Underlying mechanism of actions of tefluthrin, a pyrethroid insecticide, on voltage-gated ion currents and on action currents in pituitary tumor (GH3) cells and GnRH-secreting (GT1-7) neurons

Effective suppression of Ih and INa caused by capsazepine, known to be a blocker of TRPV1 receptor

A synthetic inhibitor of capsaicin-induced TRPV1 channel activation is called capsazepine (CPZ). In this study, we aimed to explore the effects of CPZ on hyperpolarization-activated cationic current (Ih) and voltage-gated Na + current (INa) in pituitary tumor (GH3) cells. Through patch-clamp recordings, we found that CPZ concentration-dependently inhibited Ih amplitude and slowed its activation time course. The IC50 and KD values were 3.1 and 3.16 μM, respectively. CPZ also shifted the steady-state activation curve of Ih towards a more hyperpolarized potential. However, there was no change in the gating charge of the curve. A modified Markovian model predicted the CPZ-induced decrease in the voltage-dependent hysteresis of Ih. CPZ suppressed INa in GH3 cells, without altering its activation or inactivation time course. Additionally, exposure to CPZ reduced spontaneous firing. These findings suggest that CPZ's inhibitory effects on Ih and INa are direct and not dependent on vanilloid receptor binding. This could provide light on an unidentified ionic mechanism influencing the membrane excitability of neurons and endocrine or neuroendocrine cells in vivo.

Biophysical mechanisms underlying tefluthrin-induced modulation of gating changes and resurgent current generation in the human Nav1.4 channel

Human skeletal muscle contraction is triggered by activation of Nav1.4 channels. Nav1.4 channels can generate resurgent currents by channel reopening at hyperpolarized potentials through a gating transition dependent on the intracellular Navβ4 peptide in the physiological conditions. Tefluthrin (TEF) is a pyrethroid insecticide that can disrupt electrical signaling in nerves and skeletal muscle, resulting in seizures, muscle spasms, fasciculations, and mental confusion. TEF can also induce tail currents through other voltage-gated sodium channels in the absence of Navβ4 peptide, suggesting that muscle spasms may be caused by resurgent currents. Further, intracellular Navβ4 peptide and extracellular TEF may show competitive or synergistic effects; however, their binding sites are still unknown. To address these issues, electrophysiological recordings were performed on CHO-K1 cells expressing Nav1.4 channels with intracellular Navβ4 peptide, extracellular TEF, or both. TEF and Navβ4 peptide induced a hyperpolarizing shift of activation and inactivation curves in the Nav1.4 channel. TEF also substantially prolonged the inactivation time constants, while simultaneous application of Navβ4 peptide partially reversed this effect. Resurgent currents were enhanced by TEF and Navβ4 peptide at negative potentials, but TEF more potently enhances resurgent currents and dampens decay of resurgent currents. With longer depolarization, peak resurgent currents decay was fastest with the TEF alone. Molecular docking suggested that TEF and Navβ4 peptide binding site(s) are not in the narrowest part of the channel pore, but rather in the bundle-crossing regions and in the domain linkers, respectively. TEF can induce resurgent currents independently and synergistically with Navβ4 peptide, which may explain the muscle spasms observed in TEF intoxication.

Molnupiravir, a ribonucleoside antiviral prodrug against SARS-CoV-2, alters the voltage-gated sodium current and causes adverse events

Molnupiravir (MOL) is a ribonucleoside prodrug for oral treatment of COVID-19. Common adverse effects of MOL are headache, diarrhea, and nausea, which may be associated with altered sodium channel function. Here, we investigated the effect of MOL on voltage-gated Na+ current (INa) in pituitary GH3 cells. We show that MOL had distinct effects on transient and late INa, in combination with decreased time constant in the slow component of INa inactivation. The 50% inhibitory concentration (IC50) values of MOL for suppressing transient and late INa were 26.1 and 6.3 μM, respectively. The overall steady-state current-voltage relationship of INa remained unchanged upon MOL exposure. MOL-induced alteration of INa may lead to changes in physiological function through sodium channels. Apart from its effect on inhibiting RNA virus replication, MOL exerts inhibitory effects on plasmalemma INa, which might constitute an additional yet crucial underlying mechanism of its pharmacological activity or adverse events.

Investigating the Impact of Selective Modulators on the Renin-Angiotensin-Aldosterone System: Unraveling Their Off-Target Perturbations of Transmembrane Ionic Currents

The renin-angiotensin-aldosterone system (RAAS) plays a crucial role in maintaining various physiological processes in the body, including blood pressure regulation, electrolyte balance, and overall cardiovascular health. However, any compounds or drugs known to perturb the RAAS might have an additional impact on transmembrane ionic currents. In this retrospective review article, we aimed to present a selection of chemical compounds or medications that have long been recognized as interfering with the RAAS. It is noteworthy that these substances may also exhibit regulatory effects in different types of ionic currents. Apocynin, known to attenuate the angiotensin II-induced activation of epithelial Na+ channels, was shown to stimulate peak and late components of voltage-gated Na+ current (INa). Esaxerenone, an antagonist of the mineralocorticoid receptor, can exert an inhibitory effect on peak and late INa directly. Dexamethasone, a synthetic glucocorticoid, can directly enhance the open probability of large-conductance Ca2+-activated K+ channels. Sparsentan, a dual-acting antagonist of the angiotensin II receptor and endothelin type A receptors, was found to suppress the amplitude of peak and late INa effectively. However, telmisartan, a blocker of the angiotensin II receptor, was effective in stimulating the peak and late INa along with a slowing of the inactivation time course of the current. However, telmisartan's presence can also suppress the erg-mediated K+ current. Moreover, tolvaptan, recognized as an aquaretic agent that can block the vasopressin receptor, was noted to suppress the amplitude of the delayed-rectifier K+ current and the M-type K+ current directly. The above results indicate that these substances not only have an interference effect on the RAAS but also exert regulatory effects on different types of ionic currents. Therefore, to determine their mechanisms of action, it is necessary to gain a deeper understanding.

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

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 (I_Na), 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 (I_Na(T)) or late component (I_Na(L)) of I_Na with an IC₅₀ value of 11 or 0.9 μM, respectively. Likewise, the dissociation constant for the KB-R7943-mediated block of I_Na on the basis of a minimum reaction scheme was estimated to be 0.97 μM. The presence of benzamil or amiloride could suppress the I_Na(L) magnitude. The instantaneous window Na⁺ current (I_Na(W)) activated by abrupt ascending ramp voltage (V_ramp) was suppressed by adding KB-R7943; however, subsequent addition of deltamethrin or tefluthrin (Tef) effectively reversed KB-R7943-inhibted I_Na(W). With prolonged duration of depolarizing pulses, the I_Na(L) amplitude became exponentially decreased; moreover, KB-R7943 diminished I_Na(L) magnitude. The resurgent Na⁺ current (I_Na(R)) evoked by a repolarizing V_ramp was also suppressed by adding this compound; moreover, subsequent addition of ranolazine or Tef further diminished or reversed, respectively, its reduction in I_Na(R) magnitude. The persistent Na⁺ current (I_Na(P)) activated by sinusoidal voltage waveform became enhanced by Tef; however, subsequent application of KB-R7943 counteracted Tef-stimulated I_Na(P). The docking prediction reflected that there seem to be molecular interactions of this molecule with the hNa_V1.2 or hNa_V1.7 channels. Collectively, this study highlights evidence showing that KB-R7943 has the propensity to perturb the magnitude and gating kinetics of I_Na (e.g., I_Na(T), I_Na(L), I_Na(W), I_Na(R), and I_Na(P)) and that the Na_V channels appear to be important targets for the in vivo actions of KB-R7943 or other relevant compounds.

Tefluthrin: metabolism, food residues, toxicity, and mechanisms of action

Tefluthrin is a Type I pyrethroid insecticide widely used all over the world. Residues of tefluthrin in various agricultural and animal-derived products may be related to potential human health risks. Tefluthrin metabolism in mammals involves hydrolysis of the ester bond to form cyclopropane acid and 4-methylbenzyl alcohol moieties, followed by oxidation. In this review manuscript, we provide crucial information regarding the toxicity of pyrethroids and propose natural antioxidants for amelioration poisoning in humans and animals. We call for the rational use of tefluthrin as an agrochemical product and for greater attention to the residual toxicity caused by tefluthrin in primary and succeeding crops. This greater attention is required given the global use of tefluthrin.

Characterization in Effective Stimulation on the Magnitude, Gating, Frequency Dependence, and Hysteresis of INa Exerted by Picaridin (or Icaridin), a Known Insect Repellent

Picaridin (icaridin), a member of the piperidine chemical family, is a broad-spectrum arthropod repellent. Its actions have been largely thought to be due to its interaction with odorant receptor proteins. However, to our knowledge, to what extent the presence of picaridin can modify the magnitude, gating, and/or the strength of voltage-dependent hysteresis (Hys_(V)) of plasmalemmal ionic currents, such as, voltage-gated Na⁺ current [I_Na], has not been entirely explored. In GH₃ pituitary tumor cells, we demonstrated that with exposure to picaridin the transient (I_Na(T)) and late (I_Na(L)) components of voltage-gated Na⁺ current (I_Na) were differentially stimulated with effective EC₅₀’s of 32.7 and 2.8 μM, respectively. Upon cell exposure to it, the steady-state current versus voltage relationship I_Na(T) was shifted to more hyperpolarized potentials. Moreover, its presence caused a rightward shift in the midpoint for the steady-state inactivate curve of the current. The cumulative inhibition of I_Na(T) induced during repetitive stimuli became retarded during its exposure. The recovery time course from the I_Na block elicited, following the conditioning pulse stimulation, was satisfactorily fitted by two exponential processes. Moreover, the fast and slow time constants of recovery from the I_Na block by the same conditioning protocol were noticeably increased in the presence of picaridin. However, the fraction in fast or slow component of recovery time course was, respectively, increased or decreased with an increase in picaridin concentrations. The Hys_(V)’s strength of persistent I_Na (I_Na(P)), responding to triangular ramp voltage, was also enhanced during cell exposure to picaridin. The magnitude of resurgent I_Na (I_Na(R)) was raised in its presence. Picaritin-induced increases of I_Na(P) or I_Na(R) intrinsically in GH₃ cells could be attenuated by further addition of ranolazine. The predictions of molecular docking also disclosed that there are possible interactions of the picaridin molecule with the hNa_V1.7 channel. Taken literally, the stimulation of I_Na exerted by the exposure to picaridin is expected to exert impacts on the functional activities residing in electrically excitable cells.

