中枢交感神经活性抑制对老年大鼠心肌细胞收缩功能的影响

目的探讨中枢交感神经活性抑制对老年大鼠心功能、单个心室肌细胞收缩幅度和细胞存活率的影响。方法选择月龄>18个月的SD大鼠30只,随机分为老年可乐定组和老年对照组,每组15只,另选4~6月龄的SD大鼠18只为成年组,老年可乐定组大鼠以可乐定腹腔注射2周,其他2组用生理盐水腹腔注射2周,进行血流动力学参数测定,酶分离大鼠心肌细胞,用含不同浓度钙离子或异丙肾上腺素(ISO)的KH液对心肌细胞进行表面灌流,观察心肌细胞的收缩幅度,计算其存活率。结果与成年组大鼠比较,老年对照组左心室压力最大上升和下降速率(±dp/dtmax)降低,左心室舒张末压(LVEDP)升高,且心肌细胞在不同浓度钙离子或ISO刺激下收缩幅度较成年组降低(P<0.05)。老年可乐定组大鼠±dp/dtmax改善,LVEDP降低,心肌细胞在同等条件刺激下收缩幅度较老年对照组增加(P<0.05);3组大鼠间细胞存活率无统计学差异(P>0.05)。结论抑制中枢交感神经紧张性可改善老年大鼠心功能,增加心肌细胞的收缩幅度。     

缬沙坦对心力衰竭心肌细胞收缩功能和钙瞬变的影响

目的:探讨缬沙坦对心力衰竭(HF)大鼠心肌细胞收缩功能和钙瞬变的作用。方法:结扎大鼠冠状动脉左前降支8周后,复制充血性HF模型,随机分为2组,即缬沙坦治疗组与HF对照组,分别用缬沙坦和安慰剂治疗,另设假手术组。治疗12周后,用急性酶解法获得单个大鼠心室肌细胞,用共聚焦显微镜测定单个细胞的收缩功能和钙瞬变。结果:①HF对照组左室舒张末压(LVEDP)明显大于假手术组(P<0.01),左室最大收缩压(LVSP)血压和左室内压的最大上升/下降速率(±dp/dtmax)明显小于假手术组(P<0.05、P<0.05和P<0.01);而缬沙坦治疗组LVSP和±dp/dtmax明显高于HF对照组(P<0.05和P<0.01),LVEDP明显小于HF对照组(P<0.01)。②HF对照组的心肌细胞表面积和最大舒张长度均大于假手术组(P<0.01),缩短分数明显低于假手术组(P<0.05),经缬沙坦治疗后均有明显改善(P<0.01)。③HF对照组心肌细胞的钙瞬变明显低于假手术组(P<0.01),舒张末期钙浓度明显升高(P<0.05),钙浓度下降时间明显减慢(P<0.01),经缬沙坦治疗后均明显改善(P<0.01)。结论:缬沙坦治疗能明显改善充血性HF的心肌细胞收缩功能,可能与改善HF心肌细胞钙调控异常有关。     

Ghrelin注射对大鼠血压和心肌收缩功能的影响

目的: 探讨促生长激素释放多肽(ghrelin,GRL)对大鼠心血管功能的影响及其意义。方法: 将40只成年雄性SD大鼠分为对照组和4个剂量的GRL组，静脉注射GRL后测量血流动力学指标。随后采用单细胞动态边缘检测系统测定细胞收缩功能的变化。结果: ①GRL各组平均动脉血压（MABP）较对照组明显下降（P<0.05）。②GRL各组单个心肌细胞收缩功能指标最大收缩幅度（PTA）、最大缩短和复长速率（±dL/dtmax）较对照组明显降低（P<0.05）。结论: GRL可剂量依赖性地降低大鼠的MABP，降低心肌细胞的收缩功能。     

