Choline produces cytoprotective effects against ischemic myocardial injuries: evidence for the role of cardiac m3 subtype muscarinic acetylcholine receptors

Overexpression of M₃ muscarinic receptor is a novel strategy for preventing sudden cardiac death in transgenic mice

The present study was designed to investigate the cardiac benefits of M₃ muscarinic receptor (M₃-mAChR) overexpression and whether these effects are related to the regulation of the inward rectifying K⁺ channel by microRNA-1 (miR-1) in a conditional overexpression mouse model. A cardiac-specific M₃-mAChR transgenic mouse model was successfully established for the first time in this study using microinjection, and the overexpression was confirmed by both reverse transcriptase-polymerase chain reaction and Western blot techniques. We demonstrated that M₃-mAChR overexpression dramatically reduced the incidence of arrhythmias and decreased the mortality in a mouse model of myocardial ischemia-reperfusion (I/R). By using whole-cell patch techniques, M₃-mAChR overexpression significantly shortened the action potential duration and restored the membrane repolarization by increasing the inward rectifying K⁺ current. By using Western blot techniques, M₃-mAChR overexpression also rescued the expression of the inward rectifying K⁺ channel subunit Kir2.1 after myocardial I/R injury. This result was accompanied by suppression of upregulation miR-1. We conclude that M₃-mAChR overexpression reduced the incidence of arrhythmias and mortality after myocardial I/R by protecting the myocardium from ischemia in mice. This effect may be mediated by increasing the inward rectifying K⁺ current by downregulation of arrhythmogenic miR-1 expression, which might partially be a novel strategy for antiarrhythmias, leading to sudden cardiac death.

Acetylcholine prevents angiotensin II-induced oxidative stress and apoptosis in H9c2 cells

Apoptosis of cardiomyocytes plays an important role in the development of cardiovascular diseases (CVD). Numerous studies have shown that generation of reactive oxygen species (ROS) induced by the renin-angiotensin system (RAS) is involved in this pathological process. Recent studies also suggested that acetylcholine (ACh) prevented the hypoxia-induced apoptosis of mouse ES cells by inhibiting the ROS production. However, whether ACh can inhibit the action of angiotensin II (Ang II) and subsequently prevent CVD development remains unclear. In this study, H9c2 cells were stimulated by 10(-6) M Ang II for 24 h with or without 10(-5) M ACh, 10(-5) M ACh + 10(-4) M atropine respectively. The results demonstrated that Ang II increased apoptosis index by fourfold (vs. the control group, P < 0.01), which were significantly diminished by ACh. However, the atropine (ACh receptor [AChR] inhibitor) treatment blocked the protective effect of ACh. Subsequently, Ang II significantly increases the expression and activity of NADPH oxidase so that ROS production is increased by sevenfold (vs. control group, P < 0.01). The activity and expression of caspase-3 along with the Bax/Bcl2 ratio and the levels of p38 mitogen activated protein kinase (MAPK) phosphorylation also appeared to follow a similar trend. Furthermore, we observed that ACh could reduce up-regulation of AT1 receptor expression induced by Ang II. However, all these effects of ACh were inhibited by atropine. In conclusion, ACh prevents Ang II-induced H9c2 cells apoptosis through down-regulation of the AT1 receptor and inhibition of ROS-mediated p38 MAPK activation as well as regulation of Bcl-2, Bax and caspase-3.

Whole genome network analysis of ion channels and connexins in myocardial infarction

It has been well documented that ion channels and intercellular gap junctional proteins participated in the pathophysiological processes of myocardial infarction (MI) which resulted in lethal arrhythmias and sudden cardiac death. miRNA expression is dynamically regulated during MI and altered miRNA expression can induce deregulation of ion channel genes at the post-transcriptional level. We conducted a rationally designed bioinformatics analysis combined with experimental approaches to screen key therapeutic members in the IUPHAR database and Wikipedia, a whole genome protein interaction network was established here and comprehensive topological assessment was applied to confirm the individual network status and to reflect their biological significance. Meanwhile, the number of validated and confidently predicted miRNAs regulating each gene encoding ion channel or gap junction protein was counted. miRNA analysis indicated that connexin 43 was under more intensive miRNA regulation compared with the other ion channel and gap junction proteins. Furthermore, the topological network analysis highlighted the important role of connexin 43 in MI and also identified the important biological roles of TRPV4, SCN5A, CACNA1C and TRPC6. The abnormal expression of TRPC6 was experimentally validated in 1 month MI model of rat, which implied its potential therapeutic target for MI. Our work suggested that network systems approach could gain valuable insight into the pathological mechanism of MI which has not been uncovered by previous experimental studies.

Tanshinone IIA inhibits miR-1 expression through p38 MAPK signal pathway in post-infarction rat cardiomyocytes

Tanshinone IIA is a fat-soluble pharmacologically active ingredient of Danshen, a well-known traditional Chinese medicine used for cardiovascular diseases such as coronary heart disease. Tanshinone IIA has been confirmed to suppress miR-1 and reduce the arrhythmogenesis after myocardial infarction (MI). However, the modulation mechanism is not clear. Tanshinone IIA was administrated daily for 7 days before ligation of the left anterior descending artery (LAD) and lasted for 3 months after LAD. Neonatal cardiomyocytes were exposed to 2% O(2)+95% N(2) condition for 24 h to simulate ischemia in vivo. Protein expression was examined with Western blot and miR-1 level was quantified by Real-time PCR. Our results showed that tanshinone IIA relieved ischemia-induced injury by improving the cardiac function. This beneficial effect may due to the depression of the elevated miR-1 level in ischemic and hypoxic cardiomyocytes, which subsequently restored its target Cx43 protein. Furthermore, tanshinone IIA could inhibit activated p38 MAPK and heart special transcription factors SRF and MEF2, in ischemic and hypoxic cardiomyocytes. Pretreatment with p38 MAPK inhibitor, SB203580 (10 uM), significantly relieved hypoxia-induced miR-1 increment and restored its downstream target Cx43 protein expression. These data suggest that tanshinone IIA play a role in protection cardiomyocytes from ischemic and hypoxic injury. The effect is based on inhibiting miR-1 expression through p38 MAPK signal pathway. This might provide us a new target to explore the novel strategy for ischemic cardioprotection.