Effective Perturbations by Phenobarbital on INa, IK(erg), IK(M) and IK(DR) during Pulse Train Stimulation in Neuroblastoma Neuro-2a Cells

Phenobarbital (PHB, Luminal Sodium^®) is a medication of the barbiturate and has long been recognized to be an anticonvulsant and a hypnotic because it can facilitate synaptic inhibition in the central nervous system through acting on the γ-aminobutyric acid (GABA) type A (GABA_A) receptors. However, to what extent PHB could directly perturb the magnitude and gating of different plasmalemmal ionic currents is not thoroughly explored. In neuroblastoma Neuro-2a cells, we found that PHB effectively suppressed the magnitude of voltage-gated Na⁺ current (I_Na) in a concentration-dependent fashion, with an effective IC₅₀ value of 83 µM. The cumulative inhibition of I_Na, evoked by pulse train stimulation, was enhanced by PHB. However, tefluthrin, an activator of I_Na, could attenuate PHB-induced reduction in the decaying time constant of I_Na inhibition evoked by pulse train stimuli. In addition, the erg (ether-à-go-go-related gene)-mediated K⁺ current (I_K(erg)) was also blocked by PHB. The PHB-mediated inhibition on I_K(erg) could not be overcome by flumazenil (GABA antagonist) or chlorotoxin (chloride channel blocker). The PHB reduced the recovery of I_K(erg) by a two-step voltage protocol with a geometrics-based progression, but it increased the decaying rate of I_K(erg), evoked by the envelope-of-tail method. About the M-type K⁺ currents (I_K(M)), PHB caused a reduction of its amplitude, which could not be counteracted by flumazenil or chlorotoxin, and PHB could enhance its cumulative inhibition during pulse train stimulation. Moreover, the magnitude of delayed-rectifier K⁺ current (I_K(DR)) was inhibited by PHB, while the cumulative inhibition of I_K(DR) during 10 s of repetitive stimulation was enhanced. Multiple ionic currents during pulse train stimulation were subject to PHB, and neither GABA antagonist nor chloride channel blocker could counteract these PHB-induced reductions. It suggests that these actions might conceivably participate in different functional activities of excitable cells and be independent of GABA_A receptors.

Characterization in Inhibitory Effectiveness of Carbamazepine in Voltage-Gated Na+ and Erg-Mediated K+ Currents in a Mouse Neural Crest-Derived (Neuro-2a) Cell Line

Carbamazepine (CBZ, Tegretol^®) is an anticonvulsant used in the treatment of epilepsy and neuropathic pain; however, several unwanted effects of this drug have been noticed. Therefore, the regulatory actions of CBZ on ionic currents in electrically excitable cells need to be reappraised, although its efficacy in suppressing voltage-gated Na⁺ current (I_Na) has been disclosed. This study was undertaken to explore the modifications produced by CBZ on ionic currents (e.g., I_Na and erg-mediated K⁺ current [I_K(erg)]) measured from Neuro-2a (N2a) cells. In these cells, we found that this drug differentially suppressed the peak (transient, I_Na(T)) and sustained (late, I_Na(L)) components of I_Na in a concentration-dependent manner with effective IC₅₀ of 56 and 18 μM, respectively. The overall current–voltage relationship of I_Na(T) with or without the addition of CBZ remained unchanged; however, the strength (i.e., ∆area) in the window component of I_Na (I_Na(W)) evoked by the short ascending ramp pulse (V_ramp) was overly lessened in the CBZ presence. Tefluthrin (Tef), a synthetic pyrethroid, known to stimulate I_Na, augmented the strength of the voltage-dependent hysteresis (Hys_(V)) of persistent I_Na (I_Na(P)) in response to the isosceles-triangular V_ramp; moreover, further application of CBZ attenuated Tef-mediated accentuation of I_Na(P)’s Hys_(V). With a two-step voltage protocol, the recovery of I_Na(T) inactivation seen in Neuro-2a cells became progressively slowed by adding CBZ; however, the cumulative inhibition of I_Na(T) evoked by pulse train stimulation was enhanced during exposure to this drug. Neuro-2a-cell exposure to CBZ (100 μM), the magnitude of erg-mediated K⁺ current measured throughout the entire voltage-clamp steps applied was mildly inhibited. The docking results regarding the interaction of CBZ and voltage-gate Na⁺ (Na_V) channel predicted the ability of CBZ to bind to some amino-acid residues in Na_V due to the existence of a hydrogen bond or hydrophobic contact. It is conceivable from the current investigations that the I_Na (I_Na(T), I_Na(L), I_Na(W), and I_Na(P)) residing in Neuro-2a cells are susceptible to being suppressed by CBZ, and that its block on I_Na(L) is larger than that on I_Na(T). Collectively, the magnitude and gating of Na_V channels produced by the CBZ presence might have an impact on its anticonvulsant and analgesic effects occurring in vivo.

Screening an In-House Isoquinoline Alkaloids Library for New Blockers of Voltage-Gated Na+ Channels Using Voltage Sensor Fluorescent Probes: Hits and Biases

Voltage-gated Na⁺ (Na_V) channels are significant therapeutic targets for the treatment of cardiac and neurological disorders, thus promoting the search for novel Na_V channel ligands. With the objective of discovering new blockers of Na_V channel ligands, we screened an In-House vegetal alkaloid library using fluorescence cell-based assays. We screened 62 isoquinoline alkaloids (IA) for their ability to decrease the FRET signal of voltage sensor probes (VSP), which were induced by the activation of Na_V channels with batrachotoxin (BTX) in GH3b6 cells. This led to the selection of five IA: liriodenine, oxostephanine, thalmiculine, protopine, and bebeerine, inhibiting the BTX-induced VSP signal with micromolar IC₅₀. These five alkaloids were then assayed using the Na⁺ fluorescent probe ANG-2 and the patch-clamp technique. Only oxostephanine and liriodenine were able to inhibit the BTX-induced ANG-2 signal in HEK293-hNa_V1.3 cells. Indeed, liriodenine and oxostephanine decreased the effects of BTX on Na⁺ currents elicited by the hNa_V1.3 channel, suggesting that conformation change induced by BTX binding could induce a bias in fluorescent assays. However, among the five IA selected in the VSP assay, only bebeerine exhibited strong inhibitory effects against Na⁺ currents elicited by the hNav1.2 and hNav1.6 channels, with IC₅₀ values below 10 µM. So far, bebeerine is the first BBIQ to have been reported to block Na_V channels, with promising therapeutical applications.

Inhibitory Effectiveness in Delayed-Rectifier Potassium Current Caused by Vortioxetine, Known to Be a Novel Antidepressant

Vortioxetine (VOR) is recognized to exert antidepressant actions. However, whether this drug modifies ionic currents in excitable cells remains unclear. The aim of this study was to explore the electrophysiological effects of VOR and other related compounds in pituitary GH₃ cells and in Neuro-2a cells. VOR suppressed the delayed-rectifier K⁺ current (I_K(DR)) in a concentration-, time-, and state-dependent manner. Effective IC₅₀ values needed to inhibit peak and sustained I_K(DR) were computed to be 31.2 and 8.5 μM, respectively, while the K_D value estimated from minimal binding scheme was 7.9 μM. Cell exposure to serotonin (10 μM) alone failed to alter I_K(DR), while fluoxetine (10 μM), a compound structurally similar to VOR, mildly suppressed current amplitude. In continued presence of VOR, neither further addition of propranolol nor risperidone reversed VOR-mediated inhibition of I_K(DR). Increasing VOR concentration not only depressed I_K(DR) conductance but also shifted toward the hyperpolarized potential. As the VOR concentration was raised, the recovery of I_K(DR) block became slowed. The I_K(DR) activated by a downsloping ramp was suppressed by its presence. The inhibition of I_K(DR) by a train pulse was enhanced during exposure to VOR. In Neuro-2a cells, this drug decreased I_K(DR). Overall, inhibitory effects of VOR on ionic currents might constitute another underlying mechanism of its actions.

