NS1643 (1,3-bis-[2-hydroxy-5-(trifluoromethyl)phenyl]-urea)為近幾年由NeuroSearch藥廠新開發的藥物，目前的研究已經證實了NS1643可以活化位於非洲滑爪蟾的卵和哺乳動物HEK293細胞上的ERG鉀離子通道，並且也被期許在未來可以作為因為基因突變而造成此ERG鉀離子通道功能喪失所引起的心臟疾病-long QT的治療用藥。 除此之外，NS1643此藥物在化學結構上和一些過去認為可以用來調控大型電導鈣離子活化鉀離子通道(BKCa channel)活性的活化劑，例如：NS1619、NS1608和NS11021的化學結構具有一定的相似性，互為相似物。 然而，目前除了已知NS1643可以活化ERG鉀離子通道之外，對於NS1643是否也會影響其他離子通道的活性仍不清楚。 所以在此研究，我們便利用電生理的方式去探討NS1643此化合物對於通過腦垂體前葉腫瘤細胞─GH3上的BKCa channel所產生的電流和細胞膜電位的影響。 在本實驗中首先以whole-cell的方式紀錄，可以看到NS1643能增加通過BKCa channel的電流，且此影響具有濃度依賴性的存在。 而當細胞膜兩側鉀離子等濃度(約為145 毫莫耳)的狀態下，由inside-out的紀錄中可知，NS1643可以增加BKCa channel打開的機率但並不會改變此通道的電導。 藉由進一步的計算可以觀察到NS1643會減少BKCa channel處於關閉狀態時的平均時間，但似乎不會改變通道處於打開狀態時的平均時間。 此化合物也會導致BKCa channel的活化曲線傾向於較不去極化的電位，改變約15毫伏特，且此經由NS1643所調控的離子通道活性也會依據細胞內鈣離子的濃度增加而增加。 再利用current-clamp紀錄，NS1643會明顯地減少細胞膜上動作電位的頻率。 另外，NS1643也可以增加因為利用轉移感染技術將基因α-hslo轉移至HEK293T細胞上所表現出的BKCa channel其活性。 另一方面，由本實驗室先前的研究已知在GH3此細胞模型中，隨著通過細胞膜上L-型鈣離子通道流入細胞內的鈣離子電流增加會造成細胞內的鈣離子濃度增加，而此現象也會間接地導致通過BKCa channel的電流隨之增加。 然而在本研究中並沒有觀察到NS1643具有影響通過GH3細胞上L-型鈣離子通道其電流的能力。 由此研究我們證明了NS1643具有活化腦垂體前葉腫瘤細胞上的BKCa channel的能力，並且增加通過此通道的電流。

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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