The transient receptor potential melastatin 4 channel inhibitor 9‐phenanthrol modulates cardiac sodium channel

Jian‐wen Hou, Yu‐dong Fei, Wei Li, Yi‐he Chen, Qian Wang, Ying Xiao, Yue‐peng Wang, Yi‐gang Li

9-phenanthrol, known as a specific inhibitor of transient receptor potential melastatin 4 (TRPM4) channel, has been shown to modulate cardiac electrical activity and exert antiarrhythmic property. However, its pharmacological effects remain to be fully explored. Here, we test the hypothesis that cardiac sodium current inhibition contributes to the cardioprotective effect of 9-phenanthrol. Single ventricular myocytes (VMs) and Purkinje cells (PCs) were enzymatically isolated from rabbits. Arterially perfused rabbit wedge preparations were used, transmural electrocardiogram and endocardial action potentials (APs) were simultaneously recorded. Wild type and mutated human recombinant SCN5A were expressed in HEK293 cells. Anemonia toxin II (ATX-II) was used to amplify late sodium current (INaL ) and induce arrhythmias. Whole cell patch clamp technique was used to record APs and ionic currents. 9-phenanthrol (10-50μM) stabilized ventricular repolarization and abolished arrhythmias induced by ATX-II both in isolated VMs, PCs and wedge preparations. Further study revealed that 9-phenanthrol modulated gating property of cardiac sodium channel and dose-dependently inhibited INaL and peak sodium current (INaP ) in VMs with an IC50 of 18 μM and 71.5 μM, respectively. Its INaL inhibition property was further confirmed in PCs and HEK293 cells expressing SCN5A mutation. Our results indicate that 9-phenanthrol modulates gating property of cardiac sodium channel and inhibits INaL and INaP which may contribute to its antiarrhythmic and cardioprotective benefits.