Water exchange across red cell membranes: II. Measurements by nuclear magnetic resonance T1, T2, and T12 hybrid relaxation. The effects of osmolarity, cell volume, and medium.

We have used the nuclear magnetic relaxation of water protons to measure the diffusional permeability (Pw) of human red blood cells to water as a function of concentration of nonpermeable and permeable solutes. Measurements of T1, T2, and a hybrid of the two were made and yielded the same Pw. In the presence of the nonpermeable electrolyte NaCl, membrane permeability is constant between the volumes of 70 and 105 micron3 and increases both as the cells swell and shrink beyond these limits. Changes in both the internal and external osmolarity, using the permeable solutes urea and ammonium chloride, do not affect membrane permeability. The composition of the suspending medium also has a significant effect on membrane permeability. Cells suspended in plasma have a cell water lifetime about 30% longer than cells of the same volume suspended in serum, or isotonic saline with human serum albumin. Addition of a crude preparation of fibrinogen in physiological amounts to isotonic saline and human serum albumin restores the cell water lifetime to a value similar to that observed in plasma.