Atrotoxin: a specific agonist for calcium currents in heart

Area of Science:

• Pharmacology
• Neuroscience
• Biochemistry

Background:

• Voltage-dependent calcium channels are crucial for cellular function.
• Specific labeling is needed for isolating and understanding calcium channels.
• Crotalus atrox venom contains biologically active components.

Purpose of the Study:

• To isolate and characterize a component from Crotalus atrox that modulates voltage-dependent calcium channels.
• To determine the mechanism of action of this component on calcium currents.
• To investigate its potential as a specific ligand for calcium channels.

Main Methods:

• Isolation of an active fraction from Crotalus atrox venom.
• Electrophysiological recordings on guinea pig ventricular cells to measure ion currents.
• Assays for phospholipase and protease activity.
• Radioligand binding studies using [3H]nitrendipine.
• Testing effects of extracellular vs. intracellular application.

Main Results:

• A fraction from Crotalus atrox selectively increased voltage-dependent calcium currents.
• The active component, atrotoxin, did not affect sodium or potassium currents.
• Atrotoxin acted rapidly, reversibly, and required extracellular application.
• Atrotoxin blocked [3H]nitrendipine binding to calcium channels via an allosteric mechanism.
• Cobalt and nitrendipine blocked the atrotoxin-induced increase in Ca2+ current.

Conclusions:

• Atrotoxin is a specific agonist of voltage-dependent calcium channels.
• Atrotoxin binds to the calcium channel, likely at or near the nitrendipine binding site.
• This toxin serves as a valuable tool for studying calcium channel structure and function.