Role of cardiac β1-adrenergic and A1-adenosine receptors in severe arrhythmias related to Parkinson's disease

Abstract Aims Although reduced life expectancy in Parkinson's Disease (PD) patients has been related to severe cardiac arrhythmias due to autonomic dysfunctions, its molecular mechanisms remain unclear. To investigate the role of cardiac β1-Adrenergic (β1AR) and A1-Adenosine (A1R) receptors in these dysfunctions, the pharmacological effects of stimulation of cardiac β1AR (isoproterenol, ISO), in the absence and presence of cardiac β1AR (atenolol, AT) or A1R (1,3-dipropyl-8-cyclopentyl xanthine, DPCPX) blockade, on the arrhythmias induced by Ischemia/Reperfusion (CIR) in an animal PD model were studied. Methods PD was produced by dopaminergic lesions (confirmed by immunohistochemistry analysis) caused by the injection of 6-hydroxydopamine (6-OHDA, 6 μg) in rat striatum. CIR was produced by a surgical interruption for 10 min followed by reestablishment of blood circulation in the descendent left coronary artery. On the incidence of CIR-Induced Ventricular Arrhythmias (VA), Atrioventricular Block (AVB), and Lethality (LET), evaluated by Electrocardiogram (ECG) analysis, the effects of intravenous treatment with ISO, AT and DPCPX (before CIR) were studied. Results VA, AVB and LET incidences were significantly higher in 6-OHDA (83%, 92%, 100%, respectively) than in control rats (58%, 67% and 67%, respectively). ISO treatment significantly reduced these incidences in 6-OHDA (33%, 33% and 42%, respectively) and control rats (25%, 25%, 33%, respectively), indicating that stimulation of cardiac β1AR induced cardioprotection. This response was prevented by pretreatment with AT and DPCPX, confirming the involvement of cardiac β1AR and A1R. Conclusion Pharmacological modulation of cardiac β1AR and A1R could be a potential therapeutic strategy to reduce severe arrhythmias and increase life expectancy in PD patients.

Effects of pulsed electromagnetic fields on the A2A adenosine receptor in human degenerative nucleus pulposus cells / 中华物理医学与康复杂志

Objective@#To explore the expression of the A2A adenosine receptor and the inflammatory cytokines interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in human degenerative nucleus pulposus (NP) cells after they have been treated with a pulsed electromagnetic field (PEMF).@*Methods@#Human degenerative NP cells were cultured in vitro and treated using an 0.8mT PEMF with a pulse frequency of 50Hz. The pulse width was 150μs and the exposure time was 30min, repeated 5 times at 12 hour intervals. The expression of the A2A adenosine receptor in NP cells was determined using western blotting and reverse transcription polymerase chain reactions. The expression of the inflammatory cytokines IL-1β and TNF-α were detected using enzyme-linked immunosorbent assays (ELISA). The human degenerative NP cells were also treated with an antagonist and agonist of the A2A adenosine receptor, and the expression of IL-1β and TNF-α were also determined using ELISA.@*Results@#After the PEMF treatment the expression of the A2A adenosine receptor increased significantly, while the expression of IL-1β and TNF-α decreased significantly. However, the A2A adenosine receptor antagonist reversed the inhibitory effect of the PEMF on the expression of IL-1β and TNF-α, while the agonist played an opposite role.@*Conclusion@#A PEMF can significantly inhibit the expression of IL-1β and TNF-α in human degenerative NP cells, which could be related to up-regulation of the expression of the A2A adenosine receptor in those cells.

