Figure 2.

VP_fM contrasted with a typical osmotic experiment in X. laevis oocytes with hAQP1. (A) Time course of experimental (dots) and simulated (lines) relative volumes. The osmotic gradient (∼140 mM) was created by diluting the external solution. The experiment was done using the EOO technique. The continuous line is the best-fitted response simulated with the variable water permeability model (VP_fM). The only parameter in this model is $P_f^{INI}$, which is modified by relative pressure $\left(P_i/P_0\right)$ according to Eq. 2. The best-fitted $P_f^{INI}$ for this experiment is 0.0043 cm·s⁻¹. $P_i/P_0$ was determined by the model according to Eq. 3, shown in Fig. 1C. The dashed line is the osmotic response predicted by the constant $P_f$ model (CP_fM), using the $P_f$ value obtained by fitting Eq. 1 up to 10 s (0.0040 cm·s⁻¹). All initial data for simulations (except $P_f^{INI}$) were obtained from the experiment. (B) Time course of $P_f$ obtained from the simulation shown in A. A transition in the water pathway from an open to a closed state seems to occur. (C) Time course of the relative internal pressure $\left(P_i/P_0\right)$ obtained in the same simulation.