L-type calcium current (ICa,L) and inward rectifier potassium current (IK1) are involved in QT prolongation induced by arsenic trioxide in rat

The present study was designed to study the effects of As(2)O(3) on QT interval prolongation and to explore the potential ionic mechanisms in isolated rat ventricular cardiomyocytes. The rats of As(2)O(3) group were treated with 0.8 mg·kg(-1)·d(-1) As(2)O(3) intravenously for 7 days consecutively and the control group with saline. The ECG was recorded to calculate heart rate-corrected QT interval (QTc). Single cardiomyocytes were isolated by using collagenase II, and the action potential duration (APD) and ion currents were recorded by whole-cell patch clamp. [Ca(2+)](i) was examined by confocal laser scanning microscopy. Our data showed that both QTc and APD were prolonged significantly after As(2)O(3)treatment. Meanwhile, As(2)O(3) suppressed I(K1) and shifted the reversal potential to more positive direction. Moreover, the density of I(Ca,L) was augmented significantly, and the steady-state activation curve became more negative, whereas, the inactivation and reactivation of I(Ca,L) were not changed notably after As(2)O(3) administration. Furthermore, the maximal [Ca(2+)](i) was enhanced obviously by either KCl or caffeine stimulation in As(2)O(3)-treated cardiomyocytes. Our results show that the potential mechanism of As(2)O(3)-induced QT interval prolongation in rat might be relative to disturbing the fine balance of transmembrane currents (increasing I(Ca,L) and decreasing I(K1)) and causing APD prolongation.

The case for hypoglycaemia as a proarrhythmic event: basic and clinical evidence

Recent clinical studies show that hypoglycaemia is associated with increased risk of death, especially in patients with coronary artery disease or acute myocardial infarction. This paper reviews data from cellular and clinical research supporting the hypothesis that acute hypoglycaemia increases the risk of malignant ventricular arrhythmias and death in patients with diabetes by generating the two classic abnormalities responsible for the proarrhythmic effect of medications, i.e. QT prolongation and Ca(2+) overload. Acute hypoglycaemia causes QT prolongation and the risk of ventricular tachycardia by directly suppressing K(+) currents activated during repolarisation, a proarrhythmic effect of many medications. Since diabetes itself, myocardial infarction, hypertrophy, autonomic neuropathy and congestive heart failure also cause QT prolongation, the arrhythmogenic effect of hypoglycaemia is likely to be greatest in patients with pre-existent cardiac disease and diabetes. Furthermore, the catecholamine surge during hypoglycaemia raises intracellular Ca(2+), thereby increasing the risk of ventricular tachycardia and fibrillation by the same mechanism as that activated by sympathomimetic inotropic agents and digoxin. Diabetes itself may sensitise myocardium to the arrhythmogenic effect of Ca(2+) overload. In humans, noradrenaline (norepinephrine) also lengthens action potential duration and causes further QT prolongation. Finally, both hypoglycaemia and the catecholamine response acutely lower serum K(+), which leads to QT prolongation and Ca(2+) loading. Thus, hypoglycaemia and the subsequent catecholamine surge provoke multiple, interactive, synergistic responses that are known to be proarrhythmic when associated with medications and other electrolyte abnormalities. Patients with diabetes and pre-existing cardiac disease may therefore have increased risk of ventricular tachycardia and fibrillation during hypoglycaemic episodes.

M3 muscarinic receptors promote cell survival through activation of the extracellular regulated kinase (ERK1/2) pathway

Activation of certain subtypes of the muscarinic acetylcholine receptor can enhance cell survival. In SK-N-SH human neuroblastoma cells, muscarinic acetylcholine receptor activation induces phosphorylation of CREB and induction of EGR1, transcription factors associated with cell growth and survival. We identified the M3 muscarinic acetylcholine receptor subtype as being primarily responsible for these transcription factor responses after stimulation with carbachol, using subtype-preferring receptor antagonists and muscarinic snake toxins. In a cell survival/death model in SK-N-SH cells deprived of serum growth factors, carbachol increased cell viability, an effect blocked by the non-specific muscarinic antagonist atropine and the M3-preferring antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), suggesting that the M3 receptor is also driving the survival response in these cells. This cytoprotection is largely dependent on activation of the p44/42 extracellular regulated kinase (ERK1/2) pathway. Understanding such survival signalling pathways is important for both potential interventions in neurodegenerative disease and for targeting neuroblastoma and malignancies of the central nervous system.

