These are transmembrane proteins called ion channels.
Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of all living cells (see cell potential), allowing ions to flow down their electrochemical gradient.[1] They are present in the membranes that surround all biological cells. The study of ion channels is known as channelomics and involves many scientific techniques such as voltage clamp electrophysiology (particularly patch clamp), immunohistochemistry and RT-PCR.