The permeability of the human red cell to deuterium oxide (heavy water)

Using a stopped‐flow device, the osmotic water permeability of human red cells to D 2 O and H 2 O was studied as a function of temperature and under the influence of the sulfhydryl reagent paracholoromercuribenzene sulfonic acid (PCMBS), an inhibitor of water transport. The ratio, permeability (D 2 O)/permeability (H 2 O) at each temperature can be predicted simply by assuming that permeability varies inversely with macroscopic viscosity. When water permeability is inhibited with PCMBS, this dependency on viscosity vanishes; the inhibited permeabilities in D 2 O and H 2 O are indistinguishable.