Figure 2.
Sensitivity of the electrical component in Hv1 gating to changes in pHI. (A) A four-state sequential model was used to fit the activation kinetics of Hv1, where the first three states of the model are nonconductive (closed, C1-C3), whereas the last one was the conductive state (open, O). All forward (αi) and backward (βi) transition rates were considered to be voltage-sensitive (Eqs. 1 and 2). (B) Examples set of proton currents recorded at three different pHI, while keeping pHO at 6.5. All currents (black traces) were recorded from a H.P. of -60 mV, pulsing from -80 mV to +80 mV, +120 mV and +180 mV (left to right), at pHI of 4.5, 5.5, and 6.5, respectively. The four-state model was used to simultaneously fit the activation of the currents evoked at potentials +40 mV and above in each condition (red traces). (C) Average gating charge (zi = zα,i + zβ,i) associated with each transition were calculated from the values obtained from the fit of individual experiments. The charge associated with the first and second transition (z1 and z2, respectively) average ∼ 2.5 e-, suggesting that they emerged from the gating of each one of the voltage sensors. These charge values were not statistically different, except for z2 that was 3.0 ± 0.4 (n = 8) at pHI 4.5 and 2.4 ± 0.3 (n = 5) at pHI 6.5 (∗; p > 0.05). For the third transition, the values of z3 were not different (p < 0.05) at pHI 4.5 (1 × 10−5 ± 1 × 10−5) and 5.5 (1.5 × 10−5 ± 6 × 10−6), but there was a statistically significant increase (∗∗; p < 0.05) at pHI 6.5 (2.6 × 10−5 ± 1.6 × 10−6). To see this figure in color, go online.