Mexiletine hydrochloride inhibits NaV1.4 channels heterologously expressed in Xenopus oocytes. A. Time course of Nav1.4 current amplitude changes as a result of 1 mM Mexiletine hydrochloride (ab141823) application (marked by the horizontal bar), for each of the two test pulses. B. Currents were elicited by a double test pulse protocol applied every 10 sec, which is schematically described on the top panel. For the first pulse the holding potential is -120 mV while the second pulse is preceded by 300 ms at 60 mV. On the bottom; superimposed example current responses to the voltage stimulation, before (black) and during application of 1 mM Mexiletine hydrochloride (green).