Activation of cardiac muscarinic M3 receptors induces delayed cardioprotection by preserving phosphorylated connexin43 and up-regulating cyclooxygenase-2 expression

BACKGROUND AND PURPOSE

Activation of muscarinic M(3) mucarinic acetylcholine receptors (M(3)-mAChRs) has been previously shown to confer short-term cardioprotection against ischaemic injuries. However, it is not known whether activation of these receptors can provide delayed cardioprotection. Consequently, the present study was undertaken to investigate whether stimulation of M(3)-mAChRs can induce delayed preconditioning in rats, and to characterize the potential mechanism.

EXPERIMENTAL APPROACH

Rats were pretreated (24 h), respectively, with M(3)-mAChRs agonist choline, M(3)-mAChRs antagonist 4-DAMP or M(2)-mAChRs antagonist methoctramine followed by the administration of choline. This was followed by 30 min of ischaemia and then 3 h of reperfusion. Ischaemia-induced arrhythmias and ischaemia-reperfusion (I/R)-induced infarction were determined. The phosphorylation status of connexin43 (Cx43) after 30 min ischaemia, and the expression level of Hsp70, cyclooxygenase-2 (COX-2) and iNOS effected by administration of choline were also measured.

KEY RESULTS

Compared to the control group, pretreatment with choline significantly decreased ischaemia-induced arrhythmias, reduced the total number of ventricular premature beats, the duration of ventricular tachycardia episodes and markedly reduced I/R-induced infarct size. Furthermore, choline attenuated ischaemia-induced dephosphorylation of Cx43, and up-regulated the expression of Hsp70 and COX-2. Administration of 4-DAMP abolished these changes, while methoctramine had no effect.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that stimulation of M(3)-mAChRs with choline elicits delayed preconditioning, which we propose is the result of up-regulation of the expression of COX-2 and inhibition of the ischaemia-induced dephosphorylation of Cx43. Therefore, M(3)-mAChRs represent a promising target for rendering cardiomyocytes tolerant to ischaemic injury.

The antiarrhythmic effect and possible ionic mechanisms of pilocarpine on animal models

This study was designed to evaluate the effects of pilocarpine and explore the underlying ionic mechanism, using both aconitine-induced rat and ouabain-induced guinea pig arrhythmia models. Confocal microscopy was used to measure intracellular free-calcium concentrations ([Ca(2+)](i)) in isolated myocytes. The current data showed that pilocarpine significantly delayed onset of arrhythmias, decreased the time course of ventricular tachycardia and fibrillation, reduced arrhythmia score, and increased the survival time of arrhythmic rats and guinea pigs. [Ca(2+)](i) overload induced by aconitine or ouabain was reduced in isolated myocytes pretreated with pilocarpine. Moreover, M(3)-muscarinic acetylcholine receptor (mAChR) antagonist 4-DAMP (4-diphenylacetoxy-N-methylpiperidine-methiodide) partially abolished the beneficial effects of pilocarpine. These data suggest that pilocarpine produced antiarrhythmic actions on arrhythmic rat and guinea pig models induced by aconitine or ouabain via stimulating the cardiac M(3)-mAChR. The mechanism may be related to the improvement of Ca(2+) handling.

Tanshinone IIA protects against sudden cardiac death induced by lethal arrhythmias via repression of microRNA-1

BACKGROUND AND PURPOSE

Tanshinone IIA is an active component of a traditional Chinese medicine based on Salvia miltiorrhiza, which reduces sudden cardiac death by suppressing ischaemic arrhythmias. However, the mechanisms underlying the anti-arrhythmic effects remain unclear.

EXPERIMENTAL APPROACH

A model of myocardial infarction (MI) in rats by ligating the left anterior descending coronary artery was used. Tanshinone IIA or quinidine was given daily, before (7 days) and after (3 months) MI; cardiac electrical activity was monitored by ECG recording. Whole-cell patch-clamp techniques were used to measure the inward rectifying K(+) current (I(K1)) in rat isolated ventricular myocytes. Kir2.1 and serum response factor (SRF) levels were analysed by Western blot and microRNA-1 (miR-1) level was determined by real-time RT-PCR.

KEY RESULTS

Tanshinone IIA decreased the incidence of arrhythmias induced by acute cardiac ischaemia and mortality in rats 3 months after MI. Tanshinone IIA restored the diminished I(K1) current density and Kir2.1 protein after MI in rat ventricular myocytes, while quinidine further inhibited I(K1)/Kir2.1. MiR-1 was up-regulated in MI, possibly due to the concomitant increase in SRF, a transcriptional activator of the miR-1 gene, accounting for decreased Kir2.1. Treatment with tanshinone IIA prevented increased SRF and hence increased miR-1 post-MI, whereas quinidine did not.

CONCLUSIONS AND IMPLICATIONS

Down-regulation of miR-1 and consequent recovery of Kir2.1 may account partially for the efficacy of tanshinone IIA in suppressing ischaemic arrhythmias and cardiac mortality. These finding support the proposal that miR-1 could be a potential therapeutic target for the prevention of ischaemic arrhythmias.

