Overall, the residues in Na v 1.7 contribute 218 MV/cm, in absolute magnitude, to the projected electric field in the pore. Interestingly, we observe uneven contributions from each domain: DI contributes a total of 76.3 MV/cm, DII, 44.9 MV/cm, DIII, 49.4 MV/cm and DIV, 40.2 MV/cm (in absolute magnitude). This could be due to a proximity effect between the protein residues and the location at which the fields are calculated. Indeed, if the residues in DI were closer to the water molecules that serve as probes, then we would expect a higher overall contribution from DI. However, a plot of the absolute value of the projected field as a function of the inverse residue-probe distance reveal no such trend (Figure ). On the contrary, we see in Figure that the contribution of residues at equal distance to the probes, regardless of the domain, can vary by orders of magnitude. This suggests that the marked differences in contributions from each domain is due to the specific nature of the underlying residues. This difference between domains in generating electric fields in Na v 1.7's pore is consistent with the fact that mammalian Na v s have four homologous, yet different, domains. In contrast, bacterial channels have four identical domains, and rationalizing the importance of domain asymmetry in mammals remains a formidable challenge. Our results show that the computation of electric fields enables a quantitative assessment of the relative importance of each domain, and each specific residue, on setting the electrostatic environment in the Na v 1.7's pore.