Endogenous ion channels expressed in human embryonic kidney (HEK-293) cells

Mammalian expression systems, particularly the human embryonic kidney (HEK-293) cells, combined with electrophysiological studies, have greatly benefited our understanding of the function, characteristic, and regulation of various ion channels. It was previously assumed that the existence of endogenous ion channels in native HEK-293 cells could be negligible. Still, more and more ion channels are gradually reported in native HEK-293 cells, which should draw our attention. In this regard, we summarize the different ion channels that are endogenously expressed in HEK-293 cells, including voltage-gated Na⁺ channels, Ca²⁺ channels, K⁺ channels, Cl^- channels, nonselective cation channels, TRP channels, acid-sensitive ion channels, and Piezo channels, which may complicate the recording of the heterogeneously expressed ion channels to a certain degree. We noted that the expression patterns and channel profiles varied with different studies, which may be due to the distinct originality of the cells, cell culture conditions, passage numbers, and different recording protocols. Therefore, a better knowledge of endogenous ion channels may help minimize potential problems in characterizing heterologously expressed ion channels. Based on this, it is recommended that HEK-293 cells from unknown sources should be examined before transfection for the characterization of their functional profile, especially when the expression level of exogenous ion channels does not overwhelm the endogenous ion channels largely, or the current amplitude is not significantly higher than the native currents.

Activation of Voltage-Gated Na+ Current by GV-58, a Known Activator of CaV Channels

GV-58 ((2R)-2-[(6-{[(5-methylthiophen-2-yl)methyl]amino}-9-propyl-9H-purin-2-yl)amino]butan-1-ol) is recognized to be an activator of N- and P/Q-type Ca²⁺ currents. However, its modulatory actions on other types of ionic currents in electrically excitable cells remain largely unanswered. This study was undertaken to explore the possible modifications caused by GV-58 in ionic currents (e.g., voltage-gated Na⁺ current [I_Na], A-type K⁺ current [I_K(A)], and erg-mediated K⁺ current [I_K(erg)]) identified from pituitary GH₃ lactotrophs. GH₃ cell exposure to GV-58 enhanced the transient and late components of I_Na with varying potencies; consequently, the EC₅₀ values of GV-58 required for its differential increase in peak and late I_Na in GH₃ cells were estimated to be 8.9 and 2.6 μM, respectively. The I_Na in response to brief depolarizing pulse was respectively stimulated or suppressed by GV-58 or tetrodotoxin, but it failed to be altered by ω-conotoxin MVIID. Cell exposure to this compound increased the recovery of I_Na inactivation evoked by two-pulse protocol based on a geometrics progression; however, in its presence, there was a slowing in the inactivation rate of current decay evoked by a train of depolarizing pulses. The existence of GV-58 also resulted in an increase in the amplitude of ramp-induced resurgent and window I_Na. The presence of this compound inhibited I_K(A) magnitude, accompanied by a shortening in inactivation time course of the current; however, it mildly decreased I_K(erg). Under current-clamp conditions, GV-58 increased the frequency of spontaneous action potentials in GH₃ cells. Moreover, in NSC-34 motor neuron-like cells, the presence of GV-58 not only raised I_Na amplitude but also reduced current inactivation. Taken together, the overall work provides a noticeable yet unidentified finding which implies that, in addition to its agonistic effect on Ca²⁺ currents, GV-58 may concertedly modify the amplitude and gating kinetics of I_Na in electrically excitable cells, hence modifiying functional activities in these cells.

Zingerone Modulates Neuronal Voltage-Gated Na+ and L-Type Ca2+ Currents

Zingerone (ZO), a nontoxic methoxyphenol, has been demonstrated to exert various important biological effects. However, its action on varying types of ionic currents and how they concert in neuronal cells remain incompletely understood. With the aid of patch clamp technology, we investigated the effects of ZO on the amplitude, gating, and hysteresis of plasmalemmal ionic currents from both pituitary tumor (GH₃) cells and hippocampal (mHippoE-14) neurons. The exposure of the GH₃ cells to ZO differentially diminished the peak and late components of the I_Na. Using a double ramp pulse, the amplitude of the I_Na(P) was measured, and the appearance of a hysteresis loop was observed. Moreover, ZO reversed the tefluthrin-mediated augmentation of the hysteretic strength of the I_Na(P) and led to a reduction in the I_Ca,L. As a double ramp pulse was applied, two types of voltage-dependent hysteresis loops were identified in the I_Ca,L, and the replacement with BaCl₂-attenuated hysteresis of the I_Ca,L enhanced the I_Ca,L amplitude along with the current amplitude (i.e., the I_Ba). The hysteretic magnitude of the I_Ca,L activated by the double pulse was attenuated by ZO. The peak and late I_Na in the hippocampal mHippoE-14 neurons was also differentially inhibited by ZO. In addition to acting on the production of reactive oxygen species, ZO produced effects on multiple ionic currents demonstrated herein that, considered together, may significantly impact the functional activities of neuronal cells.

The Evidence for Sparsentan-Mediated Inhibition of INa and IK(erg): Possibly Unlinked to Its Antagonism of Angiotensin II or Endothelin Type a Receptor

Sparsentan is viewed as a dual antagonist of endothelin type A (ET_A) receptor and angiotensin II (AngII) receptor and it could be beneficial in patients with focal segmental glomerulosclerosis. Moreover, it could improve glomerular filtration rate and augment protective tissue remodeling in mouse models of focal segmental glomerulosclerosis. The ionic mechanisms through which it interacts with the magnitude and/or gating kinetics of ionic currents in excitable cells were not thoroughly investigated. Herein, we aimed to examine the effects of varying sparsentan concentrations on ionic currents residing in pituitary GH₃ somatolactotrophs. From whole-cell current recordings made in GH₃ cells, sparsentan (0.3–100 μM) differentially inhibited the peak and late components of voltage-gated Na⁺ current (I_Na). The IC₅₀ value of sparsentan required to exert a reduction in peak and late I_Na in GH₃ cells was 15.04 and 1.21 μM, respectively; meanwhile, the K_D value estimated from its shortening in the slow component of I_Na inactivation time constant was 2.09 μM. The sparsentan (10 μM) presence did not change the overall current–voltage relationship of I_Na; however, the steady-state inactivation curve of the current was shifted to more negative potential in its presence (10 μM), with no change in the gating charge of the curve. The window I_Na activated by a brief upsloping ramp was decreased during exposure to sparsentan (10 μM); moreover, recovery of peak I_Na became slowed in its presence. The Tefluthrin (Tef)-stimulated resurgent I_Na activated in response to abrupt depolarization followed by the descending ramp pulse was additionally attenuated by subsequent application of sparsentan. In continued presence of Tef (3 μM) or β-pompilidotoxin (3 μM), further application of sparsentan (3 μM) reversed their stimulation of I_Na. However, sparsentan-induced inhibition of I_Na failed to be overcome by subsequent application of either endothelin 1 (1 μM) or angiotensin II (1 μM); moreover, in continued presence of endothelin (1 μM) or angiotensin II (1 μM), further addition of sparsentan (3 μM) effectively decreased peak I_Na. Additionally, the application of sparsentan (3 μM) inhibited the peak and late components of erg-mediated K⁺ current in GH₃ cells, although it mildly decreased the amplitude of delayed-rectifier K⁺ current. Altogether, this study provides a distinct yet unidentified finding that sparsentan may perturb the amplitude or gating of varying ionic currents in excitable cells.

Effective Accentuation of Voltage-Gated Sodium Current Caused by Apocynin (4'-Hydroxy-3'-methoxyacetophenone), a Known NADPH-Oxidase Inhibitor

Apocynin (aPO, 4'-Hydroxy-3'-methoxyacetophenone) is a cell-permeable, anti-inflammatory phenolic compound that acts as an inhibitor of NADPH-dependent oxidase (NOX). However, the mechanisms through which aPO can interact directly with plasmalemmal ionic channels to perturb the amplitude or gating of ionic currents in excitable cells remain incompletely understood. Herein, we aimed to investigate any modifications of aPO on ionic currents in pituitary GH₃ cells or murine HL-1 cardiomyocytes. In whole-cell current recordings, GH₃-cell exposure to aPO effectively stimulated the peak and late components of voltage-gated Na+ current (I_Na) with different potencies. The EC₅₀ value of aPO required for its differential increase in peak or late I_Na in GH₃ cells was estimated to be 13.2 or 2.8 μM, respectively, whereas the K_D value required for its retardation in the slow component of current inactivation was 3.4 μM. The current-voltage relation of I_Na was shifted slightly to more negative potential during cell exposure to aPO (10 μM); however, the steady-state inactivation curve of the current was shifted in a rightward direction in its presence. Recovery of peak I_Na inactivation was increased in the presence of 10 μM aPO. In continued presence of aPO, further application of rufinamide or ranolazine attenuated aPO-stimulated I_Na. In methylglyoxal- or superoxide dismutase-treated cells, the stimulatory effect of aPO on peak I_Na remained effective. By using upright isosceles-triangular ramp pulse of varying duration, the amplitude of persistent I_Na measured at low or high threshold was enhanced by the aPO presence, along with increased hysteretic strength appearing at low or high threshold. The addition of aPO (10 μM) mildly inhibited the amplitude of erg-mediated K+ current. Likewise, in HL-1 murine cardiomyocytes, the aPO presence increased the peak amplitude of I_Na as well as decreased the inactivation or deactivation rate of the current, and further addition of ranolazine or esaxerenone attenuated aPO-accentuated I_Na. Altogether, this study provides a distinctive yet unidentified finding that, despite its effectiveness in suppressing NOX activity, aPO may directly and concertedly perturb the amplitude, gating and voltage-dependent hysteresis of I_Na in electrically excitable cells. The interaction of aPO with ionic currents may, at least in part, contribute to the underlying mechanisms through which it affects neuroendocrine, endocrine or cardiac function.

