人参皂苷Compound K通过AMPK及SREBP1途径改善非酒精性脂肪肝的机制研究

目的：研究人参皂苷Compound K（CK）对非酒精性脂肪肝的改善作用及其与腺苷酸激活蛋白激酶（AMPK）及固醇调节元件结合蛋白（SREBP1）信号转导通路的关系。方法：采用高脂饲料喂养C57BL/6J雄性小鼠9周,建立非酒精性脂肪肝动物模型;9周后随机分为5组,正常饲料组（RD）,高脂饲料组（HFD）,给药组（HFD+CK 3,9,27 mg·kg^-1）,每天灌胃给药1次,每周测2次体质量,连续11周。实验结束后,分别称量小鼠体质量和肝质量;检测三酰甘油（TG）、胆固醇（cholesterol）、非游离脂肪酸（NEFA）、谷草转氨酶（AST）和谷丙转氨酶（ALT）水平。苏木素-伊红（HE）染色观察肝脏病理变化,Western blot法检测AMPK和乙酰辅酶A羧化酶（ACC）的磷酸化表达,PCR法检测脂肪合成转录因子SREBP1及其靶基因（FAS、SCD1）的基因表达。结果：治疗11周后,与RD组比较, HFD组小鼠肝质量及肝质量与体质量的比值显著增加（P<0.001,P<0.05）,HE染色显示HFD组较RD组肝细胞明显增大且伴有大泡性脂肪变,说明高脂饲料诱导非酒精性脂肪肝模型的建立。与HFD组比较,给药组小鼠体质量、肝质量显著降低（P<0.05）,血脂（TG、CHO、NEFA）和肝功（sAST和sALT）指标也显著降低（P<0.05,P<0.01,P<0.001）;HE染色也说明给药组能够明显改善肝脏病理状态,从而改善肝细胞脂肪变性;Western blot结果显示HFD组较RD组,AMPK和ACC磷酸化均被抑制,给药组较HFD组,AMPK和ACC均被磷酸化,且随药物浓度的增加,磷酸化越明显;PCR法结果显示HFD较RD组,脂肪合成转录因子SREBP1及其靶基因表达显著增强,而在给药组上述基因表达均显著被抑制。结论：CK对非酒精性脂肪肝具有改善作用,其机制之一可能是通过激活AMPK和ACC的磷酸化、抑制脂肪合成转录因子SREBP1及其靶基因的表达来实现的。     

丹皮酚对小鼠酒精性脂肪肝中Adip/CaMKKβ/AMPK通路的影响

目的研究Adip/CaMKKβ/AMPK通路是否参与丹皮酚(paeonol,Pae)治疗小鼠酒精性脂肪肝的过程。方法在小鼠酒精性脂肪肝模型的基础上给予丹皮酚治疗后,通过ELISA法检测小鼠血清中各炎症因子和TG、TC,同时用ELISA法检测小鼠血清中Adip和ACC表达水平,用qPCR法及Westren blot法检测小鼠肝组织Adip、CaMKKβ、AMPKα和SREBP1c核酸和蛋白水平。 结果 Adip表达水平在各处理组无显著变化;酒精诱导增加炎症因子和TG、TC表达,降低了CaMKKβ和AMPKα在核酸和蛋白磷酸化水平上的表达,水飞蓟宾与丹皮酚降低了炎症因子和TG、TC表达,提高了CaMKKβ和AMPKα在核酸和蛋白磷酸化水平上的表达;酒精诱导增加了SREBP1c在核酸和蛋白水平上的表达,水飞蓟宾与丹皮酚降低了SREBP1c的表达。 结论 从Adip/CaMKKβ/AMPK信号传导的变化验证了丹皮酚可通过此信号转导来减轻酒精性脂肪肝的脂肪变性损伤和炎症水平。     

