Potassium ion channel. Computer artwork of a KcsA potassium ion (K+) channel (ribbons) embedded in a phospholipid (spheres) cell membrane (horizontal, centre). Ion channels are membrane-spanning proteins that form pores in cell membranes and act as pathways for the movement of inorganic ions into and out of the cell (bottom). The KcsA channel is composed of four identical subunits. K+ channels have many functions including regulating hormone secretion, generating nerve impulses, and controlling the pace of the heart.