Kaura D, Takeda N, Sethi R, Wang X, Nagano M, Dhalla N S
Division of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada.
Mol Cell Biochem. 1996;157(1-2):191-6.
In view of the lack of information regarding the status of beta-adrenoceptor mediated signal transduction mechanisms at severe stages of congestive heart failure, the status of beta-adrenoceptors, G-proteins and adenylyl cyclase activities was examined in 220-275 day old cardiomyopathic hamster hearts. Although no changes in the Kd values for beta 1- and beta 2-adrenoceptors were seen, the number of beta 1-adrenoceptors, unlike that of beta 2-adrenoceptors, was markedly decreased in cardiac membranes from failing hearts. The activation of adenylyl cyclase in the failing hearts by different concentrations of isoproterenol was also attenuated in comparison to the control preparations. The basal adenylyl cyclase activity in cardiac membranes from the failing hearts was not altered; however, the stimulated enzyme activities, when measured in the presence of forskolin, NaF or Gpp(NH)p were depressed significantly. The functional activity of Gs-proteins (measured by cholera toxin stimulation of adenylyl cyclase) was depressed whereas that of Gi-proteins (measured by pertussis toxin stimulation of adenylyl cyclase) was increased in the failing hearts. Not only were the Gs- and Gi-protein contents (measured by immunoblotting) increased, the bioactivities of these proteins as determined by ADP-ribosylations in the presence of cholera toxin and pertussis toxin, respectively, were also higher in failing hearts in comparison to the control values. Northern blot analysis revealed that the signals for Gs- and Gi-protein mRNAs were augmented at this stage of heart failure. These results indicate that the loss of adrenergic support at severe stages of congestive heart failure in cardiomyopathic hamsters may involve a reduction in the number of beta 1-adrenoceptors, and an increase in Gi-protein contents as well as bioactivities in addition to an uncoupling of Gs-proteins from the catalytic site of adenylyl cyclase in cardiac membrane.
鉴于在充血性心力衰竭严重阶段β-肾上腺素能受体介导的信号转导机制的状态信息匮乏，对220 - 275日龄心肌病仓鼠心脏中的β-肾上腺素能受体、G蛋白和腺苷酸环化酶活性的状态进行了检测。尽管β1和β2肾上腺素能受体的解离常数（Kd值）没有变化，但与β2肾上腺素能受体不同，衰竭心脏的心膜中β1肾上腺素能受体的数量显著减少。与对照制剂相比，不同浓度异丙肾上腺素对衰竭心脏中腺苷酸环化酶的激活作用也减弱。衰竭心脏心膜中的基础腺苷酸环化酶活性没有改变；然而，当在福斯高林、氟化钠或鸟苷-5'-三磷酸（Gpp(NH)p）存在下测量时，刺激后的酶活性显著降低。在衰竭心脏中，Gs蛋白的功能活性（通过霍乱毒素刺激腺苷酸环化酶来测量）降低，而Gi蛋白的功能活性（通过百日咳毒素刺激腺苷酸环化酶来测量）增加。不仅Gs和Gi蛋白的含量（通过免疫印迹法测量）增加，与对照值相比，分别在霍乱毒素和百日咳毒素存在下通过ADP-核糖基化测定的这些蛋白的生物活性在衰竭心脏中也更高。Northern印迹分析显示，在心力衰竭的这个阶段，Gs和Gi蛋白mRNA的信号增强。这些结果表明，心肌病仓鼠在充血性心力衰竭严重阶段肾上腺素能支持的丧失可能涉及β1肾上腺素能受体数量的减少、Gi蛋白含量及其生物活性的增加，此外还包括Gs蛋白与心膜中腺苷酸环化酶催化位点的解偶联。