Non-quantal release of acetylcholine from parasympathetic nerve terminals in the right atrium of rats

Acetylcholinesterase (AChE) inhibitors provoke typical cholinergic effects in the isolated right atrium of the rat due to the accumulation of acetylcholine (ACh). Our study was designed to show that in the absence of vagal impulse activity, ACh is released from the parasympathetic nerve fibres by means of non-quantal secretion. The conventional microelectrode technique was used to study changes in action potential (AP) configuration in the right atrium preparation of rats during application of AChE inhibitors. Staining with the lipophilic fluorescent dye FM1-43 was used to demonstrate the presence of endocytosis in cholinergic endings. The AChE inhibitors armin (10(7)-10(5)m) and neostigmine (10(7) to 5 x 10(6)m) caused a reduction of AP duration and prolonged the cycle length. These effects were abolished by atropine and were therefore mediated by ACh accumulated in the myocardium during AChE inhibition. Putative block of impulse activity of the postganglionic neurons by tetrodotoxin (5 x 10(7)m) and blockade of ganglionic transmission by hexomethonium (2 x 10(4)m), as well as blockade of all forms of quantal release with Clostridium botulinum type A toxin (50 U ml(1)), did not alter the effects of armin. Experiments with FM1-43 dye confirmed the effective block of exocytosis by botulinum toxin. Selective inhibition of the choline uptake system using hemicholinium III (10(5)m), which blocks non-quantal release at the neuromuscular junction, suppressed the effects of AChE inhibitors. Thus, accumulation of ACh is likely to be caused by non-quantal release from cholinergic terminals. We propose that non-quantal release of ACh, shown previously at the neuromuscular junction, is present in cholinergic postganglionic fibres of the rat heart in addition to quantal release.

Reciprocal regulation between M3 muscarinic acetylcholine receptor and protein kinase C-epsilon in ventricular myocytes during myocardial ischemia in rats

We have studied the association between M(3) muscarinic acetylcholine receptors (M(3)-mAChR) and protein kinase C-epsilon (PKC-epsilon) during ischemic myocardial injury using Western blot analysis and immunoprecipitation technique. Myocardial ischemia (MI) induced PKC-epsilon translocation from cytosolic to membrane fractions. This translocation participated in the phosphorylation of M(3)-mAChR in membrane fractions, which could be abolished by the inhibitor of PKC, chelerythrine chloride. On the other hand, M(3)-mAChR could also regulate the expression of PKC-epsilon in ischemic myocardium. Choline (choline chloride, an M(3) receptor agonist, administered at 15 min before occlusion) strengthened the association between PKC-epsilon and M(3)-mAChR. However, blockade of M(3)-mAChR by 4-diphenylacetoxy-N-methylpiperidine methiodide (an M(3) receptor antagonist, administered at 20 min before occlusion) completely inhibited the effect of choline on the expression of PKC-epsilon. We conclude that the translocation of PKC-epsilon is required for the phosphorylation of M(3)-mAChR; moreover, increased PKC-epsilon activity is associated with M(3)-mAChR during MI. This reciprocal regulation is likely to play a role in heart signal transduction during ischemia between ventricular myocytes.

MicroRNA-1 downregulation by propranolol in a rat model of myocardial infarction: a new mechanism for ischaemic cardioprotection

AIMS

The present study was designed to investigate whether the beneficial effects of beta-blocker propranolol are related to regulation of microRNA miR-1.

METHODS AND RESULTS

We demonstrated that propranolol reduced the incidence of arrhythmias in a rat model of myocardial infarction by coronary artery occlusion. Overexpression of miR-1 was observed in ischaemic myocardium and strikingly, administration of propranolol reversed the up-regulation of miR-1 nearly back to the control level. In agreement with its miR-1-reducing effect, propranolol relieved myocardial injuries during ischaemia, restored the membrane depolarization and cardiac conduction slowing, by rescuing the expression of inward rectifying K(+) channel subunit Kir2.1 and gap junction channel connexin 43. Our results further revealed that the beta-adrenoceptor-cAMP-Protein Kinase A (PKA) signalling pathway contributed to the expression of miR-1, and serum response factor (SRF), which is known as one of the transcriptional enhancers of miR-1, was up-regulated in ischaemic myocardium. Moreover, propranolol inhibited the beta-adrenoceptor-cAMP-PKA signalling pathway and suppressed SRF expression.

CONCLUSION

We conclude that the beta-adrenergic pathway can stimulate expression of arrhythmogenic miR-1, contributing to ischaemic arrhythmogenesis, and beta-blockers produce their beneficial effects partially by down-regulating miR-1, which might be a novel strategy for ischaemic cardioprotection.

Muscarinic receptors prevent oxidative stress-mediated apoptosis induced by domoic acid in mouse cerebellar granule cells

In mouse cerebellar granule neurons (CGNs) low concentrations of domoic acid (DomA) induce apoptotic cell death, which is mediated by oxidative stress; apoptosis is more pronounced in CGNs from Gclm (-/-) mice, which lack the modifier subunit of glutamate cysteine ligase (GCL) and have very low GSH levels. By activating M(3) muscarinic receptors, the cholinergic agonist carbachol inhibits DomA-induced apoptosis, and the anti-apoptotic action of carbachol is more pronounced in CGNs from Gclm (+/+) mice. Carbachol does not prevent DomA-induced increase in reactive oxygen species, suggesting that its anti-apoptotic effect is downstream of reactive oxygen species production. Carbachol inhibits DomA-induced activation of Jun N-terminal (JNK) and p38 kinases, increased translocation to mitochondria of the pro-apoptotic protein Bax, and activation of caspase-3. Carbachol activates extracellular signal-regulated kinases 1/2 (ERK1/2) MAPK and phospahtidylinositol-3 kinase (PI3K) in CGNs from both genotypes. However, while the protective effect of carbachol is mediated by ERK1/2 MAPK in CGNs from both mouse genotypes, inhibitors of PI3K are only effective at antagonizing the action of carbachol in CGNs from Gclm (+/+) mice. In CGNs from both Gclm (+/+) and (-/-) mice, carbachol induces a MAPK-dependent increase in the level of the anti-apoptotic protein Bcl-2. In contrast, carbachol causes a PI3K-dependent increase in GCL activity and of GSH levels only in CGNs from Gclm (+/+) mice. Such increase in GCL is not because of a transcriptionally-mediated increase in glutamate cysteine ligase catalytic subunit or glutamate cysteine ligase modifier subunit, but rather to an increase in the formation of the GCL holoenzyme. The results indicate that multiple pathways may contribute to the protective action of carbachol toward DomA-induced apoptosis. Compromised GCLM expression, which is also found in a common genetic polymorphism in humans, leads to lower GSH levels, which can exacerbate the neurotoxicity of DomA, and decreases the anti-apoptotic effectiveness of muscarinic agonists.

