In biology, an<unk> , also called an ion pump, is a transmembrane protein that moves ions across a plasma membrane against their concentration gradient.  Such ion pumps can use energy from a variety of sources, including ATP or the concentration gradient of another ion (sometimes called an "ion exchanger").  Symporters transport an ions down their concentration gradient to fuel the transport of another type of ion in the same direction, while antiporters also use the concentration gradient in this same manner but transport in the opposite direction.  For a more detailed description of one particular kind of ion pump, see Na+/K+-ATPase.
Ion transporter
Ion channel
Calcium channel
Receptor 
Voltage-gated ion channel
Light-gated ion channel
Chloride channel
Magnesium transporters