The central focus of this renewal will be on the molecular understanding of the macromolecular organization and functions of glial potassium, bicarbonate and water transport proteins in the mammalian retina. How transport proteins work together to coordinate the transport of solutes and water across glial cell membranes is a fundamental question in neurobiology and retinal physiology. In the preceding period, we have identified the critical role of Kir4.1 channels in the regulation of extracellular potassium concentration in the retina. This study consists of a series of steps aimed to further elucidate the composition, architecture and functions of water channels (AQP4), potassium channels (Kir4.1) and sodium bicarbonate cotransporters in retinal glia. The specific aims are the following: 1) to verify the hypothesis that potassium and water channels associate with the dystrophin glycoprotein complex (DGC) in Muller cell membranes, 2) to test the hypothesis that extracellular ligand signaling to the DGC is crucial for the highly localized expression of potassium and water channels in Muller cells, 3) determine the molecular identity of sodium bicarbonate cotransporter systems in Muller cells and verify whether they associate with the DGC, 4) extend our studies of the function of Kir4.1 channels to the retinal and optic nerve astrocytes. Potassium and water channels and sodium bicarbonate cotransporters play a critical role in potassium and acid-base buffering in retina and defects in their subunit assembly and macromolecular organization may be implicated in human diseases. The molecular understanding of the events that are central to their regulated expression is therefore essential for developing our knowledge in the area of retinal function in health and in diseases.