Characterization of Direct Perturbations on Voltage-Gated Sodium Current by Esaxerenone, a Nonsteroidal Mineralocorticoid Receptor Blocker

Esaxerenone (ESAX; CS-3150, Minnebro^®) is known to be a newly non-steroidal mineralocorticoid receptor (MR) antagonist. However, its modulatory actions on different types of ionic currents in electrically excitable cells remain largely unanswered. The present investigations were undertaken to explore the possible perturbations of ESAX on the transient, late and persistent components of voltage-gated Na⁺ current (I_Na) identified from pituitary GH₃ or MMQ cells. GH₃-cell exposure to ESAX depressed the transient and late components of I_Na with varying potencies. The IC₅₀ value of ESAX required for its differential reduction in peak or late I_Na in GH₃ cells was estimated to be 13.2 or 3.2 μM, respectively. The steady-state activation curve of peak I_Na remained unchanged during exposure to ESAX; however, recovery of peak I_Na block was prolonged in the presence 3 μM ESAX. In continued presence of aldosterone (10 μM), further addition of 3 μM ESAX remained effective at inhibiting I_Na. ESAX (3 μM) potently reversed Tef-induced augmentation of I_Na. By using isosceles-triangular ramp pulse with varying durations, the amplitude of persistent I_Na measured at high or low threshold was enhanced by the presence of tefluthrin (Tef), in combination with the appearance of the figure-of-eight hysteretic loop; moreover, hysteretic strength of the current was attenuated by subsequent addition of ESAX. Likewise, in MMQ lactotrophs, the addition of ESAX also effectively decreased the peak amplitude of I_Na along with the increased current inactivation rate. Taken together, the present results provide a noticeable yet unidentified finding disclosing that, apart from its antagonistic effect on MR receptor, ESAX may directly and concertedly modify the amplitude, gating properties and hysteresis of I_Na in electrically excitable cells.

The Integrated Effects of Brivaracetam, a Selective Analog of Levetiracetam, on Ionic Currents and Neuronal Excitability

Brivaracetam (BRV) is recognized as a novel third-generation antiepileptic drug approved for the treatment of epilepsy. Emerging evidence has demonstrated that it has potentially better efficacy and tolerability than its analog, Levetiracetam (LEV). This, however, cannot be explained by their common synaptic vesicle-binding mechanism. Whether BRV can affect different ionic currents and concert these effects to alter neuronal excitability remains unclear. With the aid of patch clamp technology, we found that BRV concentration dependently inhibited the depolarization-induced M-type K⁺ current (I_K(M)), decreased the delayed-rectifier K⁺ current (I_K(DR)), and decreased the hyperpolarization-activated cation current in GH3 neurons. However, it had a concentration-dependent inhibition on voltage-gated Na⁺ current (I_Na). Under an inside-out patch configuration, a bath application of BRV increased the open probability of large-conductance Ca²⁺-activated K⁺ channels. Furthermore, in mHippoE-14 hippocampal neurons, the whole-cell I_Na was effectively depressed by BRV. In simulated modeling of hippocampal neurons, BRV was observed to reduce the firing of the action potentials (APs) concurrently with decreases in the AP amplitude. In animal models, BRV ameliorated acute seizures in both OD-1 and lithium-pilocarpine epilepsy models. However, LEV had effects in the latter only. Collectively, our study demonstrated BRV’s multiple ionic mechanism in electrically excitable cells and a potential concerted effect on neuronal excitability and hyperexcitability disorders.

Effective Activation by Kynurenic Acid and Its Aminoalkylated Derivatives on M-Type K+ Current

Kynurenic acid (KYNA, 4-oxoquinoline-2-carboxylic acid), an intermediate of the tryptophan metabolism, has been recognized to exert different neuroactive actions; however, the need of how it or its aminoalkylated amide derivative N-(2-(dimethylamino)ethyl)-3-(morpholinomethyl)-4-oxo-1,4-dihydroquinoline-2-carboxamide (KYNA-A4) exerts any effects on ion currents in excitable cells remains largely unmet. In this study, the investigations of how KYNA and other structurally similar KYNA derivatives have any adjustments on different ionic currents in pituitary GH₃ cells and hippocampal mHippoE-14 neurons were performed by patch-clamp technique. KYNA or KYNA-A4 increased the amplitude of M-type K⁺ current (I_K(M)) and concomitantly enhanced the activation time course of the current. The EC₅₀ value required for KYNA- or KYNA-A4 -stimulated I_K(M) was yielded to be 18.1 or 6.4 μM, respectively. The presence of KYNA or KYNA-A4 shifted the relationship of normalized I_K(M)-conductance versus membrane potential to more depolarized potential with no change in the gating charge of the current. The voltage-dependent hysteretic area of I_K(M) elicited by long-lasting triangular ramp pulse was observed in GH₃ cells and that was increased during exposure to KYNA or KYNA-A4. In cell-attached current recordings, addition of KYNA raised the open probability of M-type K⁺ channels, along with increased mean open time of the channel. Cell exposure to KYNA or KYNA-A4 mildly inhibited delayed-rectifying K⁺ current; however, neither erg-mediated K⁺ current, hyperpolarization-activated cation current, nor voltage-gated Na⁺ current in GH₃ cells was changed by KYNA or KYNA-A4. Under whole-cell, current-clamp recordings, exposure to KYNA or KYNA-A4 diminished the frequency of spontaneous action potentials; moreover, their reduction in firing frequency was attenuated by linopirdine, yet not by iberiotoxin or apamin. In hippocampal mHippoE-14 neurons, the addition of KYNA also increased the I_K(M) amplitude effectively. Taken together, the actions presented herein would be one of the noticeable mechanisms through which they modulate functional activities of excitable cells occurring in vivo.

Effectiveness of Columbianadin, a Bioactive Coumarin Derivative, in Perturbing Transient and Persistent INa

Columbianadin (CBN) is a bioactive coumarin-type compound with various biological activities. However, the action of CBN on the ionic mechanism remains largely uncertain, albeit it was reported to inhibit voltage-gated Ca²⁺ current or to modulate TRP-channel activity. In this study, whole-cell patch-clamp current recordings were undertaken to explore the modifications of CBN or other related compounds on ionic currents in excitable cells (e.g., pituitary GH₃ cells and HL-1 atrial cardiomyocytes). GH₃-cell exposure to CBN differentially decreased peak or late component of voltage-gated Na⁺ current (I_Na) with effective IC₅₀ of 14.7 or 2.8 µM, respectively. The inactivation time course of I_Na activated by short depolarization became fastened in the presence of CBN with estimated K_D value of 3.15 µM. The peak I_Na diminished by 10 µM CBN was further suppressed by subsequent addition of either sesamin (10 µM), ranolazine (10 µM), or tetrodotoxin (1 µM), but it was reversed by 10 µM tefluthrin (Tef); however, further application of 10 µM nimodipine failed to alter CBN-mediated inhibition of I_Na. CBN (10 µM) shifted the midpoint of inactivation curve of I_Na to the leftward direction. The CBN-mediated inhibition of peak I_Na exhibited tonic and use-dependent characteristics. Using triangular ramp pulse, the hysteresis of persistent I_Na enhanced by Tef was noticed, and the behavior was attenuated by subsequent addition of CBN. The delayed-rectifier or erg-mediated K⁺ current was mildly inhibited by 10 µM CBN, while it also slightly inhibited the amplitude of hyperpolarization-activated cation current. In HL-1 atrial cardiomyocytes, CBN inhibited peak I_Na and raised the inactivation rate of the current; moreover, further application of 10 µM Tef attenuated CBN-mediated decrease in I_Na. Collectively, this study provides an important yet unidentified finding revealing that CBN modifies I_Na in electrically excitable cells.

Inhibitory Effectiveness of Gomisin A, a Dibenzocyclooctadiene Lignan Isolated from Schizandra chinensis, on the Amplitude and Gating of Voltage-Gated Na+ Current

Gomisin A (Gom A), a lignan isolated from Schisandra chinensis, has been reported produce numerous biological activities. However, its action on the ionic mechanisms remains largely unanswered. The present experiments were undertaken to investigate the possible perturbations of Gom A or other related compounds on different types of membrane ionic currents in electrically excitable cells (i.e., pituitary GH₃ and pancreatic INS-1 cells). The exposure to Gom A led to the differential inhibition of peak and end-pulse components of voltage-gated Na⁺ current (I_Na) in GH₃ cells with effective IC₅₀ of 6.2 and 0.73 μM, respectively. The steady-state inactivation curve of I_Na in the presence of Gom A was shifted towards a more hyperpolarized potential. However, neither changes in the overall current-voltage relationship nor those for the gating charge of the current were demonstrated. The application of neither morin (10 μM) nor hesperidin (10 μM) perturbed the strength of I_Na, while sesamine could suppress it. However, in the continued presence of Gom A, the addition of sesamine failed to suppress I_Na further. Gom A also effectively suppressed the strength of persistent I_Na activated by long ramp voltage command, and further application of tefluthrin effectively attenuated Gom A-mediated inhibition of the current. The presence of Gom A mildly inhibited erg-mediated K⁺ current, while a lack of change in the amplitude of hyperpolarization-activated cation current was observed in its presence. Under cell-attached current recordings, the exposure to Gom A resulted in the decreased firing of spontaneous action currents with a minimal change in AC amplitude. In pancreatic INS-1 cells, the presence of Gom A was also noticed to inhibit peak and end-pulse components of I_Na differentially with the IC₅₀ of 5.9 and 0.84 μM, respectively. Taken together, the emerging results presented herein provide the evidence that Gom A can differentially inhibit peak and sustained I_Na in endocrine cells (e.g., GH₃ and INS-1 cells).

