Sipatrigine (BW 619C89) is a Neuroprotective Agent and a Sodium Channel and Calcium Channel Inhibitor

Block of TREK and TRESK K2P channels by lamotrigine and two derivatives sipatrigine and CEN-092

TREK and TRESK K2P channels are widely expressed in the nervous system, particularly in sensory neurons, where they regulate neuronal excitability. In this study, using whole-cell patch-clamp electrophysiology, we characterise the inhibitory effect of the anticonvulsant lamotrigine and two derivatives, sipatrigine and 3,5-diamino-6-(3,5-bistrifluoromethylphenyl)-1,2,4-triazine (CEN-092) on these channels.

Sipatrigine was found to be a more effective inhibitor than lamotrigine of TREK-1, TREK-2 and TRESK channels. Sipatrigine was slightly more potent on TREK-1 channels (EC₅₀ = 16 μM) than TRESK (EC₅₀ = 34 μM) whereas lamotrigine was equally effective on TREK-1 and TRESK. Sipatrigine was less effective on a short isoform of TREK-2, suggesting the N terminus of the channel is important for both inhibition and subsequent over-recovery. Inhibition of TREK-1 and TREK-2 channels by sipatrigine was reduced by mutation of a leucine residue associated with the norfluoxetine binding site on these channels (L289A and L320A on TREK-1 and TREK-2, respectively) but these did not affect inhibition by lamotrigine. Inhibition of TRESK by sipatrigine and lamotrigine was attenuated by mutation of bulky phenylalanine residues (F145A and F352A) in the inner pore helix. However, phosphorylation mutations did not alter the effect of sipatrigine. CEN-092 was a more effective inhibitor of TRESK channels than TREK-1 channels.

It is concluded that lamotrigine, sipatrigine and CEN-092 are all inhibitors of TREK and TRESK channels but do not greatly discriminate between them. The actions of these compounds may contribute to their current and potential use in the treatment of pain and depression.

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Lamotrigine blocks TREK and TRESK potassium channels at clinical concentrations.

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Sipatrigine is more effective than lamotrigine at blocking TREK and TRESK channels.

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Mutation of norfluoxetine binding site on TREK channels attenuates sipatrigine block.

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Residues in the inner pore region of TRESK channels regulate sipatrigine block.

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The novel lamotrigine derivative, CEN-092, blocks TRESK channels.

Lamotrigine as a mood stabilizer: insights from the pre-clinical evidence

INTRODUCTION

Lamotrigine (LTG) is a well-established anticonvulsant that is also approved for the prevention of mood relapses in bipolar disorder. However, the mechanisms underlying LTG mood stabilizing effects remain unclear. Areas covered: Herein, the pre-clinical evidence concerning LTG's' mode of action in depression and mania is reviewed. Bottlenecks and future perspectives for this expanding and promising field are also discussed. Pre-clinical studies have indicated that neurotransmitter systems, especially serotoninergic, noradrenergic and glutamatergic, as well as non-neurotransmitter pathways such as inflammation and oxidative processes might play a role in LTG's antidepressant effects. The mechanisms underlying LTG's anti-manic properties remain to be fully explored, but the available pre-clinical evidence points out to the role of glutamatergic neurotransmission, possibly through AMPA-receptors. Expert opinion: A major limitation of current pre-clinical investigations is that there are no experimental models that recapitulate the complexity of bipolar disorder. Significant methodological differences concerning time and dose of LTG treatment, administration route, animal strains, and behavioral paradigms also hamper the reproducibility of the findings, leading to contradictory conclusions. Moreover, the role of other mechanisms (e.g. inositol phosphate and GSK3β pathways) implicated in the mode of action of different mood-stabilizers must also be consolidated with LTG.

A systematic review of calcium channel blocker use and cognitive decline/dementia in the elderly

OBJECTIVE

Treating hypertension in those aged at least 80 years is now recommended; however, the best antihypertensive to choose remains unexplored. Calcium channel blocker (CCB) use has been associated with a decreased risk of incident dementia in a younger hypertensive group but with an increased risk of cognitive decline in the very elderly. Either result could have a large impact on a vulnerable population. The aim of this review was to assess the evidence relating CCB use to later cognitive decline or dementia in the very elderly.

