Apamin, a highly specific Ca2+ blocking agent in heart muscle.

Area of Science:

• Cardiology
• Neuropharmacology
• Biophysics

Background:

• Apamin, a bee venom peptide, is known to block specific calcium-dependent potassium channels in muscle cells.
• Naturally occurring and stimulated slow action potentials (APs) are crucial for cardiac function.

Purpose of the Study:

• To investigate the effect of apamin on slow action potentials (APs) in cultured chick heart cells.
• To determine if quinidine can reverse apamin-induced blockade of cardiac slow channels.

Main Methods:

• Cultured cell reaggregates from chick hearts were used to study slow APs.
• Electrophysiological recordings were performed on isolated chick ventricular cells.
• Dose-dependent effects of apamin and reversal by quinidine were assessed.

Main Results:

• Apamin effectively blocked naturally occurring and isoproterenol-induced slow APs in a dose-dependent manner.
• The blockade by apamin was not reversible with standard washout but was reversed by quinidine.
• Fast action potentials remained unaffected by apamin and were restored upon washout.

Conclusions:

• Apamin is a highly specific blocker of cardiac calcium-dependent potassium channels involved in slow APs.
• Apamin exhibits tight binding to these slow channels, inhibiting cardiac electrical activity.
• Quinidine acts as an antagonist to apamin binding, suggesting a potential therapeutic application.