Figure 1. Mean steady-state current–voltage (I–V) relationships in control oocytes and oocytes expressing wild-type NBCe1 or NBCn1.

A, control oocytes injected with water (n = 5). B, oocytes expressing NBCe1 (n = 7). C, oocytes expressing NBCn1 (n = 7). Oocytes were clamped at −60 mV and voltage was stepped from −140 to +60 mV for 100 ms in 20 mV increments. The recordings were done in the pH 7.40 HCO₃⁻-free ND96 solution (○) or in a comparable solution buffered to pH 7.40 with 5% CO₂–26 mm HCO₃⁻(•). The difference I_HCO3 – I_ND96 is an estimate of the electrogenic cotransport current (▴).