Comparative volumetric analysis between hSGLT1-expressing and ROMK2-expressing oocytes. (A) Comparison of long time-course experiments, including an hypotonic shock of −20 mOsm/kg at the end of each experiment. (B) Enlarged depiction of early events in volume changes. The water flow at 30 s of transport was determined from the slope of the empirical fit. For these specific experiments, the water permeabilities were 6.13 × 10−4 cm/s for the SGLT1-, and 2.38 × 10−4 cm/s for the ROMK2-expressing oocyte. The osmotic pressures deduced from their swelling at t = 30 s are, after normalization to a standard 1 μA current, 6.8 mOsm and 1.7 mOsm for SGLT1 and ROMK2, respectively.