Figure 7.
Measurement of Vrev in W207F and in WT hHV1. (A–D) Families of currents in a cell expressing W207F channels were elicited by depolarizing pulses applied in 10-mV increments up to the voltage shown. When it is positive to Vthreshold, Vrev is easily obtained by interpolating between inward and outward currents, as in families at pHo 6 (A) or 7 (C). In the same cell at pHo 8 (B and E) and 9 (D and F), Vrev was extracted from the reversal of tail currents. In this cell, Vrev at pHo 6, 7, 8, and 9 was 102, 52, 7, and −10 mV; EH was 117, 58, 0, and −58 mV, respectively. Loss of proton selectivity is indicated by the large deviation of Vrev from EH at high pHo. In WT hHV1, the shift in Vrev obtained by tail currents at pHo 8 (G) and 9 (H) was nearly Nernstian. Both cells in this figure contained pHi 8 solutions. The holding potential was −20 (G), −30 (C), −40 (A, B, E, and H), or −60 mV (D and F). Prepulses were to 60 (E and F), 20 (G), or 10 mV (H).