Effects of electroacupuncture on the expression of adenosine receptors in the heart tissue of myocardial ischemia rats / 中国针灸

<p><b>OBJECTIVE</b>To explore the impact of electroacupuncture (EA) on the protein expression of adenosine receptors in the heart of the rats with myocardial ischemia (MI).</p><p><b>METHODS</b>Thirty healthy male SD rats were divided randomly into a control group (=6), a model group (=12) and an EA group (=12). We ligated the left anterior descending artery (LAD) for MI model in the model group and EA group, and exposed the heart after opening the chest without ligation in the control group. EA, 2 Hz /15 Hz and 1.5-2 mA, was applied at bilateral"Neiguan"(PC 6) in the EA group for 20 min, once a day for continuous 5 days. No intervention except grabbing and fixation was used in the control group and model group. We applied 2% TTC staining to observe the infarct size of myocardium, colorimetry to analyze serum lactic dehydrogenase (LDH), creatine kinase (CK), creatine kinase isoenzyme (CK-MB), radio-immunity assessment to detect cardiac troponin T (cTnT), Western blot to evaluate the adenosine A1 receptor (A1AR), A2aAR, A2bAR and A3AR.</p><p><b>RESULTS</b>After treatment, myocardial infarction of (27.56±3.24)% was obvious in the model group; the myocardial infarction in the EA group was (21.04±3.61)%, with statistical significance (<0.05). The expressions of serum LDH, CK, CK-MB and cTnT levels in the model group increased compared with those in the control group (all<0.01), and the expressions of LDH, CK, CK-MB and cTnT levels in the EA group decreased compared with those in the model group (<0.05，<0.01). The A1AR expression in the model group was not different from that in the control group (>0.05), and A2aAR、A2bAR、A3AR expressions decreased (<0.05,<0.01). A2aAR and A2bAR expressions in the EA group increased compared with those in the model group (both<0.01), and there was no statistical significance between A1AR and A3AR expressions (both>0.05). .</p><p><b>CONCLUSION</b>EA may achieve cardioprotective effect by regulating the expressions of A2aAR and A2bAR in myocardial tissue, which induce the corresponding signal cascade for reducing myocardial infarction area.</p>

Research progress of adenosine receptors in fibrosis diseases / 中国药理学通报

The fibrosis can occur in many kinds of organs,and its sustained progress may lead to organ structural damage and functional decline,and even the organ failure,which threatens the human health and the life seriously.Adenosine is an endogenous purine nucleoside that can be generated in various tissues of the body and regulate a multitude of body functions via the combina-tion with four different kinds of G protein-coupled receptors.Re-cent studies have found that adenosine receptors play an impor-tant role in regeneration tissue and fibrosis process.To under-stand the processes may be helpful to the treatment of fibrosis diseases.This review makes a summary on latest research pro-gress of adenosine receptors in fibrosis diseases.

A2B Adenosine Receptors in SH-SY5Y Cells-Functional Approaches.

The diversity in intracellular signalling downstream of adenosine receptors is dependent on the receptor subtype activated by adenosine. A1 and A2A are considered high affinity receptors while A2B and A3 are considered as low affinity receptors. Despite the apparent widespread distribution of A2B in every cell of every species, the receptor number and low affinity for adenosine and its analogue, makes it the least wellcharacterised adenosine receptor. A2B adenosine receptors are classically coupled to Gs protein and elevation of cAMP levels in target cells, although, A2B have also been known to couple to Gq and not just Gs proteins, and also to couple to Mitogen activated protein kinases (MAPK). In the present study, changes in intracellular calcium concentration ([Ca2+]i) and MAPK phosphorylation following subtype-specific and non-specific agonists and antagonists stimulation were investigated in human neuroblastoma SH-SY5Y cell line. In conclusion, our results indicate that SH-SY5Y cells express A2B adenosine receptors that are coupled to stimulation of Extracellular regulated kinase (ERK1/2) mitogen activated protein (MAP) kinases.

Advance in Anti-depression of Adenosine (review) / 中国康复理论与实践

@# Adenosine is an important signaling molecule of the central nervous system (CNS). Adenosine typically released in the phosphorylated form(ATP), together with neurotransmitter, both of which are encapsulated in the synaptic vesicles. Once released into the synaptic space, adenosine molecules will bind to their three categories of receptors, namely A1 receptor (A1R), A2 receptor (A2R), A3 receptor (A3R), and therefore start G protein mediated signaling pathways, resulting in various and extensive biological effects. It has been discovered in recent years that adenosine has a certain level of anti-depression effect, although its mechanisms are yet to be elucidated. This review summarized the researches focusing on anti-depression roles of both adenosine and its receptors.

