Riluzole inhibits Kv4.2 channels acting on the closed and closed inactivated states.

Riluzole is an anticonvulsant drug also used to treat the amyotrophic lateral sclerosis and major depressive disorder. This compound has antiglutamatergic activity and is an important multichannel blocker. However, little is known about its actions on the Kv4.2 channels, the molecular correlate of the A-type K+ current (IA) and the fast transient outward current (Itof). Here, we investigated the effects of riluzole on Kv4.2 channels transiently expressed in HEK-293 cells. Riluzole inhibited Kv4.2 channels with an IC50 of 190 ± 14 µM and the effect was voltage- and frequency-independent. The activation rate of the current (at +50 mV) was not affected by the drug, nor the voltage dependence of channel activation, but the inactivation rate was accelerated by 100 and 300 µM riluzole. When Kv4.2 channels were maintained at the closed state, riluzole incubation induced a tonic current inhibition. In addition, riluzole significantly shifted the voltage dependence of inactivation to hyperpolarized potentials without affecting the recovery from inactivation. In the presence of the drug, the closed-state inactivation was significantly accelerated, and the percentage of inactivated channels was increased. Altogether, our findings indicate that riluzole inhibits Kv4.2 channels mainly affecting the closed and closed-inactivated states.

Jingzhaotoxin-X, a gating modifier of Kv4.2 and Kv4.3 potassium channels purified from the venom of the Chinese tarantula Chilobrachys jingzhao

Background:The tarantula Chilobrachys jingzhao is one of the largest venomous spiders in China. In previous studies, we purified and characterized at least eight peptides from C. jingzhao venom. In this report, we describe the purification and characterization of Jingzhaotoxin-X (JZTX-X), which selectively blocks Kv4.2 and Kv4.3 potassium channels.Methods:JZTX-X was purified using a combination of cation-exchange HPLC and reverse-phase HPLC. The amino-acid sequence was determined by automated Edman degradation and confirmed by mass spectrometry (MS). Voltage-gated ion channel currents were recorded in HEK293t cells transiently transfected with a variety of ion channel constructs. In addition, the hyperalgesic activity of JZTX-X and the toxin´s effect on motor function were assessed in mice.Results:JZTX-X contained 31 amino acids, with six cysteine residues that formed three disulfide bonds within an inhibitory cysteine knot (ICK) topology. In whole-cell voltage-clamp experiments, JZTX-X inhibited Kv4.2 and Kv4.3 potassium channels in a concentration- and voltage-dependent manner, without affecting other ion channels (Kv1.1, 1.2, 1.3, 2.1, delayed rectifier potassium channels, high- and low-voltage-activated Ca2+ channels, and voltage-gated sodium channels Nav1.5 and 1.7). JZTX-X also shifted the voltage-dependent channel activation to more depolarized potentials, whereas extreme depolarization caused reversible toxin binding to Kv4.2 channels. JZTX-X shifted the Kv4.2 and Kv4.3 activities towards a resting state, since at the resting potential the toxin...(AU)

Ts8 scorpion toxin inhibits the Kv4.2 channel and produces nociception in vivo.

The venom from the scorpion Tityus serrulatus (Ts) has been extensively studied mainly because of its rich cocktail of neurotoxins. Neurotoxins are the major and the most known components based on their modulation of voltage-gated ion channels. Until now, electrophysiological studies demonstrated that the Ts venom comprises toxins that affect Nav and Kv channels. However, although many studies have been conducted in this field, many peptides from Ts venom await further studies, including Ts8 toxin. Here we report the isolation and electrophysiological study of Ts8. The toxin Ts19 Frag-II was used as negative control. Ts8 demonstrates, among 20 tested channels, to be a selective modulator of Kv4.2 channels. Based on studies investigating the involvement of Kv4.2 on controlling nociception, we further investigated the modulation of pain by Ts8. Using intraplantar injections, Ts8 induced overt nociception (licking and lifting behaviors) and decreased the mechanical nociceptive threshold (hyperalgesia). Furthermore, the hyperalgesia was prolonged when intrathecal injections were performed. Independent of the severity, most of the victims stung by Ts scorpions report an intense and persistent pain as the major manifestation. The new role of Ts8 on nociception could explain, at least partially, this phenomenon. Additionally, our study also stresses the involvement of toxins specific to Nav channels and inflammatory mediators on the Ts painful sting. This work provides useful insights for a better understanding of the prolonged and intense pain associated with Ts envenoming for the development of specific therapies.

Modulation of the transient outward current (Ito) in rat cardiac myocytes and human Kv4.3 channels by mefloquine.

The antimalarial drug mefloquine, is known to be a potassium channel blocker, although its mechanism of action has not being elucidated and its effects on the transient outward current (Ito) and the molecular correlate, the Kv4.3 channel has not being studied. Here, we describe the mefloquine-induced inhibition of the rat ventricular Ito and of CHO cells co-transfected with human Kv4.3 and its accessory subunit hKChIP2C by whole-cell voltage-clamp. Mefloquine inhibited rat Ito and hKv4.3+KChIP2C currents in a concentration-dependent manner with a limited voltage dependence and similar potencies (IC50=8.9µM and 10.5µM for cardiac myocytes and Kv4.3 channels, respectively). In addition, mefloquine did not affect the activation of either current but significantly modified the hKv4.3 steady-state inactivation and recovery from inactivation. The effects of this drug was compared with that of 4-aminopyridine (4-AP), a well-known potassium channel blocker and its binding site does not seem to overlap with that of 4-AP.

Delta opioids reduce the neurotransmitter release probability by enhancing transient (KV4) K+-currents in corticostriatal synapses as evaluated by the paired pulse protocol.

Field recordings were used to determine the influence of delta-opioid receptor activation on corticostriatal synaptic transmission. Application of the selective delta-opioid receptor agonist, [Tyr-D-Pen-Gly-Phe-D-Pen]-enkephalin (DPDPE, 1 microM), decreased the amplitude of the field-excitatory synaptic potential and at the same time increased the paired pulse ratio (PPR) suggesting a presynaptic site of action. This response reversed rapidly when DPDPE was washed and blocked by 1 nM of the selective delta-receptor antagonist naltrindole. Neither omega-conotoxin GVIA (1 microM) nor omega-agatoxin TK (400 nM), blockers of N- and P/Q-type Ca2+-channels, respectively, nor TEA (1 mM), blocker of some classes of K+-channels, occluded the effects of DPDPE. Instead, 1 mM 4-AP or 400 microM Ba2+ occluded completely the effects of DPDPE. Therefore, the results suggest that the modulation by delta opioids at corticostriatal terminals is mediated by transient (KV4) K+-conductances.