Inhibition of Nav1.7 channel by a novel blocker QLS-81 for alleviation of neuropathic pain.

Voltage-gated sodium channel Nav1.7 robustly expressed in peripheral nociceptive neurons has been considered as a therapeutic target for chronic pain, but there is no selective Nav1.7 inhibitor available for therapy of chronic pain. Ralfinamide has shown anti-nociceptive activity in animal models of inflammatory and neuropathic pain and is currently under phase III clinical trial for neuropathic pain. Based on ralfinamide, a novel small molecule (S)-2-((3-(4-((2-fluorobenzyl) oxy) phenyl) propyl) amino) propanamide (QLS-81) was synthesized. Here, we report the electrophysiological and pharmacodynamic characterization of QLS-81 as a Nav1.7 channel inhibitor with promising anti-nociceptive activity. In whole-cell recordings of HEK293 cells stably expressing Nav1.7, QLS-81 (IC50 at 3.5 ± 1.5 µM) was ten-fold more potent than its parent compound ralfinamide (37.1 ± 2.9 µM) in inhibiting Nav1.7 current. QLS-81 inhibition on Nav1.7 current was use-dependent. Application of QLS-81 (10 µM) caused a hyperpolarizing shift of the fast and slow inactivation of Nav1.7 channel about 7.9 mV and 26.6 mV, respectively, and also slowed down the channel fast and slow inactivation recovery. In dissociated mouse DRG neurons, QLS-81 (10 µM) inhibited native Nav current and suppressed depolarizing current pulse-elicited neuronal firing. Administration of QLS-81 (2, 5, 10 mg· kg-1· d-1, i.p.) in mice for 10 days dose-dependently alleviated spinal nerve injury-induced neuropathic pain and formalin-induced inflammatory pain. In addition, QLS-81 (10 µM) did not significantly affect ECG in guinea pig heart ex vivo; and administration of QLS-81 (10, 20 mg/kg, i.p.) in mice had no significant effect on spontaneous locomotor activity. Taken together, our results demonstrate that QLS-81, as a novel Nav1.7 inhibitor, is efficacious on chronic pain in mice, and it may hold developmental potential for pain therapy.

A bivalent antihypertensive vaccine targeting L-type calcium channels and angiotensin AT1 receptors.

BACKGROUND AND PURPOSE: Hypertension has been the leading preventable cause of premature death worldwide. The aim of this study was to design a more efficient vaccine against novel targets for the treatment of hypertension. EXPERIMENTAL APPROACH: The epitope CE12, derived from the human L-type calcium channel (CaV 1.2), was designed and conjugated with Qß bacteriophage virus-like particles to test the efficacy in hypertensive animals. Further, the hepatitis B core antigen (HBcAg)-CE12-CQ10 vaccine, a bivalent vaccine based on HBcAg virus-like particles and targeting both human angiotensin AT1 receptors and CaV 1.2 channels, was developed and evaluated in hypertensive rodents. KEY RESULTS: The Qß-CE12 vaccine effectively decreased the BP in hypertensive rodents. A monoclonal antibody against CE12 specifically bound to L-type calcium channels and inhibited channel activity. Injection with monoclonal antibody against CE12 effectively reduced the BP in angiotensin II-induced hypertensive mice. The HBcAg-CE12-CQ10 vaccine showed antihypertensive effects in hypertensive mice and relatively superior antihypertensive effects in spontaneously hypertensive rats and ameliorated L-NAME-induced renal injury. In addition, no obvious immune-mediated damage or electrophysiological adverse effects were detected. CONCLUSION AND IMPLICATIONS: Immunotherapy against both AT1 receptors and CaV 1.2 channels decreased the BP in hypertensive rodents effectively and provided protection against hypertensive target organ damage without obvious feedback activation of renin-angiotensin system or induction of dominant antibodies against the carrier protein. Thus, the HBcAg-CE12-CQ10 vaccine may provide a novel and promising therapeutic approach for hypertension.

