Fig. S3.
Predicted dependence of the swelling of the rod OS disc stack on Hooke’s law constant kH of the interlinked stack. (Left) Steady-state rod OS fractional volume increase as a function of light-stimulated osmolarity increase, ΔΠ0/RT (steady-state solution to Eq. S6) for different values of kH (Eq. S4). The leftmost (solid black) curve represents kH = 0, i.e., purely osmotic equilibrium. The black solid circles are the values that apply to the results of Fig. 1, for which cytoplasmic swelling was 20.5%. (Right) kH plotted as a function of osmolarity increase, corresponding to the black solid circles in the Left. Nonzero kH values imply an osmolarity increase (abscissa) greater than the purely osmotic equilibrium (blue solid circle). (Calculations are for the experiment in Fig. 1.) In estimating a value for a molecular spring constant between discs, we assumed an osmotic increment of 75 mOsM (red arrow), 10 mOsM above the minimum level (65 mOsM) dictated by the conclusion that the saturated elongation (Figs. 1 and 3) corresponds to an osmotic equilibrium.