M2受体和IKACh在犬室上组织的分布特点及胺碘酮对IKACh和胆碱能心房颤动的影响

目的 研究迷走神经刺激(VS)诱发心房颤动(房颤)的情况及M2受体和IKACh在犬心房、心耳及其相邻大静脉的分布特点及胺碘酮对IKACh的影响,探讨其治疗胆碱能房颤的机制.方法 10只犬分别给予切断迷走神经、VS、VS+胺碘酮(分别做为对照组、VS组和胺碘酮组)后,观察心房肌动作电位(APD)的变化及诱发房颤的情况.后分离出左右心耳、左右心房、肺静脉和上腔静脉,用Western印记法观察M2受体蛋白在上述组织的分布;并用组织块酶解法分离左右心耳、左右心房、肺静脉和上腔静脉的单个细胞,采用膜片钳全细胞法观察IKACh在上述部位的离子流密度;观察应用胺碘酮后IKACh的变化.结果 对照组无一例诱发出房颤;VS组4例诱发房颤,诱发率为40%;胺碘酮组1例诱发房颤,诱发率为10%.胺碘酮组诱发房颤的比率比VS组有明显降低(P＜0.05).IKACh在左右心房都表现出强的内向整流性,在超极化有逐渐升高的内向电流,而在去极化表现快速衰减的外向电流,M2受体和IKACh电流密度显示在左右心耳和左心房比右心房、肺静脉和上腔静脉高[M2受体0.66±0.08,0.67±0.08 and 0.51±0.06 vs 0.35±0.04,0.33±0.04 and 0.32±0.03,P＜0.05;IKACh(20.36±0.91)pA/pF,(21.34±0.92)pA/pF and(14.17±0.65)pA/pF vs(10.34±0.62)pA/pF,(8.24±0.45)pA/pF and(7.65±0.42)pA/pF,P＜0.05];2 mM胺碘酮阻断后,IKACh密度明显降低,左右心房的IKACh密度没有明显差异,但心耳的密度仍比心房高.结论 M2受体和IKACh电流密度在心耳明显高于心房和相邻静脉的分布,心耳可能在胆碱能房颤诱发中有重要作用,而肺静脉和上腔静脉的作用较小;胺碘酮可以阻断IKACh并减少左右心房IKACh大小的差异,此可能是其治疗胆碱能房颤的机制.     

Differential densities of cholinergic nerves in canine supraventricular regions of hearts

PurposeCholinergic nerve plays an important role in the induction and maintenance of atrial fibrillation (AF). Cholinergic innervation at supraventricular tissues is considered to be the histological basis and intervention-associated target site for the arrhythmia; however, the distribution of cholinergic nerve in supraventricular tissues has not been clearly studied. In this study, we investigated the cholinergic nerve innervation in canine supraventricular regions of hearts.MethodsWe performed histological and immunohistochemical staining on canine tissues of left atrial appendage (LAA), right atrial appendage (RAA), left atrium (LA), right atrium (RA), atrial septum (AS), crista terminalis (CT), pulmonary vein (PV), and super vena cava (SVC) using hematoxylin and eosin (H&E) and antibodies to choline acetyltransferase.ResultsNormal canine cardiovascular histological structures were shown from H&E staining. Cholinergic nerve densities at LAA and RAA were significantly higher than LA, which was higher than RA, but no significant difference was observed between LAA and RAA. Furthermore, RA was significantly higher than AS, CT, PV, and SVC and there were no significant differences among the latter four.ConclusionThe heterogeneity of different densities of cholinergic nerve innervation of canine supraventricular regions establishes the histological basis of cholinergic nerve-mediated pathological conditions.     

Changes in I K, ACh single-channel activity with atrial tachycardia remodelling in canine atrial cardiomyocytes

