title: Reflection coefficients and water permeability in rat proximal tubule.
abstract: Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reflection coefficients. All perfusates contained cyanide to inhibit active transport; the tubular perfusate was isotonic and the peritubular capillaries were perfused with solutions made hypertonic with NaCl, NaHCO3, L-glucose, or sodium ferrocyanide. Measurements of recollected fluid enabled a precise mean gradient and ionic fluxes to be calculated; net water flux was measured with inulin. Imposed gradients always partly dissipated. Reflection coefficients were 0.59 +/- 0.01 for NaCl, 0.87 +/- 0.04 for NaHCO3-, and 0.96 +/- 0.07 for ferrocyanide, assuming that L-glucose was 1. Water permeability of the proximal tubule was 1,030 microns/s. Ionic permeability of Cl- (21.6 +/- 1.3 X 10(-5) cm/s) was greater than that for Na+ (13.3 +/- 2.7 X 10(-5) cm/s); permeability for L-glucose was 5.4 +/- 1.3 X 10(-5), and for ferrocyanide ions 2.7 +/- 0.9 X 10(-5) cm/s. It is concluded that in rat proximal tubule both NaCl and NaHCO3 have reflection coefficients less than 1.0 and solute asymmetry across the epithelium is a significant driving force for fluid reabsorption. Furthermore the data suggest that there is a significant contribution of solvent drag to solute movement.
authors: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
authors: R
authors: R
authors: Green
authors: G
authors: G
authors: Giebisch
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001834:Body Water / Q000502:physiology; D002196:Capillaries / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000502:physiology; D004848:Epithelium / Q000502:physiology; D007687:Kidney Tubules, Proximal / Q000098:blood supply / Q000502:physiology*; D008297:Male; D008433:Mathematics; D008962:Models, Theoretical; D009994:Osmolar Concentration; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001639:Bicarbonates; D002712:Chlorides