On the mechanism of fluid transport across corneal endothelium and epithelia in general.
The mechanism by which fluid is transported across epithelial layers is still unclear. The prevalent idea is that fluid traverses these layers transcellularly, driven by local osmotic gradients secondary to electrolyte transport and utilizing the high osmotic permeability of aquaporins. However, recent findings that some aquaporin knockout mice epithelia transport fluid sow doubts on local osmosis. This review discusses recent evidence in corneal endothelium that points instead to electro-osmosis as the mechanism underlying fluid transport. In this concept, a local recirculating electrical current would result in electro-osmotic coupling at the level of the intercellular junctions, dragging fluid via the paracellular route. The text also mentions possible mechanisms for apical bicarbonate exit from endothelial cells, and discusses whether electro-osmosis could be a general mechanism.
College of Physicians and Surgeons, Columbia University, New York, New York, 10032, USA. jf20@columbia.edu
Jorge
J
Fischbarg
D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000502:physiology; D001692:Biological Transport; D001826:Body Fluids / Q000502:physiology*; D003315:Cornea / Q000502:physiology*; D004563:Electrochemistry; D004727:Endothelium / Q000502:physiology; D007365:Intercellular Junctions / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009995:Osmosis / Q000502:physiology; D028021:Sodium-Potassium-Chloride Symporters / Q000502:physiology
D020346:Aquaporins; D028021:Sodium-Potassium-Chloride Symporters