1 should have similar profiles of activity and affinity in Nav1.2. However, our present data show a distinct evidence (see Fig. 1, Fig. 2 and Fig. 3 and Table 2). As observed, both CGTX-II and δ-AITX-Bcg1a induce different effects on Nav1.1 and 1.2. On Nav1.1 and 1.6, the peptides indeed shifted the Boltzmann inactivation curves to

more depolarized potentials and maintain a pedestal (see Fig. 2), by the induction of a persistent current (steady-state current – Ass), in contrary to that observed for the other clones investigated and also reports by other authors [27] and [28]. This characterizes a population of bound channels that do not inactivate. In Nav1.2, the observed effects are distinct: CGTX-II causes some slight shift in the Boltzmann curves for either activation and deactivation toward more negative potentials, while δ-AITX-Bcg1a do not alter these values. This effect may be due to BIBW2992 cell line the occurrence of a persistent current (Ass), which in turn strongly modify the so called “window current” that

is known to be able to alter the neuronal resting potential and shift activation to more hyperpolarized potential. In addition, the increase in the persistent currents by both peptides is negligible, in comparison to Nav1.1. This clearly suggests Selumetinib mouse that the binding site of type 1 toxins is not restricted only to the supposed site 3, between segments S3 and S4 of domain IV, in agreement with previous results [23]. Also, a similar discrete shift of activation toward more hyperpolarized potentials was only observed in the toxin ApC when tested in G protein-coupled receptor kinase rat DRG neurons [27], suggesting that these sea anemone type 1 toxins might act in some way as a β-scorpion fashion,

facilitating depolarization of affected cells. Thus, further site-directed mutagenesis studies in other regions of Navs should be performed in order to determine the other contact regions between channel and sea anemone toxins, as obviously other topological areas of such channels are involved in these interactions. Moreover, these biophysical parameters also reinforce the suggestion of dissimilar contact surfaces of each toxin among different sodium channel isoforms. In terms of the charge distribution of the peptides and the role of positively charged amino acids, similar controversial results were found. As for ATX-II, a Lys at position 35 was described to be crucial for activity on rat Nav1.2 [25], while for the same molecule that amino acid was not demonstrated either to alter its binding properties on neuronal cockroach membranes or decrease activity of human Nav1.5 expressed in Xenopus laevis oocytes [22]. In ApB case, a Lys in the same position was demonstrated to be determinant for its potency and activity, either in K37A or K37D substitutions [5]. Especially in the ApB-K37D mutant, its potency was drastically affected.