Some cells, such as red blood cells, readily transport water, whereas the water permeability of other cells, such as neurons, is nearly undetectable. For years, researchers wondered why water transport seems to occur in some tissues but not in others. Was there an ion-transport channel doing double-duty as a water channel, or did proteins expressed in certain membranes make them leaky to water? The mystery remained until 1992, when, for the first time, Peter Agre and colleagues identified a dedicated water channel protein, aquaporin-1 (AQP-1)—work that earned Agre the Nobel Prize in 2003.
