Distribution of Like-muscarinic Acetylcholine Receptor M2 in the Brain of Three Castes of Polyrhachis vicina

The cholinergic system plays an important role in the central nervous system of insects and is closely related to the complex behavior of insects. The immunohistochemical technique was performed to detect the expression of like-muscarinic acetylcholine receptor M2 in the brain of three castes of Polyrhachis vicina. A positive expression of like-muscarinic acetylcholine receptor M2 was observed in the mushroom body, central body and antennal lobes of the ant brain; but there is great diversity in their location and intensity among worker, queen and male ants. It is speculated that like-muscafinic acetylcholine receptor M2 plays a critical role in the central nervous system, in terms of projecting visual information and olfactory information into the protocerebrum and integrating many inputs.

M_(4) muscarinic receptors regulates dopamine/DARPP-32 signaling and glutamate transmis⁃sion to balance dopaminergic D1 function in mouse dorsal striatum

OBJECTIVE Abnormal striatal dopaminergic and glutamatergic neurotransmis⁃sion is central to the pathophysiology of schizo⁃phrenia.In this study,we investigated the roles of M4 receptor interplay with D1 signaling in stria⁃tal neurotransmission that affect glutamatergic transmission to control the etiology of neuropsy⁃chiatric disorders.METHODS To study dorsal striatum(DS)region-specific neuronal and behav⁃ioral responses modulated by M4 receptors,we used clustered regularly interspaced short palin⁃dromic repeats-associated protein 9 technology to generate mice lacking M4 in the dorsal stria⁃tum(DS-M4-KD).The M4 positive allosteric modu⁃lator,VU0467154,were used to study the phar⁃macologically profiles with M4 receptor stimula⁃tion in WT mice.Oxotremorine M(Oxo-M),a no subtype-selective muscarinic agonist,was used to show that mAchRs activation,in order to dissect the particular function of M4,in DS-M4-KD mice.Open filed test and forced swim test were used to assess the change of psychiatric-like behav⁃iors.Western blotting and immunohistochemistry were used to detect protein levels of phosphory⁃lation site of dopamine-and cAMP-regulated phosphoprotein of 32 ku(DARPP-32).Whole-cell patch-clamp recording was used to assess M4-mediated cholinergic inhibition of glutamater⁃gic synaptic input transmission.RESULTS West⁃ern blotting and immunohistochemistry assay showed VU0467154(5 mg·kg-1,ip)promoted phosphorylation of DARPP-32 at Thr75,and atten⁃uated D1-dependent phosphorylation of DARPP-32 at Thr34 within the mouse DS.Consistently,the Oxo-M(4μg,icv)also increased DARPP-32 phosphorylation at site Thr75 to reversed phos⁃phorylation at site Thr34 in WT mice,but not in DS-M4-KD mice.In parallel with altered DARPP-32 responses,VU0467154 or Oxo-M evoked a psychological stress response and reversed D1-induced hyperlocomotion in mice in open field test and force swim tests.However,Oxo-M sup⁃pression of D1-depengdeng behavioral respons⁃es was impaired in DS-M4-KD mice.Whole-cell patch recording showed that VU0467154 or Oxo-M mediated endogenous cholinergic inhibition of miniature excitatory postsynaptic currents through M4 receptors,which in turn suppressed D1-depen⁃dent glutamatergic synaptic transmission in the DS.CONCLUSION This study provides evidence for the role of M4 receptors in regulation of dopa⁃mine/DARPP-32 signaling and glutamate respons⁃es in the DS,and therefore modulation of psychi⁃atric behaviors associated with D1 signaling.This results indicate the mechanisms of treatments targeting M4 in psychiatric disorders.

