The KCNQ family of voltage-gated K⁺ channels includes 5 known members: KCNQ1 to KCNQ5. Structurally, the KCNQ family belongs to the six transmembrane domain category of K⁺ channels. KCNQ family members can form either homomultimeric or heteromultimeric channels with different functional consequences. For example, KCNQ2 and KCNQ3 heteromultimers give rise to a much larger channel current than when either protein is expressed alone, probably due to enhanced plasma membrane expression of the combined channel. Indeed, KCNQ2/KCNQ3 heteromultimers are believed to be the molecular correlates of the so-called M current. This current is a K⁺ neuronal current that is strongly inhibited by the activation of the M₁ subtype of the muscarinic acetylcholine receptor. KCNQ5 is also expressed in visceral smooth muscle⁴ and skeletal muscle.