ALTERED SIGNALING IN CARDIAC HYPERTROPHY AND FAILURE

心脏对慢性压力超负荷的适应会导致心肌肥大和信号转导的改变，以补偿交感神经张力和作功的增加。这些适应性变化导致cGMP水平升高，下调β肾上腺素能受体的调节。这一提议的假设是，cGMP的负面功能效应有助于肥厚的补偿，当这种内源性刹车失灵时，就会发生心力衰竭。其具体目的是确定cGMP负性影响的机制是通过依赖cGMP的cAMP磷酸二酯酶(PDE)还是通过蛋白激酶G对A和C的相互作用而引起cAMP的变化，通过对比代偿者和衰竭肥厚心脏(快速起搏)的信号级联改变来阐明这些机制中的哪一种导致肥厚心脏失代偿，并通过cAMP PDE的进一步慢性改变来证实它们之间的相关性。从正常、肥厚(主动脉狭窄模型)和衰竭心脏的成年犬分离的心肌细胞将被用来确定信号的后期产生变化对功能(视频边缘检测)和氧气消耗(PO2电极)的影响。这些机制在控制局部功能和氧气成本方面的相对重要性将在完整的心脏中得到测试。体内实验将在麻醉开胸犬肥厚诱导6个月后进行，并与对照组进行比较。局部心肌作功将通过节段长度(超声尺寸晶体)和收缩力量(微型测力计)进行评估。同一区域的氧气消耗量将根据局部血流量(放射性微球或流动探头)和局部血红蛋白的氧气饱和度(显微分光光度法)来确定。这些生理测量将与cAMP、cGMP、相应的磷酸二酯酶和蛋白激酶A、G和C的生化分析相结合，并与钙瞬变测量相关联。最终目标是确定启动失代偿并导致充血性心力衰竭的机制。建议的影响：对这些机制的了解将允许开发新的治疗策略来预防人类充血性心力衰竭的发展。

Adaptation of the heart to chronic pressure overload leads to cardiac hypertrophy and alterations in signal transduction to compensate for increased sympathetic tone and work. These adaptive changes lead to increases in cGMP levels down regulation of beta adrenergic receptors. The hypothesis of this proposal is that the negative functional effects of cGMP contribute to compensation in hypertrophy and that, when this endogenous brake fails, heart failure develops. The specific aim is to determine if the mechanism of cGMP's negative impact is through changes in cAMP via the cGMP-dependent cAMP phosphodiesterases (PDE) or through interactions of protein kinase G on A and C, to elucidate which of these mechanisms causes the hypertrophied heart to decompensate by contrasting the alterations in the signaling cascade of the compensated with that of failing hypertrophied heart (rapid pacing) and to confirm their relevance by further chronic alteration of the cAMP PDEs. Cardiac myocytes isolated from adult dogs with normal, hypertrophied (aortic stenosis model) and failing hearts will be used to determine the effects of postproduction changes in signaling on function (video edge detection) and O2 consumption (PO2 electrode). The relative importance of these mechanisms in controlling regional function and O2 costs will be tested in the intact heart. The in vivo experiments will be conducted in anesthetized, open-chest dogs 6 months after induction of hypertrophy with or without failure and compared to controls. Regional myocardial work will be assessed from segment length (ultrasonic dimension crystals) and contractile force (miniature force gauges). O2 consumption of the same area will be determined from regional blood flow (radioactive microspheres or flow probe) and regional O2 saturation of hemoglobin (microspectrophotometry). These physiological measurements will be combined with biochemical assays for cAMP, cGMP, the respective phosphodiesterases and protein kinases A, G and C and correlated with Ca transient measurements. The ultimate goal is to determine the mechanism that initiates decompensation and leads to congestive heart failure. Impact of the proposal: the understanding of these mechanisms will permit the development of new therapeutic strategies to prevent the development of congestive heart failure in man.