METHODS

A systematic review of the literature was carried out. The databases Medline, PubMed, Embase and Psychinfo were searched from 1980 to 22 August 2013. Abstracts were reviewed by two independent reviewers and papers meeting the inclusion criteria were extracted.

RESULTS

One thousand, nine hundred and sixty-eight records were reviewed and 10 articles reporting on nine studies retained and extracted. Data were primarily from cohort studies. Only one reported a randomized controlled trial comparing CCBs with placebo. Populations, comparator groups, follow-up times, outcomes and exposure varied and overall results were mixed. It was not possible to combine all studies, but those reporting Alzheimer's disease outcomes were combined to produce an overall risk ratio of 0.79 (95% confidence interval 0.53-1.17).

CONCLUSION

At present, there is no clear evidence to suggest that CCB use increases or decreases risk of cognitive decline or dementia in the very elderly. A robust clinical trial is now required to resolve this.

Sipatrigine could have therapeutic potential for major depression and bipolar depression through antagonism of the two-pore-domain K+ channel TREK-1

Major depressive disorder (MDD) is a chronic, recurring and potentially life-threatening mental illness. Current treatments are inadequate - many depression medications, although safe and effective, generally have a slow onset of clinical benefit and around half of the MDD patients do not show full remission with optimized treatment. Therefore, there is still a need for the development of faster-acting and more effective medication for MDD. Recent studies have demonstrated that the TREK-1 protein, one of the 17 members of the two-pore domain K+ (K2P) potassium channel family, is inhibited by the antidepressant fluoxetine. Deletion of TREK-1 in mice caused a substantially reduced elevation of corticosterone levels under stress, and produced behaviour similar to that of naive animals treated with fluoxetine in various behavioural tests. These findings suggested that the blocker of the TREK-1 channel might potentially be a new type of antidepressant. Sipatrigine (BW619C89), a neuroprotective agent, has been found to be a potent antagonist of TREK-1. Its related compound, lamotrigine, has been approved for the treatment of bipolar depression and is used to supplement antidepressant medication in patients with treatment-resistant depression. Furthermore, in addition to its antagonistic effect on TREK-1, sipatrigine is also a glutamate release inhibitor. Excessive glutamatergic neurotransmission is associated with depressive-like behaviours and inhibiting glutamate neurotransmission may be implicated in antidepressant therapeutic mechanisms. From the above findings of the effects of sipatrigine on TREK-1 and glutamate neurotransmission, it is hypothesised that sipatrigine could have potential therapeutic effects for MDD or bipolar depression. Further evaluation of its antidepressant therapeutic and toxic effects in animal models is needed before clinical application.

The neuroprotective agent sipatrigine blocks multiple cardiac ion channels and causes triangulation of the ventricular action potential

Sipatrigine (BW 619C89), a blocker of neuronal Na+ and Ca2+ channels that is structurally related to lamotrigine, has been shown to be neuroprotective in models of cortical ischaemia. Although associated with cardiovascular effects in animal models in vivo, there is no published information concerning the effects of sipatrigine on cardiac ion currents and action potentials (AP). The aim of the present study was to examine the effects of sipatrigine on the delayed rectifier currents (I(Kr) and I(Ks)), the inward rectifier current (I(K1)), the L-type Ca2+ current (I(Ca,L)) and the fast Na+ current (I(Na)), as well as on AP duration at 30% (APD30) and 90% (APD90) repolarization, in guinea-pig isolated ventricular myocytes. Each of the currents was inhibited by sipatrigine, demonstrating the drug to be a relatively broad-spectrum blocker of cation channels in the heart. However, sipatrigine was a comparatively more potent inhibitor of I(Kr) (IC50 = 0.85 micromol/L) and I(Ks) (IC50 = 0.92 micromol/L) than of I(K1) (IC50 = 5.3 micromol/L), I(Ca,L) (IC50 = 6.0 micromol/L) and I(Na) (IC50 = 25.5 micromol/L). Consistent with block of I(Kr), I(Ks) and I(K1), sipatrigine (1-30 micromol/L) produced a concentration-dependent prolongation of APD90. Although lower concentrations of sipatrigine (< or = 3 micromol/L) caused APD(30) prolongation, higher concentrations (> or = 10 micromol/L) shortened APD30, consistent with an involvement of I(Ca,L) blockade. The contrasting effects of sipatrigine on APD30 and APD90 at higher concentrations resulted in a marked concentration-dependent triangulation of the AP. 5. The results of the present study demonstrate that sipatrigine, at concentrations previously shown to be neuroprotective in vitro, modulates cardiac K+, Ca2+ and Na+ currents and repolarization of the cardiac ventricular action potential.

