Proton gating is not involved. (A) Representative single-channel currents from the mutant V538L channels at different extracellular pHs. Currents were evoked by 1 µM capsaicin at either −60 mV (bottom row) or +60 mV (top row) in symmetrical solutions (2 M KCl). The V538L mutation, which abrogates proton activation of TRPV1, did not eliminate proton inhibition of single-channel conductance. (B) Similar recordings from the E600Q mutant channels. Proton block of unitary current amplitudes remained after neutralization of E600, which abolishes the potentiation effect of low pH on channel activation and gating. (C and D) Comparison of unitary current amplitudes of the mutant channels with wild type at different pH values. (C) V_h = −60 mV. (D) V_h = +60 mV. Both mutants and the wild type had similar current amplitudes at each tested pH_o.