Choline produces antiarrhythmic actions in animal models by cardiac M3 receptors: improvement of intracellular Ca2+ handling as a common mechanism

It is well known that choline has protective effects on ischemic arrhythmias. We designed the present study to evaluate the antiarrhythmic effects of choline and to detect its related mechanisms in aconitine-induced rat and ouabain-induced guinea pig models of arrhythmia. Laser scanning confocal microscopy and patch-clamp technique were utilized to study the action of choline on intracellular calcium concentration and L-type calcium current (ICa-L) of cardiac myocytes. M3 receptor antagonist 4-DAMP (4-diphenylacetoxy-N-methylpiperidine-methiodide) was applied preliminarily to evaluate the role of the M3 receptor. Choline significantly increased the survival time of arrhythmic rats and guinea pigs, delayed the onset of arrhythmias and ventricular tachycardia, and decreased the arrhythmia score. The overload of intracellular Ca2+ induced by aconitine or ouabain was reduced in isolated myocytes pretreated with choline. Choline reduced the increased density of ICa-L induced by aconitine or ouabain. Moreover, the beneficial effects of choline were reversed by 4-DAMP. Choline produced antiarrhythmic actions on arrhythmia models by stimulating the cardiac M3 receptor. The mechanism may be related to the improvement of Ca2+ handling.

M3 muscarinic acetylcholine receptor is associated with beta-catenin in ventricular myocytes during myocardial infarction in the rat

1. The present study was designed to investigate whether the M(3) muscarinic acetylcholine receptors (mAChR) is associated with beta-catenin in the ventricular myocardium during ischaemic myocardial injury and to determine the possible mechanism/s involved. 2. Rat hearts were subjected to coronary artery ligation for 1 and 6 h or 1 month to establish a myocardial ischaemia (MI) model. In the acute MI model, 16 rats were randomized into four groups: (i) control; (ii) ischaemia (rats were subjected to 20 min coronary occlusion); (iii) choline (10 mg/kg, i.v., choline chloride, an M(3) receptor agonist, was administered 15 min before occlusion); and (iv) 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP; 0.12 mg/kg 4-DAMP, an M(3) receptor antagonist, was administered 20 min before occlusion, followed 5 min later by 10 mg/kg, i.v., choline chloride). Immunochemistry, western blot analysis and immunoprecipitation were used to determine the expression and localization of beta-catenin and the M(3) mAChR. 3. Myocardial ischaemia caused a time-dependent increase in the expression of beta-catenin. Moreover, a physical association was found between beta-catenin and the M(3) mAChR in intercalated discs. This association was enhanced by prolonged ischaemia. Administration of choline before ischaemia not only increased beta-catenin expression, but also strengthened the association between beta-catenin and the M(3) mAChR. However, blockade of M(3) mAChR by 4-DAMP completely inhibited the effect of choline on the expression of beta-catenin. In addition, MI increased phosphorylation of the M(3) mAChR. 4. The results indicate that increased beta-catenin activity is associated with M(3) mAChR during MI. This association is likely to play a role in heart signal transduction during ischaemia between neighbouring ventricular myocardiocum.

Inotropic effects and mechanisms of matrine, a main alkaloid from Sophora flavescens AIT

It has been well documented that matrine, a tetracyclo-quinolizindine alkaloid, possessed a positive inotropic effect. However, the underlying mechanisms at the cellular and ion channel levels have not been completely clarified. Therefore, the present study was designed to identify the cellular target and the mechanisms of inotropic effect of matrine. Guinea pig papillary muscles were used to study the contractile force of the heart and ventricular myocytes were used to study L-type calcium channel (ICa-L) and intracellular calcium concentration ([Ca2+]i). In electrically driven papillary muscles, matrine enhanced the contractile force in a dose-dependent manner and the positive inotropic effect was not inhibited by alpha- and beta-adrenergic receptor antagonists. In ventricular myocytes, matrine also increased ICa-L in a dose-dependent manner and shifted the inactivation curve toward right. Matrine markedly enhanced the KCl-induced elevations of [Ca2+]i. In a conclusion, ICa-L might be a main target of matrine. Matrine enhanced [Ca2+]i by stimulating ICa-L and exerted positive inotropic effects on electrically driven guinea pig papillary muscles.

Role of M3 receptor in aconitine/barium-chloride-induced preconditioning against arrhythmias in rats

We demonstrated here that an initial treatment with aconitine- or barium-chloride-induced arrhythmias and resulted in reduced susceptibility of the heart to the induction of arrhythmias by a repeated drug treatment 24 h after the initial one, a delayed preconditioning cardioprotection. This delayed preconditioning was accompanied by enhanced expression of cardiac muscarinic M(3) receptor and abolished by M(3)-selective antagonist. We conclude that muscarinic M(3) receptors might play an important role in conferring the pharmacological preconditioning against arrhythmias. This study thus expands our understanding of the cellular function and pathophysiological roles of muscarinic M(3) receptor and reconsolidates our view of cardioprotective effects of muscarinic M(3) receptor on myocardium.