Topiramate Inhibits the Initiation of Plateau Potentials in CA1 Neurons by Depressing R-type Calcium Channels

PURPOSE

Cholinergic-dependent plateau potentials (PPs) are intrinsically generated conductances that can elicit ictal-type seizure activity. The aim of this study was to investigate the actions of topiramate (TPM) on the generation of PPs.

METHODS

We used whole-cell patch-clamp recordings from CA1 pyramidal neurons in rat hippocampal slices to examine the effects of TPM on the PPs.

RESULTS

In current-clamp mode, action potentials evoked PPs after cholinergic receptor stimulation. Therapeutically relevant concentrations of TPM (50 microM) depressed the PPs evoked by action potentials. Surprisingly, in voltage-clamp mode, we discovered that the cyclic nucleotide-gated (CNG) current that underlies PP generation (denoted as I(tail)) was not depressed. However, significantly longer depolarizing voltage steps were required to elicit I(tail). This suggested that the calcium entry trigger for evoking PPs was depressed by TPM and not I(tail) itself. TPM had no effect on calcium spikes in control conditions; however, TPM did reduce calcium spikes after cholinergic-receptor stimulation. We recently found that R-type calcium spikes are enhanced by cholinergic-receptor stimulation. Therefore we isolated R-type calcium spikes with a cocktail containing tetrodotoxin, omega-conotoxin MVIIC, omega-conotoxin-GVIA, omega-agatoxin IVA, and nifedipine. R-type calcium spikes were significantly depressed by TPM. We also examined the effects of TPM on recombinant Ca(V)2.3 calcium channels expressed in tsA-201 cells. TPM depressed currents mediated by Ca(V)2.3 subunits by a hyperpolarizing shift in steady-state inactivation.

CONCLUSIONS

We have found that TPM reduces ictal-like activity in CA1 hippocampal neurons through a novel inhibitory action of R-type calcium channels.

Actions of the sodium channel inhibitor 202W92 on rat midbrain dopaminergic neurons

Excessive glutamatergic activity is implicated in Parkinson's disease (PD) and sodium channel blockade, resulting in inhibition of glutamate release, is a potential therapeutic approach to PD therapy. Beneficial effects of riluzole and lamotrigine have been reported in animal models of PD, but these compounds have relatively low potency as sodium channel inhibitors and also inhibit N and P/Q-type calcium channels. 202W92, a structural analog of lamotrigine, is a potent sodium channel inhibitor, with no effect on N, P/Q-type channels. Here we present the effects of 202W92 on single patch-clamped dopaminergic neurons. 202W92 (> or =10 microM) inhibited spontaneous action potential firing and reduced amplitude and frequency of evoked action potentials. It also inhibited the frequency of 4-aminopyridine (4-AP)- and electrically evoked excitatory postsynaptic currents (EPSCs) and GABAergic inhibitory postsynaptic currents (IPSCs), with >80% inhibition at 10 microM (IC(50) 1.5 microM). EPSC and IPSC amplitudes were partially inhibited. 202W92 did not affect postsynaptic responses to locally applied glutamate and GABA, nor spontaneously occurring mini-IPSCs. These actions of 202W92 are compatible with sodium channel inhibition and depression of transmitter release.

Actions of sipatrigine, 202W92 and lamotrigine on R-type and T-type Ca2+ channel currents

Relatively little has been published on the pharmacology of R-type and T-type Ca(2+) channels. Here, whole-cell Ca(2+) channel currents were recorded from human embryonic kidney 293 cell-lines transfected with either alpha1E subunits (R-type currents) or alpha1G or alpha1I subunits (T-type currents). R-type currents were inhibited by sipatrigine and the related compound 202W92 (R-(-)-2,4-diamino-6-(fluromethyl)-5-(2,3,5-trichlorophenyl)pyrimidine) with IC(50) 10 and 56 microM, respectively. A therapeutic concentration of lamotrigine (10 microM) inhibited R-type currents (30%) but was without effect on alpha1I-mediated T-type currents. Lamotrigine was also a weak inhibitor of T-type currents mediated by alpha1G subunits (<10% inhibition by 100 microM).

