Fig. 2.
Differential expression of BK channels between gonadotrophs and somatotrophs. A, A two-pulse protocol was used to monitor IKCaactivation by voltage-gated Ca2+ entry. This protocol consisted of a 100 msec conditioning pulse to −10 mV to activated VGCCs, followed by a 500 msec test pulse to +90 mV, during which the peak IK was monitored.B, Change in [Ca2+]ievoked by two-pulse protocol and by the test pulse alone in gonadotrophs (left) and somatotrophs (right). C, Extracellular Ca2+ removal reduced IKevoked by the two-pulse protocol in gonadotrophs and somatotrophs.D, The net IKCaactivated by the two-pulse protocol in gonadotrophs (n = 9) and somatotrophs (n = 15) was obtained by subtracting the current evoked in Ca2+-deficient medium from the control current.E, Application of 1 μm paxilline reducedIK evoked by the two-pulse protocol in gonadotrophs and somatotrophs. F, The net paxilline-sensitive IBK activated by the two-pulse protocol in gonadotrophs (n = 11) and somatotrophs (n = 15). The mean ± SEMs of the peak IKCa andIBK evoked during the test pulse are shown in D and F, respectively. The peakIBK isolated by 100 nm IBTX subtraction in gonadotrophs (n = 5) and somatotrophs (n = 10) was 0.089 ± 0.012 and 0.521 ± 0.36 nA/pF, respectively. To account for differences in cell size between gonadotrophs and somatotrophs, we normalized all currents to the membrane capacitance of each cell that was examined.