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Neurotoxins that act selectively on voltage-dependent cardiac calcium channels
A M Brown1, A Yatani, A E Lacerda
1Department of Physiology and Molecular Biophysics, Baylor College of Medicine, Houston, TX 77030.
Abstract:
We searched for and found a toxin that acts specifically on cardiac calcium channels. This toxin, which we have designated TaiCatoxin (TCX), was purified from the venom of the Australian Taipan snake (Oxyuranus s. scutellatus), one of the world's most poisonous snakes. TCX is a highly charged, basic polypeptide with a molecular weight of 8,000. It blocks high- but not low-threshold cardiac calcium channels in a voltage-dependent manner and has no effect on potassium or sodium channels. The block occurs at nanomolar concentrations, is reversible, and is due to binding at an extracellularly facing site on the channel itself.
Insights
Researchers discovered TaiCatoxin (TCX), a snake venom toxin that specifically blocks cardiac calcium channels. This toxin offers a new tool for studying heart electrical activity and calcium channel function.
Area of Science:
- Pharmacology
- Toxicology
- Cardiovascular Physiology
Background:
- Cardiac calcium channels are crucial for heart electrical activity.
- Snake venom toxins are a source of novel bioactive compounds.
Purpose of the Study:
- To identify and characterize toxins that specifically target cardiac calcium channels.
- To investigate the mechanism of action of a novel toxin from Australian Taipan snake venom.
Main Methods:
- Purification of TaiCatoxin (TCX) from Oxyuranus s. scutellatus venom.
- Electrophysiological studies to assess TCX effects on cardiac calcium channels.
- Analysis of TCX binding characteristics and molecular properties.
Main Results:
- TCX, a basic polypeptide (8,000 MW), selectively blocks high-threshold cardiac calcium channels.
- The channel block is voltage-dependent, reversible, and occurs at nanomolar concentrations.
- TCX does not affect sodium or potassium channels, binding to an extracellular site.
Conclusions:
- TaiCatoxin is a potent and specific blocker of cardiac calcium channels.
- TCX provides a valuable pharmacological tool for investigating cardiac electrophysiology.
- The toxin's specific action highlights the potential of snake venom components in drug discovery.