Cannabidiol Selectively Binds to the Voltage-Gated Sodium Channel Nav1.4 in Its Slow-Inactivated State and Inhibits Sodium Current.

Chiung-Wei Huang,Jian-Lin Chen,Ming-Jen Lee,Pi-Chen Lin

doi:10.3390/biomedicines9091141

Abstract

Cannabidiol (CBD), one of the cannabinoids from the cannabis plant, can relieve the myotonia resulting from sodium channelopathy, which manifests as repetitive discharges of muscle membrane. We investigated the binding kinetics of CBD to Nav1.4 channels on the muscle membrane. The binding affinity of CBD to the channel was evaluated using whole-cell recording. The CDOCKER program was employed to model CBD docking onto the Nav1.4 channel to determine its binding sites. Our results revealed no differential inhibition of sodium current by CBD when the channels were in activation or fast inactivation status. However, differential inhibition was observed with a dose-dependent manner after a prolonged period of depolarization, leaving the channel in a slow-inactivated state. Moreover, CBD binds selectively to the slow-inactivated state with a significantly faster binding kinetics (>64,000 M−1 s−1) and a higher affinity (Kd of fast inactivation vs. slow-inactivation: >117.42 μM vs. 51.48 μM), compared to the fast inactivation state. Five proposed CBD binding sites in a bundle crossing region of the Nav1.4 channels pore was identified as Val793, Leu794, Phe797, and Cys759 in domain I/S6, and Ile1279 in domain II/S6. Our findings imply that CBD favorably binds to the Nav1.4 channel in its slow-inactivated state.

Highlights

The voltage-gated sodium channel is a hetero-multimeric protein composed of a large ion-conducting, voltage-sensing α-subunit and a few smaller β-subunits [1,2,3,4,5]
Considering the lack of therapy for myotonia resulting from Nav 1.4 channel mutations, we investigated whether CBD could represent another drug of choice for the treatment of symptoms
Our study showed that CBD binds more selectively to the slow-inactivated state with a fast-binding kinetics (>64,000 M−1 s−1 ) and a high affinity (Kd of slow-inactivation is approximately 31.5 μM) (Figure 6)

Summary

Introduction

The voltage-gated sodium channel is a hetero-multimeric protein composed of a large ion-conducting, voltage-sensing α-subunit and a few smaller β-subunits [1,2,3,4,5]. The voltage-gated sodium channel Nav 1.4 of the skeletal muscle is a heterodimer consisting of a pore-forming α and a regulatory β1-4 subunit [6,7]. The α-subunit contains four homologous domains (DI–DIV), each with six transmembrane segments [6,7]. The S4 segments in each domain, containing positive amino acid residues and functioning as voltage sensors, can move outward to alter the channel conformation and modify its biophysical property [1,2,3,4,5,6,7]. The different charge residues of the S4 segments play an important role in determining domain-specific functions [6,7]. The S4 segments in the domains DI and DII are thought to be key molecules for the activation of the sodium channel, whereas the S4s in DIII and DIV regulate the fast inactivation process

Results

Discussion

Conclusion