Electrophysiological characterization of a small molecule activator on human ether-a-go-go-related gene (hERG) potassium channel.

The human ether-a-go-go-related gene (hERG) encodes the K+ channel that carries the rapid component of the delayed rectifier current in the human heart. Reduction of hERG activity induced by gene mutations or pharmacological inhibition is responsible for the type 2 form of long QT syndrome in patients which can develop into ventricular arrhythmia and sudden cardiac death. Therefore, pharmacological activation of hERG may lead to therapeutic potential for cardiac arrhythmias. In this study we characterized a small and novel compound, N-(2-(tert-butyl)phenyl)-6-(4-chlorophenyl)-4-(trifluoromethyl) nicotinamide, HW-0168, that exhibits potent activation of hERG channel with an EC50 of 0.41 ± 0.2 µM. Using whole-cell patch clamp recording of HEK293 cells stably expressed hERG channels, we found that HW-0168 dramatically increased current amplitude about 2.5 folds and slowed down current inactivation about 4 folds. HW-0168 shifted the voltage-dependent channel activation to hyperpolarizing direction about 3.7 mV and the voltage-dependent channel inactivation to depolarizing direction about 9.4 mV. In addition, recording of guinea-pig ventricular cells confirmed that HW-0168 shortened the action potential duration. In conclusion, we identified a novel hERG channel activator HW-0168 that can be used for studying the physiological role of hERG in cardiac myocytes and may be beneficial for treating long QT syndrome.

Discovery of Tarantula Venom-Derived NaV1.7-Inhibitory JzTx-V Peptide 5-Br-Trp24 Analogue AM-6120 with Systemic Block of Histamine-Induced Pruritis.

Inhibitors of the voltage-gated sodium channel NaV1.7 are being investigated as pain therapeutics due to compelling human genetics. We previously identified NaV1.7-inhibitory peptides GpTx-1 and JzTx-V from tarantula venom screens. Potency and selectivity were modulated through attribute-based positional scans of native residues via chemical synthesis. Herein, we report JzTx-V lead optimization to identify a pharmacodynamically active peptide variant. Molecular docking of peptide ensembles from NMR into a homology model-derived NaV1.7 structure supported prioritization of key residues clustered on a hydrophobic face of the disulfide-rich folded peptide for derivatization. Replacing Trp24 with 5-Br-Trp24 identified lead peptides with activity in electrophysiology assays in engineered and neuronal cells. 5-Br-Trp24 containing peptide AM-6120 was characterized in X-ray crystallography and pharmacokinetic studies and blocked histamine-induced pruritis in mice after subcutaneous administration, demonstrating systemic NaV1.7-dependent pharmacodynamics. Our data suggests a need for high target coverage based on plasma exposure for impacting in vivo end points with selectivity-optimized peptidic NaV1.7 inhibitors.

Pharmacological characterization of potent and selective NaV1.7 inhibitors engineered from Chilobrachys jingzhao tarantula venom peptide JzTx-V.

