Modulation of the Voltage-Gated Proton Channel Hv1 by Small Gating-Modifier Ligands

Abstract

The human voltage-gated proton channel Hv1 is activated by depolarization and intracellular acidification to maintain the cell's neutral pH. It belongs to voltage-gated cation channels, consisting of a typical voltage sensor domain (VSD) but lacking a canonical pore domain. These channels assemble as dimers and recent data indicate strong cooperativity between the two subunits. Recently, guanidine derivatives were found to act as open channel blockers on the Hv1 VSD. Here we show that the gating modifiers NH29 and NH34, two diphenylamine carboxylate derivatives, act as Hv1 channel openers. NH29 was recently shown to exert opposite gating-modifier effects on the VSD of Kv7.2 potassium channels and TRPV1 cationic channels operating as opener and blocker of Kv7.2 and TRPV1 currents, respectively. Both compounds increase the Hv1 current amplitude by more than 2.5-fold at + 50 mV and produce a left-shift in the voltage dependence of channel activation by about −15 mV. We found that NH29 and NH34 change the proton selectivity of Hv1 channels and produce a left-shift of about −10 mV in the reversal potentials both in symmetrical (pH 7.0) and asymmetrical pH solutions (pHi 5.5/pHo 7.0). Our results also show that the mutation R211S in S4 profoundly affects the modulatory properties of the compounds. The S4 residue R211 was previously suggested to be crucial for Hv1 proton selectivity by interacting with D112 in S1. In mutant R211S, NH29 does not act anymore as an opener but rather inhibits Hv1 currents. Other Hv1 mutations are currently tested in order to determine how Hv1 channels interact with these small ligands and to elucidate Hv1 selectivity and gating mechanisms.