Comparison of observed and model-simulated changes in the mean Na⁺ and K⁺ content of RBCs during the dehydration-rehydration protocol. RBCs were treated as described for Figure 1A and sampled for their Na⁺ and K⁺ contents, measured by flame photometry (see “Materials and methods”). (B) The Lew-Bookchin red cell model⁴¹  was used to simulate the sequence followed in the experiment of Figure 3A to estimate the required changes in Na⁺ and K⁺ permeabilities (P_Na, P_K) that would reproduce the extents and time course of the measured mean Na⁺ and K⁺ content changes in panel A. The P_Na and P_K values used for the fit shown were 0.015 h⁻¹ (P_Na through Pcat, a 10-fold increase over the normal mean electrodiffusional component of the Na⁺ permeability of about 0.0015 h^{−1 41,43} ) and 10 h⁻¹ (P_K through Gardos channels), respectively. The electrodiffusional anion permeability was set at 50 h⁻¹ to represent the effect of 10 mM SCN⁻.⁴²