AIMS: Although atrial tachycardia (AT) remodelling promotes agonist-independent, constitutively active, acetylcholine-regulated K+-current (I K,ACh) that increases susceptibility to atrial fibrillation (AF), the underlying changes in I K,Ach channel function are unknown. This study aimed to establish how AT remodelling affects I K,ACh single-channel function. METHODS AND RESULTS: I K,ACh single-channel activity was studied via cell-attached patch-clamp in isolated left atrial cardiomyocytes of control and AT (7 days, 400 min(-1)) dogs. Atrial tachycardia prolonged the mean duration of induced AF from 44 +/- 22 to 413 +/- 167 s, and reduced atrial effective refractory period at a 360 ms cycle length from 126 +/- 3 to 74 +/- 5 ms (n = 9/group, P < 0.001). In the absence of cholinergic stimulation, single-channel openings with typical I K,ACh conductance and rectification properties were sparse under control conditions. Atrial tachycardia induced prominent agonist-independent I K,ACh activity because of increased opening frequency (fo) and open probability (Po: approximately seven- and 10-fold, respectively, vs. control), but did not alter open time-constant, single-channel conductance, and membrane density. With maximum I K,ACh activation (10 micromol/L carbachol), channel Po was enhanced much more in control cells ( approximately 42-fold) than in AT-remodelled myocytes (approximately five-fold). The selective Kir3 current blocker tertiapin-Q (100 nmol/L) reduced fo and Po at -100 mV by 48 and 51%, respectively (P < 0.05 for each), without altering other channel properties, confirming the identity of I K,ACh. Atrial tachycardia had no significant effect on mRNA or protein expression of either of the subunits (Kir3.1, Kir3.4) underlying I K,ACh. CONCLUSION: Atrial tachycardia increases agonist-independent constitutive I K,ACh single-channel activity by enhancing spontaneous channel opening, providing a molecular basis for AT effects on macroscopic I K,ACh observed in previous studies, as well as associated refractoriness abbreviation and tertiapin-suppressible AF promotion. These results suggest an important role for constitutive I K,Ach channel opening in AT remodelling and support its interest as a potential target for AF therapy.     

Cholinergic atrial fibrillation: I(K,ACh) gradients determine unequal left/right atrial frequencies and rotor dynamics

OBJECTIVE: We tested the hypothesis that left atrial (LA) myocytes are more sensitive to acetylcholine (ACh) than right atrial (RA) myocytes, which results in a greater dose-dependent increase in LA than RA rotor frequency, increased LA-to-RA frequency gradient and increased incidence of wavelet formation during atrial fibrillation (AF). METHODS AND RESULTS: AF was induced in seven Langendorff-perfused sheep hearts in the presence of ACh (0.1-4.0 microM) and studied using optical mapping and bipolar recordings. Dominant frequencies (DFs) were determined in optical and electrical signals and phase movies were used to identify rotors and quantify their dynamics. DFs in both atria increased monotonically with ACh concentration until saturation, but the LA frequency predominated at all concentrations. Rotors were also seen more often in the LA, and although their life span decreased, their frequency and number of rotations increased. Patch-clamp studies demonstrated that ACh-activated potassium current (I(K,ACh)) density was greater in LA than RA sheep myocytes. Additionally, ribonuclease protection assay demonstrated that Kir3.4 and Kir3.1 mRNAs were more abundant in LA than in RA. CONCLUSIONS: A greater abundance of Kir3.x channels and higher I(K,ACh) density in LA than RA myocytes result in greater ACh-induced speeding-up of rotors in the LA than in the RA, which explains the ACh dose-dependent changes in overall AF frequency and wavelet formation.     

Differential phosphorylation-dependent regulation of constitutively active and muscarinic receptor-activated IK,ACh channels in patients with chronic atrial fibrillation

OBJECTIVE: In chronic atrial fibrillation (cAF) the potassium current IK,ACh develops agonist-independent constitutive activity. We hypothesized that abnormal phosphorylation-dependent regulation underlies the constitutive IK,ACh activity. METHODS: We used voltage-clamp technique and biochemical assays to study IK,ACh regulation in atrial appendages from 61 sinus rhythm (SR), 11 paroxysmal AF (pAF), and 33 cAF patients. RESULTS: Compared to SR basal current was higher in cAF only, whereas the muscarinic receptor (2 micromol/L carbachol)-activated IK,ACh was smaller in pAF and cAF. In pAF the selective IK,ACh blocker tertiapin abolished the muscarinic receptor-activated IK,ACh but excluded agonist-independent constitutive IK,ACh activity. Blockade of type-2A phosphatase and the subsequent shift to increased muscarinic receptor phosphorylation (and inactivation) reduced muscarinic receptor-activated IK,ACh in SR but not in cAF, pointing to an impaired function of G-protein-coupled receptor kinase. Using subtype-selective kinase inhibitors we found that in SR the muscarinic receptor-activated IK,ACh requires phosphorylation by protein kinase G (PKG), protein kinase C (PKC), and calmodulin-dependent protein kinase II (CaMKII), but not by protein kinase A (PKA). In cAF, constitutive IK,ACh activity results from abnormal channel phosphorylation by PKC but not by PKG or CaMKII, whereas the additional muscarinic receptor-mediated IK,ACh activation occurs apparently without involvement of these kinases. In cAF, the higher protein level of PKCepsilon but not PKCalpha, PKCbeta1 or PKCdelta is likely to contribute to the constitutive IK,ACh activity. CONCLUSIONS: The occurrence of constitutive IK,ACh activity in cAF results from abnormal PKC function, whereas the muscarinic receptor-mediated IK,ACh activation does not require the contribution of PKG, PKC or CaMKII. Selective drug targeting of constitutively active IK,ACh channels may be suitable to reduce the ability of AF to become sustained.     

