伊班磷酸 (Ibandronate sodium)是屬於一種含氮雙磷酸鹽類藥物，對於治療骨質疏鬆症(osteoporosis)而言，被認為一種有效抗骨質疏鬆藥物。先前研究報告指出，伊班磷酸會影響腎臟中的腎小管功能。此化合物並不會藉由人類及動物的代謝系統而進行分解，並且會累積在腎臟中。此外，根據以前的研究發現，在大白鼠中伊班磷酸會造成腎臟中的遠曲小管、集尿管過度肥大及過度增生。然而，它是否會對腎臟細胞之細胞膜上的離子通道產生任何作用目前仍然不清楚。因此，在我們的研究當中，主要是探討這個藥物針對腎臟中的腎小管細胞- MDCK 細胞之中，其細胞膜上電流可能變化及作用機制。我們利用細胞膜箝制(patch-clamp)的技術來評估腎小管細胞的電生理特性。首先，我們利用完整細胞膜式紀錄(whole-cell recordings)的方式做觀察，加入了伊班磷酸後MDCK細胞上電壓依賴性鉀離子電流(voltage-dependent K+ currents, IK) 的振幅強度下降，而在伊班磷酸所誘導的電壓依賴性鉀離子電流抑制作用可由加入硫化氫(H2S)來逆轉。其次，以細胞連接片紀錄(cell-attached recordings)的方式觀察，從實驗中觀察到細胞暴露於伊班磷酸下所造成的大型電導鈣離子活化鉀離子通道(BKCa channels)活性抑制效果呈現濃度依賴性關係；然而，伊班磷酸並不會改變大型電導鈣離子活化鉀離子通道的電導。但這個藥物會造成這株細胞中的大型電導鈣離子活化鉀離子通道的活化曲線往較正的膜電位移動了約22毫伏特。另外，發現細胞在暴露於伊班磷酸的情況下，不僅會導致大型電導鈣離子活化鉀離子通道的通道開啟機率降低而且會縮短通道平均開啟時間的慢組成。在細胞膜伸展下給予負壓，伊班磷酸所經由的大型電導鈣離子活化鉀離子通道活性之抑制作用的振幅並不會有所差異。在伊班磷酸的存在下，這些通道的敏感性鈣離子會被改變。而且，伊班磷酸也能有效抑制中型電導鈣離子活化鉀離子通道(IKCa channels)活性，且加入DCEBIO或 9-phenanthrol (已知IKCa通道刺激劑) 後而被有效逆轉其作用。另外我們在反轉錄聚合酵素鏈鎖反應(reverse transcription-PCR)的實驗中顯示MDCK細胞中有KCNN4 mRNA的表現。最後，在電壓-膜片箝制紀錄(current-clamp recordings)中，我們發現伊班磷酸會造成MDCK細胞的膜電位產生去極化，而加入DCEBIO 或 PF573228之後伊班磷酸所誘導的去極化現象就會被逆轉回來。總結本篇的實驗研究，透過伊班磷酸對於鈣離子活化鉀離子通道的抑制作用可能有助於瞭解這類藥物之藥理學或毒理學的作用機制，並且這類結構相似的雙磷酸鹽-伊班磷酸對於在活體中腎小管細胞的活性功能會有更進一步的了解。

Ibandronate sodium (Iban) is a highly potent nitrogen-containing bisphosphonate and effective for the treatment of osteoporosis. It was previously reported to influence the function of renal tubular cells. According to previous studies, Iban is not metabolized in either human or animal and it can then accumulate in the kidney; consequently, it produces hypertrophy and hyperplasia of distal tubules and collecting ducts in the rats. However, whether this drug has any effects on membrane ion channels in kidney cells remains largely unclear. This study was conducted to investigate the possible effects of this drug on ionic currents functionally expressed in MDCK renal tubular cells. In whole-cell recordings, Iban decreased the amplitude of voltage-dependent K+ current (Ik) in MDCK cells. Iban-induced inhibition of IK was reversed by further addition of hydrogen sulfide (H2S). In cell-attached recordings, cell exposure to Iban decreased the activity of large-conductance Ca2+-activated K+ (BKCa) channels in a concentration-dependent manner; however, it suppressed BKCa channel activity with no modifications on single-channel conductance of these channels. This compound caused a shift in the activation curve to a positive membrane potential by approximately 22 mV of BKCa channels in these cells. However, during exposure to it not only decreased probability of channel openings but also shortened slow component of mean open time for BKCa channels. The magnitude of Iban-mediated inhibition of BKCa-channel activity did not differ significantly in membrane stretch with negative pressure. Moreover, Ca2+ sensitivity of these channels was modified in the presence of this compound. Iban also effectively suppressed the activity of intermediate-conductance Ca2+-activated K+ (IKCa) channels, and DCEBIO or 9-phenanthrol effectively reversed its effects. In the RT-PCR experiment, the mRNA expression of KCNN4 could be detected in these cells. Under current-clamp recordings, Iban caused membrane depolarization of MDCK cells and DCEBIO or PF573228 reversed Iban-induced depolarization. Taken together, our results clearly showed that the role of suppression by Iban on the activity of Ca2+-activated K+ channels may contribute to the understanding mechanism of pharmacological or toxicological actions of this compound and its structurally similar bisphosphonates on renal tubular cells if similar findings occur in vivo.

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