Characteristics of A|1 and A|2 adenosine receptors upon the acetylcholine release in the rat hippocampus

As it has been reported that the depolarization induced acetylcholine (ACh) release is modulated by activation of presynaptic A1 adenosine heteroreceptor and various lines of evidence suggest the A2 adenosine receptor is present in the hippocampus. The present study was undertaken to delineate the role of adenosine receptors on the hippocampal ACh release. Slices from the rat hippocampus were equilibrated with (3H)choline and then the release amount of the labelled product, (3H)ACh, which was evoked by electrical stimulation (rectangular pulses, 3 Hz, 2 ms, 24 mA, 5 V/cm-1, 2 min), was measured, and the influence of various adenosine receptor-related agents on the evoked tritium outflow was investigated. And also, the drug-receptor binding assay was performed in order to confirm the presence of A1 and A2 adenosine receptors in the rat hippocampus. N-ethylcarboxamidoadenosine (NECA), a potent adenosine receptor agonist with nearly equal affinity at A1 and A2 adenosine receptors, in concentrations ranging from 1apprx30 muM, decreased the electrically-evoked (3H)ACh release in a concentration-dependent manner without affecting the basal rate of release. And the effect of NECA was significantly inhibited by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 2 micrometer), a selective A1 adenosine receptor antagonist, but was not influenced by 3,7-dimethyl-1-propargylxanthine (DMPX, 5 micrometer, a specific A2 adenosine receptor antagonist. N6-Cyclopentyladenosine (CPA), a selective A1 adenosine receptor agonist, in doses ranging from 0.1 to 10 micrometer, reduced evoked (3H)ACh release in a dose-dependent manner without the change of the basal release. And the effect of CPA was significantly inhibited by 2 micrometer DPCPX treatment. 2-P-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride (CGS-21680C), a potent A2 adenosine receptor agonist, in concentrations ranging from 0.1 to 10 micrometer, did not alter the evoked ACh release. In the drug-receptor binding assay, the binding of (3H)2-chloro-N6-Cyclopentyladenosine ((3H)CCPA) to the- A1 adenosine receptor of rat hippocampal membranes was inhibited by CPA (Ki = 1.22 nM), NECA (Ki=10.17 nM) and DPCPX (Ki-161.86 nM), but not by CGS-21680C (Ki=2,380 nM) and DMPX (Ki-22,367 nM). However, the specific binding of (3H)CGS-21680C to the A2 adenosine receptor was not observed. These results suggest that the A1 adenosine heteroreceptor play an important role in evoked ACh release, but the presence of A2 adenosine receptor is not confirmed in this study.

The role of adenosine receptors on acetylcholine release in the rat striatum

As it has been reported that the depolarization induced acetylcholine (ACh) release is modulated by activation of presynaptic A-1 adenosine heteroreceptor and various evidence suggest that indicate the A-2 adenosine receptor is present in the striatum, this study was undertaken to delineate the role of adenosine receptors on the striatal ACh release. Slices from the rat striatum were equilibrated with (3H)choline and then the release amount of the labelled product, (3H)ACh, which was evoked by electrical stimulation (rectangular pulses, 3 Hz, 2 ms, 24 mA, 5 Vcm-1, 2 min), was measured, and the influence of various agents on the evoked tritium outflow was investigated. And also, quantitative receptor autoradiography and drug-receptor binding assay were performed in order to confirm the presence and characteristics of A-1 and A-2 adenosine receptors in the rat striatum. Adenosine (10 ~ 100 micrometer) and N-6-cyclopentyladenosine (CPA, 1 ~ 100 micrometer) decreased the (3H)ACh release in a dose-dependent manner without changing the basal rate of release in the rat striatum. The reducing effects of ACh release by adenosine and CPA were abolished by 8-cyclopentyl-1,3-dipropy-lxanthine (DPCPX, 2 micrometer), a selective A-1 adenosine receptor antagonist, treatment. The effect of adenosine was potentiated markedly by 3,7-dimethyl-1-propargylxanthine (DMPX, 10 micrometer), a specific A-2 adenosine receptor antagonist. 2-P-(2-carboxyethyl)phenethylamimo-5'-N- ethylcarboxamidoadenosine hydrochloride (CGS-21680C), in concentrations ranging from 0.01 to 10 micrometer, a recently introduced potent A-2 adenosine receptor agonist, increased the(3 H)ACh release in a dose related fashion without changing the basal rate of release. These effects were completely abolished by DMPX (10 micrometer). In autoradiogaphy experiments, (3H)2-chloro-N-6-cyclopentyladenosine ((3 H)CCPA) bindings were highly localized in the hippocampus and the cerebral cortex. Additionally, lower levels of binding were found in the striatum. However, (3H)CGS-21680C bindings were highly localized in the striatal region with the greatest density of binding found in the caudate nucleus and putamen. Lower levels of binding were also found in the nucleus accumbens and olfactory tubercle. In drug-receptor binding assay, binding of (3H)CCPA to A-1 adenosine receptors of rat striatal membranes was inhibited by CPA (K-i = 1.6nM) and N-ethylcarboxamidoadenosine (NECA, K-i = 12.9 nM), but not by CGS-21680C (K-i = 2609.2 nM) and DMPX (K-i = 19,386 nM). In contrast, (3H)CGS-21680C binding to A-2 adenosine receptors was inhibited by CGS-21680C (K-i = 47.6 rim) and NECA (K-i = 44.9 nM), but not by CPA (K-i = 2099.2 nM) and DPCPX (K-i = 19,207 nM). The results presented here suggest that both types of A-1 and A-2 adenosine heteroreceptors exist and play an important role in ACh release in the rat striatal cholinergic neurons.