Identification of voltage-gated sodium channel NaV1.7 inhibitors for chronic pain therapeutic development is an area of vigorous pursuit. In an effort to identify more potent leads compared to our previously reported GpTx-1 peptide series, electrophysiology screening of fractionated tarantula venom discovered the NaV1.7 inhibitory peptide JzTx-V from the Chinese earth tiger tarantula Chilobrachys jingzhao. The parent peptide displayed nominal selectivity over the skeletal muscle NaV1.4 channel. Attribute-based positional scan analoging identified a key Ile28Glu mutation that improved NaV1.4 selectivity over 100-fold, and further optimization yielded the potent and selective peptide leads AM-8145 and AM-0422. NMR analyses revealed that the Ile28Glu substitution changed peptide conformation, pointing to a structural rationale for the selectivity gains. AM-8145 and AM-0422 as well as GpTx-1 and HwTx-IV competed for ProTx-II binding in HEK293 cells expressing human NaV1.7, suggesting that these NaV1.7 inhibitory peptides interact with a similar binding site. AM-8145 potently blocked native tetrodotoxin-sensitive (TTX-S) channels in mouse dorsal root ganglia (DRG) neurons, exhibited 30- to 120-fold selectivity over other human TTX-S channels and exhibited over 1,000-fold selectivity over other human tetrodotoxin-resistant (TTX-R) channels. Leveraging NaV1.7-NaV1.5 chimeras containing various voltage-sensor and pore regions, AM-8145 mapped to the second voltage-sensor domain of NaV1.7. AM-0422, but not the inactive peptide analog AM-8374, dose-dependently blocked capsaicin-induced DRG neuron action potential firing using a multi-electrode array readout and mechanically-induced C-fiber spiking in a saphenous skin-nerve preparation. Collectively, AM-8145 and AM-0422 represent potent, new engineered NaV1.7 inhibitory peptides derived from the JzTx-V scaffold with improved NaV selectivity and biological activity in blocking action potential firing in both DRG neurons and C-fibers.

Single Residue Substitutions That Confer Voltage-Gated Sodium Ion Channel Subtype Selectivity in the NaV1.7 Inhibitory Peptide GpTx-1.

There is interest in the identification and optimization of new molecular entities selectively targeting ion channels of therapeutic relevance. Peptide toxins represent a rich source of pharmacology for ion channels, and we recently reported GpTx-1 analogs that inhibit NaV1.7, a voltage-gated sodium ion channel that is a compelling target for improved treatment of pain. Here we utilize multi-attribute positional scan (MAPS) analoging, combining high-throughput synthesis and electrophysiology, to interrogate the interaction of GpTx-1 with NaV1.7 and related NaV subtypes. After one round of MAPS analoging, we found novel substitutions at multiple residue positions not previously identified, specifically glutamic acid at positions 10 or 11 or lysine at position 18, that produce peptides with single digit nanomolar potency on NaV1.7 and 500-fold selectivity against off-target sodium channels. Docking studies with a NaV1.7 homology model and peptide NMR structure generated a model consistent with the key potency and selectivity modifications mapped in this work.

Sustained inhibition of the NaV1.7 sodium channel by engineered dimers of the domain II binding peptide GpTx-1.

Many efforts are underway to develop selective inhibitors of the voltage-gated sodium channel NaV1.7 as new analgesics. Thus far, however, in vitro selectivity has proved difficult for small molecules, and peptides generally lack appropriate pharmacokinetic properties. We previously identified the NaV1.7 inhibitory peptide GpTx-1 from tarantula venom and optimized its potency and selectivity via structure-guided analoging. To further understand GpTx-1 binding to NaV1.7, we have mapped the binding site to transmembrane segments 1-4 of the second pseudosubunit internal repeat (commonly referred to as Site 4) using NaV1.5/NaV1.7 chimeric protein constructs. We also report that select GpTx-1 amino acid residues apparently not contacting NaV1.7 can be derivatized with a hydrophilic polymer without adversely affecting peptide potency. Homodimerization of GpTx-1 with a bifunctional polyethylene glycol (PEG) linker resulted in a compound with increased potency and a significantly reduced off-rate, demonstrating the ability to modulate the function and properties of GpTx-1 by linking to additional molecules.

Engineering potent and selective analogues of GpTx-1, a tarantula venom peptide antagonist of the Na(V)1.7 sodium channel.

NaV1.7 is a voltage-gated sodium ion channel implicated by human genetic evidence as a therapeutic target for the treatment of pain. Screening fractionated venom from the tarantula Grammostola porteri led to the identification of a 34-residue peptide, termed GpTx-1, with potent activity on NaV1.7 (IC50 = 10 nM) and promising selectivity against key NaV subtypes (20× and 1000× over NaV1.4 and NaV1.5, respectively). NMR structural analysis of the chemically synthesized three disulfide peptide was consistent with an inhibitory cystine knot motif. Alanine scanning of GpTx-1 revealed that residues Trp(29), Lys(31), and Phe(34) near the C-terminus are critical for potent NaV1.7 antagonist activity. Substitution of Ala for Phe at position 5 conferred 300-fold selectivity against NaV1.4. A structure-guided campaign afforded additive improvements in potency and NaV subtype selectivity, culminating in the design of [Ala5,Phe6,Leu26,Arg28]GpTx-1 with a NaV1.7 IC50 value of 1.6 nM and >1000× selectivity against NaV1.4 and NaV1.5.

