臺灣博碩士論文加值系統

　　一、本實驗室過去初步研究結果顯示在正常Tyrode灌注液中加入ACh會使倉鼠離體右心房動作電位期間（action potential duration, APD）縮短，收縮力減少。此外在某些具有自動節律右心房中，ACh還能誘導早期反應（premature responses, PR）以及纖維顫動（atrial fibrillation, AF），一般認為AF是由於再進入機轉引起的心律不整。
　　二、當Tyrode溶液中的鈣離子濃度由2.7增加至8.1 mM以及鉀離子濃度由4減少至1mM時，以2 Hz電刺激驅動右心房時，會使心房細胞APD縮短、心舒期出現後電位（afterpotential）、增強心房肌收縮，並誘發PR及AF，以上作用可以被verapamil抑制，因此是鈣離子過量蓄積的結果。
　　三、本論文的研究目的，是以灌流ACh及高鈣低鉀溶液兩種不同方式誘發倉鼠離體心房產生再進入不整節律，比較敘利亞心肌病變倉鼠（DCM）及健康倉鼠（F1B）的差異，以利未來進一步探討心肌病變的異常興奮收縮連結。
　　四、右心房標本大小約4×8×1mm，取自27隻心肌變病倉鼠（Bio 14.6，雄性，17-31 週大），病鼠心臟有擴張及局部心肌細胞壞死的現象。另取健康倉鼠（F1B與NSC）心房當對照組。在一系列的實驗中，也取竇房結及左心房為標本作研究。
　　五、右心房動作電位以傳統微電極技術探測，收縮張力則以張力轉換器連接放大器記錄。ACh(0.1, 1及10 μM)加入灌流液中，每一種濃度約灌流7分鐘。洗去ACh後，標本以2HZ電刺激驅動並灌注8.1 mM [Ca]o及1mM [K]o溶液（最長90分鐘）。每3-5分鐘暫時停止電刺激20秒，以觀察是否有靜息後激發性的心律不整。
　　另有一系列實驗，置右心房於正常Tyrode溶液中自發搏動，再給予3-30秒的高頻（30Hz）電刺激，比較健康及心肌病變倉鼠右房對高頻率刺激的反應，以及是否誘發AF。
　　六、實驗結果顯示ACh在較低濃度（0.1及1μM）即可使APD明顯縮短，並且使收縮張力減少，但需要高濃度10μM ACh才能明顯延長自動週期。ACh也能引發高頻AF(33±3Hz)產生，AF發生的同時伴隨有張力波動（tension oscillation）、收縮綜合（summation）以及攣縮（contracture）產生。AF發生率在正常（F1B）倉鼠右房為7/12。在剪去竇房結外圍的部份心耳組織以減小標本質量（由平均約24mg減小為約12mg）後不再有AF產生。相對的，在以2Hz電刺激驅動的左心房，ACh同樣有縮短APD及抑制收縮力的作用，但不會誘發AF。心肌病變倉鼠右心房及竇房結對ACh的反應大致類似。唯一在統計上意義的區別是12隻心肌病變鼠右心房中只有1隻產生AF。
　　七、以高鈣低鉀溶液灌流也能使右心房誘發AF，而正常倉鼠AF發生率（10/12）比病變倉鼠（4/12, P<0.05）高。同樣地，高頻率（30Hz）電刺激右心房只能誘導正常倉鼠產生AF（發生率5/8，高於病變組0/8，P<0.05）。
　　八、Pirenzepine (1μM)對抗ACh縮短APD90及抑制收縮力的PA2值（6.77±0.11及6.71±0.09, n=7）與文獻上記載pirenzepine對天竺鼠心房作用的pA2值（6.53）類似。但低於pirenzepine在雞心房作用的pA2值（7.76±0.18）。
　　九、結論：
　　　　1.在過半的健康敘利亞倉鼠離體右心房ACh經由muscarinic(M)受體的活化很容易引發AF，而心肌病變倉鼠則否。Atropine及pirenzepine兩者均可對抗ACh的興奮及抑制作用，依據pirenzepine對抗ACh作用在M受體的pA2值，ACh應該是作用在M2亞型受體上。
　　　　2.健康倉鼠心房還可以使用高鈣低鉀溶液灌流及高頻率電刺激等水同的實驗方法來引發AF。對心肌病變的右心房而言，這三種實驗方法者很難引起AF，其原因不能完全以心肌病變動物心臟M受體及其訊息傳遞有缺陷來解釋。可能還有其他因素如心肌病變心房細胞不反應期較長，及興奮性較差有關。

　　1.In our previous experiments in isolated hamster atria, acetylcholine (ACh) had been shown to reduce the action potential duration (APD) and the twitch force in all preparations but in addition could induce premature responses and fibrillation (AF) in certain right atria beating spontaneously in normal Tyrode solution. AChinduced AF are assumed to be related to nonuniform shortenting of refractory period in different atrial cells.
