Inactivated voltage-gated sodium channels are preferentially targeted in cinacalcet block of mouse neocortical action potentials

Abstract

Voltage-gated sodium channel (VGSC) activation is essential for action potential generation in the brain. Allosteric calcium-sensing receptor (CaSR) agonist, cinacalcet, strongly and ubiquitously inhibits VGSC currents in neocortical neurons via an unidentified, G-protein-dependent blocking molecule. The mechanisms by which VGSC characteristics influence cinacalcet-mediated inhibition are not well understood. Here, using whole-cell patch clamp methods, we investigated the voltage-dependence of cinacalcet-mediated inhibition of VGSCs and the channel state preference of cinacalcet. The rate of inhibition of VGSC currents was accelerated at more depolarized holding potentials. Cinacalcet shifted the voltage-dependence of both fast and slow inactivation of VGSCs in the hyperpolarizing direction. Utilizing a simple model, the voltage-dependence of VGSC current inhibition may be explained if the affinity of the blocking molecule to the channel states follows the sequence: fast-inactivated > slow-inactivated > resting. The state dependence of block contributes to the non-linearity of action potential block by cinacalcet. This dynamic and abundant signaling pathway by which G-proteins regulate VGSC currents provides an important voltage-dependent mechanism for modulating central neuronal excitability. Key points summaryVoltage-gated sodium channels are essential for the action potential generation and propagation that is central to physiological function in excitable cells. VGSC inhibitors are useful therapies to treat epilepsy, pain, and cardiac arrhythmias. Cinacalcet inhibits VGSC currents strongly and the underlying G-protein dependent signaling pathway occurs in the vast majority of neocortical and hippocampal neurons. Here we demonstrate that cinacalcet inhibits the VGSC current by activating a downstream blocking molecule that preferentially binds to the fast-inactivated state, that the blocking molecule stabilizes the inactivated states, and that cinacalcet impacts neuronal excitability in a non-linear manner. Characterization of the mechanism by which cinacalcet operates will facilitate the determination of its role in regulating neocortical excitability and the identification of new therapeutic targets for epilepsy, pain, and arrythmias.