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| Research Statement |
Our main area of interest is epithelial physiology and biophysics. Within that field, we are especially drawn to questions in epithelial transport processes: how do epithelia transport fluid and electrolytes, what makes membrane proteins special, how are they structured, and how do they function. We use a variety of techniques that pertain to epithelial electrophysiology, molecular biology and biochemistry, cell biology, and theoretical biology.
Over the years, our research has focused on ocular epithelial layers, and among them, on one in particular, the corneal endothelium. This layer transports fluid out of the corneal stroma, and in so doing maintains it relatively dehydrated and transparent, which is fundamental for vision. Years ago we discovered that that transport activity is accompanied by a small but measurable electrical potential difference across the layer(1). We then proceeded to characterize the influence that ambient electrolytes have on transport across that layer (5). Later on, we developed special methodology to detect fluid movements with nanoliter accuracy (6), and used it to determine routes of fluid movement across the corneal endothelium (8). Armed with these and other techniques, we went on to characterize this transport mechanism (3, 13, 16-18). In addition, we used our methods to uncover similar fluid transport mechanisms across two other ocular layers, the lens epithelium (2) and the conjunctival epithelium (15).
In the last decade, we have explored two possible explanations for how fluid is transported by the endothelium, local osmosis and electro-osmosis. To explore local osmosis, we had to determine the presence and localization of water channels in this layer (14, 20). Although we found aquaporin 1 to be present, we also determined that its absence in knockout mice does not affect fluid transport much (work in progress), which poses difficulties to account for fluid transport by local osmosis. As for the electro-osmosis hypothesis, our initial results showed an unclear picture (11), but more recent experiments have yielded evidence consistent with that hypothesis (19). We are embarking on work to elucidate the point conclusively.
Our interest in water movements led naturally to the exploration of membrane proteins that could serve as pathways for water movement. In so doing, at one point we uncovered water movements across glucose transporters (4), and thought they might be related to water channel proteins. However, later it became clear that the water channels were different proteins, aquaporins. Our interest led us to explore water movements across hypothetical water channels (10), and across AQP1 (12). In addition, the passage of water across the facilitative glucose transporter Glut1 that we observed led us to postulate a channel-like structure for membrane transporter proteins (7), and gave us ideas on how Glut1 might be structured. Recently we succeeded in developing by modeling a three-dimensional structure for Glut1 (21) that accounts for molecular biological and biochemical evidence. That structure also yields clues on how Glut1 loses its function in a pathogenic mutant (9). Work in our laboratory continues along these two main lines of interest, epithelial transport and membrane proteins.
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| Staff |
Senior Technician:
Ana Davis
Associate Research Scientist:
Pavel Iserovich, Ph.D.
Kunyan Kuang, M.D.
Staff Associate:
Li Ma, M.D.
Jose M. Sanchez, O.D.
Quan Wen, M.D.
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