV pulses from a holding potential of −80 mV every 10 s. Traces recorded in the presence of paroxetine (10, 30, and 100 µM) were superimposed. The solid lines and dotted line represent double exponential fits and the zero current, respectively. (B) In the double exponential fits in (A), the fast component (with a time constant τD) was considered paroxetine-induced decay of Kv3.1 current because the slow component represents intrinsic channel inactivation. The inverse of τD obtained at +40 mV was plotted against paroxetine concentrations. The solid line represents the least-squares fit of the data with the equation 1/τD=k+1[D]+k−1. The binding (k+1) and unbinding (k−1) rate constants were obtained from the slope and y-intercept of the fitted line. Data are expressed as means±SEM.

• 

  Fig. 5 Paroxetine prolongs the deactivation time course of Kv3.1 channels.(A) Kv3.1 tail currents were induced by repolarizing pulses between −100 and −20 mV after a 300-ms depolarizing pulse of +40 mV. Only tail currents at varying repolarizing potentials are shown. (B) In the same cell, tail currents were recorded in the presence of 30 µM paroxetine. (C) Two tail currents recorded at −40 mV repolarizing potential were superimposed (selected from A and B). Note the crossover of two trail currents (arrow). The solid lines over the current traces represent the monoexponential least-squares fits of the tail currents. (D) Deactivation time constants at −40 mV repolarizing potential were obtained from the single exponential fits in (C). *p<0.05. The dotted lines in A–C represent the zero current. Data are expressed as means±SEM.

• 

  Fig. 6 Paroxetine induces use-dependent inhibition of Kv3.1 channels.(A) Kv3.1 currents were repetitively activated by +40 mV pulses for 300 ms, 15 times at 1 Hz in the absence and presence of 30 µM paroxetine. Fifteen traces in a given stimulus train are superimposed. The dotted lines represent the zero current. Left, expanded views of the activation phases of the Kv3.1 currents. (B) The peak amplitudes of Kv3.1 currents in a given train of pulses were normalized to the peak amplitude of the first current in the same train. The depolarizing pulses were delivered at 1 (circles) or 2 Hz (triangles) in the absence (open symbols) and presence (closed symbols) of 30 µM paroxetine. Data are expressed as means±SEM.

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