二氢杨梅素经激活SIRT1-AMPK通路抑制高脂饮食诱导的肥胖小鼠肝脏脂质沉积

目的探究二氢杨梅素(dihydromyricetin,DHM)对高脂饮食诱导的肥胖小鼠肝脏脂质蓄积的作用及其机制。方法C57BL/6J小鼠60只,随机分为6组(n=10):①ND组:正常饲料;②ND+L-DHM组:正常饲料+低剂量DHM(125 mg·kg^-1·d^-1);③ND+H-DHM组:正常饲料+高剂量DHM(250 mg·kg^-1·d^-1);④HFD组:高脂饲料;⑤HFD+L-DHM组:高脂饲料+低剂量DHM;⑥HFD+H-DHM组:高脂饲料+高剂量DHM。记录小鼠体重;16周后,测空腹血脂;计算体脂重量;肝脏HE和油红O染色;荧光定量PCR和Western blot检测肝脏SIRT1、AMPK、ACC、FAS、SREBP-1和PPARα、CPT1的表达。结果与ND组相比,HFD组小鼠体重、体脂、血清TG、TC、HDL水平明显增加;肝脏内脂肪蓄积增加,肝脏SREBP-1c、FAS、ACC1表达增加,而PPARα、CPT1、SIRT1和AMPK表达下降。经DHM处理后,HFD小鼠上述指标发生逆转;但ND小鼠上述指标无明显改变。结论DHM可能通过激活SIRT1-AMPK通路抑制脂质合成,促进脂质分解,改善高脂饮食诱导的肥胖小鼠肝脏脂质沉积。     

丹红注射液对高脂血症大鼠肝脏AMPK/SREBP-1/ACC通路的影响

目的探讨丹红注射液(Danhong injection,DHI)对大鼠高脂血症的作用及机制。方法采用高脂饲料制备大鼠高脂血症模型,检测各组大鼠肝脏腺苷酸激活蛋白激酶(AMPK)、p-AMPK、胆固醇调节元件结合蛋白(SREBP-1)、乙酰辅酶A羧化酶(ACC)、p-ACC的蛋白表达水平。结果给予丹红注射液后,肝脏AMPK、SREBP-1和ACC的蛋白表达水平明显降低(P<0.05),p-ACC和p-AMPK的蛋白表达水平明显升高(P<0.05)。结论丹红注射液通过增强AMPK的活化,抑制SREBP-1和ACC的活性,促进脂肪酸氧化,减少脂质沉积,有效降低了高脂血症大鼠的血脂水平。     

粗壮女贞总苷降脂作用及其基于AMPK通路的降脂作用机制研究

目的探讨粗壮女贞总苷(total phenylpropanoid glycoside from CN,CNTG)降脂作用及其基于AMPK通路的降脂作用机制。方法 Syrian金黄地鼠随机分为正常组、高脂模型组、阳性药非诺贝特组及CNTG高、中、低剂量组。除正常组外,其余各组地鼠应用高脂饲料诱导建立混合型高脂血症模型。造模1周后取血,检测血清TC、TG、LDL-C、HDL-C含量,确定模型形成。之后连续给药4周,在给药2周、3周及4周后分别取血,检测血清中TC、TG、LDL-C和HDL-C的含量。在给药4周后剖取肝脏,进行肝脏TG、TC含量测定和肝脏病理学检测。并应用实时定量PCR检测CNTG对肝脏中AMPK、CD36、CPT1、ACC的mRNA表达的影响;用Western blot法检测AMPK和其上游调控蛋白LKB1的磷酸化蛋白和总蛋白水平,并检测HMG-Co A还原酶的蛋白表达量。结果给药2周、3周、4周后,与模型组相比,CNTG高剂量组血清中的TC、TG、LDL-C含量均明显降低(P<0.05,P<0.01);肝脏中TC、TG含量明显降低(P<0.01);并可明显减轻肝细胞病变。实时定量PCR结果显示,与模型组相比,CNTG可以明显升高AMPK的相对表达量(P<0.01),但CD36、ACC和CPT1的相对表达量无明显变化。Western blot结果显示,与模型组相比,CNTG高剂量组肝脏中的LKB1、phospho-LKB1及phospho-AMPKα的相对表达量均提高(P<0.05),差异具有显著性。结论 CNTG能有效降低高脂血症金黄地鼠的血脂和肝脂水平,其机制可能是CNTG促进肝脏中LKB1磷酸化以激活AMPK,从而调控机体脂质代谢。     

