To function normally all cells must maintain ion homeostasis and regulate water content.The lens is unusual because it is made from a packed mass of fiber cells that areincapable of independently maintaining ion and water homeostasis. The fiber cells relyon ion transport mechanisms in a monolayer of epithelial cells at the lens surface. NaK-ATPase and NKCC1 activity are particularly important. To monitor and control thisarrangement the lens has come to rely on exquisitely specialized remote controlmechanisms that utilize TRPV4 and TRPV1 channels. A TRPV4 feedback loop sensesswelling in the fiber mass and increases NaK-ATPase activity to compensate. A TRPV1feedback loop senses shrinkage in the fiber mass and increases NKCC1 activity tocompensate. The feedback loops are important. They explain homeostatic regulation oflens ion transport as well as intracellular hydrostatic pressure and they fit with theMathias model of lens circulation. TRPV4 and TRPV1 appear to be master controllers oflens homeostasis. The specific aims are: (1) Test the hypothesis that theTRPV4/hemichannel/NaK-ATPase response to swelling stretch involves a functional linkbetween TRPV4 and the actin cytoskeleton; (2) Test the hypothesis that theTRPV1/ERK/NKCC1 response to shrinkage involves a functional link between TRPV1and the tubulin cytoskeleton; (3) Explore reserve mechanisms of lens ion and waterhomeostasis. Aims 1 and 2 focus on unanswered mechanistic questions regardingTRPV4 and TRPV1 activation by opposing mechanical stimuli TRPV4-dependenthemichannel opening and the mechanism of NKCC1 activation. Aim 3 follows up pilotstudies on reserve mechanisms that support slower homeostatic responses or serve as afail-safe backup. The proposed studies are highly significant as regards human visionbecause preservation of lens transparency and refractive index gradient depends on ionand water homeostasis.