Figure 7.

Steady-state currents induced by αMDG and phlorizin in WT and Q457R mutant proteins. Seven days after injection with cRNA, oocytes expressing WT and mutant SGLT1 were perfused with 100 mM NaCl buffer and currents were measured using a 2-electrode voltage clamp. The difference in steady-state currents measured in the absence and in the presence of αMDG or phlorizin (Pz) is plotted at each test potential from −150 to +50 mV. A. In WT, 25 mM αMDG induced Na⁺ inward current (1500 nA at −150 mV) whereas 0.1 mM Pz blocked the Na⁺ leak current (+143 nA at −150 mV). B. In Q457R mutant, both 100 mM αMDG and 0.5 mM Pz inhibited the Na⁺ leak current (+180 and + 360 nA at −150 mV, respectively). Similar results were obtained on oocytes from 3 different frog donors. The oocyte expressing Q457R-cRNA is the same one as shown in the oocyte in Figure 8B (Q/V with and without sugar) and Figure 5 (freeze-fracture).