Aquaporin-1 is a protein that functions as a water channel in cell membranes. It facilitates the rapid transport of water molecules in and out of cells, playing a crucial role in maintaining fluid balance in various tissues, including the kidneys and the eyes. This protein is essential for processes like urine concentration and the regulation of intraocular pressure. Discovered in the late 1990s, Aquaporin-1 is part of a larger family of aquaporins, which are found in many organisms. Its structure allows it to selectively permit water passage while blocking ions and other solutes, making it vital for cellular hydration and homeostasis.