METABOLIC KINETICS OF BRAIN MUSCARINIC CHOLINERGIC RECEPTORS IN NORMAL AND HYPOTHYROID MICE

A technique for studying in vivo the production rate and turnover rate constant of mouse brain M-receptors was established. A single injection of 25 mg / kg of Benzilylcholine Mustard to living mice resulted in 90 % irreversible block of brain M-receptors. The time course of the receptor density was then monitored by 3H-QNB binding assay and the production rate and turnover rate constant were calculated from the time course curve with a computer program. It was found that in normal mice the turnover rate constant was about 0.035 h-1 (half-life was about 20 h) and the production rate was 30-42 fmol / (h ·mg protein). Parallel experiments revealed a significant slow down of the turnover of brain M-receptors in hypothyroid mice (turnover rate constant was 0.0257±0.0012 h-1 in hypothyroid vs. 0.0356±0.0021 h-1 in normal) while the production rate was not changed significantly. The results suggest that thyroid hormones have a regulatory action on the turnover of brain M-receptors and the elevation of brain M-receptor density together with slow down of the turnover of brain M- receptors is probably one of the important mechanisms relevant to the brain dysfunction in hypothyroidism.

Effect of organophosphorus insecticides on phosphorylation of the M_2 muscarinic acetylcholine receptor

BACKGROUND： Organophosphorus insecticides may promote the accumulation of acetylcholine at synapses and the neuromuscular junction by inhibiting acetylcholinesterase activity to cause disturbance of neural signal conduction and induce a toxic reaction. Organophosphorus insecticides may act on M2 muscarinic acetylcholine receptors, whose combination with G proteins is regulated by phosphorylation of G protein-coupled receptor kinase 2. OBJECTIVE： To investigate the effects of organophosphorus insecticides on the phosphorylation of G protein-coupled receptor kinase 2-mediated M2 muscarinic acetylcholine receptors and to reveal other possible actions of organophosphorus insecticides. DESIGN, TIME AND SETTING： An observational study, which was performed in the Central Laboratory of Shenyang Medical College, and Department of Physiological Sciences, College of Veterinary Medicine, Oklahoma State University from June 2002 to December 2004. MATERIALS： Paraoxon, parathion, chlorpyrifos, and chlorpyrifos oxon were provided by Chem Service Company, USA, [γ -p^32] ATP and [^35S]GTP γ S by New England Nuclear Life Science Products, and recombinant β 2-adrenergic receptor membrane protein by Sigma Company, USA. METHODS： The M2 muscarinic acetylcholine receptor was extracted and purified from pig brain using affinity chromatography. Subsequently, the purified M2 muscarinic acetylcholine receptor, G protein-coupled receptor kinase 2, and [γ -p^32] ATP were incubated with different concentrations of paraoxon and chlorpyrifos oxon together. The mixture then underwent polyacrylamide gel electrophoresis, and the gel film was dried and radioactively autographed to detect phosphorylation of the M2 muscarinic acetylcholine receptor. Finally, the radio-labeled phosphorylated M2 receptor protein band was excised for counting with an isotope liquid scintillation counter. MAIN OUTCOME MEASURES： Effects of chlorpyrifos oxon, paraoxon, chlorpyrifos, and parathion in different concentrations on the phosphorylation of the M2 muscarinic acetylcholine receptor; effects of chlorpyrifos oxon on the phosphorylation of the β -adrenergic receptor. RESULTS： Chlorpyrifos oxon could completely inhibit the phosphorylation of the M2 muscarinic acetylcholine receptor, and its IC50 was 70 μ mol/L. Chlorpyrifos could also inhibit the phosphorylation of the M2 muscarinic acetylcholine receptor. However, paraoxon and parathion could not inhibit the phosphorylation of the M2 muscarinic acetylcholine receptor. Chlorpyrifos oxon in different concentrations could also not inhibit the phosphorylation of the β 2-adrenergic receptor catalyzed by G protein-coupled receptor kinase 2. CONCLUSION： Different kinds of organophosphorus insecticides have different effects on the phosphorylation of the G protein-coupled receptor kinase 2-mediated M2 muscarinic acetylcholine receptor. Organophosphorus insecticides possibly have different toxic effects.