β-肾上腺素受体介导运动训练对老年大鼠心脏缺血预处理效应的影响

目的探讨运动训练能否恢复老年大鼠心脏缺血预处理(IP)效应及β-肾上腺素受体(β-AR)的可能作用机制。方法健康雄性SD成年或老年大鼠,实验分组:成年对照组、老年对照组和老年运动组,每组20只。老年运动组大鼠每天负重5%游泳,5次/w,持续90 d。离体心脏灌流行IP和(或)缺血再灌注(I/R),使用不同β-肾上腺素受体激动剂或阻滞剂,分离单个心肌细胞,测心肌细胞收缩幅度、存活率等。结果长期运动训练使老年鼠左心室重量增加显著,左心室/体重比显著增加(P<0.05)。IP显著改善I/R损伤的成年大鼠和长期运动训练老年鼠的心功能,左心室收缩压(LVSP)、±dp/dtmax升高,左心室舒张末压(LVEDP)显著降低;提高了成年鼠和运动训练老年鼠的心肌细胞收缩幅度,但不能提高老年对照鼠心肌细胞收缩幅度;提高了成年鼠和运动训练老年鼠的心肌细胞存活率,但不能提高老年对照鼠心肌细胞存活率。IP时阻断β1-AR,IP不能恢复三组大鼠的心肌细胞收缩幅度;阻断β2-AR,IP能够恢复成年鼠,却不是老年对照鼠和运动训练老年鼠的心肌细胞收缩幅度。结论 IP可部分恢复运动训练老年大鼠的I/R损伤的心功能,其可能机制不仅涉及β1-AR的作用,β2-AR发挥着更为特别的作用。     

不同周龄大鼠心肌细胞收缩/舒张功能的研究

目的研究不同周龄对大鼠心肌细胞收缩/舒张功能的影响。方法SD大鼠分为三个周龄组:A组(12~15周)、B组(36~41周)和C组(51~55周),并以常规酶解法分离成年大鼠心肌细胞,观察分离即刻(D时间点)、复钙1h后(E时间点)和电刺激10min后(F时间点)心肌细胞成活率,采用IonOptix单细胞动缘探测系统同步检测心肌细胞的收缩幅度、收缩/舒张速度和钙瞬变等,这些指标均由计算机自动实时采集并记录。结果复钙1h后和电刺激10min后心肌细胞成活率降低均有统计学意义(P<0.05或P<0.01),周龄越大越明显,随着周龄的增大,心肌细胞收缩幅度(峰值高度,ph)、心肌细胞收缩幅度/单个心肌细胞的长度百分比(ph/bl%)、最大收缩速率(maxi mal velocity of contraction, dL/dt)、最大舒张速率(maxi mal velocity of relaxation,-dL/dt)和钙瞬变幅度(FFI)降低,ph在A组、B组和C组分别为(0.14±0.06),(0.12±0.05),(0.11±0.05)μm;ph/bl%分别为(9.17±3.54)%、(7.14±2.58)%和(6.56±2.36)%; dL/dt分别为(2.01±0.74),(1.82±0.51),(1.51±0.56)μm/s;-dL/dt分别为(2.10±0.75),(1.70±0.62),(1.41±0.52)μm/s;FFI分别为(0.38±0.05),(0.35±0.04),(0.25±0.05)。其中C组ph/bl%、 dL/dt、-dL/dt和FFI均较A组显著降低(P<0.05),降低幅度分别为27%,26%,33%和31%。结论随着周龄的增大,分离大鼠心肌细胞的成活率下降,大鼠心肌细胞的收缩/舒张功能降低,钙瞬变幅度减小。     

