The long-term goal of this project is to understand the role of junctional channels in the lens and their role in cataract formation. Its principal foci are on the channels formed by MIP and on communication between lens cells via channel pathways. MIP channels have been extensively studied in lipid bilayers, but have not been observed in vivo. Phosphorylation and Ca+ +-calmodulin affect the voltage dependence of the MIP channels in bilayers, and it may be that lipid composition also modulates the function of MIP. MIP channels in vivo may not have been detected because they are normally shut down, most likely by the Ca+ +-calmodulin mechanism. MIP belongs to a growing family of proteins whose members are found in tissues ranging from roots to red cells. Those members of the family which have known functions are transport proteins which facilitate the passive movement of small neutral molecules. Many of them act as water channels, and this seems to be the most likely function of MIP in the lens. Recently it has been possible to apply double patch clamping, confocal microscopy, and dye injection to the study of lens-derived cells. It is also possible to study the function of MIP in exogenous expression systems.
Our specific aims are: 1. Investigate the modulation of MIP channels in lipid bilayers. There are three important parts to this aim: to complete the study of the modulation of channel conductance by calmodulin, to ask if cytoplasmic factors are capable of modulating channel conductance, and to determine the change in the channel's volume as it closes or opens. 2. Study the properties of MIP in two expression systems. Expressing MIP in oocytes and Sf9 cells will allow measurements of water flux and electrical properties as well as measurement of the transport of a variety of other substances transported by proteins of the MIP family. These experiments should have an excellent chance of revealing the function of MIP. 3. Study the junctional permeabilities of lens cells in vivo and in dissociated cells. These experiments are aimed at connecting lens physiology with the growing field of the study of the transport properties of the MIP family. We hope that they will aide in ending the embarrassing an ironic condition that the eponymous member of the family still has an unknown function!

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Physiology Study Section (PHY)
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University of California Irvine
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Fields, James B; Németh-Cahalan, Karin L; Freites, J Alfredo et al. (2017) Calmodulin Gates Aquaporin 0 Permeability through a Positively Charged Cytoplasmic Loop. J Biol Chem 292:185-195
Reichow, Steve L; Clemens, Daniel M; Freites, J Alfredo et al. (2013) Allosteric mechanism of water-channel gating by Ca2+-calmodulin. Nat Struct Mol Biol 20:1085-92
Clemens, Daniel M; Németh-Cahalan, Karin L; Trinh, Lien et al. (2013) In vivo analysis of aquaporin 0 function in zebrafish: permeability regulation is required for lens transparency. Invest Ophthalmol Vis Sci 54:5136-43
Hall, James E (2012) Through a glass darkly. EMBO Mol Med 4:1-2