新型鈣離子通道阻斷劑labedipinedilols在心臟之電生理反應機制與抗心律不整作用之研究

Electrophysiological and antiarrhythmic studies of new-type calcium channel blockers, labedipinedilols, on cardiac myocytes and tissues

黃安祥(An-Hsiang Huang)

指導教授 ： 陳英俊 ； 葉竹來

高雄醫學大學/醫學院/醫學研究所/碩士(2003年)

摘要

Labedipinedilol-A, -B和-C是三個合成的二氫呲啶型衍生物，在結構上具有甲型、乙型腎上腺激素性受體阻斷與鈣離子通道阻斷作用的官能基團。在先前的研究中已證實，labedipinedilol-A, -B和-C在大白鼠身上，表現出具有甲型、乙型腎上腺激素性受體阻斷與鈣離子通道阻斷之三合一治療特性。然而，對於這些藥物在單一細胞層級的電生理學特性一直都還沒有去研究。本研究主要之目的是闡明labedipinedilol-A, -B和-C對於心臟細胞離子機轉的作用，並且評估labedipinedilol-A的抗心律不整活性。
在全細胞膜電位鉗定狀態下，對大白鼠單一心室細胞使用膜片鉗定技術來測定動作電位、鈉離子電流、L型鈣離子電流、瞬時外流鉀離子電流以及內向整流鉀離子電流。在從大白鼠心臟分離出的心室細胞中，labedipinedilol-A可以依濃度相關性地縮短動作電位期間與降低動作電位幅度，但是對於靜止膜電位並沒有明顯影響。
全細胞膜電位鉗定實驗顯示，於低鈉溶液中紀錄鈉離子電流時，labedipinedilol-A可以依濃度相關性地抑制鈉離子電流。在細胞外給予labedipinedilol-A可以明顯地降低L型鈣離子電流的振幅，且顯示濃度相關性的抑制現象。相反地，對於瞬時外流鉀離子電流與內向整流鉀離子電流，在給予labedipinedilol-A之後電流反而會增強。由此得知，labedipinedilol-A是一個鈉離子通道與L型鈣離子通道阻斷劑，卻也是瞬時外流鉀離子通道與內向整流鉀離子通道活化劑。
在拮抗乙型腎上腺激素性受體的實驗中發現，labedipinedilol-A可以競爭性地拮抗乙型腎上腺激素性受體作用劑(-)isoproterenol對於L型鈣離子電流的作用。
在研究labedipinedilol-A對強心配糖體ouabain誘發天竺鼠離體心房心律不整之保護作用的實驗中，結果顯示labedipinedilol-A能明顯延長ouabain誘發離體心房心律不整發作的時間。
在研究labedipinedilol-B和-C對大白鼠心室細胞的動作電位、鈉離子電流、L型鈣離子電流之影響的實驗中，labedipinedilol-B和-C具有類似labedipinedilol-A的作用，同樣能對單一心室細胞縮短其動作電位期間和降低動作電位幅度。依照藥物縮短動作電位期間的程度由強至弱排列，分別為labedipinedilol-A > labedipinedilol-C > labedipinedilol-B。
如同labedipinedilol-A的作用，labedipinedilol-B和-C也可以抑制心室細胞之鈉離子電流與L型鈣離子電流的尖峰振幅。對於鈉離子電流抑制作用的程度，由強至弱依序排列分別為labedipinedilol-A > labedipinedilol-B > labedipinedilol-C。而對於L型鈣離子電流的抑制作用，由強至弱排列分別為labedipinedilol-C > labedipinedilol-A > labedipinedilol-B。這些藥物對於大白鼠心室細胞L型鈣離子電流的抑制作用皆比nifedipine的作用強。Labedipinedilol-A, -B和-C對於鈉離子電流與L型鈣離子電流抑制作用強弱之差異，主要是來自於結構上官能基的不同。像是labedipinedilol-B在苯環上缺少一個methoxy moiety，不同於labedipinedilol-A和-C。此供電子基具有影響藥物生物活性的作用，能讓藥物與受體或離子通道有較高的結合活性。
總而言之，這些實驗結果能提供新型鈣離子通道阻斷劑labedipinedilol-A, -B和-C在心臟組織作用之離子機轉的些許解釋，以及在臨床藥物治療上新的方向。

