Fig. 5.
Relationship between spike amplitude and delayed rectifying K+ channel activation in somatotrophs. A, Simultaneous measurement of membrane potential and [Ca2+]i before and during the application of 100 nm IBTX in a spontaneously active somatotroph. The dashed lines indicate the change in peak spike amplitude with and without (IBTX) BK channel activation. B, Representative tracing of the isolated delayed rectifying K+ current (IDR) in response to 1 sec membrane potential steps from a holding potential of −90 mV to −90, −20, −10, 0, and 10 mV. C, Current–voltage relation of the early (0–25 msec; filled circles) and late (990–1000 msec; open circles) IDRevoked by 1 sec membrane potential steps from −80 to 20 mV (holding potential, −90 mV; mean ± SEM; n = 6).D, Time constant (τ) of IDRactivation during 1 sec membrane potential steps from a holding potential of −90 mV to −20, −10, 0, and 10 mV. The time constant of activation for the IDR was best determined by a single exponential fit.