Pharmacology of ischemia-induced glutamate efflux from rat cerebral cortex in vitro

Simulated ischemic conditions (hypoxia-hypoglycaemia) in vitro enhanced glutamate efflux from rat cerebrocortical prisms. Here we characterised efflux mechanisms using pharmacological tools. The Na(+) channel blocker TTX (1 microM) did not affect ischemia-induced efflux, while sipatrigine (100 microM), a Na(+)/Ca(2+) channel blocker and omega-conotoxin MVIIC (2 microM), an N/P/Q type Ca(2+) channel blocker, inhibited efflux by fractions of 0.53 and 0.46, respectively (1.00 corresponding to total inhibition). Omission of extracellular Ca(2+) and addition of EGTA (2 mM) inhibited ischemia-induced efflux only during the first 25 min of incubation. A similar result was observed on omission of extracellular Ca(2+) together with addition of La(3+) (10 microM) and Mg(2+) (6 mM). TTX, sipatrigine and La(3+)/Mg(2+) all inhibited control efflux. Ischemia-induced efflux was sensitive to the volume activated anion channel inhibitor NPPB (100 microM) only after the first 25 min of incubation, with the maximal fraction inhibited being 0.54. The glutamate transporter inhibitor D,L-TBOA reduced ischemia-induced efflux throughout a 45-min incubation period, and enhanced efflux from control tissue. D,L-TBOA inhibited efflux at 30 min by a maximum fraction of 0.49, at 50 microM. These data indicate that the early phase of ischemia-induced glutamate efflux is in part Ca(2+) dependent, while the later phase involves volume activated anion currents and both phases involve excitatory amino acid transporters.

Excitatory amino acid antagonists for acute stroke

BACKGROUND

Focal cerebral ischaemia causes release of excitatory amino acid (EAA) neurotransmitters, principally glutamate, with resultant over-stimulation of EAA receptors and downstream pathways. Excess glutamate release is a pivotal event in the evolution of irreversible ischaemic damage in animal models of ischaemia, and drugs that modulate glutamate action either by inhibiting its release, or blocking post-synaptic receptors, are potent neuroprotective agents. Many clinical trials with EAA modulating drugs have been conducted, none individually demonstrating efficacy.

OBJECTIVES

To synthesise all the available data on all different classes of EAA modulators and to evaluate evidence of effects on outcome systematically.

SEARCH STRATEGY

Relevant trials were identified in the Specialised Register of Controlled Trials (last searched May 2001). In addition, MEDLINE and EMBASE online searches for the terms "neuroprotection" (and its variants), "neuroprotective agent", for all individual drugs and drug classes included in the review, hand searches of conference proceedings from European, International, American Heart Association and Princeton conferences on Stroke, American Neurological Association and American Academy of Neurology meetings from 1992-2001, and direct contact with individual investigators and pharmaceutical companies.

SELECTION CRITERIA

Trials were included if they were randomised, controlled studies giving agents with pharmacological properties that included modification of release of EAAs, or blockade of EAA receptors, in stroke within 24h of onset. Efficacy analysis was restricted to trials with a parallel group design: dose escalation studies were excluded. Intention-to-treat analyses were performed on all data. Outcome had to be reported in terms of death or dependence 1-12 months after the acute event.

DATA COLLECTION AND ANALYSIS

Data were available for 36 of 41 relevant trials identified, involving 11,209 subjects. Data were unavailable for 632 participants (517 in trials fulfilling criteria for efficacy analysis). Seven trials did not report disability data, which were available for 29 trials involving 10,802 subjects. Twenty one of these trials, involving 10,342 subjects, were parallel group studies included in the primary efficacy analysis. Efficacy analysis included data derived from 9 trials not primarily designed to assess efficacy (1022 subjects). The primary (efficacy) end-point was the proportion of patients dead or disabled at final follow-up (defined by Barthel Index<60 at 3 months by preference). Mortality was a secondary end-point. Drugs were considered as individual agents, and also grouped principally into categories of ion channel modulators (glutamate release inhibition) and NMDA antagonists.