Inhibition of 5-HT(3) receptors-activated currents by cannabinoids in rat trigeminal ganglion neurons.

This study investigated the modulatory effect of synthetic cannabinoids WIN55,212-2 on 5-HT(3) receptor-activated currents (I(5-HT3)) in cultured rat trigeminal ganglion (TG) neurons using whole-cell patch clamp technique. The results showed that: (1) The majority of examined neurons (78.70%) were sensitive to 5-HT (3-300 µmol/L). 5-HT induced inward currents in a concentration-dependent manner and the currents were blocked by ICS 205-930 (1 µmol/L), a selective antagonist of the 5-HT(3) receptor; (2) Pre-application of WIN55,212-2 (0.01-1 µmol/L) significantly inhibited I(5-HT3) reversibly in concentration-dependent and voltage-independent manners. The concentration-response curve of 5-HT(3) receptor was shifted downward by WIN55,212-2 without any change of the threshold value. The EC(50) values of two curves were very close (17.5±4.5) µmol/L vs. (15.2±4.5) µmol/L and WIN55,212-2 decreased the maximal amplitude of I(5-HT3) by (48.65±4.15)%; (3) Neither AM281, a selective CB1 receptor antagonist, nor AM630, a selective CB2 receptor antagonist reversed the inhibition of I(5-HT3) by WIN55,212-2; (4) When WIN55,212-2 was given from 15 to 120 s before 5-HT application, inhibitory effect was gradually increased and the maximal inhibition took place at 90 s, and the inhibition remained at the same level after 90 s. We are led to concluded that-WIN55,212-2 inhibited I(5-HT3) significantly and neither CB1 receptor antagonist nor CB2 receptor antagonist could reverse the inhibition of I(5-HT3) by WIN55,212-2. Moreover, WIN55,212-2 is not an open channel blocker (OCB) of 5-HT(3) receptor. WIN55,212-2 significantly inhibited 5-HT-activated currents in a non-competitive manner. The inhibition of I(5-HT3) by WIN55,212-2 is probably new one of peripheral analgesic mechanisms of WIN55,212-2, but the mechanism by which WIN55,212-2 inhibits I(5-HT3) warrants further investigation.

The discovery of aminopyrazines as novel, potent Na(v)1.7 antagonists: hit-to-lead identification and SAR.

Herein the discovery of a novel class of aminoheterocyclic Na(v)1.7 antagonists is reported. Hit compound 1 was potent but suffered from poor pharmacokinetics and selectivity. The compact structure of 1 offered a modular synthetic strategy towards a broad structure-activity relationship analysis. This analysis led to the identification of aminopyrazine 41, which had vastly improved hERG selectivity and pharmacokinetic properties.

Discovery and hit-to-lead optimization of pyrrolopyrimidines as potent, state-dependent Na(v)1.7 antagonists.

Herein we describe the discovery, optimization, and structure-activity relationships of novel potent pyrrolopyrimidine Na(v)1.7 antagonists. Hit-to-lead SAR studies of the pyrrolopyrimidine core, head, and tail groups of the molecule led to the identification of pyrrolopyrimidine 48 as exceptionally potent Na(v)1.7 blocker with good selectivity over hERG and improved microsomal stability relative to our hit molecule and pyrazolopyrimidine 8 as a promising starting point for future optimization efforts.

Discovery and optimization of aminopyrimidinones as potent and state-dependent Nav1.7 antagonists.

