# The Role of the Sodium Channel Beta Subunit in Cardiac Conduction

> **NIH NIH R01** · VIRGINIA POLYTECHNIC INST AND ST UNIV · 2020 · $439,192

## Abstract

ABSTRACT: This project seeks to characterize a novel mechanism of cardiac action potential (AP)
conduction and develop new approaches to treat arrhythmias based on the insights gained. We have reported
that the Nav1.5 subunit of the Na+ channel is concentrated at the Cx43 (Gja1) gap junction (GJ) edge in an
intercalated disk nanodomain called the perinexus. The high concentration of Na+ channels and narrow inter-
membrane width at the perinexus are consistent with theoretical predictions of a structural unit that may
support ephaptic conduction. The hypothesis tested is that the β subunit of the Na+ channel complex is the
central organizing element of this unit: The ephapse. Our premise is that the adhesion function of β1 (Scn1b)
promotes the formation of specialized regions of inter-membrane contact within intercalated disks. This
arrangement is envisaged as enabling trans-interacting Na+ channels to form between myocytes, facilitating
cell-to-cell conduction of AP. Furthermore, we propose that agonists that maintain ephapse adhesion could
constitute new therapies to mitigate arrhythmogenic conduction defects following myocardial infarction. In
support of the hypothesis, data is provided from super-resolution, electron, and immuno-electron microscopy
and smart patch clamp (SPC) studies that Nav1.5 and β1 subunits, as well as active Na+ channels, are
concentrated in the perinexus. Moreover, we have developed a novel β1 inhibitor - a 19 amino acid mimetic
of the adhesion domain of β1 (βadp1). In electric cell-substrate impedance sensing assays, βadp1 caused
loss of adhesion between cells heterologously over-expressing β1. Infusion of βadp1 into hearts resulted in
dose-dependent: (1) Widening of the perinexal cleft consistent with β1 de-adhesion; (2) Conduction slowing;
and (3) Increased ventricular arrhythmia incidence. Importantly, while inhibition of β1 adhesion appeared to
have no effect on whole-cell Na+ currents, SPC revealed a selective decrease in GJ-associated Na+ channel
activity. Finally, preliminary data is shown for a rationally designed agonist of β1-mediated trans-interaction
(dbl-βadp) that promotes adhesion between β1 over-expressing cells. To test the hypotheses that: (1) β1 is
required for stabilizing trans-interacting Na+ channels at the ephapse; and (2) β1-mediated adhesion is an
anti-arrhythmic target: Aim 1 will determine the requirement of β1 and Cx43 GJs for the hypothesized ephaptic
mechanism. Mice encoding Scn1b and Gja1 null alleles, together with the β1 trans-adhesion inhibitor βadp1,
will be used in studies of the structure and autonomous function of the hypothesized ephapse. Aim 2 will
determine the role of β1 adhesion on Na+ channel activity and remodeling and AP conduction in myocyte
monolayers. A GJ-plaque-forming, but functionally incompetent Cx43 mutant (L90V) will be used in a strategy
to study the contribution of the ephaptic mechanism to conduction independent of GJ coupling. Aim 3 will
develop efficient molec...

## Key facts

- **NIH application ID:** 9923757
- **Project number:** 5R01HL141855-03
- **Recipient organization:** VIRGINIA POLYTECHNIC INST AND ST UNIV
- **Principal Investigator:** ROBERT G GOURDIE
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $439,192
- **Award type:** 5
- **Project period:** 2018-07-01 → 2022-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9923757

## Citation

> US National Institutes of Health, RePORTER application 9923757, The Role of the Sodium Channel Beta Subunit in Cardiac Conduction (5R01HL141855-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9923757. Licensed CC0.

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