益肾排毒丸调节AMPK/ACC信号通路对db/db小鼠肝损伤的保护作用研究

目的：探究益肾排毒丸（YSPDW）对db/db小鼠肝损伤的保护作用及其对脂代谢通路的影响机制。方法：C57BL/6小鼠作为空白对照组、8周龄的db/db小鼠分为非酒精性脂肪肝（non-alcoholic fatty liver disease,NAFLD）模型组、益肾排毒丸治疗组和二甲双胍阳性对照组。给药8周后检测小鼠肝脏系数、随机血糖、肝功能（丙氨转氨酶ALT、谷草转氨酶AST）、血脂（总胆固醇TC、三酰甘油TG、高密度脂蛋白胆固醇HDL-C、低密度脂蛋白胆固醇LDL-C）、肝脏脂质（TC、TG）、肝脏抗氧化因子（谷胱甘肽过氧化物酶GSH-Px、谷胱甘肽GSH、超氧化物歧化酶SOD、丙二醛MDA、过氧化氢酶CAT）、肝脏炎性因子（TNF-α、IL-6、IL-1β、MCP-1）等指标的变化。HE和PAS染色评估小鼠肝脏形态变化、脂肪变性和糖原沉积。Western blot检测脂代谢AMPK/ACC信号通路相关蛋白表达。结果：与模型组相比,益肾排毒丸给药组和二甲双胍组小鼠随机血糖和肝脏系数显著降低。生化指标检测结果显示益肾排毒丸可显著降低NAFLD模型小鼠血清AST、ALT、TC、TG水平和肝组织TC、TG、MDA水平,升高HDL-C含量,发挥肝保护作用;ELISA结果表明益肾排毒丸能明显升高NAFLD小鼠肝组织GSH-Px、GSH和SOD活性,显著降低肝脏炎性细胞因子TNF-α、IL-6、IL-1β和MCP-1的水平,表明益肾排毒丸可增加机体抗氧化能力,抑制炎症因子释放。HE和PAS结果显示益肾排毒丸可明显减轻肝组织脂肪变性和炎症细胞浸润,改善肝细胞的结构和形态完整。Western blot结果表明,益肾排毒丸能激活AMPK/ACC信号通路,显著增加模型小鼠肝脏p-AMPK和p-ACC蛋白表达。结论：益肾排毒丸可能通过促进AMPK/ACC信号通路来改善肝脏氧化应激、炎性反应,减少脂质合成,从而改善NAFLD的肝损伤。     

金丝桃苷对高脂饮食引起的肥胖伴胰岛素抵抗小鼠的保护作用

目的 研究金丝桃苷对高脂饮食引起的肥胖伴胰岛素抵抗小鼠的代谢保护作用。方法 将30只C57BL/6小鼠随机分为对照组、高脂组及金丝桃苷组,对照组小鼠给予普通饲料,高脂组及金丝桃苷组给予高脂饲料,喂养14周后建模成功(n=10)。金丝桃苷组灌胃给予金丝桃苷,对照组给予溶媒,灌胃9周后收集血清,检测生化指标及细胞因子,qRT-PCR法检测肝脏内糖脂代谢相关基因,并观察肝脏形态。结果 给予金丝桃苷后,金丝桃苷组小鼠的体重和空腹血糖较高脂组明显降低(P<0.05),且葡萄糖耐受能力显著增强(P<0.05)。金丝桃苷组小鼠的血清TC、TG、LDL及HDL水平显著低于高脂组(P<0.05),肝脏内脂质沉积也较高脂组减少,而脂联素和瘦素水平均明显高于高脂组(P<0.05)。与高脂组相比,金丝桃苷组小鼠SREBP1c、ACC、FAS基因表达降低,而AMPK基因表达增加(P<0.05)。结论 金丝桃苷可降低高脂饮食小鼠的体重和血糖,改善胰岛素抵抗,抑制脂质合成,这些作用可能与AMPK及下游信号通路有关。     

