A Novel Drug Binding Site on Voltage-Gated Sodium Channels in Rat Brain

Riddall, Dieter; Leach, Michael J.; Garthwaite, John

doi:10.1124/mol.105.015966

Cited by 17 publications

(12 citation statements)

References 33 publications

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“…Moreover, point mutations of the external residues (e.g., in the external part of D4S6 or in the D4 external pore loop, the latter being equivalent to W1716 in Na v 1.2) would significantly alter the access of external QX-314 and local anesthetics binding to the channel pore (Ragsdale et al, 1994;Qu et al, 1995;Wang et al, 1998;Lee et al, 2001;Tsang et al, 2005). Binding assays of [ 3 H]BW202W92 of the lamotrigine family also support an external binding site for the anticonvulsants (Riddall et al, 2006). Most intriguingly, occupancy of the external pore mouth of Na + channels by external Na + would delicately alter the local geometry to make diclofenac (a structural analogue of carbamazepine and also an inactivation stabilizer of the channel) an opportunistic blocker of the pore (Yang and Kuo, 2005).…”

Section: Two-electrode Intracellular Recordingmentioning

confidence: 93%

The external pore loop interacts with S6 and S3-S4 linker in domain 4 to assume an essential role in gating control and anticonvulsant action in the Na+ channel

Yang

Hsieh

Kuo

2009

Journal of General Physiology

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Carbamazepine, phenytoin, and lamotrigine are widely prescribed anticonvulsants in neurological clinics. These drugs bind to the same receptor site, probably with the diphenyl motif in their structure, to inhibit the Na+ channel. However, the location of the drug receptor remains controversial. In this study, we demonstrate close proximity and potential interaction between an external aromatic residue (W1716 in the external pore loop) and an internal aromatic residue (F1764 in the pore-lining part of the sixth transmembrane segment, S6) of domain 4 (D4), both being closely related to anticonvulsant and/or local anesthetic binding to the Na+ channel. Double-mutant cycle analysis reveals significant cooperativity between the two phenyl residues for anticonvulsant binding. Concomitant F1764C mutation evidently decreases the susceptibility of W1716C to external Cd2+ and membrane-impermeable methanethiosulfonate reagents. Also, the W1716E/F1764R and G1715E/F1764R double mutations significantly alter the selectivity for Na+ over K+ and markedly shift the activation curve, respectively. W1716 and F1764 therefore very likely form a link connecting the outer and inner compartments of the Na+ channel pore (in addition to the selectivity filter). Anticonvulsants and local anesthetics may well traverse this “S6 recess” without trespassing on the selectivity filter. Furthermore, we found that Y1618K, a point mutation in the S3-4 linker (the extracellular extension of D4S4), significantly alters the consequences of carbamazepine binding to the Na+ channel. The effect of Y1618K mutation, however, is abolished by concomitant point mutations in the vicinity of Y1618, but not by those in the internally located inactivation machinery, supporting a direct local rather than a long-range allosteric action. Moreover, Y1618 could interact with D4 pore residues W1716 and L1719 to have a profound effect on both channel gating and anticonvulsant action. We conclude that there are direct interactions among the external S3-4 linker, the external pore loop, and the internal S6 segment in D4, making the external pore loop a pivotal point critically coordinating ion permeation, gating, and anticonvulsant binding in the Na+ channel.

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Section: Two-electrode Intracellular Recordingmentioning

confidence: 93%

The external pore loop interacts with S6 and S3-S4 linker in domain 4 to assume an essential role in gating control and anticonvulsant action in the Na+ channel

Yang

Hsieh

Kuo

2009

Journal of General Physiology

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“…Previous studies indicated that activation of PKC sensitizes TRPV1 responses (Cesare and McNaughton 1996;Premkumar and Ahern 2000;Riddall et al 2006). For this reason we tested two different PKC antagonists, 20 M sphingosine and 1 M BIM, on their ability to modulate responses to capsaicin in anisotonic conditions.…”

Section: Modulators Of Capsaicin's Responses To Changes In Tonicitymentioning

confidence: 99%

Changes in Osmolality Sensitize the Response to Capsaicin in Trigeminal Sensory Neurons

