## **Core Concept**
The afterdepolarization phase in an action potential (AP) record is primarily related to changes in ionic movements across the cell membrane, specifically involving potassium (K+) and sometimes calcium (Ca2+) ions. This phase can be crucial for the regulation of the excitability of the cell.

## **Why the Correct Answer is Right**
The correct answer, , involves the movement of potassium ions out of the cell. During the repolarization phase of the action potential, potassium channels open, allowing K+ ions to leave the cell, which brings the membrane potential back towards the resting potential. This outward movement of positively charged ions is what primarily drives the repolarization and initial afterdepolarization phases.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately describe the primary ionic basis for afterdepolarization.
- **Option B:** This option is incorrect as it suggests an inward movement of a positively charged ion or an outward movement of a negatively charged ion, which does not align with the known mechanisms of repolarization and afterdepolarization.
- **Option D:** This option is incorrect because it implies an inward movement of calcium ions during afterdepolarization. While calcium ions do play a role in certain types of afterdepolarizations (like calcium-induced afterdepolarizations), the primary and most direct ionic basis for afterdepolarization involves potassium.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that afterdepolarizations can lead to premature beats or arrhythmias if they reach threshold potential. This is particularly relevant in cardiac myocytes, where early afterdepolarizations (EADs) and delayed afterdepolarizations (DADs) can predispose to dangerous arrhythmias like Torsades de Pointes.

## **Correct Answer:** .