4,9-Anhydrotetrodotoxin (13072-89-4) is a highly selective blocker of the Na(v1.6) sodium channel. (IC50's: Na(v1.2) = 260 nM, Na(v1.3) = 341 nM, Na(v1.4) = 988 nM, Na(v1.5) = 11.6 μM, Na(v1.6) = 7.8 nM, Na(v1.7) = 1.27 μM, Na(v1.8) = >30 μM.).1 It has recently been shown to also potently block human Nav1.1 channels.2
1) Rosker et al. (2007), The TTX metabolite 4,9-anhydro-TTX is a highly specific blocker of the Na(v1.6) voltage-dependent sodium channel; Am.J.Physiol.Cell Physiol., 293 C783.
2) Denomme et al. (2020), The voltage-gated sodium channel inhibitor, 4,9-anhydrotetrodotoxin, blocks human Nav1.1 in addition to Nav1.6; Neurosci. Lett. 724 134853