What is the primary contributor to membrane potential?

The primary contributor to membrane potential is the potassium (K) leak channels. These channels allow potassium ions to move out of the cell more freely than other ions. As potassium exits the cell, it leaves behind negatively charged proteins and other anions that cannot cross the membrane, creating a negative charge inside the cell relative to the outside. This difference in charge establishes the resting membrane potential, typically around -70mV in many cells.

While the sodium-potassium pump plays a crucial role in maintaining the gradients of sodium and potassium across the membrane, it is not the primary factor that creates the actual membrane potential itself. Instead, it continuously works to pump three sodium ions out of the cell and two potassium ions into the cell, which helps to maintain the concentration gradients.

The accumulation of charged ions contributes to membrane potential to some extent but is mainly influenced by the selective permeability of the membrane, particularly to potassium ions. Therefore, the K leak channels are the key contributor to the resting membrane potential due to their role in allowing potassium to diffuse out of the cell more than any other ions.