關鍵字

鈣離子通道阻斷劑 ； 電生理 ； 心律不整

並列摘要

Labedipinedilol-A, -B and -C are synthetic 1,4-dihydropyride derivatives with ?/?-adrenoceptor and calcium channel blockading activities. As demonstrated previously, labedipinedilol-A, -B and -C have been described with triple blocking activities on ?/?-adrenergic receptor and L-type calcium channel, functioning in a molecule displaying monotherapy properties on rats. However, a direct electrophysiological characterization of these drugs has not yet been documented at single cell level. The aim of present study is to elucidate the ionic mechanisms underlying the labedipinedilol-A, -B and -C actions on cardiac myocytes and to assess the antiarrhythmic activities.
Under the whole-cell configuration, we investigate the effects of labedipinedilol-A on action potential, sodium current (INa), L-type calcium current (ICaL), transient outward potassium current (Ito), and inward rectifier potassium current (IK1) in single isolated ventricular myocytes from rats by using patch-clamp techniques. In single isolated ventricular myocytes form rats, labedipinedilol-A abbreviate markedly action potential duration (APD) and reduce in action potential amplitude (APA) in a concentration-dependent manner, but having no effect on the resting membrane potential (RMP).
Whole-cell voltage clamp study reveals that labedipinedilol-A produces a concentration-dependent reduction in sodium current (INa) amplitude, recorded in low [Na+]o solution. Extracellular application of labedipinedilol-A significantly reduces the peak amplitude of L-type calcium current (ICaL) with concentration-dependent inhibition. On the contrary, both the transient outward potassium current (Ito) and inward rectifier potassium currents (IK1) are enhanced by the addition of labedipinedilol-A. These results indicate that labedipinedilol-A acts as a inhibitor of the sodium and L-type calcium channel, but a activator of the transient outward and inward rectifier potassium channel.
In the experiment of antagonizing ?-adrenergic receptors, labedipinedilol-A can competitively antagonize the effect of β-adrenoceptor agonist, (-)isoproterenol, on L-type calcium current.
We investigate the protective effect of labedipinedilol-A on ouabain-induced arrhythmia in isolated whole atria from guinea-pigs. The results indicate that labedipinedilol-A significantly prolongs the onset time of extra-systole (arrhythmia) induced by ouabain in isolated atria.
We also investigate the effects of labedipinedilol-B and -C on action potential, sodium current and L-type calcium current in single isolated ventricular myocytes form rats. Similar to labedipinedilol-A, labedipinedilol-B and -C inhibit the action potential duration and action potential amplitude. According to the extent of shortening of action potential duration, the sequences are labedipinedilol-A > labedipinedilol-C > labedipinedilol-B in turn.
Similar to the actions of labedipinedilol-A, labedipinedilol-B and -C also inhibit the peak amplitude of sodium and L-type calcium current in ventricular myocytes isolated from rats. The degrees of inhibition of sodium current are labedipinedilol-A > labedipinedilol-B > labedipinedilol-C, respectively. The sequences of inhibitory effects for L-type calcium current are labedipinedilol-C > labedipinedilol-A > labedipinedilol-B, respectively. All of them are stronger than nifedipine for L-type calcium current in isolated rat ventricular myocytes. The different inhibitory capacity for sodium and L-type calcium current of labedipinedilol-A, -B, and -C are originated from the functional group in the structure. Such as the structure of labedipinedilol-B lacks a methoxy moiety on phenyl ring, differ from labedipinedilol-A and -C. The electron-donating substituent, i.e. methoxy, plays an important role in affecting biological activities. The methoxy moiety on phenyl ring is beneficial for receptor or channel binding.
These findings may provide some explanations of ionic mechanism for the effects of new-type calcium channel blockers, labedipinedilol-A, -B and -C, in the cardiac myocytes and a new aspect of their possible clinical therapeutic actions.

並列關鍵字

calcium channel blocker ； electrophysiology ； arrhythmia

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