Sethi R, Bector N, Takeda N, Nagano M, Jasmin G, Dhalla N S
Division of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Mol Cell Biochem. 1994 Nov 23;140(2):163-70. doi: 10.1007/BF00926754.
In order to explain the attenuated sympathetic support during the development of heart failure, the status of beta-adrenergic mechanisms in the failing myocardium was assessed by employing cardiomyopathic hamsters (155-170 days old) at moderate degree of congestive heart failure. The norepinephrine turnover rate was increased but the norepinephrine content was decreased in cardiomyopathic hearts. The number and the affinity of beta receptors in the sarcolemmal preparations were not changed in these hearts at moderate stage of congestive heart failure. While the basal adenylyl cyclase activity was not altered in sarcolemma, the stimulation of enzyme activity by NaF, forskolin, Gpp(NH)p or epinephrine was depressed in hearts from these cardiomyopathic hamsters. Since G-proteins are involved in modifying the adenylyl cyclase activity, the functional and bioactivities as well as contents of both Gs and Gi proteins were determined in the cardiomyopathic heart sarcolemma. The functional stimulation of adenylyl cyclase by cholera toxin, which activates Gs proteins, was markedly depressed whereas that by Pertussis toxin, which inhibits Gi proteins, was markedly augmented in cardiomyopathic hearts. The cholera toxin and pertussis toxin catalyzed ADP-ribosylation was increased by 37 and 126%, respectively; this indicated increased bioactivities of both Gs and Gi proteins in experimental preparations. The immunoblot analysis suggested 74 and 124% increase in Gs and Gi contents in failing hearts, respectively. These results suggest that depressed adenylyl cyclase activation in cardiomyopathic hamsters may not only be due to increased content and bioactivity of Gi proteins but the functional uncoupling of Gs proteins from the adenylyl cyclase enzyme may also be involved at this stage of heart failure.
为了解释心力衰竭发展过程中交感神经支持减弱的现象，我们通过使用中度充血性心力衰竭的心肌病仓鼠（155 - 170日龄）来评估衰竭心肌中β - 肾上腺素能机制的状态。在心肌病心脏中，去甲肾上腺素周转率增加，但去甲肾上腺素含量减少。在充血性心力衰竭的中度阶段，这些心脏肌膜制剂中β受体的数量和亲和力没有变化。虽然肌膜中的基础腺苷酸环化酶活性没有改变，但这些心肌病仓鼠心脏中，氟化钠、福斯高林、Gpp(NH)p或肾上腺素对酶活性的刺激作用受到抑制。由于G蛋白参与调节腺苷酸环化酶活性，因此我们测定了心肌病心脏肌膜中Gs和Gi蛋白的功能、生物活性以及含量。在心肌病心脏中，激活Gs蛋白的霍乱毒素对腺苷酸环化酶的功能刺激作用明显降低，而抑制Gi蛋白的百日咳毒素对其刺激作用则明显增强。霍乱毒素和百日咳毒素催化的ADP - 核糖基化分别增加了37%和126%；这表明实验制剂中Gs和Gi蛋白的生物活性均增加。免疫印迹分析表明，衰竭心脏中Gs和Gi含量分别增加了74%和124%。这些结果表明，心肌病仓鼠中腺苷酸环化酶激活受抑可能不仅是由于Gi蛋白含量和生物活性增加，在心力衰竭的这个阶段，Gs蛋白与腺苷酸环化酶的功能解偶联也可能起作用。
