Figure 10.

Identification of the selectivity filter of hH_V1. The replacement of Asp¹¹² by serine converts the human proton channel hH_V1 into an anion channel. Tail current measurements at symmetrical pH 5.5 with ∼130 mM TMA⁺ CH₃SO₃⁻ in pipette and bath (top) and after bath replacement with TMA⁺ Cl⁻ (bottom) reveal that V_rev shifted nearly −50 mV, indicating higher permeability to Cl⁻ than to CH₃SO₃⁻. In each, a 4-s depolarizing prepulse activated the conductance, then the voltage was stepped back to a range of voltages in 10-mV increments to determine the zero current potential, V_rev. [Unpublished figure by Deri Morgan, from a study reported in Musset et al. (362).]