Liu

Chen²,

Liedtke³

et al. 2007

Journal of Neurophysiology

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Changes in tonicity in the peripheral nervous system can activate nociceptors and produce pain. Under local inflammatory conditions the peripheral terminals of nociceptors are subject to deviations from isotonicity. Previously it was shown that several members of the TRP(V) family of ion channels are responsive to changes in tonicity. Here we explore how changes in tonicity affect TRPV1 receptor-mediated responses to capsaicin in dissociated rat trigeminal ganglion (TG) neurons. Using whole cell patch-clamp and calcium imaging, we found that mild anisotonicity (260 and 348 mOsm/kg for hypotonicity and hypertonicity, respectively) strikingly sensitized the capsaicin-evoked current, I(caps). Confocal immunolocalization studies also revealed a modest anisotonicity-mediated redistribution of TRPV1 toward the plasma membrane of TG neurons. With respect to downstream signaling pathways, tonicity-induced sensitization of I(caps) was dependent on whether hypo- or hypertonic stimuli were applied. Specifically, antagonism of PKA- and PI3K-activated pathways appreciably reduced the hypertonicity-induced sensitization of I(caps), whereas inhibition of PKC-mediated pathways selectively reduced the sensitization produced by hypotonic solutions. In summary, whereas the overall effects of hypo- and hypertonicity resulted in a similar pattern of potentiation of I(caps), intracellular signaling pathways were selective for hypo- versus hypertonicity-induced tuning of capsaicin-activated currents.

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“…This profile is similar to the antiepileptic drugs carbamazepine (CBZ), lamotrigine (LTG), and DPH, all of which are selective for the former experimental seizure model over the latter (Miller et al, 1986;Lang et al, 1993;Meldrum, 2002). It is now generally accepted that CBZ, LTG, and DPH share a common primary mode of action (although postulated novel molecular target sites may contribute to the distinct pharmacological profiles of the drugs in different cellular compartments; Cunningham and Jones, 2000;Poolos et al, 2002;Riddall et al, 2006) in altering fast inactivation gating of voltage-gated sodium channels (Willow et al, 1985;Lang et al, 1993;Ragsdale et al, 1996), producing tonic and use-dependent blockade.…”

mentioning

confidence: 99%

The Investigational Anticonvulsant Lacosamide Selectively Enhances Slow Inactivation of Voltage-Gated Sodium Channels

Errington

Stöhr²,

Heers³

et al. 2007

Mol Pharmacol

399

345

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We hypothesized that lacosamide modulates voltage-gated sodium channels (VGSCs) at clinical concentrations (32-100 M). Lacosamide reduced spiking evoked in cultured rat cortical neurons by 30-s depolarizing ramps but not by 1-s ramps. Carbamazepine and phenytoin reduced spike-firing induced by both ramps. Lacosamide inhibited sustained repetitive firing during a 10-s burst but not within the first second. Tetrodotoxin-sensitive VGSC currents in N1E-115 cells were reduced by 100 M lacosamide, carbamazepine, lamotrigine, and phenytoin from V h of Ϫ60 mV. Hyperpolarization (500 ms) to Ϫ100 mV removed the block by carbamazepine, lamotrigine, and phenytoin but not by lacosamide. The voltage-dependence of activation was not changed by lacosamide. The inactive Sstereoisomer did not inhibit VGSCs. Steady-state fast inactivation curves were shifted in the hyperpolarizing direction by carbamazepine, lamotrigine, and phenytoin but not at all by lacosamide. Lacosamide did not retard recovery from fast inactivation in contrast to carbamazepine. Carbamazepine, lamotrigine, and phenytoin but not lacosamide all produced frequency-dependent facilitation of block of a 3-s, 10-Hz pulse train. Lacosamide shifted the slow inactivation voltage curve in the hyperpolarizing direction and significantly promoted the entry of channels into the slow inactivated state (carbamazepine weakly impaired entry into the slow inactivated state) without altering the rate of recovery. Lacosamide is the only analgesic/anticonvulsant drug that reduces VGSC availability by selective enhancement of slow inactivation but without apparent interaction with fast inactivation gating. The implications of this unique profile are being explored in phase III clinical trials for epilepsy and neuropathic pain.

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A Novel Drug Binding Site on Voltage-Gated Sodium Channels in Rat Brain

Abstract: The effectiveness of several antiepileptic, analgesic, and neuroprotective drugs is attributable to state-dependent inhibition of voltage-gated sodium channels. To help characterize their site and mode of action on sodium channels, a member of the lamotrigine family,

Cited by 17 publications

References 33 publications

The external pore loop interacts with S6 and S3-S4 linker in domain 4 to assume an essential role in gating control and anticonvulsant action in the Na+ channel

The external pore loop interacts with S6 and S3-S4 linker in domain 4 to assume an essential role in gating control and anticonvulsant action in the Na+ channel

Changes in Osmolality Sensitize the Response to Capsaicin in Trigeminal Sensory Neurons

The Investigational Anticonvulsant Lacosamide Selectively Enhances Slow Inactivation of Voltage-Gated Sodium Channels

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