35Cl- and 2H NMR measurement of intracellular water volume in renal proximal tubules

Knowledge of cell water volume is essential for the calculation of concentrations of intracellular ions and metabolites in kidney tubules. The authors have developed a method which utilizes 35Cl- NMR as a measure of extracellular volume and 2H NMR in combination with a membrane-impermeant shift reagent Dy(DTPA) as a measure of the ratio of intra- and extracellular water volumes. Measurement of extracellular volume by 35Cl- NMR is possible since intracellular 35Cl- resonance is broadened beyond detection in most cells. The 2H NMR measurements exploit the fact that only extracellular water is in direct contact with Dy(DTPA). 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. Denoting the extracellular volume as a fraction of the total volume by S/sub o/, and as a fraction of the total water volume by H/sub o/, the fractional cell water content, W = [(1/H/sub o/) -1]/[(1/S/sub o/)-1], can be calculated. Rat proximal tubule suspensions were prepared by the method developed in their laboratory. The water content was found to be 76.9 +/- 5% (anti +/- x SD, n = 4) at room temperature and 78.6% at 370C. Increasing extracellular osmolality from 295 to 330 mosm/kg, by addition of mannitol, decreased the water content to 70.8%. The authors results are in good agreement with the previously reported values of 69-82%, obtained by other methods. Thus, NMR is an accurate, noninvasive method for measuring the water content of renal cells