Figure 4.

Effect of GAL-021 on mean open (A) and closed (B) times of BK_Ca channels in GH₃ cells. Inside-out current recordings were made in these experiments and the potential was maintained at +60 mV. Cells were immersed in high-K⁺ solution which contained 0.l μM Ca²⁺. The open- and closed-time histograms under control conditions (i.e., GAL-021 is not present) are illustrated in the left side of each panel, while those acquired during the exposure to 3 μM GAL-021 are in the right side. Of note, the abscissa and ordinate in each panel show the scale of apparent open- or closed-time histograms (msec, in a logarithmic scale) and the square root of the event numbers ($\sqrt{\mathrm{n}}$), respectively. Control data were acquired from measurements of 361 channel openings with a total record time of 1 min, whereas those taken in the presence of GAL-021 were taken from 333 channel openings with a total recording time of 2 min. Nonlinear continuous line in each histogram was least-squares fitted by single- or two-exponential function, while the broken line(s) in each lifetime distribution are pointed at the values of the time constants in open or closed state(s). Of note, the fast and slow components in mean closed time of the channel became prolonged in the presence of 3 μM GAL-021, despite its inability to modify mean open time.