黄连素通过对高脂小鼠肝脏、胰腺中PCSK9和LDLR的不同调控改善高脂血症和高胰岛素血症

目的 观察黄连素对高脂小鼠肝脏、胰腺中PCSK9和LDLR的不同调控，探讨其减缓高脂血症和高胰岛素血症的新作用机制。方法 SPF级C57BL/6J小鼠随机分为3组：正常对照组(普通饮食喂养)、高脂饲料组(高脂饮食喂养)、黄连素组(高脂饮食喂养同时灌胃黄连素)。自动血糖仪检测空腹血糖值；酶联免疫法(ELISA)测空腹血清胰岛素水平，计算血糖与胰岛素比值。ELISA测空腹血清PCSK9水平；酶标仪和相应的试剂盒检测血清中的甘油三酯、总胆固醇、高密度胆固醇、低密度胆固醇的含量。HE染色法观察肝脏和胰腺的组织形态变化。Western blotting检测肝脏和胰腺中PCSK9和LDLR蛋白的表达。结果 黄连素能降低血清中胆固醇的含量，同时明显降低血浆中PCSK9的含量，减少肝脏PCSK9蛋白表达，增加肝脏表面LDLR蛋白表达；改善高脂诱导的胰岛素抵抗，减少胰岛细胞肥大及空泡数量，增加胰腺表面PCSK9蛋白表达，减少胰腺表面LDLR蛋白表达。结论 黄连素调节高脂饮食小鼠PCSK9的表达和分泌，具有组织特异性，在肝脏中增强LDLR介导的胆固醇细胞摄取，同时在胰腺中抑制LDLR介导的胆固醇摄取，从而改善高脂饮食诱导的肝脏脂肪性病变和胰岛素抵抗。     

洋甘菊总黄酮通过抑制ACC/FAS/DGAT2通路减少ApoE-/-小鼠三酰甘油合成

目的： 探究洋甘菊总黄酮通过调节ACC/FAS/DGAT2通路减少ApoE^-/-小鼠三酰甘油合成的药理作用机制。方法： 用乙醇回流提取和大孔树脂分离纯化法获得洋甘菊总黄酮;高脂饲料喂养法建立ApoE^-/-小鼠高脂模型;以C57BL/6J小鼠为空白对照组,ApoE^-/-小鼠分成模型组,非诺贝特组（30 mg·kg^-1）,洋甘菊总黄酮低、中、高剂量组（88,176,352 mg·kg^-1）;空白对照组和模型组分别用基础饲料和高脂饲料喂养,其余组小鼠高脂饲料喂养的同时灌胃给药干预8周。检测小鼠血清三酰甘油（TG）、总胆固醇（TC）、高密度脂蛋白胆固醇（HDL-C）、低密度脂蛋白胆固醇（LDL-C）水平;HE染色和油红O染色观察小鼠肝脏脂肪变性情况;免疫组化法检测二酰基甘油酰基转移酶2（DGAT2）蛋白表达水平;Western Blot法检测肝组织乙酰辅酶A羧化酶（ACC）、脂肪酸合成酶（FAS）、DGAT2蛋白表达水平。结果： 与空白对照组相比,模型组小鼠TG、TC、LDL-C、ACC、FAS、DGAT2水平均明显升高,HDL-C水平明显降低;与模型组相比,非诺贝特组和洋甘菊总黄酮各剂量组脂肪变性情况明显减轻。与模型组相比,非诺贝特组、洋甘菊总黄酮各剂量组TG、TC、LDL-C、ACC、FAS水平均明显降低,HDL-C水平明显升高;非诺贝特组和洋甘菊总黄酮中、高剂量组DGAT2水平明显降低。结论： 洋甘菊总黄酮可以抑制ApoE^-/-小鼠三酰甘油合成,改善血脂水平,可能与其下调ACC/FAS/DGAT2通路表达有关。     

