QX-314 is a quarternary lidocaine derivative which acts as a local anesthetic and a strong sodium channel protein inhibitor of intracellular voltage-sensitive sodium ion conductance. QX-314 effectively blocks cardiac Na⁺ channels when applied from either side of the membrane, but blocks neuronal Na⁺channels only from the intracellular side. Externally applied QX-314 was shown to inhibit high frequency activity in sensory nerves. The Na⁺ dependent action potential is completely blocked approximately five minutes after impalement with approximately 50 mM QX-314 containing microelectrode, whereas the low-threshold Ca²⁺ spike is still generated.