Interaction of high concentrations of riluzole with recombinant skeletal muscle sodium channels and adult-type nicotinic receptor channels
ABSTRACT Riluzole is a neuroprotective drug that modulates glutamergic transmission but also blocks the inactivated state of voltage-gated neuronal sodium channels at very low concentrations (about 0.1 microM). After nausea, the most common adverse effect of riluzole is asthenia, which could be due to a block of muscle sodium channels or acetylcholine receptor channels. Using the patch-clamp technique, we applied riluzole on recombinant voltage-gated skeletal muscle sodium and adult nicotinic acetylcholine receptor channels expressed in a mammalian cell line (HEK 293). Riluzole blocked the inactivated state of voltage-gated skeletal muscle sodium channels, shifting the midpoint of the steady-state inactivation curve to more negative potentials, but only in comparatively high concentrations (> or = 0.1 mM). At these concentrations, riluzole also caused an open-channel block at acetylcholine receptor channels. We conclude that riluzole has only a mild blocking effect on the inactivated state of voltage-gated skeletal muscle sodium channels and nicotinic acetylcholine receptor channels. As the plasma concentration of riluzole in amyotrophic lateral sclerosis (ALS) patients approximates 2 microM, it seems unlikely that asthenia is caused by a block of skeletal muscle sodium channels or acetylcholine receptor channels by riluzole.
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ABSTRACT: The transient receptor potential channel TRPC5 is a Ca(2+) -permeable cation channel, which is predominantly expressed in the brain. TRPC5 is activated in a phospholipase C-dependent way by still unidentified endogenous messengers. Recently, modulators of TRPC5, like Ca(2+) , pH, and phospholipids have been identified. However, the role of TRPC5 in vivo is only poorly understood. Novel specific modulators might be useful to improve the knowledge about TRPC5 function. Novel modulators of TRPC5 were identified in a compound screen of approved drugs and natural compounds. TRPC5-activating compounds were characterized regarding their potency and selectivity by fluorometric calcium imaging. Electrophysiological measurements were performed to analyze the biophysical properties of the channel activation. Riluzole was identified as a novel activator of TRPC5 (EC50 9.2 ± 0.5 μM). The activation mechanism is independent from G Protein signaling and phospholipase C activity. Riluzole-induced TRPC5 currents were additionally potentiated by La(3+) . Utilizing TRPC5 mutants, where the La(3+) binding site was deleted, confirmed that riluzole and La(3+) exert diverse mechanisms of action on TRPC5. Recordings of excised inside-out patches revealed a relatively direct action of riluzole on TRPC5. Here, we show that riluzole activates TRPC5 in a heterologous expression system and endogenously expressed TRPC5 in the U-87 glioblastoma cell line. Riluzole does not activate any other member of the TRPC family and could therefore, despite its action on other ion channels, provide an useful pharmacological tool to identify TRPC5-specific currents in immortalised cell lines or in acutely isolated primary cells.British Journal of Pharmacology 10/2013; 171(1). DOI:10.1111/bph.12436 · 4.99 Impact Factor
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ABSTRACT: Denervated muscles undergo fibrillations due to spontaneous activation of voltage-gated sodium (Na(+)) channels generating action potentials. Fibrillations also occur in patients with amyotrophic lateral sclerosis (ALS). Riluzole, the only approved drug for ALS treatment, blocks voltage-gated Na(+) channels, but its effects on muscle Na(+) channels and fibrillations are yet poorly characterized. Using patch-clamp technique, we studied riluzole effect on Na(+) channels in cultured myotubes from ALS patients. Needle electromyography was used to study fibrillation potentials (Fibs) in ALS patients during riluzole treatment and after one week of suspension. Patients were clinically characterized in all recording sessions. In myotubes, riluzole (1 μM, a therapeutic concentration) reduced Na(+) current by 20%. The rate of rise and amplitude of spikes evoked by depolarizing stimuli were also reduced. Fibs were detected in all patients tested during riluzole treatment and riluzole washout had no univocal effect. Our study indicates that, in human myotubes, riluzole partially blocks Na(+) currents and affects action potentials but does not prevent firing. In line with this in vitro finding, muscle Fibs in ALS patients appear to be largely unaffected by riluzole.12/2014; 2014:946073. DOI:10.1155/2014/946073
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ABSTRACT: Riluzole, the only drug available against amyotrophic lateral sclerosis (ALS), has recently been shown to block muscle ACh receptors (AChRs), raising concerns about possible negative side-effects on neuromuscular transmission in treated patients. In this work we studied riluzole's impact on the function of muscle AChRs in vitro and on neuromuscular transmission in ALS patients, using electrophysiological techniques. Human recombinant AChRs composed of α(1)β(1)δ subunits plus the γ or ε subunit (γ- or ε-AChR) were expressed in HEK cells or Xenopus oocytes. In both preparations, riluzole at 0.5 μm, a clinically relevant concentration, reversibly reduced the amplitude and accelerated the decay of ACh-evoked current if applied before coapplication with ACh. The action on γ-AChRs was more potent and faster than on ε-AChRs. In HEK outside-out patches, riluzole-induced block of macroscopic ACh-evoked current gradually developed during the initial milliseconds of ACh presence. Single channel recordings in HEK cells and in human myotubes from ALS patients showed that riluzole prolongs channel closed time, but has no effect on channel conductance and open duration. Finally, compound muscle action potentials (CMAPs) evoked by nerve stimulation in ALS patients remained unaltered after a 1 week suspension of riluzole treatment. These data indicate that riluzole, while apparently safe with regard to synaptic transmission, may affect the function of AChRs expressed in denervated muscle fibres of ALS patients, with biological consequences that remain to be investigated.The Journal of Physiology 03/2012; 590(Pt 10):2519-28. DOI:10.1113/jphysiol.2012.230201 · 4.54 Impact Factor