Active transport mechanisms maintain the potential difference across the membrane by moving ions against their concentration gradient. This requires energy input, usually in the form of ATP hydrolysis. The sodium-potassium pump, or Na+/K+-ATPase, is an example of an active transport mechanism that maintains the membrane potential.

The sodium-potassium pump is a membrane protein that transports three sodium ions out of the cell for every two potassium ions that it brings in. This creates a net negative charge inside the cell, which helps to maintain the membrane potential. The sodium-potassium pump is also responsible for regulating the cell volume by controlling the movement of water into and out of the cell.

Other active transport mechanisms include the calcium pump, which transports calcium ions out of the cell, and the hydrogen pump, which transports hydrogen ions into the cell. These active transport mechanisms help to maintain the proper concentrations of ions inside the cell, which is essential for cellular function.