The sodium-potassium pump (Na+-K+
ATPase) maintains concentration gradients of both sodium (higher
outside the cell) and potassium (higher inside the cell)
Gated channels continue to be
investigated by researchers. This image of a gated potassium
channel shows four pieces that fit together to barely allow K+ through a
narrow channel when the gate is open. The surprising way in which
the gating mechanism works can be seen in the animation at