　　2.In contrast, when [Ca]o in Tyrode solution was increased from 2.7 to 8.1 mM and [K]o was reduced from 4 to 1 mM, right atrium driven at 2 Hz also could develop premature responses and AF. The atrial tachyarrhythmias generated in high-Ca and low-K superfusate were preceded by afterpotentials, accompanied with an increase in twitch and diastolic tensions and inhibited by verapamil, thus were consequence of intracellular Ca2+ overloading.
　　3.The aim of the present experiments was to study the vulnerabilit of the myopathic hamster atria versus healthy atria to AF induced by superfusate containing ACh or high [Ca]o and low [K]o.
　　4.Right atrium about 4×8×1 mm in dimension was obtained from 20 cardiomyopathic Syrian hamwters (Bio, 14.6, male, 17-31 weeks in age) at midstage of cardiac dilatation with focal myocardial necrosis. Atria obtained from healthy hamsters (F1B and NSC) were used as control. In a number of experiments, isolated sinoatrial tissues and left atria were also used.
　　5.APs were recorded with the use of conventional micrelectrde techniques and twitch force by a transduer. Each right atrium was allowed to beat spontaneously and was exposed to ACh (0.1, 1 and 10 μM) for 7 min each concentration.
　　6.After washout of ACh, the atrium was driven at 2 Hz in a superfusate containing 8.1 mM [Ca]o and 1 mM [K]o (for 90 min). Brief interruption of the drive for 20 sec was used occasionally to reveal the absence or presence of post-rest triggered arrhythmias. High frequency (30 Hz) pacing was also used to induce tachyarrhythmias in right atria of 8 healthy versus 8 myopathic hamsters.
　　7.ACh (0.1~10μM) reduced APD and decreased twitch force in a concentration-dependent manner in all right atria but significantly prolonged spontaneous cycle length only at 10 μM. ACh could also induce high frequency (mean±se=33±3 Hz) AF along with tension oscillation, summation of contraction and contracture in 7 of 12 control (F1B) preparations. The arrhythmogenic effects of ACh were abolished by reducing the mass of the right atrial tissues or by treatment with atropine. In contrast, the same concentration of ACh did not induced AF in left atria driven at a constant rate and induced AF in only 1 of the 12 myopathic (Bio 14.6) right atria.
　　8.Exposure to high-[Ca]o and low-[K]o superfusate also could iduce higher incidence of AF in right atria obtained from the control than those from the myopathic hamsters. The incidence of AF was 10 (37±2 Hz) in 12 control atria and 4 (29±2 Hz) in 12 myopathic atria. The difference in incidence between the two groups of hamsters was statistically significant (P<0.05) by chi square analysis Similarly, high frequency pacing induced high incidence of AF only in control atria (5 in 8 versus 0 in 8 myopathic atria, P<0.05).
　　9.Pirenzepine (1 μM) antagonized the reduction of APD90 and twitch force induced by ACh with pA2 values (6.77±0.11 and 6.79±0.09, respectively, n=7) similar to those observed in guinea-pig atria but lower than those observed in chicken atria (pA2=7.76±0.18) reported in literature.
　　10.ACh readily induces AF through an activation of the muscarinic cholinergic receptors in healthy Syrian hamster but not in myopathic hamster. Both atropine and pirenzepine antagonized the inhibitory and the excitatory actions of ACh. It is suggested that the muscarinic receptors belong to the M2 subtype according to their affinities for pirenzepine.
　　11.Since AF induced by 3 different experimental methods methods occurred significantly less frequent in myopthic atria, the assumed defective muscarinic receptors and their signal transduction pathways might not be the sole reason for the resistance to ACh-induced AF in this animal model of human idiopathic cardiomyopathy Generalized reduction in the excitability and prolongation of the refractory period in myopathic atrial cells might be related to the lower incidence of techyarrhythmias.