| Summary: | 碩士 === 國立成功大學 === 生理學研究所 === 97 === NS1643 (1,3-bis-[2-hydroxy-5-(trifluoromethyl)phenyl]-urea) was recently demonstrated to active hERG K+ channels expressed in Xenopus laevis oocytes and mammalian HEK293 cells and as anti-arrhythmic drug to treat long QT syndrome caused from the loss-of-function of hERG K+ channel. In addition, NS1619, NS1608 and NS11021, which were previously demonstrated to be the modulators of BKCa (large-conductance Ca2+-activated K+) channel, are chemical structurally-related compounds of NS1643. However, it remains unknown whether NS1643 could have any effects on other types of ion channels. In this study, electrophysiological measurements will be used to examine the possible effects of NS1643 on ionic BKCa currents and membrane potential in GH3 cells derived from a rat prolactin-secreting pituitary tumor. In whole-cell recordings, NS1643 activated Ca2+-activated K+ currents (IK(Ca)) in a concentration-dependent fashion. In single-channel recordings with an inside-out configuration performed in symmetrical K+ solution (145 mM), NS1643 enhanced the probability of BKCa-channel openings with no change in single-channel conductance. Alternatively, mean closed time of BKCa channels was reduced in the presence of NS1643, but no significant change in mean open time was observed. This compound caused the activation curve of BKCa channels to less depolarized voltages by approximately 15 mV. NS1643-stimulated channel activity depended on intracellular Ca2+ concentration. In current-clamp recordings, NS1643 significantly decreased firing frequency. In addition, NS1643 enhanced BKCa-channel activity in HEK293T cells transfected with α-hslo. On the other hand, the amplitudes of IK(Ca) in GH3 cells were reported to increase by the influx of Ca2+ through L-type Ca2+ channels. However, the NS1643 was not shown to affect L-type Ca2+ currents in GH3 cells. Taken together, we provide the first evidence to show that NS1643 can interact with BKCa channels to increase the amplitudes of IK(Ca) in pituitary tumor (GH3) cells.
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