Final answer:
The correct answer is option D. low density of K+, high density of Na+, as this combination favors rapid depolarization and delayed repolarization, facilitating the generation of an action potential.
Step-by-step explanation:
To optimize the generation and sustainment of an action potential, a strategic balance in the density of voltage-gated channels is crucial. The initiation of an action potential on the depolarization of the cell membrane, primarily propelled by the influx of Na+ ions through activated voltage-gated Na+ channels. Optimal conditions for this process involve a high density of Na+ channels, expediting depolarization. Once the action potential reaches its zenith, the closure of Na+ channels and the opening of voltage-gated K+ channels facilitate repolarization by enabling the efflux of K+ ions.
Therefore, to prolong and facilitate the action potential, a low density of K+ channels is preferred. This arrangement delays the exit of K+, extending the duration of depolarization and making it easier to achieve and sustain the action potential. In summary, the most conducive combination is a high density of Na+ channels coupled with a low density of K+ channels, exemplified by option D.