AduoLa Fuzhenglin Down-regulates Microwave-induced Expression of β_1-adrenergic Receptor and Muscarinic Type 2 Acetylcholine Receptor in Myocardial Cells of Rats

This paper is aimed to study the effect of ADL on expression of ~z-AR and Mz-AchR in myocardial cells of rats exposed to microwave radiation. Immunohistochemistry, Western blot and image analysis were used to detect the expression of ~I-AR and Mz-AchR in myocardial cells at 7 and 14 d after microwave exposure. The results show that the expression level was higher in microwave exposure group and 0.75 g/（kg.d） ADL group than in sham operation group and significantly lower in 1.5 and 3.0 g/（kg.d） ADL groups than in microwave group. So we have a conclusion that the expression of I^z-AR and Mz-AchR is down-regulated in myocardial cells of rats exposed to microwave radiation. ADL can protect rats against microwave-induced heart tissue injury.

M3 Muscarinic Acetylcholine Receptor Antagonist Darifenacin Protects against Pulmonary Fibrosis through ERK/NF-κB/miR-21 Pathway

Idiopathic pulmonary fibrosis is an untreatable lethal lung disease, which is related to the aberrant proliferation of fibroblasts. M3 muscarinic acetylcholine receptor (M3-mAChR) activation exerts proliferative effect on various kinds of cells. However, whether M3-mAChR inhibition has a protective effect on pulmonary fibrosis remains unexplored. A rat model of pulmonary fibrosis was established by intratracheal instillation of bleomycin. Darifenacin was used to block M3-mAChR. Histological changes were observed using Masson’s Trichrome and hematoxylin and eosin (HE) staining. Hydroxyproline was measured by Hydroxyproline detection kit. Transforming growth factor β1 (TGF-β1) and tumor necrosis factor-α (TNF-α) were measured by enzyme-linked immunosorbent assay (ELISA). In vitro, pulmonary fibroblasts were isolated from lungs of neonatal rat. After treatment, the cell viability, Hydroxyproline level was measured by MTT and Hydroxyproline detection kit respectively. The expression level of extracellular signal-regulated kinase (ERK), nuclear factor kappa-B (N-NF-κB), and microRNA-21 (miR-21) was detected by western blot or quantitative real-time PCR (qRT-PCR). Darifenacin relieved the fibrotic effects provoked by bleomycin. The expression level of hydroxyproline, TGF-β1 and TNF-α level was all downregulated after darifenacin treatment. In lung fibroblasts, darifenacin decreased cell viability and hydroxyproline level induced by bleomycin. Besides, phosphorylation-ERK and nuclear N-NF-κB protein level was downregulated, as well as miR-21 level. M3-mAChR antagonist darifenacin attenuates bleomycin-induced pulmonary fibrosis in rats, which may relate to the ERK/NF-κB/miRNA-21 signaling pathway.

Expression and Significance of ECP, 25-(OH)D3 and M2 receptors in Children with Acute Attack of Asthma

