The Na+ Channel Inactivation Gate Is a Molecular Complex

Abstract

Electrical activity in nerve, skeletal muscle, and heart requires finely tuned activity of voltage-gated Na+ channels that open and then enter a nonconducting inactivated state upon depolarization. Inactivation occurs when the gate, the cytoplasmic loop linking domains III and IV of the α subunit, occludes the open pore. Subtle destabilization of inactivation by mutation is causally associated with diverse human disease. Here we show for the first time that the inactivation gate is a molecular complex consisting of the III-IV loop and the COOH terminus (C-T), which is necessary to stabilize the closed gate and minimize channel reopening. When this interaction is disrupted by mutation, inactivation is destabilized allowing a small, but important, fraction of channels to reopen, conduct inward current, and delay cellular repolarization. Thus, our results demonstrate for the first time that physiologically crucial stabilization of inactivation of the Na+ channel requires complex interactions of intracellular structures and indicate a novel structural role of the C-T domain in this process.

Pathogenic mechanism of recurrent mutations of SCN8A in epileptic encephalopathy

“…This observation is consistent with previous studies demonstrating a direct role of the C‐terminal domain in fast inactivation 29, 33. Interaction of the C‐terminus of sodium channel Na v 1.5 with its inactivation gate was shown to stabilize the inactivated state 31, 34. Exchange of C‐terminal domains between sodium channels Na v 1.2, Na v 1.5, and Na v 1.6 results in partial transfer of inactivation properties 28, 33.…”

“…Due in part to the multiple intramolecular interactions within the sodium channel α subunit,31, 32 substitution of a single amino acid often has multiple effects on sodium channel function.…”

Functional Interactions between Distinct Sodium Channel Cytoplasmic Domains through the Action of Calmodulin

“…2, B and C) is consistent with numerous studies showing that mutations in the two cytoplasmic domains have concordant effects on the voltage dependence of inactivation, and suggests functional interaction between these regions (9, 29 -31). Moreover, evidence has accumulated in support of interactions between CaM, the C terminus, and the DIII-DIV linker (13,24).…”

“…In addition, the DIII-DIV linker has recently been implicated as a site for CaM interaction (13,14,24). Moreover, it has been proposed that CaM is required to stabilize the interaction of the C terminus with the DIII-DIV linker (13).…”

Phosphorylation of the A-kinase-anchoring Protein Yotiao Contributes to Protein Kinase A Regulation of a Heart Potassium Channel

“…All of the constructs were sequenced. GST fusion proteins of Yotiao fragments were then grown in DE3 cells as described previously (21).…”