胺碘酮与胺碘酮联合用药治疗心房纤颤疗效的比较

目的:观察单纯用药与联合用药对心房纤颤（房颤）治疗效果。方法: 选择119例房颤患者随机分为2组:单纯用药组54例,给予静脉胺碘酮150~300 mg后,继之以口服胺碘酮维持;联合用药组65例,使用极化液、硝酸甘油和小剂量利尿剂、胺碘酮,胺碘酮使用的剂量与方法同单纯用药组。观察两组房颤转复率和窦性维持率。结果: 联合用药组的房颤转复率较单纯组明显提高（80% vs. 94%,P＜0.05）,复律时间减少［（55±19） vs.(39±15） s,P＜0.05］,追踪复律半年后的维持率,联合用药组明显高于单纯用药组（81% vs. 95%,P＜0.05）。复查B超显示:联合用药后,左心房内经明显缩小,从［(46±6) mm减少到(42±6) mm,P＜0.05］,左心室舒张末期内径缩小,从(52±7) mm减少到(45±6) mm(P<0.05);而单纯用药组这两项指标均无明显改变。结论: 联合用药组较单纯用药组能明显提高对房颤患者的转复率和窦性维持率。     

Age-related changes in the atrial muscarinic type 2 receptor and their effects on atrial fibrillation vulnerability in rabbits

Aging plays an important role in increased vulnerability to atrial fibrillation (AF). Mediated by activity at the muscarinic type 2 receptor (M2R), the parasympathetic nerve contributes to the onset of AF. The purpose of this study was to investigate whether aging changes the distribution of M2R in the atrial myocardium and to determine the impact of these changes on AF vulnerability. Expression of M2R in the atrial myocardium was evaluated by immunostaining and Western blot in three groups—young (3 months old), mature (8 months old) and senescent (36–48 months old) rabbits. AF inducibility was recorded with and without cervical vagal stimulation (VS) in vivo in all groups. AF inducibility, the atrial effective refractory period (AERP) and the monophasic action potential (MAP) were recorded in an additional seven senescent rabbits before and after topical administration of tropicamide. The results showed that the density of M2R in the left atrial free wall (LAFW) was significantly higher than that in other parts of the atria. The left atrial appendage had a higher level of M2R expression than the right atrium. The M2R density of the epicardial side was greater than that of endocardial side in both atria. The senescent group had a significant increase in M2R expression in the LAFW relative to the mature group. AF inducibility was also higher in the senescent group than in the other two groups. After tropicamide administration in the senescent rabbits, AF inducibility decreased significantly, the VS-induced decrease in AERP and MAP duration at 90% repolarization (MAPD90) of LAFW was attenuated, and the dispersion of the AERP and MAPD90 increase was attenuated. In conclusion, our results suggested that there is spatial heterogeneity in the M2R distribution in the atria of the rabbit. The density of M2R in the LAFW increased with the aging of rabbits. This change in M2R enhanced the heterogeneity of the M2R distribution and contributed to the change in age-related AF vulnerability.     

Observations on the occurrence of atrial fibrillation in paroxysmal supraventricular tachycardia

Paroxysmal supraventricular tachycardia (PSVT) and atrial fibrillation (AF) are both supraventricular arrhythmias, but their mechanisms are completely different. This study determines the incidence of symptomatic AF in a group of patients followed closely during routine outpatient care for PSVT. Thirty-nine patients with PSVT were followed for up to 4 years using telephone transmission of the electrocardiogram to document symptomatic arrhythmias. The cumulative proportion of patients who had AF was calculated using the Kaplan-Meier life-table method. In addition, we examined the importance of clinical variables traditionally believed to influence the occurrence of AF. The cumulative proportion of patients who had AF during follow-up was 13% at 3 months, 16% at 6 months, 22% at 1 year and 29% at 2 years. In most patients the start of AF was documented during an attack of PSVT rather than de novo as another primary arrhythmia. PSVT occurred significantly earlier during an observation period without treatment in patients in whom AF developed (p = 0.03). The occurrence of AF was not related to age, number of years of PSVT, heart rate during tachycardia or coexistent heart disease.     