The Specific Effects of OD-1, a Peptide Activator, on Voltage-Gated Sodium Current and Seizure Susceptibility

OD-1, a scorpion toxin, has been previously recognized as an activator of voltage-gated Na⁺ currents. To what extent this agent can alter hippocampal neuronal Na⁺ currents and network excitability and how it can be applied to neuronal hyperexcitability research remains unclear. With the aid of patch-clamp technology, it was revealed that, in mHippoE-14 hippocampal neurons, OD-1 produced a concentration-, time-, and state-dependent rise in the peak amplitude of I_Na. It shifted the I_Na inactivation curve to a less negative potential and increased the frequency of spontaneous action currents. Further characterization of neuronal excitability revealed higher excitability in the hippocampal slices treated with OD-1 as compared with the control slices. A stereotaxic intrahippocampal injection of OD-1 generated a significantly higher frequency of spontaneous seizures and epileptiform discharges compared with intraperitoneal injection of lithium-pilocarpine- or kainic acid-induced epilepsy, with comparable pathological changes. Carbamazepine significantly attenuated OD-1 induced seizures and epileptiform discharges. The OD-1-mediated modifications of I_Na altered the electrical activity of neurons in vivo and OD-1 could potentially serve as a novel seizure and excitotoxicity model.

Telmisartan, an Antagonist of Angiotensin II Receptors, Accentuates Voltage-Gated Na+ Currents and Hippocampal Neuronal Excitability

Telmisartan (TEL), a non-peptide blocker of the angiotensin II type 1 receptor, is a widely used antihypertensive agent. Nevertheless, its neuronal ionic effects and how they potentially affect neuronal network excitability remain largely unclear. With the aid of patch-clamp technology, the effects of TEL on membrane ion currents present in hippocampal neurons (mHippoE-14 cells) were investigated. For additional characterization of the effects of TEL on hippocampal neuronal excitability, we undertook in vivo studies on Sprague Dawley (SD) rats using pilocarpine-induced seizure modeling, a hippocampal histopathological analysis, and inhibitory avoidance testing. In these hippocampal neurons, TEL increased the peak amplitude of I_Na, with a concomitant decline in the current inactivation rate. The TEL concentration dependently enhanced the peak amplitude of depolarization-elicited I_Na and lessened the inactivation rate of I_Na. By comparison, TEL was more efficacious in stimulating the peak I_Na and in prolonging the inactivation time course of this current than tefluthrin or (-)-epicatechin-3-gallate. In the continued presence of pioglitazone, the TEL-perturbed stimulation of I_Na remained effective. In addition, cell exposure to TEL shifted the steady-state inactivation I_Na curve to fewer negative potentials with no perturbations of the slope factor. Unlike chlorotoxin, either ranolazine, eugenol, or KMUP-1 reversed TEL-mediated increases in the strength of non-inactivating I_Na. In the cell-attached voltage-clamp recordings, TEL shortened the latency in the generation of action currents. Meanwhile, TEL increased the peak I_Na, with a concurrent decrease in current inactivation in HEKT293T cells expressing SCN5A. Furthermore, although TEL did not aggravate pilocarpine-induced chronic seizures and tended to preserve cognitive performance, it significantly accentuated hippocampal mossy fiber sprouting. Collectively, TEL stimulation of peak I_Na in combination with an apparent retardation in current inactivation could be an important mechanism through which hippocampal neuronal excitability is increased, and hippocampal network excitability is accentuated following status epilepticus, suggesting further attention to this finding.

Effects of Sesamin, the Major Furofuran Lignan of Sesame Oil, on the Amplitude and Gating of Voltage-Gated Na+ and K+ Currents

Sesamin (SSM) and sesamolin (SesA) are the two major furofuran lignans of sesame oil and they have been previously noticed to exert various biological actions. However, their modulatory actions on different types of ionic currents in electrically excitable cells remain largely unresolved. The present experiments were undertaken to explore the possible perturbations of SSM and SesA on different types of ionic currents, e.g., voltage-gated Na⁺ currents (I_Na), erg-mediated K⁺ currents (I_K(erg)), M-type K⁺ currents (I_K(M)), delayed-rectifier K⁺ currents (I_K(DR)) and hyperpolarization-activated cation currents (I_h) identified from pituitary tumor (GH₃) cells. The exposure to SSM or SesA depressed the transient and late components of I_Na with different potencies. The IC₅₀ value of SSM needed to lessen the peak or sustained I_Na was calculated to be 7.2 or 0.6 μM, while that of SesA was 9.8 or 2.5 μM, respectively. The dissociation constant of SSM-perturbed inhibition on I_Na, based on the first-order reaction scheme, was measured to be 0.93 μM, a value very similar to the IC₅₀ for its depressant action on sustained I_Na. The addition of SSM was also effective at suppressing the amplitude of resurgent I_Na. The addition of SSM could concentration-dependently inhibit the I_K(M) amplitude with an IC₅₀ value of 4.8 μM. SSM at a concentration of 30 μM could suppress the amplitude of I_K(erg), while at 10 μM, it mildly decreased the I_K(DR) amplitude. However, the addition of neither SSM (10 μM) nor SesA (10 μM) altered the amplitude or kinetics of I_h in response to long-lasting hyperpolarization. Additionally, in this study, a modified Markovian model designed for SCN8A-encoded (or Na_V1.6) channels was implemented to evaluate the plausible modifications of SSM on the gating kinetics of Na_V channels. The model demonstrated herein was well suited to predict that the SSM-mediated decrease in peak I_Na, followed by increased current inactivation, which could largely account for its favorable decrease in the probability of the open-blocked over open state of Na_V channels. Collectively, our study provides evidence that highlights the notion that SSM or SesA could block multiple ion currents, such as I_Na and I_K(M), and suggests that these actions are potentially important and may participate in the functional activities of various electrically excitable cells in vivo.

Effectiveness in the Block by Honokiol, a Dimerized Allylphenol from Magnolia Officinalis, of Hyperpolarization-Activated Cation Current and Delayed-Rectifier K+ Current

Background: Honokiol (HNK), a dimer of allylphenol obtained from the bark of Magnolia officinalis was demonstrated to exert an array of biological actions in different excitable cell types. However, whether or how this compound can lead to any perturbations on surface-membrane ionic currents remains largely unknown. Methods: We used the patch clamp method and found that addition of HNK effectively depressed the density of macroscopic hyperpolarization-activated cation currents (I_h) in pituitary GH₃ cells in a concentration-, time- and voltage-dependent manner. By the use of a two-step voltage protocol, the presence of HNK (10 μM) shifted the steady-state activation curve of I_h density along the voltage axis to a more negative potential by approximately 11 mV, together with no noteworthy modification in the gating charge of the current. Results: The voltage-dependent hysteresis of I_h density elicited by long-lasting triangular ramp pulse was attenuated by the presence of HNK. The HNK addition also diminished the magnitude of deactivating I_h density elicited by ramp-up depolarization with varying durations. The effective half-maximal concentration (IC₅₀) value needed to inhibit the density of I_h or delayed rectifier K⁺ current identified in GH₃ cells was estimated to be 2.1 or 6.8 μM, respectively. In cell-attached current recordings, HNK decreased the frequency of spontaneous action currents. In Rolf B1.T olfactory sensory neurons, HNK was also observed to decrease I_h density in a concentration-dependent manner. Conclusions: The present study highlights the evidence revealing that HNK has the propensity to perturb these ionic currents and that the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel is proposed to be a potential target for the in vivo actions of HNK and its structurally similar compounds.

Effectiveness in the inhibition of dapagliflozin and canagliflozin on M-type K+ current and α-methylglucoside-induced current in pituitary tumor (GH3) and pheochromocytoma PC12 cells

Dapagliflozin (DAPA) or canagliflozin (CANA), Na⁺-dependent glucose co-transporter type 2 (SGLT2) inhibitors, were used for treatment of type II diabetes mellitus. Addition of DAPA or CANA suppressed M-type K⁺ current (I_K(M)) in pituitary tumor (GH₃) and pheochromocytoma PC12 cells. The IC₅₀ value for DAPA- or CANA-mediated inhibition of I_K(M) in GH₃ cells was 0.11 or 0.42 μM, respectively. The presence of DAPA (0.1 μM) shifted the steady-state activation of I_K(M) to less depolarized potential without changing the gating charge of the current. During high-frequency depolarizing pulses, I_K(M) magnitude was reduced by DAPA; however, DAPA-induced block of I_K(M) remained effective. The amplitude of neither erg-mediated K⁺ current nor hyperpolarization-activated cation current in GH₃ cells was modified in the presence of 1 μM DAPA. Alternatively, addition of DAPA, CANA, phlorizin or chlorotoxin effectively suppressed α-methylglucoside-(αMG-) induced current (I_αMG) in GH₃ cells, albeit inability of tefluthrin (activator of I_Na) to suppress this current. DAPA shifted the charge-voltage relation of presteady-state I_αMG in a rightward and downward direction with no change in the gating charge of the I_αMG. Under current-clamp recordings, subsequent additions of DAPA, but still in the continued presence of αMG, increased the firing rate of spontaneous action potentials stimulated by αMG. Our results suggested that activity of SGLT was expressed functionally in GH₃ and PC12 cells. Therefore, inhibitory actions of DAPA or CANA on the amplitude and gating of I_K(M) might provide a yet unidentified mechanism through which the SGLT1 or SGLT2 activity were attenuated in unclamped cells occurring in vivo.