CDP-choline prevents cardiac arrhythmias and lethality induced by short-term myocardial ischemia-reperfusion injury in the rat: involvement of central muscarinic cholinergic mechanisms

In the present study, we aimed to determine whether cytidine-5'-diphosphatecholine (CDP-choline or citicoline) can improve the outcome of short-term myocardial ischemia-reperfusion injury in rats. Ischemia was produced in anesthetized rats by ligature of the left anterior descending coronary artery for 7 min followed by a reperfusion period of 7 min. Reperfusion-induced ventricular tachycardia (VT), ventricular fibrillation (VF), survival rate, and changes in arterial pressure were evaluated. Saline (1 ml/kg), CDP-choline (100, 250,and 500 mg/kg), or lidocaine (5 mg/kg) was intravenously injected in the middle of the ischemic period. Intracerebroventricular (i.c.v.) mecamylamine (50 microg) or atropine sulfate (10 microg) pretreatments were made 10 min before the coronary occlusion period. Pretreatment with intravenous (i.v.) atropine methylnitrate (2 and 5 mg/kg; i.v.) or bilateral vagotomy was performed 5 min before the induction of ischemia. An in vivo microdialysis study was performed in the nucleus ambiguus area (NA); choline and acetylcholine levels were measured in extracellular fluids. In control rats, VT, VF, and lethality were observed in 85%, 60% and 50% of the animals, respectively. Intravenous CDP-choline produced a short-term increase in blood pressure and reduced the incidence of VT, VF, and lethality dose-dependently when injected in the middle of the ischemic period. CDP-choline at doses of 250 and 500 mg/kg completely prevented death. Intracerebroventricular atropine sulfate pretreatment completely abolished the protective effect of CDP-choline, while mecamylamine pretreatment had no effect on the drug. CDP-choline increased the levels of extracellular choline and acetylcholine in the NA area. Bilateral vagotomy completely abolished the protective effect of CDP-choline in the reperfusion period. Moreover, the intravenous pretreatment with atropine methylnitrate produced dose-dependent blockade in the reduction of VT, VF, and mortality rates induced by CDP-choline. Neither of these pretreatments except mecamylamine affected the pressor effect of CDP-choline. Intracerebroventricular mecamylamine attenuated the increase in blood pressure induced by CDP-choline. In conclusion, intravenously injected CDP-choline prevents cardiac arrhythmias and death induced by short-term myocardial ischemia-reperfusion injury. Activation of central muscarinic receptors and vagal pathways mediates the protective effect of CDP-choline. The protective effect of CDP-choline is not related to its pressor effect.

Acetylcholine inhibits long-term hypoxia-induced apoptosis by suppressing the oxidative stress-mediated MAPKs activation as well as regulation of Bcl-2, c-IAPs, and caspase-3 in mouse embryonic stem cells

This study examined the effect of acetylcholine (ACh) on the hypoxia-induced apoptosis of mouse embryonic stem (ES) cells. Hypoxia (60 h) decreased both the cell viability and level of [3H] thymidine incorporation, which were prevented by a pretreatment with ACh. However, the atropine (ACh receptor [AChR] inhibitor) treatment blocked the protective effect of ACh. Hypoxia (90 min) increased the intracellular level of reactive oxygen species (ROS). On the other hand, ACh inhibited the hypoxia-induced increase in ROS, which was blocked by an atropine treatment. Subsequently, the hypoxia-induced ROS increased the level of p38 mitogen activated protein kinase (MAPK) and Jun-N-terminal kinase (JNK) phosphorylation, which were inhibited by the ACh pretreatment. Moreover, hypoxic exposure (90 min) increased the level of nuclear factor-kappa B (NF-kappa B) phosphorylation, which was blocked by a pretreatment with SB 203580 (p38 MAPK inhibitor) or SP 600125 (JNK inhibitor). However, hypoxia (60 h) decreased the protein levels of Bcl-2 and c-IAPs (cellular inhibitor of apoptosis proteins) but increased the level of caspase-3 activation. All these effects were inhibited by a pretreatment with ACh. In conclusion, ACh prevented the hypoxia-induced apoptosis of mouse ES cells by inhibiting the ROS-mediated p38 MAPK and JNK activation as well as the regulation of Bcl-2, c-IAPs, and caspase-3.

MHP-133, a drug with multiple CNS targets: potential for neuroprotection and enhanced cognition

MHP-133 is one of a novel series of compounds designed to target multiple brain substrates expected to have synergistic actions in the treatment of cognitive and neurodegenerative disorders such as Alzheimer's disease. The strategy was to develop compounds with multiple targets relevant for enhancing cognition and memory, but avoiding the serious side effects attributed to high potency cholinergic agonists. MHP-133 was shown to interact with subtypes of cholinergic, serotonergic, and imidazoline receptors and to weakly inhibit acetylcholinesterase activity. In vitro, the drug enhanced nerve growth factor (TrkA) receptor expression; it prevented excitotoxicity in a hippocampal slice preparation; and increased the secretion of soluble (non-toxic) amyloid precursor protein. MHP-133 also enhanced cognitive performance by rats and by non-human primate in tasks designed to assess working memory. The results of this study are consistent with the potential use of MHP-133 in the treatment of neurodegenerative disorders such as Alzheimer's disease.

