Figure 4. Effect of FN on single-channel BK currents in cells loaded with BAPTA.

A, current recording from a cell-attached patch held at V_h=+70 mV with cell in 140 K⁺ bath solution containing 1 mm Ca²⁺ (depicted by inset diagram). Cell was pre-loaded with BAPTA-AM (10 μm) for 15 min. The patch pipette tip was dipped into 140 K⁺ pipette solution containing 0.5 mm Ca²⁺, 50 nm apamin and 1 μm TRAM-34, then back-filled with the same solution containing FN (10 μg ml⁻¹). Calibration bar: 10 pA, 50 s. An expanded trace is shown in the lower panel, with at least 2 large-conductance channels evident. Time calibration bar: 1 s. Zero current level is indicated by dash at left. B, average I–V plot obtained from experiments similar to panel A with current amplitude measured ∼5 min after gigaseal formation at various holding potentials from −80 mV to +80 mV. The mean slope conductance of the channel was 230 pS (n = 2). C, average NP_o (mean ± s.e.m.) at +80 mV measured during the first (control) and fifth (FN) minutes using the same protocol as in panel A.