Mechanisms of Na and Ca Transport Across the Plasma Membranes of Squid Giant Axons, Structure-Function Relationships

细胞内部对于细胞外介质是电负性的。然而，与带正电荷的Na和Ca离子积聚到细胞内的自然趋势相反，它们更多地集中在细胞的外部。为了保持这种情况，必须在消耗能量的同时进行净稳定的钠和钙挤压。对于钙，位于质膜中的两种蛋白质为此目的而合作：(I)钙泵，它使用来自ATP水解的能量；(Ii)钠/钙交换，尽管它从向内的钠梯度获得能量，但也受到ATP的刺激。这些研究将表征使用鱿鱼巨轴突的钠/钙交换器的结构-功能关系。在透析下，这种制剂是独一无二的，因为它允许几乎完全的生物化学控制细胞内和细胞外环境以及跨膜电势。对以下具体问题的回答有望增加我们对特殊的电化学障碍如何阻止它们移动的理解。(I)ATP刺激是直接施加在交换器上，还是涉及其他结构，可能是激酶？(Ii)哪些氨基酸(蛋白质的结构单位)与交换器的功能有关？在这种情况下，将使用已知的选择性封闭不同氨基酸或化学基团的化合物。细胞内Ca~(2+)排出系统的ı！调节血流和血压以及神经和内分泌功能。

The interior of the cells is electronegative respect to the extracellular media. However, against the natural tendency of the positively charged Na and Ca ions to accumulate into the cells, they are much more concentrated in the external side. To maintain that situation a net steady Na and Ca extrusion must take place while energy is consumed. For Ca, two proteins located in the plasma membrane cooperate to that end: (i) the Ca pump, which uses energy from ATP hydrolysis, and (ii) the Na/Ca exchange which, though it takes that energy from the inward Na gradient, is also stimulated by ATP. The studies will characterize the structure-function relationships of the Na/Ca exchanger employing the squid giant axon. Under dialysis, this preparation is unique for it allows almost complete biochemical control of intra and extracellular environments and also of the transmembrane electrical potential. Answers to the following specific questions can be expected to provide an increase in our understanding of how extraordinary electrochemical barriers to their movements. (i) Is ATP stimulation is exerted directly on the exchanger or are other structures, perhaps kinases, involved? (ii) What amino acids (structural units of proteins) are relevant to the functions of the exchanger? In this case compounds known to selectively block different amino acids or chemical groups will be used. The physiological relevance of the Ca extruding systems is evidenced by the fact that intracellular ıCa! regulated blood flow and pressure and neural and endocrine functions.