What is the net effect when both calcium rise and potassium disturbances are present?

What is the net effect when both calcium rise and potassium disturbances are present?

• A. Prolonged repolarization
• B. Increased calcium-triggered depolarizations
• C. Shortened repolarization
• D. Prolonged repolarization and increased calcium-triggered depolarizations

Answer: (D)

The main idea is how ionic disturbances shape the cardiac action potential and triggered activity. A rise in intracellular calcium increases the likelihood of calcium-triggered depolarizations (such as delayed afterdepolarizations) because the excess Ca2+ drives inward currents via the Na+/Ca2+ exchanger and other calcium-dependent channels. A potassium disturbance that prolongs repolarization lengthens the action potential, extending the time window in which afterdepolarizations can occur. When both happen, you get both effects: the repolarization phase stays prolonged, and there are more opportunities for calcium-triggered depolarizations to occur. So the net result is prolonged repolarization and increased calcium-triggered depolarizations.

The main idea is how ionic disturbances shape the cardiac action potential and triggered activity. A rise in intracellular calcium increases the likelihood of calcium-triggered depolarizations (such as delayed afterdepolarizations) because the excess Ca2+ drives inward currents via the Na+/Ca2+ exchanger and other calcium-dependent channels. A potassium disturbance that prolongs repolarization lengthens the action potential, extending the time window in which afterdepolarizations can occur. When both happen, you get both effects: the repolarization phase stays prolonged, and there are more opportunities for calcium-triggered depolarizations to occur. So the net result is prolonged repolarization and increased calcium-triggered depolarizations.