Objective:To study the expression and significance of ECP, 25-(OH)D3 and M2 receptors in children with acute attack of asthma.Methods: Seventy children with bronchial asthma who first visited our hospital from September 2016 to September 2018 were divided into chronic persistence group, remission group and acute attack group. Thirty healthy children who underwent physical examination in our hospital were selected and divided into control group. The levels of ECP, 25-(OH) D3 and M2 receptors were analyzed by ELISA, and Pearson correlation analysis was performed.Results: Compared with the control group, the levels of ECP and M2 receptors in chronic persistence group, remission group and acute attack group increased, while the levels of 25-(OH)D3 decreased, with statistical difference (P<0.05). The levels of ECP and M2 receptors in acute attack group were higher than those in chronic persistence group, and the levels of 25-(OH)D3 were lower than those in chronic persistence group (P<0.05). The levels of ECP and M2 receptors in acute attack group were higher than those in remission group, and the levels of 25-(OH)D3 were lower than those in remission group (P<0.05). Compared with mild children, the levels of ECP and M2 receptors increased and 25-(OH)D3 decreased in moderate and severe children (P<0.05). Compared with moderate children, the levels of ECP and M2 receptors increased and 25-(OH)D3 decreased in severe children (P<0.05).There was a negative correlation between ECP and 25-(OH)D3 (r=-0.380, P=0.038);a negative correlation between 25-(OH)D3 and M2 receptor (r=-0.448,P=0.013);and a positive correlation between ECP and M2 receptor (r=0.450,P=0.013).Conclusions:The expression of ECP and M2 receptors increased during the acute attack of bronchial asthma in children, while the expression of 25-hydroxyvitamin D3 decreased during the acute attack of bronchial asthma in children. The correlation among ECP, 25-(OH) D3 and M2 receptors is significant in the clinical diagnosis of acute attack of bronchial asthma in children.

Expression Imbalance of Cholinergic M₂and M₃Receptors Contributes to the Motility Reduction of the Small Intestine in Spleen Qi Deficiency

Objective: To study roles of cholinergic M2 and M3 receptors in the motility reduction of small intestine (SI) in spleen qi deficiency. Methods: 16 male SD rats were randomly divided in the control group and spleen qi deficiency group (model group)—8 rats each group;spleen qi deficiency model of the improper diet and overfatigue was established;the SI propelling rate (SIPR) was used to evaluate the SI motility;ELISA was used to measure concentrations of acetylcholine (ACh), cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) in the SI tissue;immohistochemistry was employed to detect expressions of cholinergic M2 and M3 receptors. Results: Compared with those in the control group, SIPR was reduced;expression of M2 receptors was increased;and expression of M3 receptors and concentrations of cAMP and PKA were decreased, significantly, in the model group. Conclusions: Expression imbalance of cholinergic M2 and M3 receptors might contribute to the motility reduction of the SI in spleen qi deficiency.

Research on Autoantibodies Against Myocardialβ_1-adrenergic and M_2 Cholinergic Receptors in Patients With Chronic Keshan Disease

Objectives To explore the relationship between serum autoantibodies against myocardial β1-adrenergic, M2-cholinergic receptors and chronic Keshan disease （CKD）. Methods The second extracellular loops of β1 and M2 receptors on human cardiomyocytes were used as the antigens. Enzyme linked immunosorbent assay （ELISA） was applied to determine serum autoantibodies against myocardial β1 and ME receptors in 32 CKD patients. 31 healthy subjects from endemic area were selected as the control. Results Positive rate of autoantibodies against myocardial β1 adrenergic （51.3%, 17/32） and M2 cholinergic （56.3% , 18/32） receptors were significantly higher than those in the control （9.7%, 3/ 31; 12.9%, 4/31） （both P〈 0.01）. Both positive rate and titers of above autoantibodies in NYHA Ⅱ - Ⅲ CKD patients were significantly higher than those in NYHA Ⅳ, demonstrating an apparently positive correlation between serum antibodies against myocardial β1 and M2 receptors （r=0.95）. Conclusions Autoantibodies against myocardial β1 and M2 receptors were found in sera of CKD patients; distribution of positive rate and titers of the autoantibodies in CKD patients in various NYHA are significantly different. classes of cardiac function

Muscarinic acetylcholine receptor M1 mediates prostate cancer cell migration and invasion through hedgehog signaling

The autonomic nervous system contributes to prostate cancer proliferation and metastasis. However, the exact molecular mechanism remains unclear. In this study, muscarinic acetylcholine receptor M1 （CHRM1） expression was measured via immunohistochemical analysis in human prostate cancer tissue array slides. PC-3, LNCaP, and A549 cells were treated with pirenzepine or carbachol, and the cell migration and invasion abilities were evaluated. Western blotting and quantitative real-time PCR were performed to measure GLI family zinc finger 1 （GLI1）, patched 1 （PTCH1）, and sonic hedgehog （SHH） expression levels. High expression of CHRM1 was found in early-stage human prostate cancer tissues. In addition, the selective CHRM1 antagonist pirenzepine inhibited PC-3, LNCaP, and A549 cell migration and invasion, but the agonist carbachol promoted the migration and invasion of these three cell lines. Muscarinic signaling can be relayed by hedgehog signaling. These data show that CHRM1 is involved in the regulation of prostate cancer migration and invasion through the hed^eho~ si^nalin~ ~athwav.