MAIN RESULTS

There was no significant heterogeneity of outcome amongst individual drugs, or of drug classes either for the primary efficacy analysis (death or dependence) or for mortality at final follow-up. For the primary efficacy analysis, odds of death or dependence were 1.03 [95% confidence interval 0.96-1.12], and for mortality 1.02 [0.92-1.12]. Neither ion channel modulators (death or dependence 1.02 [0.90-1.16]) nor NMDA antagonists (death or dependence 1.05 [0.95-1.16]) differed from the principal analysis including all compounds. Trends for increased mortality with three NMDA antagonists were seen - selfotel (OR 1.19 [0.81-1.74]), aptiganel (OR 1.32 [0.91-1.93]) and gavestinel (OR 1.12 [0.95-1.32]) - but this did not achieve significance for the NMDA antagonists considered as a class (1.09 [0.96-1.23]). Aptiganel was also associated with a trend towards worse functional outcome (OR 1.20 [0.88-1.65]) although this was not the case for either of the other two compounds. No statistically significant detriment of psychotomimetic NMDA antagonists was found, although a trend towards higher mortality in this sub-group was seen (OR 1.25 [0.96-1.64]).

REVIEWER'S CONCLUSIONS

There was no evidence of significant benefit or harm from drugs modulating excitatory amino acid action. Reductio]).

REVIEWER'S CONCLUSIONS

There was no evidence of significant benefit or harm from drugs modulating excitatory amino acid action. Reduction of death or dependence by 8% or more has been excluded for gavestinel and lubeluzole, which contribute most of the data for this review. However, mechanistic understanding of neuroprotection is too poor to extrapolate from these two failed development plans to all glutamate modulators. Further clinical trials of neuroprotective agents remain justified, since confidence limits around estimates of effect remain wide for most agents, and cannot reliably exclude benefit. Although numbers of patients are too small to confirm or refute a trend towards increased mortality with some NMDA antagonists, further commercial development of these agents is exceedingly unlikely.

Lamotrigine derivatives and riluzole inhibit INa,P in cortical neurons

The persistent, slowly inactivating fraction of the sodium current is involved in key functions in the CNS such as dendritic integration of synaptic inputs and cellular excitability. We have studied whether established anti-epileptic drugs and neuroprotective agents target the persistent sodium current. Two lamotrigine derivatives (sipatrigine and 202W92) and riluzole inhibited the persistent sodium current at low, therapeutic concentrations. In contrast, lamotrigine and the classical antiepileptic agents phenytoin and valproic acid blocked the fast-inactivating sodium channel but failed to affect the persistent fraction. The ability to influence either mode of channel activity may represent a defining feature of each drug subclass, changing profoundly their clinical indications. Given the damaging role of a sustained influx of sodium in both pharmaco-resistant seizures or excitotoxic insults, we suggest the utilization of drugs that suppress the persistent conductance.

Neuroprotective actions in vivo and electrophysiological actions in vitro of 202W92

202W92 (R-(-)-2,4-diamino-6-(fluromethyl)-5-(2,3,5-trichlorophenyl)pyrimidine) is a novel compound in the same chemical series as the antiepileptic drug lamotrigine and the neuroprotective sipatrigine. Here 202W92 was quantitatively assessed as a neuroprotective agent in focal cerebral ischaemia, and as an inhibitor of sodium and calcium channels and of synaptic transmission. In the rat permanent middle cerebral artery occlusion (MCAO) model of acute focal ischaemia, 202W92 reduced infarct volume by 75% in cortex and by 80% in basal ganglia, with ED(50) approximately 2 mg/kg (single i.v. dose, 10 min post-occlusion). In whole-cell current recordings from single cells, 202W92 completely and reversibly inhibited voltage gated sodium channels (IC(50) 3 x 10(-6) M) in rat freshly-isolated cortical neurons and in the GH(3) pituitary cell line. 202W92 also inhibited a nifedipine-sensitive fraction (approximately 35%) of native high-voltage-activated (HVA) calcium current in rat cortical neurons (IC(50) 15 x 10(-6) M) and weakly inhibited low-voltage-activated (LVA) calcium currents of the recombinant alpha1I-mediated T-type (IC(50)>100 x 10(-6) M). The drug inhibited the amplitude and frequency of 4-aminopyridine-evoked glutamatergic excitatory post-synaptic currents (EPSCs). In conclusion, 202W92 is an effective neuroprotective agent when administered post-ischaemia and a potent sodium channel inhibitor in vitro.