Development of a sensitive and accurate method for the simultaneous determination of selected insecticides and herbicide in tap water and wastewater samples using vortex-assisted switchable solvent-based liquid-phase microextraction prior to determination by gas chromatography-mass spectrometry

In this study, a switchable solvent-based liquid-phase microextraction method was developed to preconcentrate selected pesticides from tap water and wastewater matrices for determination by gas chromatography-mass spectrometry. A thorough optimization process was performed for prominent extraction parameters such as switchable solvent amount, concentration/amount of sodium hydroxide, salt type and mixing period. Optimum parameters obtained at the end of the optimization process were applied to aqueous standard solutions to validate the method. The linear dynamic ranges of all four analytes were appreciably wide with coefficient of determination values greater than 0.9997. The limits of detection and quantification (LOD and LOQ) were calculated for the analytes in the ranges of 0.38-2.0 ng/mL and 1.3-6.5 ng/mL, respectively. Spiked recovery experiments were used to validate the accuracy of the developed method and to determine the performance of the method in different sample matrices. Tap water, municipal wastewater and medical wastewater were spiked at three different concentrations and analyzed under the method's optimum conditions. The percent recovery results calculated for the samples were in the range of 79-107%, and this validated the method's accuracy and applicability to complex matrices such as municipal and medical wastewater samples.

Effects and mechanisms of pyrethroids on male reproductive system

Synthetic pyrethroids are used as insecticides in agriculture and a variety of household applications worldwide. Pyrethroids are widely distributed in all environmental compartments and the general populations are exposed to pyrethroids through various routes. Pyrethroids have been identified as endocrine-disrupting chemicals (EDCs) which are responsible for the male reproductive impairments. The data confirm pyrethroids cause male reproductive damages. The insecticides exert the toxic effects on male reproductive system through various complex mechanisms including antagonizing androgen receptor (AR), inhibiting steroid synthesis, affecting the hypothalamic-pituitary-gonadal (HPG) axis, acting as estrogen receptor (ER) modulators and inducing oxidative stress. The mechanisms of male reproductive toxicity of pyrethroids involve multiple targets and pathways. The review will provide further insight into pyrethroid-induced male reproductive toxicity and mechanisms, which is crucial to preserve male reproductive health.

Efficient Cardiac Differentiation of Human Amniotic Fluid-Derived Stem Cells into Induced Pluripotent Stem Cells and Their Potential Immune Privilege

Mature mammalian hearts possess very limited regenerative potential. The irreversible cardiomyocyte loss after heart injury can lead to heart failure and death. Pluripotent stem cells (PSCs) can differentiate into cardiomyocytes for cardiac repair, but there are obstacles to their clinical application. Among these obstacles is their potential for post-transplant rejection. Although human amniotic fluid-derived stem cells (hAFSCs) are immune privileged, they cannot induce cardiac differentiation. Thus, we generated hAFSC-derived induced PSCs (hAFSC-iPSCs) and used a Wnt-modulating differentiation protocol for the cardiac differentiation of hAFSC-iPSCs. In vitro studies using flow cytometry, immunofluorescence staining, and patch-clamp electrophysiological study, were performed to identify the characteristics of hAFSC-iPSC-derived cardiomyocytes (hAFSC-iPSC-CMs). We injected hAFSC-iPSC-CMs intramuscularly into rat infarcted hearts to evaluate the therapeutic potential of hAFSC-iPSC-CM transplantation. At day 21 of differentiation, the hAFSC-iPSC-CMs expressed cardiac-specific marker (cardiac troponin T), presented cardiomyocyte-specific electrophysiological properties, and contracted spontaneously. Importantly, these hAFSC-iPSC-CMs demonstrated low major histocompatibility complex (MHC) class I antigen expression and the absence of MHC class II antigens, indicating their low immunogenicity. The intramyocardial transplantation of hAFSC-iPSC-CMs restored cardiac function, partially remuscularized the injured region, and reduced fibrosis in the rat infarcted hearts. Therefore, hAFSC-iPSCs are potential candidates for the repair of infarcted myocardium.

Characterization of Convergent Suppression by UCL-2077 (3-(Triphenylmethylaminomethyl)pyridine), Known to Inhibit Slow Afterhyperpolarization, of erg-Mediated Potassium Currents and Intermediate-Conductance Calcium-Activated Potassium Channels

UCL-2077 (triphenylmethylaminomethyl)pyridine) was previously reported to suppress slow afterhyperpolarization in neurons. However, the information with respect to the effects of UCL-2077 on ionic currents is quite scarce. The addition of UCL-2077 decreased the amplitude of erg-mediated K⁺ current (I_K(erg)) together with an increased deactivation rate of the current in pituitary GH₃ cells. The IC₅₀ and K_D values of UCL-2077-induced inhibition of I_K(erg) were 4.7 and 5.1 μM, respectively. UCL-2077 (10 μM) distinctly shifted the midpoint in the activation curve of I_K(erg) to less hyperpolarizing potentials by 17 mV. Its presence decreased the degree of voltage hysteresis for I_K(erg) elicitation by long-lasting triangular ramp pulse. It also diminished the probability of the opening of intermediate-conductance Ca²⁺-activated K⁺ channels. In cell-attached current recordings, UCL-2077 raised the frequency of action currents. When KCNH2 mRNA was knocked down, a UCL-2077-mediated increase in AC firing was attenuated. Collectively, the actions elaborated herein conceivably contribute to the perturbating effects of this compound on electrical behaviors of excitable cells.

The Novel Direct Modulatory Effects of Perampanel, an Antagonist of AMPA Receptors, on Voltage-Gated Sodium and M-type Potassium Currents

Perampanel (PER) is a selective blocker of AMPA receptors showing efficacy in treating various epileptic disorders including brain tumor-related epilepsy and also potential in treating motor neuron disease. However, besides its inhibition of AMPA-induced currents, whether PER has any other direct ionic effects in different types of neurons remains largely unknown. We investigated the effects of PER and related compounds on ionic currents in different types of cells, including hippocampal mHippoE-14 neurons, motor neuron-like NSC-34 cells and U87 glioma cells. We found that PER differentially and effectively suppressed the amplitude of voltage-gated Na⁺ currents (I_Na) in mHippoE-14 cells. The IC₅₀ values required to inhibit peak and late I_Na were 4.12 and 0.78 μM, respectively. PER attenuated tefluthrin-induced increases in both amplitude and deactivating time constant of I_Na. Importantly, PER also inhibited the amplitude of M-type K⁺ currents (I_K(M)) with an IC₅₀ value of 0.92 μM. The suppression of I_K(M) was attenuated by the addition of flupirtine or ZnCl₂ but not by L-quisqualic acid or sorafenib. Meanwhile, in cell-attached configuration, PER (3 μM) decreased the activity of M-type K⁺ channels with no change in single-channel conductance but shifting the activation curve along the voltage axis in a rightward direction. Supportively, PER suppressed I_K(M) in NSC-34 cells and I_Na in U87 glioma cells. The inhibitory effects of PER on both I_Na and I_K(M), independent of its antagonistic effect on AMPA receptors, may be responsible for its wide-spectrum of effects observed in neurological clinical practice.

Effects of pyrethroid insecticides on hypothalamic-pituitary-gonadal axis: A reproductive health perspective

Pyrethroids, a class of ubiquitous insecticides, have been recognized as endocrine-disrupting chemicals (EDCs). A lot of studies have implied the endocrine-disrupting effects of pyrethroids on the hypothalamic-pituitary-gonadal (HPG) axis. However, there are few review articles regarding the effects of pyrethroids on the HPG axis of mammal and human, especially new research progress made in this area. The present review sums up the effects of pyrethroids on the HPG axis-related reproductive outcomes, including epidemiological investigations based on human biomonitoring, animal studies and in vitro tests. Mechanisms have described that the endocrine-disrupting effects of pyrethroids on mammal can be mediated via the interaction with steroid receptors, the direct action on ion channels and signaling molecules. Finally, we summarize the current research gaps and suggest future directions in this topic.

The biochemical and electrophysiological profiles of amniotic fluid-derived stem cells following Wnt signaling modulation cardiac differentiation

Owing to the beneficial properties of amniotic fluid-derived stem cells (AFSCs), including pluripotency and the lack of ethical issues associated with embryonic stem cells (ESCs), they should be a promising cell source for regenerative medicine. However, how to differentiate AFSCs into contracting cardiomyocytes has not been established. In this study, a well-established, direct cardiac differentiation protocol involving the modulation of Wnt signaling was used to differentiate Oct 3/4⁺ AFSCs into cardiomyocytes. By day 14 of cardiomyocyte differentiation, these AFSCs expressed cardiac-specific genes (i.e., cardiac troponin T and myosin light chain 2v) and proteins but could not spontaneously contract. Using the patch-clamp technique, we further characterized the electrophysiological properties of human ESC-derived cardiomyocytes (hESC-CMs) and differentiated AFSCs. We used different configurations to investigate membrane potentials and ion currents in differentiated AFSCs and hESC-CMs. Under cell-attached voltage- or whole-cell current-clamp modes, we recorded spontaneous action currents (ACs) or action potentials (APs) in hESC-CMs but not in differentiated AFSCs. Compared to hESC-CMs, differentiated AFSCs showed significantly diminished activity of both BK_Ca and IK_Ca channels, which might lead to a lack of spontaneous ACs and APs in differentiated AFSCs. These results indicated that this well-established Wnt signaling modulating cardiac differentiation protocol was insufficient to induce the differentiation of functional cardiomyocytes from Oct 3/4⁺ AFSCs. Therefore, AFSC may not be an ideal candidate for cardiomyocyte differentiation.

