Activation of single Slo2.1 channels by extracellular NFA and intracellular Na⁺. (A) Slo2.1 channels recorded during voltage ramp from +60 to −120 mV. The top panel illustrates voltage clamp protocol. Currents were recorded from a single patch under three recording conditions: cell-attached (CA) patch mode (i) or inside-out (IO) mode (ii) with a bath solution that contained 140 mM KCl, and inside-out mode (iii) with a bath solution that contained 80 mM NaCl and 60 mM KCl. (B) Slo2.1 channel activity measured during gap-free recordings at –80 mV from the same patch as in A. The closed (C) and open (O1, O2, and O3) state levels are indicated to the right of the current traces. (C) Single-channel i-V relationships for the three recording conditions as indicated. Numbers in parenthesis indicate the number of patches summarized for each data point in the order indicated by the inset legend. The slope conductance for single channels (γ) determined for −40 to −120 mV was 144 ± 8 pS for CA patches, 144 ± 6 pS for IO patches and 140 KCl bath solution, and 130 ± 7 pS for IO patches and 80 NaCl/60 KCl bath solution.