Mediates a strong voltage-dependent potassium ion permeability of excitable membranes. Assuming opened or closed conformations in response to the voltage difference across the membrane, the protein forms a potassium-selective channel through which potassium ions may pass in accordance with their electrochemical gradient. Contains a central ion-conduction pore surrounded by four voltage sensors which form the voltage-sensor paddles that move in response to membrane voltage changes through the fluid membrane interior, each voltage-sensor carrying their four positive charges across the membrane. It is thought that the S4 arginine residues move through the membrane's electric field to open the pore. Belongs to the potassium channel family.