Which ion channel type is most associated with maintaining a negative resting membrane potential during diastole in ventricular tissue?

• A. Inward rectifier channels
• B. Slow Na+ channels
• C. Transient outward channels
• D. Fast Na+ channels

Answer: (A)

The resting membrane potential in ventricular myocytes is set mainly by potassium leak conductance, especially through inward rectifier potassium channels. These channels (I_K1) provide a strong, stable K+ current when the cell is at negative potentials, pulling the membrane toward the K+ equilibrium potential and keeping it very negative during diastole. Their inward-rectifier property means they conduct best when the interior is hyperpolarized, effectively clamp the resting voltage and prevent unwanted depolarization.

The other options don’t maintain resting negativity. Fast Na+ channels drive the rapid upstroke of the action potential and are inactivated at rest; transient outward channels contribute to early repolarization during the action potential; slow Na+ currents are not the main keepers of the resting potential in ventricular tissue.