BIOLOGICAL ANTIARRHYTHMICS-SODIUM CHANNEL INTERACTING PROTEINS.

Voltage gated Na channels (NaV ) are essential for excitation of tissues. Mutations in NaV s cause a spectrum of human disease from autism and epilepsy to cardiac arrhythmias to skeletal myotonias. The carboxyl termini (CT) of NaV channels are hotspots for disease-causing mutations and are richly invested with protein interaction sites. We have focused on the regulation of NaV by two proteins that bind in this region: calmodulin (CaM) and non-secreted fibroblast growth factors (iFGF or FHF). CaM regulates NaV gating, mediating Ca2+ -dependent inactivation (CDI) in a channel isoform-specific manner, while Ca2+ -free CaM (apo-CaM) binding broadly regulates NaV opening and suppresses the arrhythmogenic late Na current ( I Na-L ). FHFs inhibit CDI, in NaV isoforms that exhibit this property, and potently suppress INa-L , the latter requiring the amino terminus of the FHF. A peptide comprised of the first 39 amino acids of FHF1A is sufficient to inhibit INa-L , constituting a credible specific antiarrhythmic.