Cerebral metabolism of [3H]-p-chloroamphetamine

The time-dependent metabolism of intraventricularly administered $\text{[}{}^3\text{H}\text{]-p-}\text{chloroamphetamine}$ was followed. The parent compound and its metabolites were recovered by high pressure liquid chromatography and characterized by high pressure liquid chromatography, thin-layer chromatography, and gas chromatography-mass spectrometry. By 4 hr after injection, two major toluene-soluble metabolites were present in brain. Their biological half-lives were different from the parent compound. On the basis of their analyses, one of the metabolites is p-chloronorephedrine, the other (P₃) is as yet unidentified. Pretreatment with Lilly 110140 prevented or markedly reduced the synthesis of both p-chloronorephedrine and P₃. Iprindole prevented the synthesis of p-chloronorephedrine. The P₃ appeared first in the brain then in the liver, suggesting that both of these organs can metabolize p-chloroamphetamine to this compound. The metabolites were recovered primarily from the nuclear and microsomal fractions following subcellular fractionation of the brain, with small quantities present in the synaptosomal fraction. The level of metabolites was higher in the brainstem than in the neocortex. Glutathione, administered simultaneously with p-chloroamphetamine either intraventricularly or intraperitoneally failed to alter the toxicity of p-chloroamphetamine.     

Clevudine University of Georgia/Abbott/Bukwang/Triangle/Yale University

The pyrimidine analog, clevudine (L-FMAU: 2'-fluoro-5-methyl-beta-L-arabinofuranosyluridine) is a potent antihepatitis B virus (HBV) and anti-Epstein-Barr virus (EBV) agent, discovered by researchers at the University of Georgia, in collaboration with Yale University and Bukwang. Bukwang transferred its technology to Triangle Pharmaceuticals in 1998 together with a license to develop clevudine worldwide except Korea [279649], [281942]. In June 1999, Triangle and Abbott Laboratories entered into a strategic alliance to copromote antiviral products including L-FMAU [326798]. In September 2000, Triangle Pharmaceuticals Inc initiated a 30-day phase I/II evaluation of clevudine in HBV-infected patients [381755]. Clevudine is a much less toxic derivative of the toxic agent P-D-FMAU. The mechanism of action of clevudine is not yet clear, but the agent induces a rapid decrease in HBV nucleic acid as doses increase from 0.3 to 10 mg/kg [319145]. It is believed that the target for clevudine lies in the viral replication mechanism. Clevudine is phosphorylated to the triphosphate form intracellularly. This is removed slowly from the cells, thus exerting a sustained inhibitory antiviral activity [178173], [320720], [320721].     

Spotlight from the American Society for Preventive Cardiology on Key Features of the 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guidelines on the Management of Blood Cholesterol

The 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol retains focus on recommendations for statin treatment in the original four statin-eligible groups [those with atherosclerotic cardiovascular disease (ASCVD), diabetes, low-density lipoprotein cholesterol (LDL-C) ≥ 190 mg/dL, and higher risk primary prevention] without the use of treatment initiation or target LDL-C levels from the earlier 2013 American College of Cardiology/American Heart Association (ACC/AHA) guideline, but has several new features. First, patients with primary prevention are divided into those who are at low (< 5%), borderline (5% to < 7.5%), intermediate (7.5% to < 20%), and high (≥ 20%) risk based on the ASCVD risk estimator. Moreover, the new guideline goes further to consider a wider range of factors [now called “risk enhancers”—premature family history of ASCVD, persistently high LDL-C, chronic kidney disease (CKD), metabolic syndrome, conditions specific to women, inflammatory diseases, and high-risk ethnicities] that can be used to better inform the treatment decision. Moreover, more detailed recommendations on how the results of coronary calcium scanning can be used to inform the treatment decision are provided, including how it may be used to “de-risk” certain patients for delaying or avoiding the use of statin therapy. There are also specific sections for cholesterol management in other patient subgroups including women, children, certain ethnic groups, those with CKD, chronic inflammatory disorders and HIV, as well as discussion on the management of hypertriglyceridemia. Importantly, for persons with known ASCVD, a distinction is made for those who are at “very high risk” based on having had two major ASCVD events or one major event and two or more other high risk conditions, such as diabetes or other major risk factors, or bypass surgery or percutaneous intervention. Finally, the concept of a threshold LDL-C for initiating a non-statin therapy (after considering highest tolerated statin dosage) is provided, with ezetimibe recommended as the key non-statin to be added if the LDL-C still remains ≥ 70 mg/dL for all ASCVD patients, and in those who are at “very high risk”, further consideration for using a proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor. While the new guideline does have greater detail (and arguably, complexity), the refinements provide a strategy for guiding the clinician to target both statin and non-statin therapy to those most likely to derive benefit.     