Clinical genetic data have shown that the product of the SCN9A gene, voltage-gated sodium ion channel Nav1.7, is a key control point for pain perception and a possible target for a next generation of analgesics. Sodium channels, however, historically have been difficult drug targets, and many of the existing structure-activity relationships (SAR) have been defined on pharmacologically modified channels with indirect reporter assays. Herein we describe the discovery, optimization, and SAR of potent aminopyrimidinone Nav1.7 antagonists using electrophysiology-based assays that measure the ligand-receptor interaction directly. Within this series, rapid functionalization at the polysubstituted aminopyrimidinone head group enabled exploration of SAR and of pharmacokinetic properties. Lead optimized N-Me-aminopyrimidinone 9 exhibited improved Nav1.7 potency, minimal off-target hERG liability, and improved rat PK properties.

Inhibition of 5-HT3 Receptors-activated Currents by Cannabinoids in Rat Trigeminal Ganglion Neurons / 华中科技大学学报（医学）（英德文版）

This study investigated the modulatory effect of synthetic cannbinoids WIN55,212-2 on 5-HT3 receptor-activated currents (I5-Hr3) in cultured rat trigeminal ganglion (TG) neurons using whole-cell patch clamp technique.The results showed that:(!) The majority of examined neurons (78.70％) were sensitive to 5-HT (3-300 μmol/L).5-HT induced inward currents in a concentrationdependent manner and the currents were blocked by ICS 205-930 (1 μmol/L),a selective antagonist of the 5-HT3 receptor; (2) Pre-application of WIN55,212-2 (0.01-1 μmol/L) significantly inhibited I5-HT3 reversibly in concentration-dependent and voltage-independent manners.The concentration-response curve of 5-HT3 receptor was shifted downward by WIN55,212-2 without any change of the threshold value.The EC50values of two curves were very close (17.5±4.5) μmol/L vs.(15.2±4.5) μmol/L and WIN55,212-2 decreased the maximal amplitude of I5-HI3 by (48.65±4.15)％; (3) Neither AM281,a selective CBI receptor antagonist,nor AM630,a selective CB2 receptor antagonist reversed the inhibition of I5-HT3by WIN55,212-2; (4) When WIN55,212-2 was given from 15 to 120 s before 5-HT application,inhibitory effect was gradually increased and the maximal inhibition took place at 90 s,and the inhibition remained at the same level after 90 s.We are led to concluded thatWIN55,212-2 inhibited I5-Hr3 significantly and neither CB1 receptor antagonist nor CB2 receptor antagonist could reverse the inhibition of I5-HT3 by WIN55,212-2.Moreover,WIN55,212-2 is not an open channel blocker (OCB) of 5-HT3 receptor.WIN55,212-2 significantly inhibited 5-HT-activated currents in a non-competitive manner.The inhibition of I5-HT3 by WIN55,212-2 is probably new one of peripheral analgesic mechanisms of WIN55,212-2,but the mechanism by which WIN55,212-2 inhibits I5-HT3 warrants further investigation.

Identification of a potent, state-dependent inhibitor of Nav1.7 with oral efficacy in the formalin model of persistent pain.

Clinical human genetic studies have recently identified the tetrodotoxin (TTX) sensitive neuronal voltage gated sodium channel Nav1.7 (SCN9A) as a critical mediator of pain sensitization. Herein, we report structure-activity relationships for a novel series of 2,4-diaminotriazines that inhibit hNav1.7. Optimization efforts culminated in compound 52, which demonstrated pharmacokinetic properties appropriate for in vivo testing in rats. The binding site of compound 52 on Nav1.7 was determined to be distinct from that of local anesthetics. Compound 52 inhibited tetrodotoxin-sensitive sodium channels recorded from rat sensory neurons and exhibited modest selectivity against the hERG potassium channel and against cloned and native tetrodotoxin-resistant sodium channels. Upon oral administration to rats, compound 52 produced dose- and exposure-dependent efficacy in the formalin model of pain.