贝那普利联合胺碘酮预防阵发性房颤复发的作用

目的 评价贝那普利联合胺碘酮预防阵发性房颤复发的疗效。方法随机选取阵发性房颤复律后患者66例，分为治疗组（Ⅱ组）32例和对照组（Ⅰ组）34例。Ⅰ组常规口服胺碘酮，Ⅱ组口服胺碘酮加贝那普利，观察12个月。结果Ⅱ组治疗后复发率明显下降并低于对照组（P〈0．05）有显著差异，左房内径亦有显著性缩小。结论 贝那普利联合胺碘酮能更有效预防阵发性房颤复发。     

Acute results of transvenous cryoablation of supraventricular tachycardia (atrial fibrillation,atrial flutter,Wolff-Parkinson-White syndrome,atrioventricular nodal reentry tachycardia)

INTRODUCTION: Radiofrequency (RF) catheter ablation currently is used for treatment of cardiac arrhythmias. Although the success rate is high for almost all supraventricular tachycardias (SVT), this technique has some drawbacks, especially when pulmonary veins (PV) are targeted for treatment of atrial fibrillation (AF). Additionally, new techniques for isolation of the PVs have the drawback that they can be used only for PV isolation and not for routine treatment of other SVTs. The aim of this study was to report on the safety and efficacy of a new cryoablation system for treatment of all SVTs. METHODS AND RESULTS: Forty-nine patients with SVT (38 men; age 48 years, range 23-76) were enrolled in the study. Five patients were withdrawn from the study before they underwent cryoablation. The remaining 44 patients were treated with cryoablation (22 AF, 15 atrial flutter, 3 accessory pathway, 2 AV nodal reentrant tachycardia, 1 AV junction ablation for permanent AF, 1 atrial tachycardia). Cryoablation was performed with the CryoCor cryoablation system, which uses a precooling system and N2O as a refrigerant. The number of freezes applied varied according to the index arrhythmia treated. Successful isolation of PVs was performed in 20 of (96%) 21 AF patients and 53 of 55 veins. The overall acute success was 98% (43/44). Fifty-three PVs were isolated (2.5/patient). The success rate was 100% (23/23) for right-sided procedures. The average and nadir temperatures reached in right-sided and left-sided procedures were -77 degrees C and -80 degrees C and -75 degrees C and -78 degrees C, respectively. No acute PV stenosis was seen. CONCLUSION: This novel cryoablation system appears to be safe and can successfully treat different types of SVTs, including AF. Isolation of PVs is possible without producing stenosis. Despite the high blood flow in the right atrial isthmus and PVs, bidirectional conduction block can be achieved.     

The effect of hyperphenylalaninaemia on the muscarinic acetylcholine receptor in the HPH-5 mouse brain

Summary Previous studies on the effect of hyperphenylalaninaemia on the development of the muscarinic acetylcholine receptor in the cerebrum of the rat, using -methylphenylalanine-induced hyperphenylalaninaemia, have shown a gradual and steady decrease in the number of binding sites for this neurotransmitter. The HPH-5 mouse, a phenylalanine hydroxylase mutant, can be hyperphenylalaninaemic without the use of a hydroxylase inhibitor. By employing quantitative autoradiography using [³H]quinuclinidylbenzilate to label muscarinic acetylcholine receptors, a refined analysis of this decrease in neurotransmitter binding sites can be made. The decrease was confirmed and is therefore due to the hyperphenylalaninaemiaper se and not to the use of the inhibitor. Various areas of the brain reacted differently to hyperphenylalaninaemia, from no change (putamen) to a gradual decrease (external layer of the olfactory bulb, parietal, occipital and cingulate areas of the cerebral cortex, CA₁ and CA₃ layer of the hippocampus) to a decrease preceded by a transient increase (frontal area of the cerebral cortex, caudate nucleus).The extent of these changes depends on the duration of exposure to hyperphenylalaninaemia as well as on the degree of brain maturation, but can even be observed in the brain of the adult mouse on a hyperphenylalaninaemic regimen for 11 days.Since the hippocampus has been shown to be involved in the long-term storage of information, damage to this structure by hyperphenylalaninaemia may provide a clue to the global mental retardation observed in untreated PKU.     

