What regulates the resting membrane and conduction of action potentials in cardiac muscle cells?

What regulates the resting membrane and conduction of action potentials in cardiac muscle cells?

• A. Pumps and channels, including Na+/K+ pumps, Ca2+ pumps, Na+ leak channels, and K+ leak channels.
• B. Only voltage-gated calcium channels.
• C. Sodium-potassium pumps alone.
• D. Chloride channels exclusively.

Answer: (A)

Resting membrane potential and the ability to propagate action potentials in cardiac muscle depend on maintaining ion gradients and small, steady leak currents across the cell membrane. The Na+/K+ ATPase pumps are essential because they actively move Na+ out of the cell and K+ into the cell, building and preserving the gradients that keep the inside of the cell negatively charged at rest. Without this pump, the gradients would dissipate, and the cell would lose its ready-to-fire state. Along with the pumps, leak pathways set the baseline voltage. A small leak of Na+ into the cell tends to depolarize, while leak channels for K+ allow K+ to exit, tending to hyperpolarize. The balance of these leaks determines the resting membrane potential and how close the cell is to the threshold for firing an action potential. In cardiac cells, this delicate balance is what shapes the excitability and timing of electrical wave propagation through the heart tissue. Ca2+ pumps also play a role by removing calcium from the cytosol after each contraction and helping reset the intracellular environment. This calcium handling is important for relaxation and for preparing the cell for subsequent excitations, indirectly supporting reliable conduction by maintaining proper cellular readiness and ion homeostasis. Voltage-gated calcium channels are important for the action potential’s plateau phase and contraction, but they don’t set the resting potential. Sodium-potassium pumps alone can’t account for the resting-state leak that shapes the membrane potential, and chloride channels alone don’t capture the primary regulators of cardiac resting potential.

Resting membrane potential and the ability to propagate action potentials in cardiac muscle depend on maintaining ion gradients and small, steady leak currents across the cell membrane. The Na+/K+ ATPase pumps are essential because they actively move Na+ out of the cell and K+ into the cell, building and preserving the gradients that keep the inside of the cell negatively charged at rest. Without this pump, the gradients would dissipate, and the cell would lose its ready-to-fire state.

Along with the pumps, leak pathways set the baseline voltage. A small leak of Na+ into the cell tends to depolarize, while leak channels for K+ allow K+ to exit, tending to hyperpolarize. The balance of these leaks determines the resting membrane potential and how close the cell is to the threshold for firing an action potential. In cardiac cells, this delicate balance is what shapes the excitability and timing of electrical wave propagation through the heart tissue.

Ca2+ pumps also play a role by removing calcium from the cytosol after each contraction and helping reset the intracellular environment. This calcium handling is important for relaxation and for preparing the cell for subsequent excitations, indirectly supporting reliable conduction by maintaining proper cellular readiness and ion homeostasis.

Voltage-gated calcium channels are important for the action potential’s plateau phase and contraction, but they don’t set the resting potential. Sodium-potassium pumps alone can’t account for the resting-state leak that shapes the membrane potential, and chloride channels alone don’t capture the primary regulators of cardiac resting potential.