Arrhythmogenic autoantibodies against calcium channel lead to sudden death in idiopathic dilated cardiomyopathy.

AIMS: Calcium channel plays an important role in the autoimmune pathogenesis of idiopathic dilated cardiomyopathy (DCM). Autoantibodies have emerged as a new upstream target of sudden death in DCM. We sought to validate the hypothesis that autoantibodies against l-type calcium channel (CC-AAbs) are arrhythmogenic and lead to sudden death in patients with DCM. METHODS AND RESULTS: We investigated sudden death and ventricular arrhythmias in 80 patients with DCM in a prospective, case follow-up survey. During a follow-up of 32 (SD 8) months, CC-AAbs-positive patients not only had a higher incidence of ventricular tachycardia (VT) but also a higher incidence of sudden death than CC-AAbs-negative patients (for VT: 59.0 vs. 24.4%, P = 0.002 and for sudden death: 20.5 vs. 4.9%, P = 0.045). Further univariate and multivariate analyses showed that the occurrence of CC-AAbs was the strongest independent predictor for sudden death (odds ratio: 10.20, 95% confidence interval: 2.43-36.78, P = 0.0027). Experimental studies in ex vivo systems using affinity-purified CC-AAbs from patients demonstrated that CC-AAbs were able to induce VT by prolongation of action potential duration (APD) and triggered activity by early afterdepolarization (EAD). CONCLUSION: Our results demonstrate for the first time to our knowledge that there is a high incidence of sudden death and VT in CC-AAbs-positive patients with DCM. Furthermore, experimental data from ex vivo systems suggest that CC-AAbs might induce VT by prolongation of APD and triggered activity by EAD.

Aconitine blocks HERG and Kv1.5 potassium channels.

ETHNOPHARMACOLOGICAL RELEVANCE: Aconitum has been widely used to treat various diseases in China for a long time. However, improper use of this drug results in severe intoxication. Aconitine (ACO), a diterpenoid alkaloid from aconitum, mainly contributes to cardio-toxic effects of aconitum and has also been commonly known to induce arrhythmias in animal models. However, its pro-arrhythmic mechanisms are not clear. AIM OF THE STUDY: The effects of ACO on HERG and Kv1.5 channels were investigated. MATERIALS AND METHODS: HERG and Kv1.5 channels were expressed in Xenopus laevis oocytes, and the resulting currents were recorded using a two-microelectrode voltage clamp technique. RESULTS: In HERG channels, ACO exhibited a blockade in a voltage- and time-dependent manner. The blockade was enhanced by further activation of currents, which were consistent with an open-channel blockade. In Kv1.5 channels, ACO produced a voltage-, time-, and frequency-dependent inhibition. The blockade was enhanced by higher rates of stimulation, consistent with preferential binding of the drug to the open state. In addition, ACO blocked Kv1.5 and HERG channels in a concentration-dependent manner with an IC(50) of 0.796+/-0.123 and 1.801+/-0.332 microM, respectively. CONCLUSIONS: ACO blocks HERG and Kv1.5 potassium channels in the open state. Blockade of potassium channels, particular the HERG channel, may be one of the important mechanisms of how ACO induces arrhythmias.

Effect of matrine on human ether à go-go related gene (HERG) channels expressed in Chinese hamster ovary cells.

OBJECTIVE: To observe the effect of matrine on human ether à go-go related gene (HERG) potassium channels expressed in Chinese hamster ovary (CHO) cells and investigate whether HERG channel is a new target of the pharmacological effect of matrine on arrhythmia and tumor METHODS: HERG channel potassium current in CHO cell was recorded using whole-cell patch-clamp technique, and the influence of matrine on the current was explored. RESULTS: Matrine inhibited HERG potassium current in a dose-dependent manner, and the 50% inhibitory concentration (IC IC(50)) was 411±23 µmol/L. Matrine had no significant effect on the activation kinetics, and mainly blocked HERG channels in their closed state. CONCLUSIONS: The blocking effect of matrine on HERG channels might be one of the mechanisms against arrythmias and tumors. Unlike most other blockers exerting blocking effect at the intracellular sites by entering the cell with the opening of HERG channel, matrine blocked HERG channels at the extracellular sites.

