Use-Dependent Block of Human Cardiac Sodium Channels by GS967

Abstract

GS967 is a recently described selective late sodium current (INaL) blocker that has been shown to exert potent antiarrhythmic effects in rabbit ventricular myocytes exposed to ATX-II. The antiarrhythmic mechanism was attributed to preferential suppression of INaL with little effect on peak sodium current (INaP). We examined the effects of GS967 on INaP and INaL recorded in tsA201 cells expressing human NaV1.5. As previously described, we observed that 1 µM GS967 exhibited tonic block of INaL (63%) to a significantly greater extent than INaP (20%) without modifying the inactivation kinetics. To test the use-dependent block (UDB) of NaV1.5, we applied a series of 50 short depolarizing pulses (20 ms) at −20 mV with different frequencies (2, 10 and 20 Hz). GS967 caused a reduction of INaP in a frequency-dependent manner (block of 31%, 73% and 85% at 2, 10 and 20 Hz, respectively) consistent with UDB. This UDB was best explained by a significant slowing of recovery from fast and slow inactivation with a significant enhancement of slow inactivation in the presence of GS967. Using the SyncroPatch 384, we observed GS967 to be a more potent use-dependent blocker of INaP (IC50 = 0.07 µM) than ranolazine (16 µM) and lidocaine (17 µM). While, GS967 was found to exert these same effects on a prototypical long-QT syndrome mutation (delKPQ), an engineered mutation at an interaction site for local anesthetics (LA) (F1760A) attenuated the effect of GS967 on UDB. Lastly, an engineered mutation known to blunt slow inactivation (F1417C) also significantly reduced the effect of GS967 on UDB. We conclude that GS967 is a preferential inhibitor of INaL human NaV1.5, but it also exerts a previously unreported strong effect on slow inactivation and recovery from inactivation resulting in substantial UDB.