Fig. 4.

Effect of Iban on the kinetic properties of BK_Ca channels in MDCK cells. (A) Mean open-time histograms of BK_Ca channels in the absence (left) and presence (right) of 10 μM Iban. Cells were bathed in high K⁺ solution containing 1.8 mM CaCl₂ and cell-attached current recordings was made with a holding potential of +50 mV. The abscissa and ordinate shown in each histogram respectively indicate the logarithm of open time (ms) and the square root of the event number. The gray dashed lines shown in each lifetime distribution are placed at the values of time constant (i.e., fast and slow components) in the open state, and the red smooth curves were well fitted by a two-exponential function. Data in the control were obtained from a measurement of 431 channel openings with a total record time of 30 s, whereas those during exposure to Iban (10 μM) were obtained from 480 channel openings with a total record time of 1 m. In (B), the kinetics of Iban-induced reduction in the slow component of mean open time of BK_Ca channels was determined. The reciprocal of time constant (1/τ_b) was derived and plotted against the Iban concentration. Data points were fitted by a linear regression, indicating that Iban-mediated reduction of mean open time occurs with a molecularity of 1. Blocking (k₊₁) and unblocking (k₋₁) rate constants derived from different Iban concentrations were 0.00153 ms⁻¹ μM⁻¹ and 0.0187 ms⁻¹, respectively. Each point represent the mean ± SEM (n = 9–12). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)