短期静脉应用胺碘酮治疗老年心房颤动的疗效分析

目的：观察短期静脉应用胺碘酮转复老年心房颤动的效果及安全性。方法：42例新发的老年房颤患者，静脉给予负荷量胺碘酮（150～300mg），并以1．0～0．5mg／min静脉维持，观察24h的转复效果及不良反应。结果：33例患者转复窦性心律（82．1％），其中1h内复律3例，1～8h内13例，8～24h内17例，复律后的心率、收缩压和舒张压均显著下降，未复律者的心室率也明显减慢（P〈0．01）。共出现3例窦性心动过缓，1例频发房性早搏，1例一过性低血压，1例静脉炎。结论：静脉应用胺碘酮转复老年新发房颤的短期成功率较高并且相对安全。     

Effect of amiodarone on dispersion of atrial refractoriness and cycle length in patients with atrial fibrillation

INTRODUCTION: Amiodarone is effective in preventing the recurrence of atrial fibrillation (AF) after cardioversion (CV). Dispersion of atrial refractoriness may be relevant to the generation of AF. We designed a study to determine the electrophysiologic effects of amiodarone in patients with previous early recurrence of AF after CV. METHODS AND RESULTS: Fifteen patients with previous AF recurrence (without antiarrhythmic drugs) after CV (CV1) were selected for amiodarone therapy and repeat CV (CVamio). Prior to CV1, mean AF cycle length (AFCL) had been recorded at four atrial sites (right atrial appendage [RAA], distal coronary sinus [DCS], right atrial lateral wall [LAT], and interatrial septum [IAS]) and dispersion of AFCL had been calculated. These patients were treated with amiodarone and, prior to CVamio, AFCL was recorded at the four atrial sites as for CV1. Between CV1 and CVamio, AFCL increased at all atrial sites: 153 +/- 13 msec to 179 +/- 14 msec at RAA, 144 +/- 12 msec to 174 +/- 18 msec at DCS, 158 +/- 13 msec to 182 +/- 16 msec at LAT, and 161 +/- 18 msec to 181 +/- 17 msec at IAS. Dispersion of AFCL decreased from 24 +/- 10 msec at CV1 to 15 +/- 11 msec at CVamio (P = 0.01). The median time in sinus rhythm increased from 3.12 hours post CV1 to 28 days post CVamio, (P < 0.02). CONCLUSION: Amiodarone causes a reduction in the dispersion of AFCL. This action may be relevant to the beneficial effects of amiodarone in patients with AF.     

Interaction of amiodarone and desethylamiodarone with the cardiac muscarinic receptor in vitro

We studied the interaction of amiodarone hydrochloride (Cordarone) and its major metabolite desethylamiodarone with the muscarinic receptor in purified canine cardiac sarcolemmal vesicles by measuring equilibrium binding of the muscarinic antagonist [3H]quinuclidinyl benzilate (QNB) and carbachol displacement of [3H]-QNB. At a [3H]-QNB concentration of 0.02 nM, equilibrium binding was inhibited by amiodarone and desethylamiodarone with an IC50 of 6.86 x 10(-6) M and 2.25 x 10(-6) M, respectively. The presence of increasing concentrations of [3H]-QNB in the incubation medium was able to reverse the inhibition seen with 1 x 10(-6) M amiodarone. Scatchard analysis of [3H]-QNB saturation isotherms (37 degrees C, pH 7.4) in the presence of 1 x 10(-6) M amiodarone showed an apparent increase in equilibrium dissociation constant (Kd) over control from 0.045 +/- 0.002 nM to 0.084 +/- 0.001 nM while maximal binding capacity (Bmax) was unaffected: 10.8 +/- 1.14 and 10.5 +/- 1.48 pmol/mg (means +/- S.E.M., n = 3), respectively. The inhibitory effect of amiodarone on equilibrium binding was highly dependent on the drug:membrane phospholipid mole ratio with effects beginning at a ratio of less than 0.1:1. Hill plot analysis was consistent with the interaction of [3H]-QNB at a single site in the presence or absence of amiodarone. Amiodarone (3 x 10(-6) M) decreased the pseudo-first order forward rate constant of [3H]-QNB (0.02 nM) with the muscarinic receptor (kobs = 4.05 +/- 0.61 x 10(-4)/s under control conditions and 2.36 +/- 0.15 x 10(-4)/s in the presence of amiodarone).(ABSTRACT TRUNCATED AT 250 WORDS)