Activation of voltage-gated sodium current and inhibition of erg-mediated potassium current caused by telmisartan, an antagonist of angiotensin II type-1 receptor, in HL-1 atrial cardiomyocytes

Telmisartan (TEL) is a non-peptide blocker of angiotensin II type-1 (AT₁ ) receptor. However, the mechanisms through which this drug interacts directly with ion currents in hearts remain largely unclear. Herein, we aim to investigate the effects of TEL the on ionic currents and membrane potential of murine HL-1 cardiomyocytes. In whole-cell recordings, addition of TEL stimulated the peak and late components of voltage-gated Na⁺ currents (I_Na ) with different potencies. The EC₅₀ values required to achieve the stimulatory effect of this drug on peak and late I_Na were 0.2 and 1.2 μmol/L, respectively, and the current-voltage relationship of peak I_Na shifted toward less-depolarized potentials during exposure to TEL. Telmisartan not only increased peak I_Na but also prolonged the inactivation time course of late I_Na . Amiodarone (Amio) or ranolazine (Ran), but not angiotensin II, could reverse TEL-mediated effects. The drug enhanced the recovery rate of I_Na inactivation and exerted an inhibitory effect on erg-mediated K⁺ and L-type Ca²⁺ currents. In whole-cell current-clamp recordings, addition of the drug resulted in prolongation of the duration of action potentials (APs) in a dose-dependent manner in HL-1 cells; Amio or Ran could reverse this increase in AP durations. Telmisartan-mediated prolongation of AP was attenuated in KCNH2 siRNA-transfected HL-1 cells. In cultured smooth muscle cells of the human coronary artery, TEL enhanced I_Na amplitudes and slowed current inactivation. Stimulation by TEL of I_Na in HL-1 cells did not simply increase current magnitude but altered current kinetics, thereby suggesting state-dependent activation. Telmisartan may have greater affinity to the open/inactivated state than to the resting state residing in Na_V channels. Collectively, TEL-mediated stimulation of I_Na and inhibition of I_K(erg) could be an important ionic mechanism underlying the increased cell excitability of HL-1 cells; these actions, however, cannot be entirely explained by its blockade of AT₁ receptor.

Differential regulation of tefluthrin and telmisartan on the gating charges of INa activation and inactivation as well as on resurgent and persistent INa in a pituitary cell line (GH3)

Voltage-gated Na⁺ currents (I_Na), known to contain many components (e.g., transient, resurgent and persistent I_Na) with unique gating properties, are involved in the generation and propagation of action potentials in excitable cells. In this study, how tefluthrin (Tef), a synthetic pyrethoid, and telmisartan (TEL), blocker of angiotensin II receptors can perturb those components of I_Na was investigated. The presence of either Tef or TEL increased the values of the gating charges of I_Na involved in the activation (z_a) and inactivation (z_i). Tef also increased the amplitude of resurgent I_Na (I_Na(R)) or persistent I_Na (I_Na(P)) in a pituitary cell line (GH₃), while TEL produced minimal effects on them. Subsequent addition of either ranolazine (a blocker of late I_Na) or d-limonene (a monoterpene), could reverse the changes by TEL or Tef on z_a or z_i. In SCN5A-expressing HEK293T cells, addition of Tef or TEL also increased the peak amplitude and the inactivation time constant of I_Na which was accompanied by the increased z_a value of I_Na. Taken together, the results indicated that Tef- or TEL-mediated changes in the gating kinetics of I_Na are linked to their actions on functional activity of neurons, neuroendocrine or endocrine cells.

Sodium Metabisulfite: Effects on Ionic Currents and Excitotoxicity

How sodium metabisulfite (SMB; Na₂S₂O₅), a popular food preservative and antioxidant, interacts with excitable membrane and induces excitotoxicity is incompletely understood. In this study, the patch-clamp technique was used to investigate and record the electrophysiological effect of SMB on electrically excitable HL-1 cardiomyocytes and NSC-34 neurons, as well as its relationship to pilocarpine-induced seizures and neuronal excitotoxicity in rats. We used Western blotting, to analyze sodium channel expression on hippocampi after chronic SMB treatment. It was found that voltage-gated Na⁺ current (I _Na) was stimulated, and current inactivation and deactivation were slowed in SMB-treated (30 μM) HL-1 cardiomyocytes. SMB-induced increases of I _Na were attenuated in cells treated with ranolazine (10 μM) or eugenol (30 μM). The current-voltage relationship of I _Na shifted to slightly more negative potentials in SMB-treated cells, the peak I _Na with an EC₅₀ value of 18 μM increased, and the steady-state inactivation curve of I _Na shifted to a more positive potential. However, the tail component of the rapidly activating delayed-rectifier K⁺ current (I _Kr) was dose-dependently inhibited. Cell-attached voltage-clamp recordings in SMB-treated cells showed that the frequency of action currents and prolonged action potential were higher. In SMB-treated NSC-34 neurons, the peak I _Na was higher; however, neither the time to peak nor the inactivation time constant (I _Na) changed. Pilocarpine-induced seizures were exacerbated, and acute neuronal damage and chronic mossy fiber sprouting increased in SMB-treated rats. Western blotting showed higher expression of the sodium channel in cells after chronic SMB treatment. We conclude that SMB contributes to the sodium channel-activating mechanism through which it alters cellular excitability and excitotoxicity in wide-spectrum excitable cells.

Cap n collar transcription factor regulates multiple genes coding for proteins involved in insecticide detoxification in the red flour beetle, Tribolium castaneum

In invertebrates, a heterodimer of xenobiotic transcription factors, cap n collar C isoform (CncC) and muscle aponeurosis fibromatosis (Maf) mediate cellular defense. In insects, these proteins regulate expression of genes involved in insecticide detoxification. In the current study, we performed sequencing of cDNA copied from RNA isolated from Tribolium castaneum pyrethroid resistant strain (QTC279) beetles injected with CncC or green fluorescence protein (GFP, control) dsRNA. Differential expression analysis of sequences identified 662 genes that showed a decrease and 91 genes that showed an increase in expression (p value ≤ 0.01 and log2 fold change of ≥ 1.5) in CncC knockdown insects when compared to their expression in control insects. We selected a subset of 27 downregulated genes and verified their differential expression using qRT-PCR. This subset of 27 genes included 21 genes with a predicted function in xenobiotic detoxification. RNAi and insecticide bioassays were employed to study the function of six of these genes coding for CYP4G7, CYP4G14, GST-1 and four ABC transporters, ABCA-UB, ABCA-A1 and ABCA-A1L and ABCA-9B involved in all three phases of insecticide detoxification. These data suggest that CncC regulates genes coding for proteins involved in detoxification of insecticides.

Association of pyrethroids exposure with onset of puberty in Chinese girls

Pyrethroids, a class of ubiquitous insecticides, have been considered as endocrine-disrupting chemicals (EDCs). Female animal studies suggested that early-life pyrethroids exposure might delay puberty onset. However, it remains unclear whether this association applies to human populations. A total of 305 girls at the ages of 9-15 years old were recruited in Hangzhou, China in this study. The concentration of the common metabolite of pyrethroids, 3-phenoxybenzoic acid (3-PBA), was analyzed in urine samples to reflect the exposure level of pyrethroids. The associations of 3-PBA with pubertal stages were evaluated using a multinomial logistic regression model. The geometric mean level of 3-PBA was 1.11 μg/L (1.42 μg/g for creatinine-adjusted concentration). There was a significant 45% reduction in odds of being in breast stage 3 (B3) per one-unit increase in the log-transformed 3-PBA levels [OR = 0.55 (95%CI: 0.31-0.98), p = 0.042]. A similar negative association was found between urinary 3-PBA levels with later onset by pubic hair stage 2 (P2) [OR = 0.56 (95%CI: 0.36-0.90), p = 0.015]. Similar negative association was also observed between urinary 3-PBA levels and pubertal onset indicated by menarche [OR = 0.51 (95%CI: 0.28-0.93), p = 0.029]. For the first time to our knowledge, this work reveals that pyrethroids exposure may increase the risk of delayed pubertal onset in girls.

Functional reconstitution of rat Nav1.6 sodium channels in vitro for studies of pyrethroid action

The ability to reconstitute sodium channel function and pharmacology in vitro using cloned subunits of known structure has greatly enhanced our understanding of the action of pyrethroid insecticides at this target and the structural determinants of resistance and interspecies selectivity. However, the use of reconstituted channels raises three critical questions: (1) Which subunits and subunit combinations should be used? (2) Which heterologous expression system is preferred? (3) Which combination of subunits and expression system best represents the function of native neuronal channels in the organism of interest? This review considers these questions from the perspective of recent research in this laboratory on the action of pyrethroid insecticides on rat Nav1.6 sodium channels by comparing the effects of heteroligomeric complex composition on channel function and insecticide response when channels are expressed in either Xenopus oocytes or stably-transformed HEK293 cells. These comparisons provide new insight into the influence of cellular context on the functional and pharmacological properties of expressed channels, the modulatory effects of sodium channel auxiliary subunits on the action of pyrethroids, and the relative fidelity of the Xenopus oocyte and HEK293 cell expression systems as model systems for studying of channel function and pyrethroid action.

