Inhibition of voltage-dependent sodium currents by cannabidiol

Voltage-gated sodium channels initiate action potentials in excitable tissues. Altering these channels' function can lead to many pathophysiological conditions. The family of voltage-gated sodium channel genes encodes 10 proteins (including Nav2.1) distributed throughout the central and peripheral nervous systems, cardiac and skeletal muscles. The SCN4A gene encodes the Nav1.4 channel, which is primarily responsible for depolarization of the skeletal muscle fibers. Many mutations in SCN4A are found and associated with the myotonic syndromes and periodic paralyses. These conditions are both considered gain-of-function and can be severely life-limiting with respect to performing everyday tasks. From a broader standpoint, hyperexcitability presents as a significant problem in other tissues besides skeletal muscles. Gain-of-function in sodium channels has been linked to a wide-range of pathophysiological conditions such as inherited erythromelalgia, epilepsy, and arrhythmias. Treating these types of pathologies requires an in-depth understanding of their underlying mechanisms. One way to gain this understanding is to investigate physiological triggers. There is also a dire need for novel ways of reducing the hyperexcitability associated with mutant sodium channels. One promising compound is the non-psychotropic component of the Cannabis sativa plant, cannabidiol. This compound has recently been shown to modulate some of the neuronal sodium channels. Although cannabidiol has shown efficacy in clinical trials, the underlying mechanism of action remains unknown. Sodium channels could be among the molecular targets for cannabidiol.In my doctoral research: 1) I studied how a single missense mutation, P1158S, in Nav1.4 causes various degrees of gain-of-function (myotonia and periodic paralysis) by using pH changes to probe P1158S gating modifications; 2) I studied the inhibitory effects of cannabidiol on voltage-dependent sodium currents; 3) I investigated the mechanism through which cannabidiol imparts inhibition. Overall, these data reveal novel insights into sodium channel hyperexcitability and pharmacologically targeting of this hyperexcitability using cannabidiol.