The PI proposes to determine at the molecular level how the cellular mechanism of fluid transport by the corneal endothelium operates. He hypothesizes that fluid transport is a particular case of volume regulation, so we will study the transporter and channel membrane proteins for which evidence suggests a role in volume regulation. Molecular identification of a comprehensive set of them in a particular tissue apparently has not been done yet. He will seek this by screening a cDNA library and analyzing mRNA contents. The PI will study protein functional characteristics by using radiolabel fluxes, by determining their role in cell volume regulation as consistent with their differential inhibition, or by expressing them or mutants he will prepare in Xenopus laevis oocytes. The cellular distribution of the component proteins will be investigated where feasible by immunolocalization. The PI hypothesizes that two different groups of transporters/channels are polarized to opposite cell sides; hence, sequential temporary activation of each group would cause cell swelling/deswelling cycles, with basolateral fluid entry followed by apical exit (vectorial fluid transport). He expects that a number of cellular processes will be spontaneously cyclic, and he will seek to develop further emerging preliminary evidence for the existence and characteristics of oscillations in the transendothelial potential difference, intracellular potential, membrane currents, and cell volume. He will also investigate whether detectable intracellular elements such as (Ca2+) display cyclic behavior consistent with the underlying hypothesis. He will continue to develop a theoretical model to provide a numerical explanation for this hypothesis on the basis of the emerging molecular biological and biophysical evidence. If time allows it, he will turn to the signaling and structural cell elements responsible for such cell behavior. He presumes that the endothelial mechanism is a general one, hence our results may be applicable to all other fluid transporting layers in the eye and the rest of the body. In particular, failure of endothelial function leads to loss of corneal transparency and eventual blindness of corneal origin; this research may help the prevention or treatment of such consequences.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Visual Sciences A Study Section (VISA)
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Fisher, Richard S
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Columbia University (N.Y.)
Schools of Medicine
New York
United States
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Sanchez, J M; Cacace, V; Kusnier, C F et al. (2016) Net Fluorescein Flux Across Corneal Endothelium Strongly Suggests Fluid Transport is due to Electro-osmosis. J Membr Biol 249:469-73
Diecke, Friedrich P J; Ma, Li; Iserovich, Pavel et al. (2007) Corneal endothelium transports fluid in the absence of net solute transport. Biochim Biophys Acta 1768:2043-8
Ma, Li; Kuang, Kunyan; Smith, Randall W et al. (2007) Modulation of tight junction properties relevant to fluid transport across rabbit corneal endothelium. Exp Eye Res 84:790-8