F A C U L T Y P R O F I L E
FISCHBARG, JORGE, M.D. Ph.D.
Coupling between fluid and electrolyte transports in epithelial layers as revealed by experiments and theory.
Office: Institute of Cardiology Research, University of Buenos Aires
Telephone: (5411) 4508-3885
Fax: (5411) 4508-3888
Dr. Fischbarg's laboratory is interested in the mechanism by which water is transported across epithelial layers. Examples are those in the kidney, digestive tube, brain, or the eye. Such mechanisms are crucial to maintain the constancy of the internal milieu, and in the case of the eye, to maintain its volume and the transparency of the organs in the visual path. Transepithelial movements of electrolytes are coupled to those of water, but how are they coupled is not known and represents the last fundamental problem unresolved in the physiology of epithelia. This laboratory has recently proposed that the coupling is electro-osmotic: a standing electrical current that recirculates around the cells would drag water across the intercellular junctions.
Although epithelial cells are not excitable, they share with neurons the characteristic of being polarized and being the site of electrical phenomena. This is put to advantage in the utilization this laboratory does of corneal endothelium, a fluid-transporting epithelium. In one approach, the electro-osmosis hypothesis is being explored by scrutinizing the electrical potential difference across the tissue for their frequency components. From this, information is being obtained on the coupling between current and water movements, and on the kinetics of the cell membrane cotransporter proteins that generate cellular electrical activity. Cellular studies include how volume regulation takes place, what is the connection between it and fluid transport, and what role if any could transcellular osmosis play in fluid transport.
The laboratory is also knowledgeable in the construction of models of epithelial transport. A recent (2005) one-dimensional model of how the corneal endothelia cell functions is being studied and implemented in other laboratories. Work continues to expand the existing model to areas of cell volume control and instantaneous water fluxes in two dimensions.
Typical questions we ask are: what role if any do protein water channels play in the fluid transport mechanism? If cells are devoid of water channels, could other membrane proteins provide aqueous pathways through the membrane? What are the topological and structural features that make possible for the leaky intercellular junctions to function as an electro-osmotic coupling site? Are these features subject to modulation? To study these problems, we utilize a variety of techniques including cell volume measurements by light scattering, detection of minute water movements across small cell and tissue patches, and cell and paracellular fluorescent microscopy. Given the ubiquitous presence of water, answers to the questions we pose are fundamental to homeostasis and may open new physiological insights, and new therapeutic approaches.
Montalbetti N, Fischbarg J. Biophysical J, in press (2009). Frequency Spectrum of Transepithelial Potential Difference Reveals Transport-Related Oscillations.
Fischbarg J, Physiol. Revs., in press (2009).Epithelial fluid transport: the enigma narrowed. The central role of the tight junction, and the supporting role of aquaporins.
Manolescu, A., Salas-Burgos, A.M., Fischbarg, J., and Cheeseman, C.I. 2005. Identification of a hydrophobic residue as a key determinant of fructose transport by the facilitative hexose transporter SLC2A7(GLUT7). J Biol Chem. 280(52):42978-83.
Diecke, F.P., Wen, Q., Iserovich, P., Li, J., Kuang, K., and Fischbarg, J. 2005. Regulation of Na-K-2Cl cotransport in cultured bovine corneal endothelial cells. Exp Eye Res. 80:777-85.
Uhlemann, A.C., Cameron, A., Eckstein-Ludwig, U., Fischbarg, J., Iserovich, P., Zuniga, F.A., East, M., Lee, A., Brady, L., Haynes, R.K., and Krishna, S. 2005. A single amino acid residue can determine the sensitivity of SERCAs to artemisinins. Nat Struct Mol Biol. 12:628-9.
Fischbarg, J., and Diecke, F.P. 2005. A mathematical model of electrolyte and fluid transport across corneal endothelium. J Membr Biol. 203:41-56.
Rodriguez ,P., Rivas, C.I., Godoy, A., Villanueva, M., Fischbarg, J., Vera, J.C., and Reyes, A.M. 2005. Redefining the facilitated transport of mannose in human cells: absence of a glucose-insensitive, high-affinity facilitated mannose transport system. Biochemistry. 44:313-20.
Salas-Burgos, A., Iserovich, P., Zuniga, F., Vera, J.C., Fischbarg, J. 2004. Predicting the three-dimensional structure of the human facilitative glucose transporter glut1 by a novel evolutionary homology strategy: insights on the molecular mechanism of substrate migration, and binding sites for glucose and inhibitory molecules. Biophys J. 87:2990-9.