骨碎补总黄酮对去卵巢大鼠组织蛋白酶K的影响

目的观察骨碎补总黄酮对去卵巢大鼠骨质疏松模型组织蛋白酶K(Cathepsin K)的血清浓度和左胫骨干骺端基因表达的影响,探讨骨碎补总黄酮防治骨质疏松的机制。方法选取3月龄雌性SD大鼠72只,随机分为6组:高剂量骨碎补总黄酮组[治疗组1,12只大鼠,切除双侧卵巢,给药剂量0.216 g/(kg·d)];中剂量骨碎补总黄酮组[治疗组2,12只大鼠,切除双侧卵巢,给药剂量0.108 g/(kg·d)];低剂量骨碎补总黄酮组[治疗组3,12只大鼠,给药剂量0.054 g/(kg·d)];雌激素组(12只大鼠,切除双侧卵巢,给予结合雌激素片0.1 mg/kg);假手术组(12只大鼠,仅切除腹腔少量脂肪和软组织,以5 mL蒸馏水灌胃);正常组(12只大鼠,不做特殊处理,以5 mL蒸馏水灌胃)。各组均在去卵巢造模成功后开始灌胃,并于造模成功后即刻、3个月、6个月每组处死4只大鼠,无菌条件下抽取静脉血,检测血清Cathepsin K浓度。取左胫骨近端干骺端标本,荧光定量PCR测定Cathepsin K mRNA表达量,用SPSS13.0软件进行数据分析。结果各治疗组、正常组与雌激素组大鼠血清Cathepsin K浓度间差异均有统计学意义(P0.05)。各治疗组与雌激素组左胫骨干骺端Cathepsin K mRNA表达量相比有统计学意义(P0.05)。各治疗组、假手术组与正常组左胫骨干骺端Cathepsin K mRNA表达量相比均有统计学意义(P0.01)。结论骨碎补总黄酮抑制去卵巢大鼠血清Cathepsin K浓度、降低左胫骨干骺端Cathepsin K mRNA表达量的作用,可能是其治疗骨质疏松症的机制之一。     

2-甲氧基雌二醇对缺血缺氧诱导的大鼠心肌细胞凋亡的影响

目的:探讨2-甲氧基雌二醇(2ME2)对缺血缺氧诱导的大鼠心肌细胞凋亡的影响,以及可能的机制。方法:清洁级健康雄性,成年,SD大鼠40只,随机分为假手术组、模型组、溶媒组和2ME两组,每组10只,构建大鼠急性心肌梗死模型,2ME两组在大鼠苏醒3 h内按24 mg/kg剂量腹腔注射2ME2,溶媒组和模型组则给予等量的二甲基亚砜或0.9%氯化钠溶液,1次/d,连续7 d,建模后第8天时,检测各组大鼠心脏功能,TUNEL法检测各组大鼠心脏梗死区心肌细胞凋亡情况,Western blot法检测各组大鼠心脏梗死区心肌组织中HIP-1α和BNIP3蛋白表达。结果:模型组和溶媒组大鼠LVEDD和LVESD均高于假手术组,而LVEF和FS均低于假手术组(P<0.05),2ME两组大鼠LVEDD和LVESD均低于模型组和溶媒组,而LVEF和FS均高于模型组和溶媒组(P<0.05);模型组和溶媒组大鼠心脏梗死区心肌细胞凋亡率均高于假手术组(P<0.05),2ME两组大鼠心脏梗死区心肌细胞凋亡率低于模型组和溶媒组(P<0.05);模型组和溶媒组大鼠心脏梗死区心肌组织中HIP-1α和BNIP3蛋白相对表达量高于假手术组(P<0.05),2ME两组大鼠心脏梗死区心肌组织中HIP-1α和BNIP3蛋白相对表达量低于模型组和溶媒组(P<0.05)。结论:2ME2可减少缺血-再灌注损伤大鼠梗死区心肌细胞凋亡,改善心脏功能,其机制可能与抑制HIP-1α及其靶基因BNIP3表达有关。     

