Figure 4.

Models of volume changes upon hypotonic challenges. A, Simulated time course of P_f. Horizontal dashed lines mark null water permeability. Up arrows mark step increase of P_f (an alternative P_f time course, pending on P_f having a zero value prior to the hypotonic challenge). Vertical lines mark the start of bath perfusion. B, Simulated time course of cell volume. Vertical lines as in A. C, A summary of the essential components of the models: (absent: 0, or present: ≠), delay (similarly), change relative to preceding P_f (gradual, g; abrupt, a; absent, 0). D, Simulated time courses of bath osmolarity, Eq. 1b to 1d (with parameter values as in Fig. 1A, b). All simulations employed Eqs. 1b to 1d and 3. Additional equations (all from Supplemental Appendix I) were used as follows: model 1: Eqs. 2d and 4 to 5, ; model 2: Eq. 2d, ; model 3: Eqs. 2e and 6, , , and , for the upper and lower lines, respectively; model 4: Eqs. 2f and 7; , delay = t_d = 10 s; model 5: Eqs. 6, 7, and 2g; all parameter values as in models 3 and 4 combined; model 6: P_f during the delay = , , and , for the upper and lower lines, respectively. E, A schematic illustration of some of the modeled vesicular mechanisms of P_f dynamics during the cell swelling phase (not all the options are included). See text for further explanations.