Figure 1. Single-channel recordings and conductance of BK_Ca channels of small DRG neurones.

A, recordings of a single BK_Ca channel in an outside-out patch in control solution, and from the same channel in symmetrical high-K⁺ solutions at the potentials given. Dotted lines indicate the closed level; filter frequency, 1 kHz; pipette solution, high-${\text{K}}_{\text{i}}^{\text{+}}$, pCa 6; 23 °C. B, I–V relationship of single BK_Ca channels in inside-out and outside-out patches. Most amplitudes were measured from point-amplitude histograms at potentials V. A few amplitudes were measured directly from original recordings displayed on a computer screen using two cursors. ○, control solution; •, symmetrical high-K⁺ solutions. In control solution the chord conductance was 71.8 ± 3.0 pS, the mean slope conductance measured below −10 mV was 53.8 ± 5.3 pS and above +10 mV it was 106.9 ± 9.1 pS (4–19 measurements). In symmetrical high-K⁺ solutions, the mean conductance was 198.9 ± 1.5 pS for inward currents (n = 4–16), and for outward currents it was 222.7 ± 4.4 pS (n = 4–13). Error bars smaller than symbol size were not plotted.