心肌肥厚的PTEN负性调控与卡托普利干预对其影响的实验研究

目的检测异丙肾上腺素(isoproterenol,ISO)诱导的心肌肥厚大鼠PTEN mRNA、蛋白水平表达及卡托普利(captopril,Cap)对其表达的影响,从而探讨PTEN的负性调控在心肌肥厚中的作用。方法24只大鼠随机分为对照组、ISO组、Cap+ISO组。利用小剂量ISO持续背部皮下注射大鼠,建立心肌肥厚模型。在观察期末,分别测定各组大鼠体重、心脏湿重、左室湿重,计算出心脏重量/体重及左室重量/体重;电镜观察超微结构的变化,并测定左室收缩末压、左室舒张末压、左心室压力上升及下降最大速率等指标。RT-PCR测定心肌组织PTEN mRNA,Western blot测定其蛋白表达。结果(1)与对照组比较,ISO组、Cap+ISO组的左室重量/体重、心脏重量/体重、左室收缩末压、左室舒张末压均升高(P≤0.05),左室压力上升及下降最大速率(±dp/dtmax)均下降(P≤0.05)。(2)与ISO组相比,Cap+ISO组的左室重量/体重、心脏重量/体重、左室收缩末压、左室舒张末压均下降(P≤0.05,P≤0.01),左室压力上升及下降最大速率(±dp/dtmax)均升高(P≤0.05,P≤0.01)。(3)与对照组比较,ISO组、Cap+ISO组的PTEN mRNA、蛋白表达均增加。(4)与ISO组比较,Cap+ISO组的PTEN mRNA、蛋白表达增加。结论ISO诱导心肌肥厚PTENmRNA、蛋白表达升高,心肌肥厚过程中存在负性调控,PTEN是一种内源性抑制心肌肥厚的重要因子。卡托普利不仅能明显抑制心肌肥厚,改善血液动力学参数,而且还能上调心肌PTEN水平,这是其抑制心肌肥厚的又一机制。     

钙敏感受体在人参皂苷Rg1防治心肌细胞损伤中的作用

目的探讨钙敏感受体(CaSR)在人参皂苷Rg1防治心肌损伤中的作用。方法选择大鼠新生乳鼠心脏组织H9C2心肌细胞于培养基中培养,实验分为对照组、异丙肾上腺素(ISO)组、低剂量组、中剂量组、高剂量组及普萘洛尔组。对照组未加任何试剂培养,ISO组加入ISO 10μmol/L作用48h,低、中、高剂量组及普萘洛尔组,分别加入人参皂苷Rg1 20μmol/L、40μmol/L、80μmol/L、普萘洛尔2μmol/L预孵育30min,再加入ISO 10μmol/L,作用48h。测定细胞体积及心肌细胞蛋白含量,观察各组心肌细胞线粒体膜电位变化、细胞内Ca2+的瞬间变化、CaSR表达及凋亡因子半胱氨酸天冬氨酸蛋白酶(caspase-3)蛋白表达。结果与对照组比较,ISO组心肌细胞蛋白含量明显增加[(28.8±2.8)μg vs(17.8±2.3)μg,P0.05];与ISO组比较,中、高剂量组及普萘洛尔组心肌细胞蛋白含量明显降低,差异有统计学意义[(21.7±2.9)μg vs(28.8±2.8)μg,P0.05;(19.6±1.8)μg vs(28.8±2.8)μg,P0.01;(19.2±2.3)μg vs(28.8±2.8)μg,P0.01)]。与对照组比较,ISO组心肌细胞肥大,线粒体膜电位降低,细胞内Ca2+浓度、CaSR表达及caspase-3蛋白表达增加。与ISO组比较,中、高剂量组心肌细胞蛋白含量明显降低,线粒体膜电位绿色荧光明显减弱,细胞内Ca2+浓度、CaSR及caspase-3表达明显降低。结论人参皂苷Rg1通过CaSR可以减轻ISO诱导的肥大心肌细胞凋亡。     

葛根素对去卵巢大鼠认知功能及海马神经元超微结构的影响

目的 观察不同浓度葛根素对去卵巢大鼠认知功能及海马CA1区、CA3区神经元电镜下形态的影响.方法 SD大鼠72只,随机分为葛根素高、中、低剂量组、阳性对照组(倍美力组)、模型组、假手术组,每组12只,除假手术组外,均摘除大鼠卵巢造成去势模型.灌胃30 d后,用Morris水迷宫检测大鼠认知功能的变化,用透射电镜观察海马CA1区、CA3区神经元形态变化.结果 在训练第6天,Morris水迷宫试验测试大鼠第一次经过平台的时间(潜伏期)与模型组比较,假手术组、阳性对照组和葛根素高剂量组有统计学意义(P＜0.05);大鼠在120 s内经过平台的次数与模型组比较,假手术组、阳性对照组和葛根素高剂量组有统计学意义(P＜0.01);与低剂量组比较,葛根素高剂量组有统计学意义(P＜0.05).透射电镜结果表明,葛根素在不同浓度(30～ 120 mg/kg)范围内,随着浓度的增大,抑制海马神经元细胞凋亡的作用越强,并有一定的剂量依赖关系.结论 葛根素可以促进去卵巢大鼠学习、记忆功能的恢复,减轻因雌激素缺乏而引起的大鼠海马神经元凋亡作用.     

