Final answer:
Amiodarone and similar potassium channel blockers affect the repolarization phase of the cardiac action potential, leading to an elongation of the action potential duration and QT interval on an ECG. It does not demonstrate α agonist effects, and it is not mainly renally excreted but rather metabolized in the liver and excreted through bile. Amiodarone prolongs instead of shortens the QTc interval.
Step-by-step explanation:
Effects of Potassium Channel Blockers Like Amiodarone on Cardiac Action Potential
Potassium channel blockers, such as amiodarone and procainamide, are medications that are used in the treatment of cardiac dysrhythmias, which are abnormal electrical activities in the heart. These drugs work by inhibiting the movement of potassium (K+) through voltage-gated K+ channels. During a cardiac action potential, these potassium channels are integral in the repolarization phase. Specifically, the part of the action potential that would be affected is the phase where the cell returns to its resting state after the depolarizing spike. By blocking potassium channels, amiodarone prolongs repolarization, leading to an elongation of the action potential duration and, consequently, the QT interval on an electrocardiogram (ECG).
Amiodarone is also known to have effects beyond potassium channel blocking, such as sodium channel blocking, calcium channel blocking, and α and β adrenergic antagonist effects, but it does not exhibit α agonist effects. It also predominantly undergoes hepatic metabolism with some excretion through the bile, rather than being mainly renally excreted. In addition, contrary to shortening the QTc interval, amiodarone is known for potentially prolonging it.