Fig. 9.
Voltage-dependent inactivation and deactivation properties of IBK in somatotrophs. A, To determine whether the BK channels in somatotrophs inactivate during sustained membrane depolarizations, we applied 1 sec depolarizing voltage steps from −90 to +70 mV (holding potential, −90 mV). B, Representative current traces of the isolated IBK from nine somatotrophs. The isolated IBK was obtained by subtracting the IBTX- or paxilline-sensitive current from the total current.C, Current–voltage relation of the early (open circles; 0–25 msec) and late (filled circles; 990–1000 msec) IBK shown in B. D, The relationship between the clearance of domain Ca2+ andIBK activation was monitored by using a modified two-pulse protocol, during which the membrane potential was stepped back to −90 mV for 0–300 msec before the application of the test pulse. E, Representative current traces evoked by the modified two-pulse protocol. F, The mean ± SEM (n = 5) of the peak IKevoked during the test pulse in the absence of a Ca2+ influx step and after an interstep interval of 0–300 msec in duration. The continuous line is a single exponential fit to the data.