A Novel Modulator of Kv3 Potassium Channels Regulates the Firing of Parvalbumin-Positive Cortical Interneurons.

Kv3.1 and Kv3.2 high voltage-activated potassium channels, which display fast activation and deactivation kinetics, are known to make a crucial contribution to the fast-spiking phenotype of certain neurons. Pharmacological experiments show that the blockade of native Kv3 currents with low concentrations of tetraethylammonium or 4-aminopyridine impairs the expression of this firing phenotype. In particular, Kv3 channels are highly expressed by fast-spiking, parvalbumin-positive interneurons in corticolimbic brain circuits, which modulate the synchronization of cortical circuits and the generation of brain rhythms. Here, we describe a novel small molecule, (5R)-5-ethyl-3-(6-{[4-methyl-3-(methyloxy)phenyl]oxy}-3-pyridinyl)-2,4-imidazolidinedione (AUT1), which modulates Kv3.1 and Kv3.2 channels in human recombinant and rodent native neurons. AUT1 increased whole currents mediated by human Kv3.1b and Kv3.2a channels, with a concomitant leftward shift in the voltage dependence of activation. A less potent effect was observed on hKv3.3 currents. In mouse somatosensory cortex slices in vitro, AUT1 rescued the fast-spiking phenotype of parvalbumin-positive-fast-spiking interneurons following an impairment of their firing capacity by blocking a proportion of Kv3 channels with a low concentration of tetraethylammonium. Notably, AUT1 had no effect on interneuron firing when applied alone. Together, these data confirm the role played by Kv3 channels in the regulation of the firing phenotype of somatosensory interneurons and suggest that AUT1 and other Kv3 modulators could represent a new and promising therapeutic approach to the treatment of disorders associated with dysfunction of inhibitory feedback in corticolimbic circuits, such as schizophrenia.

Potentiation of the anticonvulsant efficacy of sodium channel inhibitors by an NK1-receptor antagonist in the rat.

PURPOSE: Many patients with epilepsy are refractory to anticonvulsant drugs or do not tolerate side effects associated with the high doses required to fully prevent seizures. Antagonists of neurokinin-1 (NK1) receptors have the potential to reduce seizure severity, although this potential has not been fully explored in animals or humans. The present study was designed to evaluate the efficacy of the NK1-receptor antagonist, vofopitant, alone and in combination with different anticonvulsant drugs. METHODS: Studies were conducted in rats using a model of generalized seizure induced by electroshock. Drug concentrations in blood and brain were determined in parallel to distinguish pharmacodynamic from pharmacokinetic interactions. RESULTS: The NK1-receptor antagonist, GR205171 (vofopitant) had no anticonvulsant efficacy by itself, but could potentiate the anticonvulsant efficacy of lamotrigine and other sodium channel blockers. However, GR205171 had no effect on the anticonvulsant potency of either valproate or gabapentin. GR205171 did not produce central nervous system (CNS) side effects at the doses tested, and it did not potentiate side effects induced by high doses of lamotrigine. The NK1-receptor inactive enantiomer of GR205171, GR226206 did not potentiate the efficacy of lamotrigine, suggesting that effects observed with GR205171 were mediated by NK1 receptors. Analysis of the dose-effect relationship for GR205171 indicated that a high (>99%) occupancy of NK1 receptors is required for effect, consistent with previous behavioral and human clinical studies with this pharmacologic class. DISCUSSION: These results suggest that there may be benefit in adding treatment with a suitable NK1-receptor antagonist to treatment with a sodium channel blocker in patients with refractory epilepsy.

Automated patch clamping using the QPatch.

Whole-cell voltage clamp electrophysiology using glass patch pipettes (1) is regarded as the gold standard for measurement of compound activity on ion channels. Despite the high quality of the data generated by this method, in its traditional format, patch clamping has limited use in drug screening due to very low throughput. Over the years, developments in microfabrication have driven the development of planar, multi-aperture technologies that are suitable for parallel, automated patch recording techniques. Here we present detailed methods for two common applications of the planar patch technology using one of the commercially available instruments. The results demonstrate (a) the high quality of whole-cell recordings obtainable from cell lines expressing human Nav1.2 or hERG ion channels, (b) the advantages of the methodology for increasing throughput, and (c) examples of how these assays support ion channel drug discovery.

The relationship between sodium channel inhibition and anticonvulsant activity in a model of generalised seizure in the rat.

The development of novel anticonvulsant drugs with improved efficacy for the treatment of epilepsy is hindered by a lack of information regarding the quantitative relationship between target mechanism and in vivo efficacy. In the present study we have examined the correlation between the potency of structurally diverse compounds at voltage-gated sodium channels in vitro and their efficacy in a rodent model of acute generalised seizures induced by electroshock. We observed a significant correlation between the estimated affinity (Ki) of the compounds for the inactivated state of human recombinant Na(V)1.2 channels and the unbound brain concentration required for anticonvulsant efficacy. Furthermore, the data suggest that an unbound concentration equivalent to less than 50% of the Ki is sufficient for anticonvulsant effect. We noted that increasing sodium channel blocking potency was associated with increasing brain tissue binding and lipophilicity. These data suggest that there is a balance between sodium channel blocking potency in vitro and good pharmacokinetic characteristics necessary for anticonvulsant efficacy in vivo. Finally, we examined the sodium channel blocking potency of sodium valproate in relation to its anticonvulsant efficacy in vivo. We found that a higher unbound concentration of the drug in the brain was required for anticonvulsant efficacy than would be expected given its sodium channel blocking potency.