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

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 IC₅₀ 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.

Efecto de la conductancia de potasio Kv3.1 en la tasa y frecuencia de disparo de un axón no mielinado / Efect of the Kv3.1 potassium conductance in the firing frequency and firing rate of an unmyelinated axón

Objetivo: Determinar la relación entre la conductancia de potasio Kv3.1 y la tasa de disparo (Td) de un modelo neuronal llamado neurona1 formado por un soma, un cuello y un axón no mielinado durante un estímulo de corriente de 10 ms de duración y a 40°c. Materiales y métodos: A partir del software libre neuron se simuló la propagación de ráfagas de potenciales de acción a través de neuronal, variando la conductancia específica máxima de potasio Kv3.1 (G Kv31) relativa a la conductancia específica máxima de potasio (G K) estudiada por a.l. Hodgkin y a.f. Huxley en 1952, de tal forma que G Kv31+G K=1.6S/ cm². Resultados: En una estructura neuronal con las características biofísicas de neuronal, Td varía en forma sigmoidea para 0 < G Kv31/G K < 0.455 y decae exponencialmente para 0.455 < G Kv31/G K < 15, respectivamente. Para el primer caso, Td aumenta 11 veces más que la frecuencia (f) respecto del número de espigas en cada ráfaga. Conclusión: La observación de la conductancia de potasio del tipo Kv3.1 en algún tipo de neurona no implica necesariamente la propagación de ráfagas de alta tasa de disparo. Su efecto es más pronunciado (11 veces) en la modulación de Td que en el aumento de f.

Objective: To determine the relationship between the Kv3.1 potassium conductance and the firing rate (Td) in a neuronal model called neuron1, consisting of a soma, a hillock and an unmyelinated axon, during a constant current stimulus 10ms long and at 40°c. Methodology: Using the free software neuron, the propagation of action potentials along a neuronal structure called neurona1 was simulated. The maximum Kv3.1 conductance (G Kv31) relative to the maximum potassium conductance (Gk) studied in 1952 by a.l. Hodgkin and a.f. Huxley and in this paper called HH conductance, was varied such that Gk, +G Kv3.1= 1.6s/cm2. Results: In a neuronal structure with the biophysical characteristics of neuronl, Td varies in a sigmoid way for all g kv31such that 0

Open Channel Block of Kv3.1 Currents by Genistein, a Tyrosine Kinase Inhibitor

The goal of this study was to analyze the effects of genistein, a widely used tyrosine kinase inhibitor, on cloned Shaw-type K+ currents, Kv3.1 which were stably expressed in Chinese hamster ovary (CHO) cells, using the whole-cell configuration of patch-clamp techniques. In whole-cell recordings, genistein at external concentrations from 10 to 100 micrometer accelerated the rate of inactivation of Kv3.1 currents, thereby concentration-dependently reducing the current at the end of depolarizing pulse with an IC50 value of 15.71+/-0.67 micrometer and a Hill coefficient of 3.28+/-0.35 (n=5). The time constant of activation at a 300 ms depolarizing test pulses from -80 mV to +40 mV was 1.01+/-0.04 ms and 0.90+/-0.05 ms (n=9) under control conditions and in the presence of 20 micrometer genistein, respectively, indicating that the activation kinetics was not significantly modified by genistein. Genistein (20 micrometer) slowed the deactivation of the tail current elicited upon repolarization to -40 mV, thus inducing a crossover phenomenon. These results suggest that drug unbinding is required before Kv3.1 channels can close. Genistein-induced block was voltage-dependent, increasing in the voltage range (-20 mV~0 mV) for channel opening, suggesting an open channel interaction. Genistein (20 micrometer) produced use-dependent block of Kv3.1 at a stimulation frequency of 1 Hz. The voltage dependence of steady-state inactivation of Kv3.1 was not changed by 20 micrometer genistein. Our results indicate that genistein blocks directly Kv3.1 currents in concentration-, voltage-, time-dependent manners and the action of genistein on Kv3.1 is independent of tyrosine kinase inhibition.