CELLULAR CA2+ ION HOMEOSTASIS AND THE IMPACT OF AGING

该项目构成了一个机制的调查， 细胞实现胞质游离Ca 2+浓度的稳态 ((Ca2+）c），并允许（Ca2+）c响应于 激素和神经递质。 此外，它解决了混乱， 在这些控制机制可能发生在老年。 今年， 我们提出了以下问题。 (1)是什么机制 由此，激素胰高血糖素导致（Ca2+）c增加， 肝细胞？ 我们研究了蛋白质的磷酸化 在富含质膜的细胞部分中，在治疗时 与环AMP或外源性蛋白激酶A，在一个 模拟细胞暴露于胰高血糖素的过程。 直接 这种磷酸化事件与细胞内 然而，质膜对Ca2+的渗透性尚不可能。 (2)蛋白质磷酸化水平是否与 先前描述的反应性降低， 对衰老心脏中的儿茶酚胺的收缩性有什么影响 我们有 定量降低蛋白质肌钙蛋白的磷酸盐含量， I和C蛋白，对暴露于 去甲肾上腺素，当衰老动物的细胞与 那些来自年轻的成年人。 这与推断的减少有关 在衰老动物的细胞中，环AMP的净形成。 预计这也会对肌膜和 负责Ca2+转运的肌浆网蛋白。 (3)在交感神经刺激时释放的ATP 与去甲肾上腺素，有正性肌力作用， 当以适当水平添加时，（Ca2+）c的动员， 分离的心肌细胞？ 微摩尔浓度的外源性 ATP被发现是一种有效的正性肌力药， 去甲肾上腺素在相同的浓度，并产生T 电刺激时（Ca2+）c的瞬变增强。 的 反应的药理学研究与其他嘌呤 核苷酸和类似物。

This project constitutes an investigation into mechanism whereby cells achieve the homeostasis of cytosolic free Ca2+ concentrations ((Ca2+)c), and allow perturbations in (Ca2+)c in response to hormones and neurotransmitters. Further, it addressed derangements in these control mechanisms which may occur in old-age. This year, we have asked the following questions. (1) What is the mechanism whereby the hormone glucagon leads to an increase in (Ca2+)c in hepatocytes? We have investigated the phosphorylation of proteins in a cellular fraction enriched in plasma membrane, on treatment with either cyclic-AMP or exogenous protein kinase A, in a procedure which mimics exposure of the cell o glucagon. Direct correlation between such phosphorylation events and changes in plasma membrane permeability to Ca2+ is not yet possible, however. (2) Are there correlates at the level of protein phosphorylation of the previously described decreased responsiveness of contractility to catecholamines in the aging heart? We have quantitated a decreased phosphate content of the proteins troponin- I and C-protein, on exposure of isolated cardiac myocytes to norepinephrine, when cells from senescent animals are compared to those from young adults. This is linked to an inferred decreased net formation of cyclic-AMP, in cells from the senescent animals. This may be expected to have an impact also on sarcolemmal and sarcoplasmic reticulum proteins responsible for Ca2+ transport. (3) Does ATP, which is released on sympathetic stimulation together with norepinephrine, have a positive inotropic effect, linked to mobilization of (Ca2+)c, when added at appropriate levels to isolated cardiac myocytes? Micromolar concentrations of exogenous ATP were found to be as potent a positive inotrope as norepinephrine at the same concentrations, and to give rise t an enhanced transient in (Ca2+)c on electrical stimulation. The pharmacology of the response was studied with other purine nucleotides and analogs.