Cationic Modulation of Voltage-Gated Sodium Channel (Nav1.5): Neonatal Versus Adult Splice Variants-2. Divalent (Cd) and Trivalent (Gd) Ions.

A "neonatal" splice-form of the voltage-gated sodium channel Nav1.5 is functionally expressed in human cancers and potentiates metastatic cell behaviors. Splicing causes the replacement of 7 amino acids, including a negatively charged aspartate in the "adult" Nav1.5 (aNav1.5) to a positively charged lysine in the "neonatal" (nNav1.5). These changes occur in the region surrounding the DI:S3-S4 extracellular linker. The splice variants respond differently to changes in extracellular H and this could be of pathophysiological significance. However, how the two differentially charged splice variants would react to cations of higher valency is not known. We used patch-clamp recording to compare the electrophysiological effects of Cd and Gd on "adult" and "neonatal" Nav1.5 expressed stably in EBNA-293 cells. Several parameters were determined for the two channels and statistically compared. Both cations inhibited peak through reducing and induced a positive shift in the voltage range of activation. However, unlike Gd, Cd had only a weak effect on voltage dependence of activation, and no effect on voltage dependence of inactivation, recovery from inactivation, or the kinetics of activation/inactivation. The electrophysiological effects of Cd and Gd studied were essentially the same for "neonatal" and "adult" Nav1.5, although these splice variants possess differences in their external charges. In contrast, the effects of H were shown earlier to be significantly differential. Taken together, these results suggest that limited adjustment of the charged structure of pharmacological agents could enable selective targeting of neonatal Nav1.5 associated with several cancers.