Loss of function by deletion of M500/I501 in hSGLT3 and hSGLT1.

(A and B) Xenopus laevis oocytes injected with cRNA of hSGLT3[wt], hSGLT3[ΔM500] and hSGLT3[ΔI501] were recorded in the voltage clamp mode (VC, panel A) and in the current clamp mode (CC, panel B). Representative continuous recordings at a holding potential of –50 mV, 30 mM Na+ and pH 5 from oocytes expressing hSGLT3[wt] display sodium currents in response to D-glucose (75 mM) and Deoxynojirimycin (DNJ; 10μM). Currents were blocked by the specific inhibitor Phlorizin (Pz; 240 μM). Current clamp recordings of the same oocyte reveal D-glucose- and DNJ-induced depolarization as well as phlorizin-induced hyperpolarization of the cell. Using identical conditions, no current or voltage responses were observed in oocytes expressing hSGLT3[ΔM500] or hSGLT3[ΔI501]. (C) Oocytes injected with cRNA of hSGLT1[wt], hSGLT1[ΔM500] and hSGLT1[ΔI501] were measured in the absence and presence of 100 mM glucose (pH 5, 30 mM Na+ and a membrane potential of -50 mV). Oocytes expressing hSGLT1[wt] display sodium currents in response to glucose, whereas no responses were observed in oocytes expressing hSGLT1[ΔM500] or hSGLT1[ΔI501]. (D) Left panel: bar graph quantifies current amplitudes in response to either D-glucose (75 mM) or DNJ (10 μM) at -50 mV and 30 mM Na+. As a negative control, results from H2O-injected oocytes are displayed (n = 6 ± SD of two independent experiments). Right panel: bar graph quantifies current amplitudes in response to D-glucose (100 mM) at -50 mV and 30 mM Na+ of hSGLT1[wt], hSGLT1[ΔM500] and hSGLT1[ΔI501] and water controls (n = 6 ± SD of two independent experiments).