The voltage sensor is responsible for ΔpH dependence in H_v1 channels

The dissipation of acute acid loads by the voltage-gated proton channel (H_v1) relies on regulating the channel's open probability by the voltage and the ΔpH across the membrane (ΔpH = pH_ex - pH_in). Using monomeric Ciona-H_v1, we asked whether ΔpH-dependent gating is produced during the voltage sensor activation or permeation pathway opening. A leftward shift of the conductance-voltage (G-V) curve was produced at higher ΔpH values in the monomeric channel. Next, we measured the voltage sensor pH dependence in the absence of a functional permeation pathway by recording gating currents in the monomeric nonconducting D160N mutant. Increasing the ΔpH leftward shifted the gating charge-voltage (Q-V) curve, demonstrating that the ΔpH-dependent gating in H_v1 arises by modulating its voltage sensor. We fitted our data to a model that explicitly supposes the H_v1 voltage sensor free energy is a function of both the proton chemical and the electrical potential. The parameters obtained showed that around 60% of the free energy stored in the ΔpH is coupled to the H_v1 voltage sensor activation. Our results suggest that the molecular mechanism underlying the H_v1 ΔpH dependence is produced by protons, which alter the free-energy landscape around the voltage sensor domain. We propose that this alteration is produced by accessibility changes of the protons in the H_v1 voltage sensor during activation.