Pitavastatin Nissan/Kowa Yakuhin/Novartis/Sankyo

Pitavastatin (nisvastatin) is an HMG CoA reductase inhibitor being developed jointly by Nissan, Kowa Kogyo, Novartis and Sankyo for the potential treatment of atherosclerosis and hyperlipidemia.     

Amlodipine/Valsartan/Hydrochlorothiazide

Amlodipine/valsartan/hydrochlorothiazide (HCTZ) is a fixed-dose combination of the well established antihypertensive agents amlodipine (a calcium channel antagonist), valsartan (an angiotensin II receptor antagonist), and HCTZ (a thiazide diuretic). In patients with moderate or severe hypertension, triple combination therapy with amlodipine + valsartan + HCTZ produced significantly greater reductions from baseline in mean sitting systolic and diastolic BP (msSBP and msDBP) than either valsartan + HCTZ, amlodipine + HCTZ, or amlodipine + valsartan in a large, 8-week, randomized, double-blind, multinational, phase III trial. Furthermore, the proportion of patients achieving overall BP control at endpoint was significantly greater with the triple combination regimen than with any of the dual regimens, with significantly more triple combination recipients achieving msSBP and msDBP control at each assessment throughout the trial. Subgroup analyses of this study suggested that amlodipine + valsartan + HCTZ was generally more effective in reducing BP and providing overall BP control than the dual combination therapies, irrespective of age, race, gender, ethnicity, or hypertension severity. Several smaller studies provide data that support the efficacy of amlodipine + valsartan + HCTZ in patients whose BP is inadequately controlled with amlodipine + valsartan, amlodipine + HCTZ, or valsartan + HCTZ dual combination therapy. Treatment with amlodipine + valsartan + HCTZ for up to 8 weeks was generally well tolerated in the large, phase III trial, with most adverse events being transient and of mild to moderate severity.     

N-Nitroso-N-Methyldodecylamine and N-Nitroso-N-Methyltetradecylamine in household dishwashing liquids

Eleven household dishwashing liquids and four household surface cleaners were analysed for N-nitroso-N-methyldodecylamine and N-nitroso-N-methyltetradecylamine by gas chromatography with detection using a Thermal Energy Analyzer. Both nitrosamines were found in three of the dishwashing detergents and one of the surface cleaners. [1-¹⁴C]-N-Nitroso-N-methyldodecylamine was used to determine recoveries, which were between 65 and 88%. Levels of N-nitroso-N-methyldodecylamine ranged from 112 to 661 ppb and those of N-nitroso-N-methyltetradecylamine from 46 to 151 ppb. A simple method was developed to screen the products for N,N-dimethyldodecylamine-N-oxide, a surfactant ingredient suspected of being the source of these nitrosamines. By application of this method it was established that all of the products formulated with this amine oxide contained these two nitrosamines, whereas in products that did not contain this ingredient, these nitrosamines were not detected.     

PROTON AND POTASSIUM TRANSPORT BY H+/K+-ATPases

1. H⁺/K⁺-ATPases are members of the P-type ATPase multigene family. The prototypical H⁺/K⁺-ATPase is the protein that acidifies gastric luminal contents. The physiological and pharmacological significance of this pump has led to a detailed investigation of its biochemistry and molecular and cell biology. 2. Recently, a number of closely related H⁺/K⁺-ATPase isoforms have been discovered. These isoforms are present in organs other than the stomach, including the colon and kidney, where they contribute to acid—base and potassium homeostasis. The structure, expression and physiological roles of the gastric H⁺/K⁺-ATPase and other isoforms are reviewed.     

