Potassium tetramerization domain. Molecular model of a human Kv7.4 potassium ion (K+) channel coiled-coil tetramerization domain. Ion channels are membrane-spanning proteins that form a pathway for the movement of inorganic ions across cell membranes. This one 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.