The muscle-specific microRNA miR-1 regulates cardiac arrhythmogenic potential by targeting GJA1 and KCNJ2

MicroRNAs (miRNAs) are endogenous noncoding RNAs, about 22 nucleotides in length, that mediate post-transcriptional gene silencing by annealing to inexactly complementary sequences in the 3'-untranslated regions of target mRNAs. Our current understanding of the functions of miRNAs relies mainly on their tissue-specific or developmental stage-dependent expression and their evolutionary conservation, and therefore is primarily limited to their involvement in developmental regulation and oncogenesis. Of more than 300 miRNAs that have been identified, miR-1 and miR-133 are considered to be muscle specific. Here we show that miR-1 is overexpressed in individuals with coronary artery disease, and that when overexpressed in normal or infarcted rat hearts, it exacerbates arrhythmogenesis. Elimination of miR-1 by an antisense inhibitor in infarcted rat hearts relieved arrhythmogenesis. miR-1 overexpression slowed conduction and depolarized the cytoplasmic membrane by post-transcriptionally repressing KCNJ2 (which encodes the K(+) channel subunit Kir2.1) and GJA1 (which encodes connexin 43), and this likely accounts at least in part for its arrhythmogenic potential. Thus, miR-1 may have important pathophysiological functions in the heart, and is a potential antiarrhythmic target.

Chotosan, a kampo formula, ameliorates chronic cerebral hypoperfusion-induced deficits in object recognition behaviors and central cholinergic systems in mice

We previously demonstrated that the Kampo formula chotosan (CTS) ameliorated spatial cognitive impairment via central cholinergic systems in a chronic cerebral hypoperfusion (P2VO) mouse model. In this study, the object discrimination tasks were used to determine if the ameliorative effects of CTS on P2VO-induced cognitive deficits are a characteristic pharmacological profile of this formula, with the aim of clarifying the mechanisms by which CTS enhances central cholinergic function in P2VO mice. The cholinesterase inhibitor tacrine (THA) and Kampo formula saikokeishito (SKT) were used as controls. P2VO impaired object discrimination performance in the object recognition, location, and context tests. Daily administration of CTS (750 mg/kg, p.o.) and THA (2.5 mg/kg, i.p.) improved the object discrimination deficits, whereas SKT (750 mg/kg, p.o.) did not. In ex vivo assays, tacrine but not CTS or SKT inhibited cortical cholinesterase activity. P2VO reduced the mRNA expression of m(3) and m(5) muscarinic receptors and choline acetyltransferase but not that of other muscarinic receptor subtypes in the cerebral cortex. Daily administration of CTS and THA but not SKT reversed these expression changes. These results suggest that CTS and THA improve P2VO-induced cognitive impairment by normalizing the deficit of central cholinergic systems and that the beneficial effect on P2VO-induced cognitive deficits is a distinctive pharmacological characteristic of CTS.

FUNCTIONAL IMPAIRMENT OF CARDIAC TRANSIENT OUTWARD K+CURRENT AS A RESULT OF ABNORMALLY ALTERED CELLULAR ENVIRONMENT

1. Physiological functions of cardiac cells require a normal cellular environment. Under pathological conditions, there is a loss of normal cellular environment due to metabolic perturbations and other abnormalities. To test the hypothesis that cellular environmental stresses can create an electrophysiological substrate for electrical disorders in the heart, we investigated the effects of hypoxia, acidosis and ischaemia on transient outward K+ current (I(to)) in single canine ventricular myocytes. 2. The I(to) was studied because it plays a critical role in initiating cardiac repolarization and, thereby, arrhythmias. It was found that I(to) was significantly depressed by some 30% under hypoxic conditions relative to that in a normal cellular environment with normal Tyrode's solution. 3. Acidosis created by lowering the pH of the external solution from 7.4 to 7.2 produced a substantial (approximately 35%) reduction of the I(to) amplitude. 4. A marked impairment of I(to) function was consistently observed in ischaemic hearts in the canine coronary artery ligation model, with an approximate 30% decrease in the size of I(to). 5. Importantly, the impairment of I(to) under these environmental stresses was largely reversible following restoration to normal conditions. 6. The results of the present study suggest that I(to) is susceptible to changes in the cellular environment and the functional impairment of I(to) under environmental stresses contributes to arrhythmias under relevant pathological conditions of the heart.

beta(1) Receptors protect the renal afferent arteriole of angiotensin-infused rabbits from norepinephrine-induced oxidative stress