Testosterone enhances estradiol's cardioprotection in ovariectomized rats

After menopause, the development of cardiovascular disease (CVD) is due not only to estrogen decline but also to androgen decline. This study examined the effects of either estradiol (E(2)) or testosterone replacement alone or E(2)-testosterone combination on isolated myocytes in ovariectomized (Ovx) rats subjected to ischemia/reperfusion (I/R). Furthermore, we determined whether the effects are associated with β(2)-adrenoceptor (β(2)-AR). Five groups of adult female Sprague-Dawley rats were used: Sham operation (Sham) rats, bilateral Ovx rats, Ovx rats with E(2) 40?μg/kg per day (Ovx+E), Ovx rats with testosterone 150?μg/kg per day (Ovx+T), and Ovx rats with E(2) 40?μg/kg per day+testosterone 150?μg/kg per day (Ovx+E/T). We determined the lactate dehydrogenase (LDH) release, percentage of rod-shaped cells and apoptosis of ventricular myocytes from rats of all groups subjected to I/R. Then, we determined the above indices and contractile function with or without a selective β(2)-AR antagonist ICI 118?551. We also determined the expression of β(2)-AR. Our data show that either E(2) or testosterone replacement alone or E(2) and testosterone in combination decreased the LDH release, increased the percentage of rod-shaped cells, reduced apoptotic cells (%), and combination treatment appeared to be more effective than either E(2) or testosterone replacement alone. ICI 118?551 abolished the effects of the three. Combination supplementation also enhanced the expression of β(2)-AR. We concluded that in Ovx rats, testosterone enhances E(2)'s cardioprotection, while E(2) and testosterone in combination was more effective and the protective effects may be associated with β(2)-AR. The study highlights the potential therapeutic application for CVD in postmenopausal women.     

辛伐他汀对高糖损伤乳鼠心肌细胞氧化应激的影响

目的探讨辛伐他汀对高糖损伤乳鼠心肌细胞内还原型烟酰胺腺嘌呤二核苷酸磷酸(NADPH)氧化酶活性氧通路的干预作用。方法培养新生1～3 d SD雄性大鼠心肌细胞,随机分为对照组、高浓度葡萄糖刺激组(GS组)、不同浓度辛伐他汀干预组[分别为GS+10~(-7) mol/L Sim组(GS+10~(-7) Msim组)、GS+10~(-6) mol/L Sim组(GS+10~(-6) MSim组)、GS+10~(-5) mol/L Sim组(GS++10~(-5) MSim组),以MTT比色法测定各组心肌细胞活力;化学比色法测定心肌细胞丙二醛含量、超氧化物歧化酶活力及活性氧水平:RT-PCR检测细胞内NADPH氧化酶p22phox mRNA、p47phox mRNA的表达水平。结果与GS组比较,GS+10~(-7) MSim组、GS+10~(-6) MSim组、GS+10~(-5) MSim组丙二醛含量、活性氧水平明显降低.p22phox mRNA、p47phox mRNA表达明显下调,超氧化物歧化酶活力明显升高(P<0.05)。结论心肌细胞内NADPH氧化酶源性的活性氧升高是介导高糖损伤心肌细胞的重要机制,辛伐他汀可能通过抑制NADPH氧化酶-活性氧通路减轻心肌细胞损伤。     

Effects of insulin and streptozotocin-diabetes on isoproterenol-stimulated cyclic AMP production in myocytes isolated from rat heart

Isoproterenol (ISO), at concentrations of up to 10(-5) mol/L, caused a dose-dependent stimulation of cyclic AMP (cAMP) production in rat cardiomyocytes. At higher ISO concentrations, relative inhibition was seen. Insulin augmented ISO-stimulated cAMP production and appeared to mitigate the toxic effects of high ISO concentrations. This synergy between insulin and ISO observed in cardiomyocytes was not observed in adipocytes. Streptozotocin (STZ)-diabetes abolished the stimulatory effects of insulin on ISO-induced cAMP production in cardiomyocytes.     

