Binding sites for divalent cations on a resting chicken ASIC1a channel at high pH.

a, Proton dose-response curves for cASIC1a channels in 2 or 10 mM external Ca2+. Error bars represent SEM, n = 4–8 cells. Data were collected in whole-cell patch clamp configuration from adherent CHO-K1 cells transfected with cDNA for cASIC1a channels. b-d, Ba2+ anomalous difference peaks (blue mesh) contoured at 5.5 σ and mapped on a resting channel at high pH (b, channel colored by domain) with detail views of the acidic pocket (c) and central vestibule (d) binding sites. Blue spheres represent Ba2+.