Stimulatory activity of anti-peptide antibodies against the second extracellular loop of human M_2 muscarinic receptors

Obejctive To study the activity of anti peptide antibodies against the second extracellular loop of human M 2 muscarinic receptors on cAMP production and inward calcium currents (I Ca ) in guinea pig ventricular myocytes A comparison was also made with those of a muscarinic receptor agonist Methods cAMP content was determined by radioimmunoassay and the I Ca in guinea pig single ventricular cells were recorded by the whole cell patch clamp technique Results Both the muscarinic receptor agonist, carbachol (Carb 10?μmol/L), and anti peptide antibodies (Abs 100?nmol/L) could decrease basal cAMP levels (by 46 9%±4 2% and 60 2%±4 6%, respectively) and basal I Ca Both Carb (10?μmol/L) and Abs (100?nmol/L) could also inhibit the isoprenaline induced (Iso 0 8?μmol/L) increases in cAMP production (from 108 2±7 0 to 88 4±7 2? pmol/mg·protein/min for Carb and 88 6±5 1? pmol/mg· protein/min for Abs, respectively) and the increases in I Ca The muscarinic receptor antagonist atropine (Atr) was able to prevent these effects of Carb and Abs Conclusions Anti peptide antibodies against an epitope located in the second extracellular loop of human M 2 muscarinic receptors, similar to muscarinic receptor agonist, could decrease the basal I Ca and β receptor agonist stimulated increase of I Ca by decreasing the basal and β receptor agonist stimulated increase of cAMP production, and therefore could have an effect on their target receptor These results further suggest that autoimmunity may participate in the pathogenesis of human cardiomyopathy and the second extracellular loop of human M 2 muscarinic receptor could be the main immunodominant region.

用转染m2胆碱受体基因的CHO细胞观察知母皂甙元的作用

目的观察知母甾体皂甙元 (sarsasapogenin ,SAR)对M2 受体亚型的调节作用。 方法采用转染了m2胆碱受体基因的CHO细胞为模型 ,以非选择性的3H -QNB作单点放射配基结合分析。 结果CHOm2细胞受体密度在培养 48h达顶峰 ,以后呈进行性下降。SAR对下降的CHOm2细胞M2 受体密度有明显的上调作用 ,这一作用有一定浓度依赖性。 结论SAR对下降的M2 受体密度具有上调作用。

人血单个核细胞上M2、M3受体与冠脉痉挛的相关性研究

目的探讨人外周血单个核细胞上M2、M3受体表达的变化与冠状动脉痉挛的相关性。方法选择因静息性胸痛住院,且冠状动脉造影未见血管狭窄的患者29例,经乙酰胆碱激发试验分为冠状动脉痉挛组(痉挛组,20例)和非痉挛组(对照组,9例),应用ELISA分别检测并比较两组外周血单个核细胞上M2、M3受体的表达量。结果冠状动脉痉挛患者M3受体表达量显著低于对照组(P<0.01)。M2受体表达量两组无显著性差异(P>0.05)。在排除有组间差别的血中低密度脂蛋白胆固醇的影响后,两组间M3受体表达量的差别依然存在。结论M3受体与冠状动脉痉挛的发生相关,M2受体与冠状动脉痉挛的发生无相关,M3受体表达量的下降可能导致内皮功能紊乱,从而引起冠状动脉痉挛。