Kuang, K., Li, Y., Yiming, M., Sanchez, J.M., Iserovich, P., Cragoe, E.J., Diecke, F.P., and Fischbarg, J. 2004. Intracellular [Na+], Na+ pathways, and fluid transport in cultured bovine corneal endothelial cells. Exp Eye Res. 79:93-103.
Fischbarg, J., Maurice, D.M. 2004. An update on corneal hydration control. Exp Eye Res. 78:537-41.
Kuang, K., Yiming, M., Wen, Q., Li, Y., Ma, L., Iserovich, P., Verkman, A.S., and Fischbarg, J. 2004. Fluid transport across cultured layers of corneal endothelium from aquaporin-1 null mice. Exp Eye Res. 78:791-8.
Diecke, F.P., Wen, Q., Sanchez, J.M., Kuang, K., and Fischbarg, J. (2004). Immunocytochemical localization of Na+-HCO3- cotransporters and carbonic anhydrase dependence of fluid transport in corneal endothelial cells. Am J Physiol Cell Physiol. 286:C1434-42.
Joet, T., Morin, C., Fischbarg, J., Louw, AI, Eckstein-Ludwig, U., Woodrow, C., and Krishna, S. 2003. Why is the Plasmodium falciparum hexose transporter a promising new drug target? Expert Opin Ther Targets. 7:593-602.
Wang, D., Pascual, J.M., Iserovich, P., Yang, H., Ma, L., Kuang, K., Zuniga, F.A., Sun, R.P., Swaroop, K.M., Fischbarg, J., and De Vivo, D.C. 2003. Functional studies of threonine 310 mutations in Glut1: T310I is pathogenic, causing Glut1 deficiency. J Biol Chem. 278:49015-21.
Iserovich, P., Yiming, M., Wang, Z., Bildin, V.N., Reinach, P.S., and Fischbarg, J. 2002. Epidermal growth factor stimulates fluid transport in SV40 transformed rabbit lacrimal gland cells. Adv Exp Med Biol. 506(Pt A):243-7. Klepper J, Florcken A, Fischbarg J, Voit T. (2003). Effects of anticonvulsants on GLUT1-mediated glucose transport in GLUT1 deficiency syndrome in vitro. Eur J Pediatr. 162:84-9.
Reyes, A.M., Bustamante, F., Rivas, C.I., Ortega, M., Donnet, C., Rossi, J.P., Fischbarg, J., and Vera, J.C. 2002. Nicotinamide is not a substrate of the facilitative hexose transporter GLUT1. Biochemistry. 41:8075-81.
Manning, S.K., Woodrow, C., Zuniga, F.A., Iserovich, P., Fischbarg, J., Louw, A.I., and Krishna, S. 2002. Mutational analysis of the hexose transporter of Plasmodium falciparum and development of a three-dimensional model. J Biol Chem. 277:30942-9.
Iserovich, P., Wang, D., Ma, L., Yang H, Zuniga F.A., Pascual, J.M., Kuang, K., De Vivo, DC., and Fischbarg, J. 2002. Changes in glucose transport and water permeability resulting from the T310I pathogenic mutation in Glut1 are consistent with two transport channels per monomer. J Biol Chem. 277:30991-7.
Fischbarg J. 1997. The mechanism of fluid transport across corneal endothelium and other epithelial layers: A possible explanation based on cyclic cell volume regulatory changes. Brit. J. Ophthalmol., 81:1-5.
Fischbarg, J., Kuang, K., Li, J., Iserovich, P., and Wen, Q. 1997. Aquaporins and ion conductance. Science, 275, 1492.
Loike, J.D., Hickman, S., Kuang, K., Xu, M., Cao, L., Vera, J.C., Silverstein, S.C., and Fischbarg, J. 1996. Sodium/glucose cotransporters display sodium and phlorizin-dependent water permeability. Am. J. Physiol., 271:C1774-1779.
Vera, J.C., Rivas, C.I., Fischbarg, J, and Golde, D.W. 1993. Mammalian Facilitative Hexose Transporters Mediate the Transport of Dehydroascorbic Acid. Nature, 364:79-82.
Echevarría, M., Kuang, K., Iserovich, P., Li, J., Preston G.M., Agre, P., and Fischbarg, J. 1993. Cultured bovine corneal endothelial cells express CHIP28 water channels. Am. J. Physiol., 265, CP34, (Cell Biol, 34) C1349-C1355.