The Role of the Adenosine Receptor Subtypes and Protein Kinase C in Ischemic Preconditioning in the in Vivo Cat Heart

BACKGROUND: It is well known that ischemic preconditioning protects the heart against infarction or arrhythmias from a subsequent ischemic injury. Recent laboratory data indicate that the adenosine during the ischemic period may trigger protection via A1 or A3 adenosine receptor and also protein kinase C(PKC) plays a central role. This study was designed to determine the role of adenosine receptor subtypes and PKC in the preconditioning protection. METHODS: All cat heart groups were subjected to 40min ischemia and 30min reperfusion. The preconditioning protocol consists of 4min ischemia and then 10min of reperfusion 4 times. The effects of ischemic preconditioning, nonselective adenosine receptor blocker(SPT), an A1 specific antagonist(DPCPX) and protein kinase C inhibitor(Polymyxin B), on ischemic preconditioning were determined by infarction size. There were 5 groups : (1) control group (Group 1, n=10)(2) Ischemic preconditioned group(Group 2, n=9)(3) DPCPX pretreatment group(Group 3, n=6)(4) SPT preteatment group(Group 3, n=6)(5) Polymyxin B pretreatment group(Group 5, n=6). SPT and DPCPX were given intravenously 5 min before ischemic preconditioning. Polymyxin B was administered to cats for 30min during ischemic preconditioning period. RESULTS: Ischemic preconditioning only or pretreatment with DPCPX prior to preconditioning demonstrated a significant reduction in infarct size(22.6+/-1.5, 25.4+/-0.9% infarction of the risk zone, respectively, p<0.05) with respect to control, SPT-pretreatment, and polymyxin B-pretreatment groups(44.0+/-1.7, 43.0+/-2.0 and 40.3+/-0.4% infarction of the risk zone, respectively). CONCLUSIONS: Ischemic preconditioning protects heart from subsequent ischemia. Protection was blocked by SPT and protein kinase C inhibitor(polymyxin B), but not by A1 antagonist DPCPX. The cardioprotective effects by ischemic preconditioning in the in vivo cat heart appear to be dependent on A3 adenosine receptors and activation of protein kinase C.

Progress in research on effects of adenosine A1 receptors / 中国药理学通报

Many kinds of pathological irritations often make local-tissue face environmental hypoxia.These changes were messaged by increased accumulation of extracellular adenosine through their receptors.There are different roles for the four subtypes of adenosine receptors designated A1、A2a、A2b andA3.This review covers the effects of adenosine A1 receptors in different systems,such as protective effects on cells,improving immune response,regulation of blood pressure and glucose homeostasis.