抄録
In the proximal tubules, water movement from tubular lumen to peritubular capillary is the passive consequence of active solute reabsorption. This vectorial transport is characterized by a combination of many carrier proteins, expressed differently in polarized membranes, apical and basolateral membranes. In the present study, we successfully reconstructed a mathematical model of proximal tubular epithelial cells, reported by Weinstein (Am J Physiol 263: F784, 1992), on our originally developed cell simulation platform "simBio". When tubular Na+ was replaced with impermeable molecule, apical Na+ flux into the cell via Na+-driven transporter, such as Na+-glucose or Na+-H2PO4− cotransporter and Na+/H+ exchanger, was greatly reduced. Then intracellular Na+ concentration decreased gradually, resulting in the reduction of basolateral Na+ efflux via Na+-coupled transport processes such as Na+/K+ pump and Na+-3HCO3− cotransproter. According to the reduction of Na+ fluxes in each membrane, water fluxes were also greatly reduced, confirming the significance of osmosis in water reabsorption at the proximal tubules. Furthermore, known observations regarding the change of water transport in response to changes in composition of extracellular fluid, such as reduction of HCO3− and addition of cyanide and glucose, were well explained by the model. [Jpn J Physiol 55 Suppl:S113 (2005)]
