Final answer:
Inward delayed rectifier channels assist in sustaining the plateau phase and contribute to repolarization, whereas outward delayed rectifier channels help end the action potential by contributing to repolarization as well.
Step-by-step explanation:
What distinguishes inward delayed rectifier channels from outward delayed rectifier channels in terms of their function during the cardiac action potential is how they contribute to the phases of the cardiac action potential. Inward delayed rectifier channels, also known as IK1 channels, help to sustain the long plateau phase of the cardiac action potential, which is critical for ensuring the heart muscles contract properly and for maintaining the refractory period. This contributes to the repolarization phase. On the other hand, outward delayed rectifier channels, designated as IK, contribute to restoring the membrane potential to its resting state by allowing K+ ions to leave the cell, also aiding repolarization. Unlike inward channels, they do not support the plateau phase but are crucial for ending the action potential. Thus, the correct answer is: both inward and outward delayed rectifier channels contribute to repolarization.