盐酸羟考酮通过JNK/p38MAPK信号通路调控异丙肾上腺素诱导的心肌细胞凋亡的机制

目的探究盐酸羟考酮对异丙肾上腺素(ISO)诱导的心肌细胞凋亡的影响及其作用机制。方法体外培养心肌细胞H9c2,设置对照组、ISO组、盐酸羟考酮1μmol/L组、盐酸羟考酮5μmol/L组、盐酸羟考酮10μmol/L组、ISO+SB203580〔c-Jun氨基末端激酶/p38丝裂原活化蛋白激酶(JNK/p38MAPK)信号通路阻断剂〕组。噻唑蓝(MTT)法检测心肌细胞存活率;流式细胞学法检测各组心肌细胞的凋亡率;Western印迹检测心肌细胞的B淋巴细胞瘤(Bcl)-2、B淋巴细胞瘤-2相关蛋白(Bax)及JNK/p38MAPK信号通路相关蛋白的表达;测定培养细胞上清液乳脱氢酶(LDH)、肌酸激酶(CK)含量。结果与对照组比较,ISO组心肌细胞存活率降低,各给药组心肌细胞存活率明显升高(P<0.05);与对照组比较,ISO组心肌细胞的凋亡率明显升高(P<0.05),而盐酸羟考酮可显著降低细胞凋亡率(P<0.05);与ISO组比较,盐酸羟考酮10μmol/L组LDH、CK水平及Bax、磷酸化(p)-JNK、p-p38MAPK表达水平显著降低(P<0.05),Bcl-2表达水平显著升高(P<0.05);阻断JNK/p38MAPK信号通路可显著增加细胞存活率(P<0.05),降低细胞凋亡率(P<0.05),促进Bcl-2表达(P<0.05),而抑制Bax表达(P<0.05)。结论盐酸羟考酮对ISO诱导的心肌细胞损伤具有抗凋亡作用,其作用机制可能与抑制JNK/p38MAPK信号通路的活化有关。     

Force/shortening-frequency relationship in multicellular muscle strips and single cardiomyocytes of human failing and nonfailing hearts.

BACKGROUND: Force of contraction (FOC) frequency-dependently increases in multicellular muscle strip preparations of human nonfailing myocardium, whereas FOC declines in human failing myocardium with increasing stimulation frequency. We investigated whether these characteristics can be observed in single isolated myocytes. METHODS AND RESULTS: Isolated multicellular muscle strip preparations and single isolated cardiomyocytes of failing (heart transplants, dilative cardiomyopathy; n = 11) and nonfailing (donor hearts; n = 11) human hearts were studied. The changes in contraction amplitude (cell shortening in micrometers) at increasing frequency of stimulation (0.5-2 Hz) were continuously recorded with a 1-dimensional high-speed camera that detected the cell edges and measured their distance during contraction. The increase in stimulation frequency was associated with a significant decrease in FOC (2 v 0.5 Hz; 68% basal) and a decrease in cell shortening of human left ventricular cardiomyocytes from failing hearts (2 v 0.5 Hz; 65% basal). In contrast, in human nonfailing myocardium, contraction increased at increasing stimulation frequencies (2 v 0.5 Hz; FOC, 180% basal; cell shortening, 129% basal). CONCLUSIONS: The negative force-frequency relationship measured in multicellular preparations of failing human myocardium results from alterations at the single cell level.     