Molecular determinants of Kv1.5 channel block by diphenyl phosphine oxide-1.

Kv1.5 channels conduct the ultra-rapid delayed rectifier current (I(Kur)) that contributes to action potential repolarization of human atrial myocytes. Block of these channels has been proposed as a treatment for atrial arrhythmias. Diphenyl phosphine oxide-1 (DPO-1) is a novel and potent inhibitor of Kv1.5 potassium channels. The present study was undertaken to characterize the mechanisms and molecular determinants of channel block by DPO-1. Experiments were carried out on wild-type and mutant Kv1.5 channels expressed in Xenopus laevis oocytes using the standard two microelectrode voltage clamp technique. DPO-1 blocked Kv1.5 current in oocytes with an IC(50) of 0.78+/-0.12 microM at +40 mV. Block was enhanced by higher rates of stimulation, consistent with preferential binding of the drug to the open state of the channel. Ala-scanning mutagenesis of the pore domain of Kv1.5 identified the residues Thr480, Leu499, Leu506, Ile508, Leu510 and Val514 as components of the putative binding site for DPO-1, partially overlapping the site previously defined for the Kv1.5 channel blockers AVE0118 and S0100176. Block of Kv1.5 by DPO-1 was significantly reduced in the presence of Kvbeta1.3.

[Effects of telmisartan on voltage-gated Kv1.3 and Kv1.5 potassium channels expressed in Xenopus oocytes].

OBJECTIVE: To observe the effects of telmisartan on Kv1.3 and Kv1.5 potassium channels expressed in Xenopus oocytes. METHODS: Kv1.3 and Kv1.5 potassium channel currents expressed in Xenopus oocytes were recorded and observed in the absence and presence of telmisartan using standard two-microelectrode voltage clamp techniques. RESULTS: Telmisartan resulted in a concentration- and voltage-dependent inhibition effect on Kv1.3 channel current (IC(50) 2.05 micromol/L)and on Kv1.5 channel current (IC(50) 2.37 micromol/L). CONCLUSIONS: Telmisartan blocks open-state Kv1.3 channel which could be one of the mechanisms related to its immunomodulatory and anti-atherosclerosis effect. Telmisartan also blocks open-state Kv1.5 channel which might partly account for its effect on reducing the incidence of atrial fibrillation.

Glycyrretinic acid blocks cardiac sodium channels expressed in Xenopus oocytes.

ETHNOPHARMACOLOGICAL RELEVANCE: Licorice has been used to treat many ailments including cardiovascular disorders in China for long time. Recent studies have shown that the cardiac actions of licorice have been attributed to its active component, glycyrretinic acid (GA). However, its mechanism remains poorly understood. AIM OF THE STUDY: The effects of GA on the cardiac sodium currents (I(Na)), L-type calcium currents (I(Ca,L)) and hyperpolarization-activated inward currents (I(f)) were investigated. MATERIALS AND METHODS: Human isoforms of wild-type and DeltaKPQ-mutant type sodium channels were expressed in Xenopus oocytes, and the resulting currents (peak and late I(Na)) were recorded using a two-microelectrode voltage-clamp technique. A perforated patch clamp technique was employed to record I(Ca,L) and I(f) from isolated rabbit sinoatrial node pacemaker cells. RESULTS: GA inhibited peak I(Na) (33% at 90 microM) and late I(Na) (72% at 90 microM), but caused no significant effects on I(Ca,L) and I(f). CONCLUSION: GA blocked cardiac sodium currents, particularly late I(Na.) Our findings might help to understand the traditional use of licorice in the treatment of cardiovascular disorders, because reduction of sodium currents (particularly late I(Na)) would be expected to provide protection from Na(+)-induced Ca(2+) overload and cell damage.