Tetrodotoxin-resistant Na _V 1.8 cooperates with tetrodotoxin-sensitive Na _V 1 isoforms to conduct action potentials along rodent and human vagus nerves

Voltage-gated sodium channels (Na V 1s) are critical for action potential (AP) conduction in all nerves, including the vagus. Autonomic regulation of many physiological functions of visceral organs is under the control of vagal afferent and efferent fibers. Previous studies have shown diverse expression patterns of Na V 1 isoforms in different subsets of vagal neurons. However, their specific role in AP conduction remains understudied. Hence, we conducted a pharmacological analysis of various Na V 1 inhibitors and their effects on electrically-stimulated compound action potential (CAPs) in mouse (C57BL6), rat (Sprague-Dawley), and human whole vagus nerve. Human vagus nerves were derived from de-identified trachea and lung tissue provided by Lifelink Foundation. CAPs were separated into A- and C-waves and the area under the curve was measured. Tetrodotoxin (TTX, 300nM) completely abolished vagal A- and C-wave CAPs in mouse (n=4), rat (n=4) and human (n=5) experiments, indicating that TTX-sensitive Na V 1s are essential for all vagal AP conduction. PF-05089771 (mouse Na V 1.7 blocker) and ProTX-II (rat Na V 1.7 blocker) significantly reduced both the A- (50% reduction) and C-waves (75% reduction) of mouse (n=4) and rat (n=8) CAP respectively, suggesting a predominant role for the TTX-sensitive Na V 1.7. We also observed a minor but significant reduction in vagal CAPs by blocking TTX-sensitive Na V 1.6 and Na V 1.2 isoforms. Despite the fact that vagal CAPs were entirely dependent on TTX-sensitive channels, incubation with a TTX-resistant Na V 1.8-selective inhibitor, A-803467 caused a 50% reduction in both the A-and C-wave of the mouse (n=8) and rat (n=5) vagal CAP. Similar observations were noted in our human vagus studies: AP conduction was inhibited by 60% by the Na V 1.8 inhibitor A-803467 (n=7). These results indicate that TTX-sensitive channels (mainly Na V 1.7) and TTX-resistant Na V 1.8 show cooperativity in vagal AP conduction. Our studies across different species suggest that most vagal fibers require both types of Na V 1 isoforms for this process. Pharmacological inhibition of Na V 1.8 or Na V 1.7 in the vagus nerve may have profound effects on autonomic regulation of visceral organs. U01DK116311 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.