INTERACTIONS OF Na+, H2O2 AND THE Na+-Ca2+ EXCHANGER STIMULATE Ca2+ RELEASE IN CK1.4 CELLS

1. The present study aimed to demonstrate that interactions of cations, hydrogen peroxide (H₂O₂) and the Na⁺-Ca²⁺exchanger stimulate Ca²⁺ release and oscillations of cytosolic Ca²⁺ [Ca²⁺]i in non-transfected Chinese Hamster Ovary (CHO) C1 cells and in transfected CHO (CK1.4) cells that contained an expression vector coding the Na⁺-Ca²⁺ exchanger sequence. 2. The [⁴⁵Ca²⁺] uptake assay, fura-2 fluorescence imaging and 2² and 2³ factorial orthogonal statistics provide comparative, direct, efficient, quantitative and transient methods to delineate the effects of such interactions on Ca²⁺ influx, Ca²⁺release and [Ca²⁺]i in C1 and CK1.4 cells. 3. In contrast to the control of either Na⁺-, Ca²⁺- or H₂O₂-free or CI cells, an elevated [⁴⁵Ca²⁺] uptake was induced by Ca²⁺, Na⁺ and H₂O₂ individually and in combination, intracellular Ca²⁺ release was activated by H₂O₂ and by combinations of either H₂O₂ and Na⁺, H₂O₂ and the Na⁺-Ca²⁺ exchanger, Na⁺ and the Na⁺-Ca²⁺ exchanger or by H₂O₂, Na⁺ and the Na⁺-Ca²⁺ exchanger and a rise in [Ca²⁺]i was triggered by H₂O₂, Na⁺ and a combination of Na⁺ and the Na⁺-Ca²⁺exchanger. 4. These results indicate that interactions between H₂O₂, Na⁺ and the Na⁺-Ca²⁺ exchanger stimulate intracellular Ca²⁺mobilization via Ca²⁺-induced Ca²⁺ release mechanisms, ATP-activated G-protein coupled P_2y-purinoceptor-sensitive pathways, Na⁺-Ca²⁺ exchanger-mediated Ca²⁺ influx and cation-π interaction (a strong non-covalent force between the cation and the π face of an aromatic structure in the transmembrane protein). 5. The present findings provide important clues for understanding Ca²⁺ signal transduction mechanisms from the plasma membrane to the endoplasmic reticulum.     

EFFECTS OF THE OPIOID PEPTIDES [MET5]ENKEPHALIN-ARG6-PHE7 AND [MET5]ENKEPHALIN-ARG6-GLY7-LEU8 ON CHOLINERGIC NEUROTRANSMISSION IN THE RABBIT ISOLATED ATRIA

1. The effect of the opioid peptides [Met5]enkephalin-Arg6-Phe7 (MEAP) and [Met5]enkephalin-Arg6-Gly7-Leu8 (MEAGL) were compared with those of [Leu5]enkephalin and [D-Ala2,Met5]enkephalinamide (DAME) on cholinergic neurotransmission in the rabbit isolated atria. 2. Rabbit isolated atria had a resting rate of 190 beats/min. In the presence of the beta-adrenoceptor antagonist propranolol (0.3 mumol/l), atria responded to electrical field stimulation with a cholinergically mediated negative chronotropic response. The opioid peptides had no effect on the resting rate, but inhibited the negative chronotropic response to field stimulation. The IC50 values for inhibiting the cholinergic responses were 1.4 mumol/l for [Leu5]enkephalin (LE), 1.4 mumol/l for MEAP, 1.3 mumol/l for MEAGL and 0.2 mumol/l for DAME. Responses of a similar magnitude to exogenous acetylcholine were unaffected. 3. Thus, MEAP, MEAGL and LE had similar potencies but DAME was about seven times more potent in inhibiting cholinergic neurotransmission in the rabbit isolated atria. The site of inhibition appears to be prejunctional.