有机磷杀虫剂对M2受体磷酸化的影响

目的研究有机磷类杀虫剂对G蛋白结合受体激酶2介导的毒蕈碱乙酰胆碱m2受体磷酸化的影响和可能存在的其他作用途径。方法将纯化的毒蕈碱乙酰胆碱m2受体,G蛋白结合受体激酶-2,[γ-p32]ATP与对氧磷(PO)、氧毒死蜱(CPO)共同保温,聚丙烯酰胺凝胶电泳分离蛋白,放射性自显影检测m2受体磷酸化结果。结果氧毒死蜱完全抑制m2受体的磷酸化,其半数抑制浓度为(IC50)70μmol/L;毒死蜱也抑制m2受体的磷酸化,而对氧磷与对硫磷不抑制m2受体的磷酸化。结论不同的有机磷杀虫剂对m2受体的磷酸化有完全不同的作用;毒死蜱阻断m2受体的磷酸化,提示有机磷杀虫剂的毒性作用存在其他途径。

Synthesis and biological evaluation of ^(99m)Tc-HEDTA/HYNIC-MPP4 complex for 5-HT_(1A) receptor imaging

5-HT_(1A)receptor is associated with a variety of pathophysiology of neuropsychiatric disorders.Accordingly,we have synthesized a new 5-HT_(1A) receptor ligand(HYNIC-MPP4)and labeled it with^(99m)Tc using N-(2-hydroxyethyl)ethylenediaminetriacetic acid(HEDTA)as coligand.^(99m)Tc-HEDTA/HYNIC-MPP4 was prepared under pH 6 at room temperature.Biodistribution of^(99m)Tc-HEDTA/HYNIC-MPP4 in normal mice showed that this complex had moderate brain uptake(0.60%ID·g^(-1)at 2 min p.i.)and good retention.The hippocampus had the highest radioactivity uptake at 2 min p.i.(1.84%ID·g^(-1)).The ratio of Hipp/CB was 3.1 at 2 min p.i.and increased to 4.4 at 60 min p.i.After blocking with 8-hydroxy-2-(dipropylamino)tetralin,the uptake of hippocampus was decreased significantly from 1.84%ID·g^(-1) to 0.53%ID·g^(-1) at 2 min p.i.,while the cerebellum had no significant decrease.This^(99m)Tc complex could be a potent agent for 5-HT_(1A) receptor imaging.

血清M2-AAb、β1-ARAb水平与肥厚型心肌病患者左心功能的相关性研究

目的探讨肥厚型心肌病患者血清中M2乙酰胆碱能受体自身抗体(M2-AAb)、β1肾上腺素能受体自身抗体(β1-ARAb)水平与肥厚型心肌病患者左心功能的相关性。方法选取2017年1月至2019年3月于该院心血管内科住院接受治疗的126例肥厚型心肌病患者为肥厚型心肌病组,选取同期的107例体检健康者作为对照组。采用ELISA法检测肥厚型心肌病患者血清中M2-AAb、β1-ARAb水平;采用多普勒心脏超声检测左心功能各指标水平;分析肥厚型心肌病患者血清中M2-AAb、β1-ARAb水平的相关性;分析肥厚型心肌病患者血清中M2-AAb、β1-ARAb水平与左心功能指标的相关性。结果肥厚型心肌病组血清中M2-AAb、β1-ARAb水平明显高于对照组(P<0.05);两组左心室射血分数(LVEF)比较,差异无统计学意义(P>0.05)。肥厚型心肌病组左室舒张末期内径(LVD)、二尖瓣舒张早期血流速度峰值(E)/二尖瓣瓣环组织多普勒速度(E′)、左室舒张末期左心房容积(LAV)、左房容积指数(LAVI)明显高于对照组(P<0.05),E/二尖瓣舒张晚期血流速度峰值(A)低于对照组(P<0.05)。肥厚型心肌病患者血清中M2-AAb、β1-ARAb水平呈正相关;肥厚型心肌病患者血清中M2-AAb、β1-ARAb水平与LVD、E/E′、LAV、LAVI均呈正相关(P<0.05),与E/A呈负相关(P<0.05)。结论血清M2-AAb、β1-ARAb水平与肥厚型心肌病患者左心功能指标具有一定相关性。血清M2-AAb、β1-ARAb水平联合左心功能检测在肥厚型心肌病的早期诊断及病程评估中具有较高的应用价值。

