ICA 121431 is a voltage-gated sodium channel (Na
v) blocker that selectively blocks Na
v1.1 and Na
v1.3 over Na
v1.4, and Na
v1.5-1.8 channels (IC
50s = <20, 19, 240, and >10,000 nM, respectively).
1 It induces a concentration-dependent hyperpolarizing shift in voltage dependence of inactivation of Na
v1.3 channels at a concentration 1 μM but has no effect on resting channels. Substitution of the Na
v1.3 domain IV voltage-sensor domain (VSD4) with the Na
v1.5 VSD4 reduces ICA 121431 potency by approximately 500-fold.