Diffusional water permeability of red cells. Independence on osmolality.

The osmotic permeability coefficient (Lp) for human red cells has been reported to depend on the osmolality of the suspending solution. These results are also consistent with the view that the value of Lp depends on flow rectification. In this report an NMR method is used to measure the dependence of water exchange times at constant cell volume on osmolality. Our results indicate that the diffusion water permeability is constant over a large range of osmolality (300-1000 mosM) produced by the permeable solutes urea, methanol, ethanol, and glycerol. The results support the view that the apparent dependence of Lp on osmolality is due to flow rectification.