某些有机磷杀虫剂影响乙酰胆碱M2受体磷酸化的实验研究

目的研究有机磷类杀虫剂(OPs)对G蛋白结合受体激酶-2(GRK-2)介导的毒蕈碱乙酰胆碱m2受体(mAChR2)磷酸化的影响,进一步揭示OPs可能存在的其他作用途径。方法将纯化的大鼠脑mAChR2,GRK-2,同位素磷32标记的三磷酸腺苷([γ-P32]ATP)与不同浓度的对氧磷(PO)、氧毒死蜱(CPO)和毒死蜱(CPF)共同保温,聚丙烯酰胺凝胶电泳,凝胶片干燥后放射性自显影检测mAChR2磷酸化结果。将干燥凝胶片中放射性标记的磷酸化mAChR2蛋白带剪下,同位素液体闪烁计数器计数。结果CPO抑制大鼠脑mAChR2的磷酸化,其IC50为70?mol/L;CPF也抑制mAChR2的磷酸化,而PO与对硫磷(PT)不抑制mAChR2的磷酸化。CPO和CPF并不抑制同样由GRK2介导的β2肾上腺素受体(β2-AR)的磷酸化。结论CPO和CPF选择性地抑制GRK-2介导的mAChR2磷酸化,而PO和PT无此效应。说明某些有机磷类杀虫剂可能存在其它作用靶分子。

Mechanisms mediating cholinergic antral circular smooth muscle contraction in rats

AIM:To investigate the pathway(s)mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent,bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction. METHODS:Circular smooth muscle strips from the antrum of Sprague-Dawley rats were mounted in muscle baths in Krebs buffer.Isometric tension was recorded.Cumulative concentration-response curves were obtained for(+)-cis- dioxolane(cD),a nonspecific muscarinic agonist,at 10^(-8)- 10^(-4)mol/L,in the presence of tetrodotoxin(TTX,10^(-7)mol/L). Results were normalized to cross sectional area.A repeat concentration-response curve was obtained after incubation of the muscle for 90 min with antagonists for M1(pirenzepine), M2(methoctramine)and M3(darifenadn)muscarinic receptor subtypes.The sensitivity to PTX was tested by the ip injection of 100 mg/kg of PTX 5 d before the experiment.The antral circular smooth muscles were removed from PTX-treated and non-treated rats as strips and dispersed smooth muscle cells to identify whether PTX-linked pathway mediated the contractility to bethanechol. RESULTS:A dose-dependent contractile response observed with bethanechol,was not affected by TTx.The pretreatment of rats with pertussis toxin decreased the contraction induced by bethanechol.Lack of calcium as well as the presence of the L-type calcium channel blocker,nifedipine,also inhibited the cholinergic contraction,with a reduction in response from 2.5±0.4 g/mm^2 to 1.2±0.4 g/mm^2(P<0.05).The dose- response curves were shifted to the right by muscarinic antagonists in the following order of affinity:darifenacin (M_3)>methocramine(M_2)>pirenzepine(M_1). CONCLUSION:The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pathway(s)involving pertussis-toxin sensitive GTP-binding proteins and to extracellular calcium via L-type voltage gated calcium channels.The presence of the residual contractile response after the treatment with nifedipine,suggests that an additional pathway could mediate the cholinergic contraction.The involvement of more than one muscarinic receptor(functionally predominant type 3 over type 2)also suggests more than one pathway mediating the cholinergic contraction in rat antrum.