Effects of extracellular pH on the interaction of sipatrigine and lamotrigine with high-voltage-activated (HVA) calcium channels in dissociated neurones of rat cortex

Acidic extracellular pH reduced high-voltage-activated (HVA) currents in freshly isolated cortical pyramidal neurones of adult rats, shifting activation to more positive voltages (V(1/2)=-18 mV at pH 7.4, -11 mV at pH 6.4). Sipatrigine inhibited HVA currents, with decreasing potency at acidic pH (IC(50) 8 microM at pH 7.4, 19 microM at pH 6.4) but the degree of maximal inhibition was >80% in all cases (pH 6.4-8.0). Sipatrigine has two basic groups (pK(A) values 4.2, 7.7) and at pH 7.4 is 68% in monovalent cationic form and 32% uncharged. From simple binding theory, the pH dependence of sipatrigine inhibition indicates a protonated group with pK(A) 6.6. Sipatrigine (50 microM) shifted the voltage dependence of channel activation at pH 7.4 (-7.6 mV shift) but not at pH 6.4. Lamotrigine has one basic site (pK(A) 5.5) and inhibited 34% of the HVA current, with similar potency over the pH range 6.4--7.4 (IC(50) 7.5--9 microM). These data suggest that the sipatrigine binding site on HVA calcium channels binds both cationic and neutral forms of sipatrigine, interacts with a group with pK(A)=6.6 and with the channel activation process, and differs from that for lamotrigine.

A comparative assessment of the efficacy and side-effect liability of neuroprotective compounds in experimental stroke

There are many examples of compounds showing neuroprotective efficacy in animal models of stroke but not in clinical trials. It is possible that some or all of these compounds possess poor therapeutic ratios, which results in the administration of sub-efficacious doses in order to avoid the emergence of side-effects. In order to explore this possibility, this study compared the therapeutic ratios of a number of neuroprotective agents that have undergone clinical trials. Neuroprotective efficacy was established using the mouse permanent (24 h) middle cerebral artery occlusion model. Side-effect liability was determined by assessment of motor coordination using the rotarod test. The therapeutic ratio was calculated as the ratio between the minimum effective dose (MED) for significant impairment in rotarod performance and the MED for significant neuroprotection. Compounds were administered i.p. 30 min prior to rotarod testing or onset of ischemia. Drugs such as Ifenprodil, Cerestat and Selfotel, that have failed in clinical trials, were found to have very low therapeutic ratios of < or = 1, whereas compounds with more tolerable clinical side-effect profiles were found to have higher therapeutic ratios (2, 10 and 10 for Sipatrigine, Remacemide and sPBN, respectively). It is concluded that the lack of efficacy of a number of neuroprotectants in clinical trials may well be a consequence of their poor therapeutic ratios.

The neuroprotective agent sipatrigine (BW619C89) potently inhibits the human tandem pore-domain K(+) channels TREK-1 and TRAAK

We have cloned and functionally expressed the human orthologue of the mouse TRAAK gene. When cDNA for hTRAAK is expressed in either Xenopus oocytes or HEK293 cells it forms a K(+)-selective conductance and hyperpolarises the resting membrane potential. Quantitative mRNA expression analysis using Taqman revealed that hTRAAK mRNA is predominantly present in the central nervous system where it exhibits a regionally diverse pattern of expression. Like the related channel TREK-1, the activity of TRAAK was potentiated by arachidonic acid. The neuroprotective agent sipatrigine (10 microM) inhibited both hTREK-1 (73.3+/-4.4%) and hTRAAK (45.1+/-11.2%) in a reversible, voltage-independent manner. Inhibition of both channels was dose-dependent and for TREK-1 occurred with an IC(50) of 4 microM. The related compound lamotrigine, which is a better anticonvulsant but weaker neuroprotective agent than sipatrigine, was a far less effective antagonist of both channels, producing <10% inhibition at a concentration of 10 microM.