Summary:Purpose: BIA 2-093 [(S)-(-)-10-acetoxy-10,11-dihydro-5H-dibenz/b,f/azepine-5-carboxamide] is endowed with an anticonvulsant potency similar to that of carbamazepine (CBZ), but produces less cognitive and motor impairment. This study evaluated whether voltage-gated sodium channels (VGSCs) are a primary locus for the action of BIA 2-093.Methods: We used the whole-cell voltage-clamp technique in the mouse neuroblastoma cell line N1E-115 to investigate the effects of BIA 2-093 and CBZ on VGSCs, displacement of Conclusions: BIA 2-093, like CBZ, inhibits sodium currents in a voltage-dependent way by an interaction predominantly with the inactivated state of the channel and interacts with neurotoxin receptor site 2, but not with receptor site 1. BIA 2-093 displayed a potency blocking VGSCs similar to that of CBZ.

The effects of the cholinoceptor agonist, carbachol (CCh), were examined in the rat hippocampal slice preparation. Intracellular recordings from CA 1 pyramidal neurones revealed that CCh (1-3/~M) inhibited excitatory postsynaptic responses evoked by stimulation of the Schaffer collateral/commissural pathway while, at the same time, direct excitability was enhanced. Extracellularly, CCh produced a concentrationdependent reduction of the amplitude of the field excitatory postsynaptic potential (field EPSP) recorded in the CAI apical dendritic region. The muscarinic receptor antagonist, pirenzepine, competitively antagonized the effects of CCh on the field EPSP with a pA2 of 7.4. These results confirm earlier reports of a presynaptic inhibitory action of CCh in the hippocampal CAI region and provide strong evidence that this effect is mediated by muscarinic receptors of the Mt subtype.The classification of muscarinic receptors into two broad categories on the basis of their high (M0 and low (M2) affinities for the antagonist, pirenzepine [9], has prompted a number of attempts to establish the subtypes mediating the electrophysiological responses to muscarinic agonists throughout the brain [4-6, 14-16, 19]. In hippocampal CA I pyramidal neurones, both the membrane depolarization and blockade of IAHp induced by carbachol (CCh) have been attributed to an action at M1 receptors, whereas inhibition of the M-current may result from M2 receptor activation [4]. In addition to these postsynaptic effects, muscarinic agonists can also reduce the synaptically-evoked excitation of CA 1 neurones by a presynaptic mechanism [11,18]. Unfortunately, attempts to classify this latter response in terms of receptor subtype have yielded conflicting reports: both M2 [4] and Mi [16] receptors have been implicated. However, since neither of these earlier studies employed formal quantitative pharmacological procedures, conclusions from them must remain tentative. We

Extracellular recording techniques have been used in the guinea pig hippocampal slice preparation to investigate the electrophysiological actions of the organophosphate (OP) anticholinesterase soman. When applied at a concentration of 100 nM, soman induced epileptiform activity in the CA1 region in approximately 75% of slices. This effect was mimicked by the anticholinesterases paraoxon (1 and 3 M), physostigmine (30 M), and neostigmine (30 M), thus providing indirect evidence that the epileptiform response was mediated by elevated acetylcholine levels. Soman-induced bursting was inhibited by the muscarinic receptor antagonists atropine (concentrations tested, 0

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1 The effects of imidazopyrazine derivative, SCA40, on the activity of single large conductance, Ca2+-activated K+ (BKCa) channels in inside-out and outside-out patches from bovine tracheal smooth muscle (BTSM) BKCa channels when applied to either inside-out or outside-out BTSM patches, thus confirming that these compounds are activators of the BKCa channel in this preparation. 4 SCA40 (0.1 -10 pM) had no effect on the activity of BKCa channels when applied to either inside-out or outside-out patches which subsequently responded to the application of NS 004 (10-20 pM). 5It is concluded that SCA40 does not have a direct effect on BKca channel activity in BTSM patches and that the previously reported relaxant action of SCA40 on tracheal smooth muscle is unlikely to be mediated by this mechanism.

