Labedipinedilol-A 對於大鼠腦動脈平滑肌細胞之 L-型電位相關性鈣電流影響

先前的實驗中已證實 labedipinedilol-A 具有甲型、乙型腎上腺激素性受體阻斷與鈣離子通道阻斷作用，並且能抑制血管平滑肌細胞的增生作用。然而 labedipinedilol-A 對於鈣離子電流的抑制作用並還未被直接研究證實過。本研究的主要目的為闡明 labedipinedilol-A 對於 L-type 鈣離子通道之作用。我們利用傳統全細胞膜電位箝制技術來研究於大鼠腦動脈平滑肌細胞上，通過 L-type 鈣離子通道之鋇電流。此鋇電流可被 nifedipine 抑制，並且可被 Bay K8644 所活化。於電位箝制狀態下， labedipinedilol-A 可濃度相關性地抑制鋇電流，但是不改變鋇電流之電流電位相關性。此外投與 labedipinedilol-A 後可使鋇電流之穩定不活化曲線向較負電位移動。並且 labedipinedilol-A 在箝制膜電位於 –40 mV 擁有較 –80 mV時更好的抑制作用。此電位依賴性作用使labedipinedilol-A 可能對於血管平滑肌擁有更好的選擇性。前處理給予蛋白質激酶 C 抑制劑 chelerythrine (5 ?嵱)，可減弱labedipinedilol-A 抑制鋇電流之作用。然而前處理給予Rho kinase 抑制劑 Y-27632 (30 ?嵱) 則不顯著影響labedipinedilol-A 抑制鋇電流之作用。根據以上的結果，我們認為labedipinedilol-A 可濃度及電位相關性地抑制 L-type 鈣離子通道，並且此抑制作用為部分關連 PKC 路徑。

關鍵字

電位依賴性鈣離子通道；電生理；血管平滑肌細胞

並列摘要

Labedipinedilol-A has been described to have ??/??-adrenoceptor and calcium channel blocking activities, and to inhibit the proliferation of vascular smooth muscle cells. However, a direct evidence of calcium currents inhibition by labedipinedilol-A has not yet been documented. This study is to examine the effects of labedipinedilol-A on L-type calcium currents (ICa,L). We used the conventional whole cell patch-clamp technique to investigete Ba2+ currents (IBa) through L-type Ca2+ channels in rat cerebral artery myocytes. The IBa was reduced by nifedipine (1 ?嵱) and enchanced by Bay K8644 (100 nM). Under voltage-clamp conditions, labedipinedilol-A (1 ?嵱) reversibly inhibited the IBa in a concentration-dependent manner but without any change in current-voltage relationship of IBa. Additionally, labedipinedilol-A shifted the steady-state inactivation curve of IBa to more negative potentials. Labedipinedilol-A had a greater inhibitory activity holding at –40 mV than at -80 mV. This phenomenon of voltage-dependency by labedipinedilol-A might contribute to its higher potency in vascular smooth muscle. Pretreatment with the protein kinase C (PKC) inhibitor chelerythrine (5 ?嵱) attenuated the inhibition of IBa by labedipinedilol-A. However, Rho kinase inhibitor Y-27632 (30 ?嵱) failed to affect the inhibition of IBa by labedipinedilol-A. In light of these results, we suggest that labedipinedilol-A inhibits the L-type calcium channels in concentration- and voltage-dependent manners in rat cerebral artery myocytes and the effects may partially related to the PKC pathway.