Question 1

The class III drug amiodarone:&#10;A) Delays influx of sodium into the myocyte&#10;B) Blocks several potassium channels, prolonging the action potential&#10;C) Delays influx of calcium into the myocyte&#10;D) Has beta adrenergic receptor blockade properties&#10;E) All of the above are correct

Accepted Answer

Amiodarone has an extremely complex and incompletely understood spectrum of actions. It blocks several K⁺ channels. It blocks both Na⁺ and Ca⁺⁺ channels (class I and IV effects) and is a noncompetitive β receptor antagonist (class II effect).

Question 2

The action potential of a myocardial pacemaker cell differs from that of the non-pacemaker cell in that:&#10;A) The resting membrane potential is more negative in the pacemaker cells.&#10;B) The depolarization is faster in the pacemaker cell.&#10;C) Ca&#8314;&#8314; channels do not play a significant role in the pacemaker cell action potentials.&#10;D) Potassium channels conductance is primary for initiation of the action potential in pacemaker cells.&#10;E) The pacemaker cell action potential depolarization is initiated by the influx of calcium.

Accepted Answer

The myocardial pacemaker cell's sodium channels are inactivated. Calcium influx is the initiator of the depolarization that results in a slow, more prolonged action potential.

Question 3

The mechanism of action of class III antiarrhythmic drugs is:&#10;A) Sodium channel blocker&#10;B) Potassium channel blocker&#10;C) Beta adrenergic blocker&#10;D) Calcium channel blocker&#10;E) Local anesthetic action

Accepted Answer

The electrophysiologic action of class III antiarrhythmics includes the blockade of one or more of the three types of potassium channels involved in phase 3 of the action potential of myocardial cells.

Deck 22: Antiarrhythmic Drugs