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How Sodium and Calcium Ions Pass Through Batrachotoxin-Bound Sodium Channel
1Department of Biochemistry and Biomedical Sciences, Master University, Hamilton, ON L8S 4K1, Canada.
Toxins
|October 28, 2025
Summary
Batrachotoxin (BTX) binding to sodium channels enhances calcium permeation. Computational models reveal BTX-B and DEKA lysine deprotonation facilitate ion passage, explaining increased calcium influx.
Area of Science:
- Molecular Biology
- Biophysics
- Neuroscience
Background:
- Batrachotoxin (BTX) is a potent steroidal agonist that modifies sodium channel function.
- BTX binding dramatically increases calcium permeation in sodium channels.
- The precise mechanism of ion permeation and selectivity in BTX-bound channels remains unclear.
Purpose of the Study:
- To elucidate the mechanism of sodium and calcium ion permeation in BTX-bound sodium channels.
- To understand why BTX increases calcium permeation through Nav1.5 channels.
- To investigate the role of DEKA lysine protonation states in ion selectivity.
Main Methods:
- Cryo-electron microscopy (cryo-EM) structure of rat Nav1.5 with BTX-B.
- Monte Carlo energy-minimized profiles of ion permeation.
- Computational modeling of sodium and calcium ions interacting with DEKA lysine and BTX-B.
Main Results:
- Ion permeation was facilitated only when DEKA lysine and BTX-B nitrogens were deprotonated.
- Electronegative atoms of BTX-B attracted cations, stabilizing a "dunked" lysine conformation.
- This stabilization hinders lysine reprotonation and "uplifting," which normally attracts calcium.
Conclusions:
- The study proposes a mechanism for sodium and calcium ion passage through BTX-bound sodium channels.
- Deprotonation of DEKA lysine and BTX-B is crucial for cation permeation.
- BTX binding alters channel gating and selectivity, leading to increased calcium permeability.
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