# Mechanisms of sodium channel clustering at the neuromuscular junction

> **NIH NIH R01** · BAYLOR COLLEGE OF MEDICINE · 2022 · $348,480

## Abstract

Na+ channels are highly clustered at the neuromuscular junction (NMJ) deep in the junctional folds below
acetylcholine receptors (AchRs). Whereas AchRs respond to the release of acetylcholine from the motor
neuron and are responsible for the initial membrane depolarization, the clustered Na+ channels are
responsible for the muscle action potential. AchR clustering depends on a combination of agrin, neuregulin,
and activity dependent mechanisms that have been described in great detail. However, little is known about
the mechanisms responsible for NMJ Na+ channel clustering. Diseases including myotonia, periodic paralysis,
and myasthenic syndrome all disrupt the NMJ. Na+ channel clustering occurs at two other locations in the
nervous system including nodes of Ranvier and axon initial segments (AIS). Here, both cytoskeletal and
extracellular interactions participate in channel clustering and the mechanisms have been described in detail.
Remarkably, many of the same proteins involved in Na+ channel clustering at nodes and AIS are also found at
the NMJ. By analogy to nodes and AIS, we propose that NMJ Na+ channel clustering depends on similar
cytoskeletal and extracellular interactions. Aim 1 will consist of two parts designed to determine the
cytoskeletal interactions important for NMJ Na+ channel clustering. First, we will conditionally knockout
(specifically in skeletal muscle) the three Na+ channel-binding ankyrins (Ank1-3) singly and in combination.
Second, we will conditionally knockout the 4 different spectrins known to be expressed in muscle and that are
thought to link ankyrins (and Na+ channels) to the actin cytoskeleton. In both ankyrin and spectrin deficient
mice we will evaluate muscle function and Na+ channel clustering. In Aim 2 we will identify the extracellular
interactions that participate in NMJ Na+ channel clustering. First, we will generate muscle-specific knockouts
of the cell adhesion molecule Nfasc given its location at the NMJ and its important role mediating extracellular
interactions at the AIS and nodes. Second, since much less is known about the cell adhesion molecules and
extracellular matrix molecules that may underlie NMJ extracellular interactions, we will use proximity
biotinylation methods and proteomics to identify these proteins. We will then validate potential candidates
for their localization to the NMJ, and using gain and loss of function strategies determine their functions. The
aims proposed here will dramatically improve our understanding of the molecular mechanisms controlling Na+
channel clustering at the neuromuscular junction and may lead to important insights into the pathophysiology
of neuromuscular diseases and neuropathies where NMJs degenerate or function is compromised.

## Key facts

- **NIH application ID:** 10324587
- **Project number:** 5R01AR074988-03
- **Recipient organization:** BAYLOR COLLEGE OF MEDICINE
- **Principal Investigator:** MATTHEW N RASBAND
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $348,480
- **Award type:** 5
- **Project period:** 2020-01-20 → 2024-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10324587

## Citation

> US National Institutes of Health, RePORTER application 10324587, Mechanisms of sodium channel clustering at the neuromuscular junction (5R01AR074988-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10324587. Licensed CC0.

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