Eugenosedin-A 調控大鼠基底動脈平滑肌細胞之鉀離子通道研究

Eugenosedin-A activates BKCa channels in rat basilar artery myocytes

陳建甫(Chien-Fu Chen)

指導教授 ： 吳炳男

高雄醫學大學/醫學院/醫學研究所/碩士(2005年)

摘要

中文摘要
先前的研究中發現eugenosedin-A 具有拮抗 ??1/??2, ??1 和 5-HT1B/5-HT2A 接受器的活性。其不只抑制 serotonin 作用在大鼠5-HT2A 接受器引起的血管收縮，也能夠拮抗 serotonin 或 5-nonyloxytryptamine (選擇性作用於5-HT1B 接受器) 在兔子耳動脈引起的收縮作用。我們認為 eugenosedin-A可能朝高血壓的治療發展。
本研究主要目的是探討 eugenosedin-A 的作用機制，於大鼠基底動脈是如何及經由何種訊息傳遞路徑而影響離子通道的開啟作用。在這個研究中我們利用傳統性電位箝制技術來確認 eugenosedin-A 是否藉由活化 sGC/cGMP/PKG 和 AC/cAMP/PKA 兩種途徑而造成大傳導性鈣離子相依鉀通道的活化。
Eugenosedin-A (1 ?嵱) 對於延遲整流性鉀通道並沒有影響，但卻顯著的促進大傳導性鈣離子相依鉀通道的活化。而活化的大傳導性鈣離子相依鉀電流會受到charybdotoxin (ChTX, 100 nM) 或 iberiotoxin (IbTX, 100 nM) 所抑制。此外eugenosedin-A 也能夠抑制電位相依性鈣離子通道。
Eugenosedin-A導致的大傳導性鈣離子相依鉀通道的活化受到溶解型鳥糞嘌呤環化酶抑制劑 (ODQ, 10 μM)、腺苷環化酶抑制劑 (SQ22536, 10 μM)、cGMP 和 cAMP競爭性抑制劑(Rp-cGMP, 100 ?嵱 和 Rp-cAMP, 100 ?嵱)， cAMP 依賴型蛋白激酶以及cGMP 依賴型蛋白激酶抑制劑 (KT5823, 300 nM 和 KT5720, 300 nM)等抑制劑抑制。另外eugenosedin-A 也和蛋白激酶 C 抑制劑 (chelerythrine chloride, 5 ?嵱) 相同，能夠反轉PMA (100 nM) 所引起的大傳導性鈣離子相依鉀電流抑制。
由實驗結果推測，eugenosedin-A 可增加大傳導性鈣離子相依鉀電流和通道之開啟機率。此外，eugenosedin-A能夠藉由活化sGC/cGMP/PKG 和AC/cAMP/PKA 兩種途徑而造成基底動脈平滑肌細胞的過極化現象。另外其亦可以阻止 PMA 所引起的 BKCa 抑制作用。而根據inside-out 膜片箝制技術的結果，我們也不能排除Eugenosedin-A 直接活化 BKCa 通道的可能性。

關鍵字

電生理 ； 鉀通道

並列摘要

In our previous study, Eugenosedin-A was suggested to possess ??1/??2, ??1 and 5-HT1B/5-HT2A receptor-blocking activities. It not only inhibited serotonin-induced vasocontractions in rat 5-HT2A receptors, but also antagonized serotonin- or 5-nonyloxytryptamine (selective for 5-HT1B receptors)-induced contractions in the rabbit ear artery. We suggest that eugenosedin-A could be of use in the treatment of hypertension.
The main objective of this study was to address the question of whether and by what mechanisms of eugenosedin-A affects ionic currents in rat basilar artery myocytes. We employed conventional patch-clamp techniques to determine whether the BKCa channels activation by eugenosedin-A via sGC/cGMP/PKG and/or AC/cAMP/PKA cascades.
Eugenosedin-A (1 ?嵱) had no effect on the KDR current but dramatically enhanced BKCa channel activity. This increased BKCa current activity was abolished by charybdotoxin (ChTX, 100 nM) or iberiotoxin (IbTX, 100 nM). Besides, eugenosedin-A also significantly attenuated the voltage-dependent calcium channels.
BKCa current activation by eugenosedin-A was strikingly inhibited by a soluble guanylate cyclase inhibitor (ODQ, 10 ?嵱) while attenuated by an adenylate cyclase inhibitor (SQ 22536, 10 ?嵱), competitive antagonists of cGMP and cAMP (Rp-cGMP, 100 ?嵱 and Rp-cAMP, 100 ?嵱), or cGMP- and cAMP-dependent protein kinase inhibitors (KT5823, 300 nM and KT5720, 300 nM). Eugenosedin-A as well as a PKC inhibitor (chelerythrine chloride, 5 ?嵱), also could reverse PMA (100 nM) induced BKCa inhibition.
In conclusion, Eugenosedin-A increases the BKCa currents and channels open probability, thus, we suggested that it activates both sGC/cGMP/PKG and AC/cAMP/PKA cascades resulting in hyperpolarization in basilar artery myocytes, and it also prevents PMA-induced BKCa inhibition. Besides, we cannot exclude Eugenosedin-A’s direct action to open BKCa channels from the data of inside-out patchs.

並列關鍵字

potassium channel ； Eugenosedin-A ； electrophysiology

參考文獻

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