VOLUME REGULATION IN NORMAL AND CATARACTOUS LENSES

点击翻译按钮获取中文摘要

DESCRIPTION: The lens has an internal circulation that is generated by ion transport, which creates fluid movement in the same pattern. The circulation of ions depends on fiber cell gap junctions to conduct intracellular, outwardly directed fluxes of Na2+ and Ca2+, whereas the circulation of fluid depends on AQPO to carry water across fiber cell membranes in the presence of an osmotic gradient. Both transport systems are critical for homeostasis in central fiber cells, which rely on the inwardly directed extracellular circulation to convect essential nutrients and antioxidants, like glucose and ascorbate, into the lens. We plan to study lens fiber cell gap junctions and water channels, their relationship to calcium homeostasis and how compromise of transport can lead to loss of calcium homeostasis and cataract. The basic subunit of a gap junction channel is the connexin. Lens fiber cells express 2 connexin isoforms, Cx46 and Cx50. Our first aim is to answer the question: 1) What are the physiological roles of Cx46 and Cx50 in the lens? Membrane water channels form a family of proteins called aquaporins. The lens expresses 2 isoforms of aquaporins, AQP1 in the epithelium and AQPO in fiber cells. Our second aim is to answer the question: 2) Why does the lens switch expression from AQP1 to AQPO (ie what unique physiological role does AQPO fulfill in fiber cells)? We have found that compromise of membrane transport leads to loss of calcium homeostasis and a nuclear cataract. Our last aim is to answer the question: 3) Are oxidative effects on lens transparency initiated by damage to membrane transport proteins, consequent loss of calcium homeostasis and increased proteolysis? The distribution of functional gap junction channels will be evaluated using whole lens impedance techniques. Osmotic studies of isolated fiber cell membrane vesicles will determine water permeability and its regulation by pH and calcium. A newly developed technique for measuring the spatial distribution of intracellular calcium in intact lenses will be used to determine the effects of compromised transport on calcium homeostasis. Most studies involve lenses from genetically altered mice that express modified transport proteins.