In skeletal muscle, AQP4 (Aquaporin 4, also known as mercurial insensitive water channel), localizes to the sarcolemma of fast-twitch muscle fibers. Aquaporins (AQPs) are a large family of integral membrane water transport channel proteins that facilitate the transport of water through the cell membrane. Aquaporins are widely distributed and it is not uncommon for more than one type of AQP to be present in the same cell. Aquaporins are involved in renal water absorption, generation of pulmonary secretions, lacrimation and the secretion and reabsorption of cerebrospinal fluid and aqueous humor. AQP4 is the predominant aquaporin found in brain.