Increasing use by law enforcement agencies of the M26 and X26 TASER electrical incapacitation devices has raised concerns about the arrhythmogenic potential of these weapons. Using a numerical phantom constructed from medical images of the human body in which the material properties of the tissues are represented, computational electromagnetic modelling has been used to predict the currents arising at the heart following injection of M26 and X26 waveforms at the anterior surface of the chest (with one TASER 'barb' directly overlying the ventricles). The modelling indicated that the peak absolute current densities at the ventricles were 0.66 and 0.11 mA mm(-2) for the M26 and X26 waveforms, respectively. When applied during the vulnerable period to the ventricular epicardial surface of guinea-pig isolated hearts, the M26 and X26 waveforms induced ectopic beats, but only at current densities greater than 60-fold those predicted by the modelling. When applied to the ventricles in trains designed to mimic the discharge patterns of the TASER devices, neither waveform induced ventricular fibrillation at peak currents >70-fold (for the M26 waveform) and >240-fold (for the X26) higher than the modelled current densities. This study provides evidence for a lack of arrhythmogenic action of the M26 and X26 TASER devices.

1 The ability of the neuroprotective agent, lifarizine (RS‐87476), to mitigate veratridine‐, cyanide‐ and glutamate‐induced toxicity in rat embryonic cerebrocortical neurones in primary culture has been compared with that of tetrodotoxin (TTX), nitrendipine, (+)‐MK‐801 and (−)‐MK‐801. Lactate dehydrogenase (LDH) released into the culture medium was used as the indicator of cell viability.2 Incubation of cultures for 16 h in a medium containing veratridine (10−4 M), sodium glutamate (10−3M) or sodium cyanide (10−3M) resulted in consistent elevations of LDH activity in the culture medium. The ability of compounds to attenuate these elevations was expressed as the concentration required to inhibit the increases in LDH release by 50% (IC50).3 Neurotoxicity induced by veratridine was inhibited by lifarizine (IC50 = 4× 10−7M), TTX (IC50 = 3 × 10−8 M) and nitrendipine (IC50 = 3 × 10−5 M). In contrast, (+)‐MK‐801 (up to 3 × 10−5 M) was ineffective against this insult.4 Glutamate‐induced neurotoxicity was inhibited by (+)‐MK‐801 (IC50 = 1.4 × 10 −8 M) and to a lesser extent by (−)‐MK‐801 (IC50 = 1 × 10−7 M), but was unaffected by lifarizine, TTX or nitrendipine (up to 10−6M).5 (+)‐MK‐801 was effective against sodium cyanide‐induced neurotoxicity (IC50= 1.9 × 10−8M), whereas lifarizine and TTX (up to 10−6 m) and nitrendipine (up to 3 × 10−6 m) were without protective activity against this insult.6 The results demonstrate that lifarizine potently protects rat cortical neurones in vitro against a neurotoxic insult that requires activation of sodium channels for its expression, and that the compound is ineffective against insults mediated by N‐methyl‐D‐aspartate receptor activation. The weak efficacy of nitrendipine against veratridine‐induced cell death argues against the involvement of L‐type calcium channels in this insult. These data are consistent with the notion that the neuroprotective activity of lifarizine observed in vivo may be mediated by inhibition of neuronal sodium currents.

1 The actions of the neuroprotective agent, lifarizine , on voltage-dependent Na+ currents have been examined in the neuroblastoma cell line, NlE-1 15, using the whole-cell variant of the patch clamp technique. 2 At a holding potential of -80mV, lifarizine reduced the peak Na+ current evoked by a lOms depolarizing step with an IC50 of 1.3pLM. At holding potentials of -100 and -60mV the IC50 concentrations of lifarizine were 7.3pM and 0.3LM, respectively.3 At a holding potential of -100 mV, most channels were in the resting state and the IC50 value for inhibition of Na+ current should correspond to the dissociation constant of lifarizine for resting channels (KR). KR was therefore estimated to be 7.3pLM. 4 In the absence of lifarizine, recovery from inactivation following a 20s depolarization from -100 mV to 0 mV was complete within 2 s. However, in the presence of 311M lifarizine recovery took place in a biexponential fashion with time constants of 7 s and 79 s. 5Lifarizine (1 M) had no effect on steady-state inactivation curves when conditioning pre-pulses of 1 s duration were used. However, when pre-pulse durations of 1 min were used the curves were shifted to the left by lifarizine by about 10 mV. Analysis of the shifts induced by a range of lifarizine concentrations revealed that the apparent affinity of lifarizine for the inactivated state of the channel (K,) was 0.19 JM.6 Lifarizine (1I M) had no effect on chloramine-T-modified Na+ currents, suggesting no significant open channel interaction. 7 Taken together, these data show that lifarizine is a potent voltage-dependent inhibitor of Na+ currents in NIE-115 cells and that the voltage-dependence arises from an interaction of the compound with the inactivated state of the channel. The possible contribution of Na+ current inhibition to the neuroprotective actions of lifarizine is discussed.