Figure 5. Uphill transport of water by EAAT1.

The EAAT1-expressing oocyte was initially bathed in glutamate-free control solutions under clamped conditions (-30 mV). At the time indicated by the horizontal bar, glutamate (200 μm) was added to the bathing solution (+glu). This induced an immediate swelling of the oocyte; this part of the experiment is analogous to that illustrated in Fig. 1A and B. In the following three recordings the stimulation by glutamate was combined with a hyperosmotic challenge of 2.5, 5 and 15 mosmol l⁻¹ of mannitol, respectively (+man). The glutamate-induced current I_s (not shown) was about 300 nA in all four experiments (see text). It appears that the inwardly directed cotransport of water can proceed despite adverse osmotic gradients. The rates of water transport are plotted in Fig. 6A as a function of the osmotic challenge.