title: NMR measurement of intracellular water volume in rat kidney proximal tubules.
abstract: Knowledge of cell water volume is essential for the measurement of concentrations of intracellular ions and metabolites in kidney proximal tubules. We have developed a method which utilizes 35Cl-NMR as a measure of extracellular volume and 2H-NMR, in combination with a membrane-impermeable shift-reagent [Dy-DTPA]2-, as a measure of the ratio of intra- and extracellular water volumes. Measurement of extracellular volume by 35Cl-NMR is possible, since the resonance of intracellular 35Cl is too broad to be detectable in kidney cells. The 2H-NMR measurement exploits the fact that only extracellular water is in direct contact with [Dy-DTPA]2-. However, rapid exchange of water across the cell membrane results in only a single 2H2O resonance at a chemical shift which is a weighted average of the shifted extra- and unshifted intracellular water resonances. Expression of the extracellular volume as a fraction of the total volume by fCl and as a fraction of the total water-volume by fD, permits the calculation of the fractional cell-water content fw = [(1/fD)-1]/[(1/fCl)-1]. This approach was applied to proximal tubular suspensions prepared from the rat kidney. The water content was found to be 76.9 +/- 1.8% (n = 6) at 37 degrees C. Increasing extracellular osmolality from 295 to 390 mOsm/kg H2O, by addition of mannitol, decreased the water content by 21%. Our results are in good agreement with those obtained by the gravimetric method.
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000032:analysis*; D001834:Body Water / Q000032:analysis*; D005110:Extracellular Space / Q000032:analysis; D007424:Intracellular Fluid / Q000032:analysis*; D007687:Kidney Tubules, Proximal / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D009997:Osmotic Pressure; D051381:Rats