不同剂量雌激素对去势雌性大鼠海马Bcl-2和Bax蛋白表达的影响

目的分析不同剂虽17β-雌二醇（17β-estradiol,E2）干预的去势雌性大鼠海马神经元凋亡相关蛋白Bcl-2及Bax的表达,探讨雌激素的神经元保护作用及其可能机制。方法将大鼠随机分为3组：假手术组（A组）、去卵巢组（B组）、E2干预组（C组）,C组再随机分为3个剂量组。每组分别给予相应处理6周后处死。用放射免疫法（RIA）测定各组大鼠血清E2水平,采用免疫组织化学法（SP法）检测海马神经元Bcl-2及Bax蛋白的表达。结果与假手术组相比,去卵巢后大鼠海马Bcl-2蛋白表达降低（P〈0．01）,补充外源性雌激素后Bcl-2蛋白表达逐渐恢复至正常水平;去卵巢后大鼠海马Bax蛋白表达升高（P〈0．01）,补充外源性雌激素后Bax蛋白表达逐渐恢复至正常水平。结论雌激素能够不同程度的上调海马Bcl-2蛋白的表达,下调Bax蛋白的表达,从而对海马神经元具有保护作用。     

Acute antihypertrophic actions of bradykinin in the rat heart: importance of cyclic GMP

The antihypertrophic action of angiotensin (Ang)-converting enzyme (ACE) inhibitors in the heart is attributed in part to potentiation of bradykinin. Bradykinin prevents hypertrophy of cultured cardiomyocytes by releasing nitric oxide (NO) from endothelial cells, which increases cardiomyocyte guanosine 3'5'-cyclic monophosphate (cyclic GMP). It is unknown whether cyclic GMP is essential for the action of bradykinin, or whether findings in isolated cardiomyocytes apply in whole hearts, in the presence of other cell types and mechanical/dynamic activity. We now examine the contribution of cyclic GMP to the antihypertrophic action of bradykinin in cardiomyocytes and perfused hearts. In adult rat isolated cardiomyocytes cocultured with bovine aortic endothelial cells, the inhibitory action of bradykinin (10 micromol/L) against Ang II (1 micromol/L)-induced [3H]phenylalanine incorporation was abolished by the soluble guanylyl cyclase inhibitor [1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (10 micromol/L). In Langendorff-perfused rat hearts, Ang II (10 nmol/L)-induced increases in [3H]phenylalanine incorporation and atrial natriuretic peptide mRNA expression were prevented by bradykinin (100 nmol/L), the NO donor sodium nitroprusside (3 micromol/L), and the ACE inhibitor ramiprilat (100 nmol/L). The acute antihypertrophic action of bradykinin was accompanied by increased left ventricular cyclic GMP, and the ramiprilat effect was attenuated by HOE 140 (1 micromol/L, a B2-kinin receptor antagonist) or [1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (100 nmol/L). In conclusion, bradykinin exerts a direct inhibitory action against the acute hypertrophic response to Ang II in rat isolated hearts, and elevation of cardiomyocyte cyclic GMP may be an important antihypertrophic mechanism used by bradykinin and ramiprilat in the heart.     

Force/shortening[ndash ]frequency relationship in multicellular muscle strips and single cardiomyocytes of human failing and nonfailing hearts

Background: Force of contraction (FOC) frequency-dependently increases in multicellular muscle strip preparations of human nonfailing myocardium, whereas FOC declines in human failing myocardium with increasing stimulation frequency. We investigated whether these characteristics can be observed in single isolated myocytes. Methods and Results: Isolated multicellular muscle strip preparations and single isolated cardiomyocytes of failing (heart transplants, dilative cardiomyopathy; N = 11) and nonfailing (donor hearts; N = 11) human hearts were studied. The changes in contraction amplitude (cell shortening in micrometers) at increasing frequency of stimulation (0.5[ndash ]2 Hz) were continuously recorded with a 1-dimensional high-speed camera that detected the cell edges and measured their distance during contraction. The increase in stimulation frequency was associated with a significant decrease in FOC (2 v 0.5 Hz; 68% basal) and a decrease in cell shortening of human left ventricular cardiomyocytes from failing hearts (2 v 0.5 Hz; 65% basal). In contrast, in human nonfailing myocardium, contraction increased at increasing stimulation frequencies (2 v 0.5 Hz; FOC, 180% basal; cell shortening, 129% basal). Conclusions: The negative force-frequency relationship measured in multicellular preparations of failing human myocardium results from alterations at the single cell level.