Resurgent-like currents in mouse vas deferens myocytes are mediated by Na^sub V^1.6 voltage-gated sodium channels

Patch-clamp experiments were performed to investigate the molecular properties of resurgent-like currents in single smooth muscle cells dispersed from mouse vas deferens, utilizing both Na^sub V^1.6-null mice (Na^sub V^1.6^sup -/-^), lacking the expression of the Scn8a Na^sup +^ channel gene, and their wild-type littermates (Na^sub V^1.6^sup +/+^). Na^sub V^1.6 immunoreactivity was clearly visible in dispersed smooth muscle cells obtained from Na^sub V^1.6^sup +/+^, but not Na^sub V^1.6^sup -/-^, vas deferens. Following a depolarization to +30 mV from a holding potential of -70 mV (to produce maximal inactivation of the Na^sup +^ current), repolarization to voltages between -60 and +20 mV elicited a tetrodotoxin (TTX)-sensitive inward current in Na^sub V^1.6^sup +/+^, but not Na^sub V^1.6^sup -/-^, vas deferens myocytes. The resurgent-like current in Na^sub V^1.6^sup +/+^ vas deferens myocytes peaked at approximately -20 mV in the current-voltage relationship. The peak amplitude of the resurgent-like current remained at a constant level when the membrane potential was repolarized to -20 mV following the application of depolarizing rectangular pulses to more positive potentials than +20 mV. 4,9-Anhydrotetrodotoxin (4,9-anhydroTTX), a selective Na^sub V^1.6 blocking toxin, purified from a crude mixture of TTX analogues by LC-FLD techniques, reversibly suppressed the resurgent-like currents. β-Pompilidotoxin, a voltage-gated Na^sup +^ channel activator, evoked sustained resurgent-like currents in Na^sub V^1.6^sup +/+^ but not Na^sub V^1.6^sup -/-^ murine vas deferens myocytes. These results strongly indicate that, primarily, resurgent-like currents are generated as a result of Na^sub V^1.6 channel activity.[PUBLICATION ABSTRACT]