Fig. 1.

Incomplete inhibition produced by phlorizin (Pz). A: typical OFF currents for a sodium/myo-inositol transporter 2 (SMIT2)-expressing oocyte. Currents measured when the holding potential is returned to −50 mV following a 300-ms pulse to +40 or −155 mV are shown for 90 mM Na⁺ (black line), 90 mM Na⁺ with 500 μM Pz (light gray line), and 0 Na⁺ (gray line). If Pz inhibits well the OFF current from −155 mV, it is a poor inhibitor of the OFF current from +40 mV. B: transferred charges associated with the OFF currents at 0 Na⁺ (black) and 90 mM Na⁺ (gray) and 90 mM Na⁺ with 500 μM Pz (light gray) are shown (paired measurements, means ± SE for n = 4 oocytes). The strictly linear dependence of the black curve with respect to membrane potential (V_m) suggests that the transient currents in the absence of Na⁺ represent the capacitive current of the oocytes. In the presence of Pz, the transient current is close to the oocyte capacitive current from −155 to −20 mV, but for more positive V_m, the effect of Pz is progressively compromised.