Effects of the β1 auxiliary subunit on modification of Rat Na(v)1.6 sodium channels expressed in HEK293 cells by the pyrethroid insecticides tefluthrin and deltamethrin

We expressed rat Nav1.6 sodium channels with or without the rat β1 subunit in human embryonic kidney (HEK293) cells and evaluated the effects of the pyrethroid insecticides tefluthrin and deltamethrin on whole-cell sodium currents. In assays with the Nav1.6 α subunit alone, both pyrethroids prolonged channel inactivation and deactivation and shifted the voltage dependence of channel activation and steady-state inactivation toward hyperpolarization. Maximal shifts in activation were ~18 mV for tefluthrin and ~24 mV for deltamethrin. These compounds also caused hyperpolarizing shifts of ~10-14 mV in the voltage dependence of steady-state inactivation and increased in the fraction of sodium current that was resistant to inactivation. The effects of pyrethroids on the voltage-dependent gating greatly increased the size of sodium window currents compared to unmodified channels; modified channels exhibited increased probability of spontaneous opening at membrane potentials more negative than the normal threshold for channel activation and incomplete channel inactivation. Coexpression of Nav1.6 with the β1 subunit had no effect on the kinetic behavior of pyrethroid-modified channels but had divergent effects on the voltage-dependent gating of tefluthrin- or deltamethrin-modified channels, increasing the size of tefluthrin-induced window currents but decreasing the size of corresponding deltamethrin-induced currents. Unexpectedly, the β1 subunit did not confer sensitivity to use-dependent channel modification by either tefluthrin or deltamethrin. We conclude from these results that functional reconstitution of channels in vitro requires careful attention to the subunit composition of channel complexes to ensure that channels in vitro are faithful functional and pharmacological models of channels in neurons.

Actions of KMUP-1, a xanthine and piperazine derivative, on voltage-gated Na(+) and Ca(2+) -activated K(+) currents in GH3 pituitary tumour cells

BACKGROUND AND PURPOSE

7-[2-[4-(2-Chlorophenyl)piperazinyl]ethyl]-1,3-dimethylxanthine (KMUP-1) is a xanthine-based derivative. It has soluble GC activation and K(+) -channel opening activity. Effects of this compound on ion currents in pituitary GH3 cells were investigated in this study.

EXPERIMENTAL APPROACH

The aim of this study was to evaluate effects of KMUP-1 on the amplitude and gating of voltage-gated Na(+) current (INa ) in pituitary GH3 cells and in HEKT293T cells expressing SCN5A. Both the amplitude of Ca(2+) -activated K(+) current and the activity of large-conductance Ca(2+) -activated K(+) (BKCa ) channels were also studied.

KEY RESULTS

KMUP-1 depressed the transient and late components of INa with different potencies. The IC50 values required for its inhibitory effect on transient and late INa were 22.5 and 1.8 μM respectively. KMUP-1 (3 μM) shifted the steady-state inactivation of INa to a hyperpolarized potential by -10 mV, despite inability to alter the recovery of INa from inactivation. In cell-attached configuration, KMUP-1 applied to bath increased BKCa -channel activity; however, in inside-out patches, this compound applied to the intracellular surface had no effect on it. It prolonged the latency in the generation of action currents elicited by triangular voltage ramps. Additionally, KMUP-1 decreased the peak INa with a concomitant increase of current inactivation in HEKT293T cells expressing SCN5A.

CONCLUSIONS AND IMPLICATIONS

Apart from activating BKCa channels, KMUP-1 preferentially suppresses late INa . The effects of KUMP-1 on ion currents presented here constitute an underlying ionic mechanism of its actions.

Ability of naringenin, a bioflavonoid, to activate M-type potassium current in motor neuron-like cells and to increase BKCa-channel activity in HEK293T cells transfected with α-hSlo subunit

Background

Naringenin (NGEN) is a citrus bioflavonoid known to have beneficial health properties; however, the ionic mechanism of its actions remains largely unclear. In this study, we attempted to evaluate the possible effects of NGEN on K⁺ currents in NSC-34 neuronal cells and in HEK293T cells expressing α-hSlo.

Results

NGEN increased M-type K⁺ current (I_K(M)) in a concentration-dependent manner with an EC₅₀ value of 9.8 μM in NSC-34 cells. NGEN shifted the activation curve of I_K(M) conductance to the more negative potentials. In cell-attached recordings, NGEN or flupirtine enhanced the activity of M-type K⁺ (K_M) channels with no changes in single-channel amplitude. NGEN (10 μM) had minimal effect on erg-mediated K⁺ currents. Under cell-attached voltage-clamp recordings, NGEN decreased the frequency of spontaneous action currents and further application of linopirdine can reverse NGEN-induced inhibition of firing. In HEK293T cells expressing α-hSlo, this compound increased the amplitude of Ca²⁺-activated K⁺ current (I_K(Ca)). Under inside-out recordings, NGEN applied to the intracellular side of the detached patch enhanced the activity of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels. Moreover, from the study of a modeled neuron, burst firing of simulated action potentials (APs) was reduced in the presence of the increased conductances of both K_M and K_Ca channels. Fast-slow analysis of AP bursting from this model also revealed that as the conductances of both K_M and BK_Ca channels were increased by two-fold, the voltage nullcline was shifted in an upward direction accompanied by the compression of burst trajectory.

Conclusions

The present results demonstrate that activation of both K_M and BK_Ca channels caused by NGEN might combine to influence neuronal activity if similar channels were functionally co-expressed in central neurons in vivo.

Early life permethrin exposure induces long-term brain changes in Nurr1, NF-kB and Nrf-2

Pesticide exposure during brain development represents an important risk factor for the onset of brain-aging processes. Here, the impact of permethrin administered to rats from 6th to 21st day of life, at a dose near to "no observed adverse effect level" (NOAEL), was studied when animals reached 500 day-old. The permethrin treatment induced a decrease in Nurr1 gene expression in striatum, an increase in hippocampus and cerebellum, while the protein level changed only in striatum where it was increased. NF-kB p65 gene expression was increased in cerebellum, while its protein level augmented in cerebellum and in prefrontal cortex and decreased in hippocampus of treated rats compared to control ones. Nrf-2 gene expression resulted significantly higher only in cerebellum of treated animals. The results suggest that early life permethrin treatment induces long-lasting effects leading to dopaminergic neuronal disorders, monitored by Nurr1 alteration. Moreover the impairment of NF-kB and Nrf-2, important for the balance between pro- and anti-inflammatory systems, confirms that the neonatal permethrin treatment can influence genes involved with the onset of brain-ageing processes.

Electrophysiological characterization of sodium-activated potassium channels in NG108-15 and NSC-34 motor neuron-like cells

AIMS

The electrical properties of Na(+) -activated K(+) current (I(K(Na)) ) and its contribution to spike firing has not been characterized in motor neurons.

METHODS

We evaluated how activation of voltage-gated K(+) current (I(K) ) at the cellular level could be coupled to Na(+) influx through voltage-gated Na(+) current (I(N) (a) ) in two motor neuron-like cells (NG108-15 and NSC-34 cells).

RESULTS

Increasing stimulation frequency altered the amplitudes of both I(Na) and I(K) simultaneously. With changes in stimulation frequency, the kinetics of both I(Na) inactivation and I(K) activation were well correlated at the same cell. Addition of tetrodotoxin or ranolazine reduced the amplitudes of both I(Na) and I(K) simultaneously. Tefluthrin (Tef) increased the amplitudes of both I(Na) and I(K) throughout the voltages ranging from -30 to + 10 mV. In cell-attached recordings, single-channel conductance from a linear current-voltage relation was 94 ± 3 pS (n = 7). Tef (10 μm) enhanced channel activity with no change in single-channel conductance. Tef increased spike firing accompanied by enhanced facilitation of spike-frequency adaptation. Riluzole (10 μm) reversed Tef-stimulated activity of K(Na) channels. In motor neuron-like NSC-34 cells, increasing stimulation frequency altered the kinetics of both I(Na) and I(K) . Modelling studies of motor neurons were simulated to demonstrate that the magnitude of I(K(Na)) modulates AP firing.

CONCLUSIONS

There is a direct association of Na(+) and K(Na) channels which can provide the rapid activation of K(Na) channels required to regulate AP firing occurring in motor neurons.

The inhibition by di(2-ethylhexyl)-phthalate of erg-mediated K⁺ current in pituitary tumor (GH₃) cells

DEHP (bis(2-ethylhexyl)-phthalate) known to be an endocrine-disrupting chemical is a widely used phthalate. Little information regarding the effects of phthalate esters on ion currents is available. In this study, the effects of DEHP and other phthalate esters (DBEP: di(2-butoxyethyl)-phthalate and DMGP: di(2-methylglycol)-phthalate) on ion currents were investigated in pituitary GH₃ cells. Hyperpolarization-elicited K⁺ currents in GH3 cells bathed in high-K⁺, Ca²⁺-free solution were examined to evaluate the effects of DEHP, DBEP, and DMGP on the ether-a`-go-go-related-gene (erg) K⁺ current (IK(erg)). Addition of DEHP to GH₃ cells suppressed the amplitude of IK(erg) in a concentration-dependent manner with an IC₅₀ value of 16.3 μM. With a two-pulse protocol, addition of DEHP shifted the activation curve of IK(erg) to a depolarized potential by approximately 10 mV with no change in the rate of IK(erg) deactivation. This compound did not have any effects on delayed rectifier K⁺ current in GH₃ cells, while 4-aminopyridine-3-methanol (100 μM) suppressed this current significantly. DBEP (30 μM) had little or no effect on IK(erg), while DMGP (30 μM) slightly reduced it. In inside-out configuration, DEHP (30 μM) applied to the bath slightly reduced the activity of large-conductance Ca²⁺-activated K⁺ channels. DEHP (30 μM) increased the frequency of spontaneous action potentials (APs); however, this compound at the same concentration had no effect on AP firing in KCNH2 siRNA-transfected GH₃ cells. The effects described herein can contribute to their actions on functional activity of endocrine or neuroendocrine cells if similar results are found in vivo.