Figure 10. Uphill transport of water.

An rSGLT1-expressing oocyte was exposed at time zero to an osmotic gradient of 5 mosmol obtained by adding mannitol to the bathing solution. This induced a constant rate of osmotic shrinkage as given by the relative volume changes, ΔV_T/V_T, jagged line. At t= 75 s the 5 mm mannitol was replaced by 5 mmα-MDG. This gave rise to an increase in I_C and oocyte swelling despite the adverse osmotic gradient. The change in oocyte volume could be simulated using the measured value for CR of 288 and an L_p of 0.5 before sugar application and 0.67 after sugar application, in units of cm s⁻¹ (osmol l⁻¹)⁻¹ (blue line, A). V_F/V_T was taken as 0.4 and D_i as 0.5 × 10⁻⁵ cm² s⁻¹. The volume changes were also simulated assuming only osmotic transport of water (red curves), D_i values of 0.5 × 10⁻⁵ (curve d), 0.5 × 10⁻⁶ (curve c), 0.5 × 10⁻⁷ (curve b), and 0.5 × 10⁻⁸ (curve a) were tested (units, cm² s⁻¹).