Renal afferent arterioles (Aff) from angiotensin II (AngII)-infused rabbits have enhanced contractions to AngII that are normalized by tempol (superoxide dismutase mimetic), whereas contractions to norepinephrine (NE) are normal and unaffected by tempol. Tested was the hypothesis that beta-receptor stimulation with NE prevents enhanced reactivity and superoxide generation. Preconstricted Aff from AngII- or vehicle-infused rabbits were perfused at physiologic pressure. Aff from vehicle-infused rabbits had strong, endothelium-independent relaxations to dobutamine (beta(1)-receptor agonist; 78 +/- 6%; P < 0.0001; mean +/- SD) but only weak relaxations to salbutamol (beta(2)-receptor agonist; 13 +/- 3%; P < 0.05) or BRL-37,344 (beta(3)-receptor agonist; 14 +/- 3%; P < 0.05). Contractions to NE were similar in Aff from vehicle- and AngII-infused rabbits (-36 +/- 5 versus -34 +/- 3%; NS) and were unaffected by tempol (-32 +/- 4%; NS). In contrast, phenylephrine contractions (alpha(1) agonist) were enhanced in Aff from AngII-infused rabbits (-59 +/- 6 versus -46 +/- 4%; P < 0.05) and normalized by tempol. NE contractions in Aff from AngII-infused rabbits (-34 +/- 4%) were enhanced (P < 0.01) by propranolol (nonselective beta antagonist; -53 +/- 6%), CGP-20,712A (selective beta(1)-receptor antagonist; -61 +/- 9%), or Rp-cAMP (competitive inhibitor of cAMP; -56 +/- 4%); were normalized by tempol; but were unaffected by ICI-118,551 (selective beta(2)-receptor antagonist) or SR-59,230A (selective beta(3)-receptor antagonist). Superoxide generation in Aff from AngII-infused rabbits that were assessed from ethidium:dihydroethidium was enhanced by addition of CGP-20,712A to NE but was normalized by tempol. Aff have robust alpha(1)-receptor contraction and beta(1)-receptor dilation. NE elicits beta(1) signaling via cAMP that moderates oxidative stress and contractions in Aff from AngII-infused rabbits.

Choline-Modulated Arsenic Trioxide-Induced Prolongation of Cardiac Repolarization in Guinea Pig

Arsenic trioxide (As(2)O(3)) has been found to be effective for relapsed or refractory acute promyelocytic leukaemia, but its clinical use is burdened by QT prolongation, Torsade de pointes tachycardias, and sudden cardiac death. The aim of the present study was to elucidate the ionic mechanisms of As(2)O(3)-induced abnormalities of cardiac electrophysiology and the therapeutic action of choline on As(2)O(3)-caused QT prolongation in guinea pig. Intravenous administration of As(2)O(3) prolonged the QT interval in a dose- and time-dependent manner in guinea pig hearts, and the QT prolongation could be modulated by choline. By using whole-cell patch clamp technique and confocal laser scanning microscopy, we found that As(2)O(3) significantly lengthened action potential duration measured at 50 and 90% of repolarization, enhanced L-type calcium currents (I(Ca-L)), inhibited delayed rectifier potassium currents (I(K)), and increased intracellular calcium concentration ([Ca(2+)](i)) in guinea pig ventricular myocytes. Choline corrected As(2)O(3)-mediated alterations of action potential duration, I(Ca-L) and [Ca(2+)](i), but had no effect on the I(K) inhibition. As(2)O(3) markedly disturbed the normal equilibrium of transmembrane currents (increasing I(Ca-L) and suppressing I(K)) in guinea pig cardiomyocyte, and induced prolongation of action potential duration, further degenerated into QT prolongation. Choline normalized QT interval abnormality and corrected lengthened action potential duration by inhibiting the elevated I(Ca-L) and [Ca(2+)](i) in ventricular myocytes during As(2)O(3) application.

Ischemia impairs the association between connexin 43 and M3 subtype of acetylcholine muscarinic receptor (M3-mAChR) in ventricular myocytes

We used Western blot analysis to examine the expression of connexin 43 and M2/M3 acetylcholine muscarinic receptors (mAChR) and their interaction in ventricular myocytes from control and the ischemic heart. We confirmed that the connexin 43 and M2/ M3-mAChR were expressed in ventricular myocytes. Moreover, we showed that M3-mAChR was expressed in non-glycosylated (72 kDa) and glycosylated forms (115 kDa). Immunostaining showed that connexin 43 is closely associated with M3-mAChR in parts of cell membranes of myocytes. Immunoprecipitation of lysate of cardiac myocytes with M2/M3-mAChR antibody pulled down a 44 kDa protein recognized by connexin 43 antibody. Ischemia increased the expression of M3-mAChR in myocytes. The ischemiainduced increase in the M3-mAChR expression was specific because ischemia did not affect the expression of M1, M2, M4 and M5- mAChR in the heart. On the other hand, ischemia decreased the expression of connexin 43 in myocardium. We also examined the effect of ischemia on the interaction between M2/M3-mAChR and connexin 43. Ischemia suppressed the association of M3-mAChR with connexin 43 but did not affect the association of connexin 43 with M2-mAChR. Administration of choline before ischemia not only partially restored the expression of connexin 43 but also attenuated the ischemia-induced suppression of the association between connexin 43 and M3-mAChR. We conclude that connexin 43 interacts with M2/M3-mAChR and that ischemia specifically impairs the association between M3-mAChR and connexin 43.

Resveratrol, a natural ingredient of grape skin: antiarrhythmic efficacy and ionic mechanisms

Resveratrol has been demonstrated to produce a variety of biological actions. Accumulating line of evidence supported the view that resveratrol may exert protective effect on the cardiovascular system. The aim of the study was to assess the antiarrhythmic profile as well as electrophysiological properties of resveratrol. We observe the antiarrhythmic effect of resveratrol on aconitine induced rat arrhythmia, ouabain induced guinea pig arrhythmia, and coronary ligation induced rat arrhythmia animal models. Resveratrol significantly and dose-dependently increased the doses of aconitine and ouabain required to induce the arrhythmia indexes. In coronary ligation induced rat arrhythmia model, resveratrol shortened duration of arrhythmia, decreased incidence of ventricular tachycardia and mortality. Electrophysiological experiment revealed that resveratrol could shorten APD through inhibition of ICa and selective enhancement of IKs without an effect on IKr.