Inhibition of Voltage-Gated Na+ Currents Exerted by KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea), an Inhibitor of Na+-Ca2+ Exchanging Process

Abstract

KB-R7943, an isothiourea derivative, has been recognized as an inhibitor in the reverse mode of the Na+-Ca2+ exchanging process. This compound was demonstrated to prevent intracellular Na+-dependent Ca2+ uptake in intact cells; however, it is much less effective at preventing extracellular Na+-dependent Ca2+ efflux. Therefore, whether or how this compound may produce any perturbations on other types of ionic currents, particularly on voltage-gated Na+ current (INa), needs to be further studied. In this study, the whole-cell current recordings demonstrated that upon abrupt depolarization in pituitary GH3 cells, the exposure to KB-R7943 concentration-dependently depressed the transient (INa(T)) or late component (INa(L)) of INa with an IC50 value of 11 or 0.9 μM, respectively. Likewise, the dissociation constant for the KB-R7943-mediated block of INa on the basis of a minimum reaction scheme was estimated to be 0.97 μM. The presence of benzamil or amiloride could suppress the INa(L) magnitude. The instantaneous window Na+ current (INa(W)) activated by abrupt ascending ramp voltage (Vramp) was suppressed by adding KB-R7943; however, subsequent addition of deltamethrin or tefluthrin (Tef) effectively reversed KB-R7943-inhibted INa(W). With prolonged duration of depolarizing pulses, the INa(L) amplitude became exponentially decreased; moreover, KB-R7943 diminished INa(L) magnitude. The resurgent Na+ current (INa(R)) evoked by a repolarizing Vramp was also suppressed by adding this compound; moreover, subsequent addition of ranolazine or Tef further diminished or reversed, respectively, its reduction in INa(R) magnitude. The persistent Na+ current (INa(P)) activated by sinusoidal voltage waveform became enhanced by Tef; however, subsequent application of KB-R7943 counteracted Tef-stimulated INa(P). The docking prediction reflected that there seem to be molecular interactions of this molecule with the hNaV1.2 or hNaV1.7 channels. Collectively, this study highlights evidence showing that KB-R7943 has the propensity to perturb the magnitude and gating kinetics of INa (e.g., INa(T), INa(L), INa(W), INa(R), and INa(P)) and that the NaV channels appear to be important targets for the in vivo actions of KB-R7943 or other relevant compounds.

Characterization of Stimulatory Action on Voltage-Gated Na+ Currents Caused by Omecamtiv Mecarbil, Known to Be a Myosin Activator

“…In recent studies, the instantaneous INa(W) current has been shown to be detectable during the short duration of an upwardly sloping (or ascending) ramp voltage (Vramp) in various excitable cells [23,28,29]. In this study, we investigated whether the presence of OM could alter the amplitude of the non-linear INa(W) that is elicited by a brief, upwardly sloping Vramp.…”

“…The electrode used for the measurements typically had a tip resistance of 3-5 MΩ when filled with different internal solutions, as stated above. We measured different types of ionic currents in the whole-cell configuration using a modified patch-clamp technique with either an Axoclamp-2B (Molecular Devices, Sunnyvale, CA) or an RK-400 amplifier (Bio-Logic, Claix, France), as previously described [21][22][23]. We obtained GΩ-seals in an all-or-nothing fashion, resulting in a significant improvement in the signal-to-noise ratio.…”

Towards Novel Potential Molecular Targets for Antidepressant and Antipsychotic Pharmacotherapies

“…Over the last decade, there has been a rapid increase in CADD-based studies of depression, including docking studies of ligands for serotonin reuptake [171,172], MAO A and MAO B [173,174], dual action on MAO-B/AChE [175], glycogen synthase kinase [176], sodium hNaV1.2 or hNaV1.7 channels [177], serotonin receptors (5HT1A, 5-HT2A, 5-HT2C and 5-HT4) [171,[178][179][180][181], adenosine A1/A2A receptors [182], T-type calcium channels [183], tryptophan 2,3-dioxygenase [184] and sigma receptor [185]. Similarly, application of docking in psychoses involved ligands for serotonin 5HT2 and dopamine D2 receptors [186], α4β2 and α7 nicotinic acetylcholine receptors [187,188], phosphodiesterase 10A [189], MAO A and B [190], a syntaxin-binding protein (STXBP1) [191], NMDA type subunit 1 (GRIN1) [192], fatty acid binding protein 7 (FABP7) [193,194], metabotropic glutamate mGluR5 receptor [195], ionotropic GABA-A receptor [196], glycine transporter type 1 (GlyT1) [197] and kynurenine aminotransferase II (KATII) [198].…”

Ion Channels as a Potential Target in Pharmaceutical Designs

“…KN-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea) is an isothiourea derivative that is viewed to selectively suppress the reverse mode of NCX isoform 1 with an IC 50 value of 1.2–2.4 μM. However, a recent study by Wu and Yu [ 1 ] provided evidence that disclosed how, in pituitary GH 3 lactotrophs, cell exposure to KB-R7943 could inhibit a voltage-gated Na + current ( I Na ) in concentration-, time- and voltage-dependent manners. The yielded IC 50 values needed for KB-R7943 suppressed the amplitude of transient I Na ( I Na(T) ), and late I Na ( I Na(L) ) were distinguishable (i.e., 11 and 0.9 μM, respectively).…”

“…Either benzamil or amiloride, also known to be inhibitors of the NCX exchanging current, was reported to inhibit an I Na(L) amplitude. When GH 3 cells were exposed to Ca 2+ -free, Tyrode’s solution, the deactivating I Na was progressively decreased in an exponential fashion as the duration of the depolarizing voltage step became prolonged [ 1 ].…”