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

细胞内部相对于细胞外介质具有电负性。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，它们更集中在细胞的外部。为了维持这种情况，在消耗能量的同时，必须发生净稳定的钠和钙挤压。对于Ca，位于质膜上的两种蛋白质合作达到这一目的：(i) Ca泵，它使用ATP水解产生的能量；（ii） Na/Ca交换，尽管它从向内的Na梯度中获取能量，但也受到ATP的刺激。该研究将表征鱿鱼巨轴突Na/Ca交换器的结构-功能关系。在透析下，这种制备是独特的，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位。对以下具体问题的回答可以增加我们对非同寻常的电化学障碍如何影响它们的运动的理解。(i) ATP刺激是直接施加在交换物上还是涉及其他结构，也许是激酶？（ii）哪些氨基酸（蛋白质的结构单位）与交换剂的功能有关？在这种情况下，将使用已知的选择性阻断不同氨基酸或化学基团的化合物。钙挤压系统的生理相关性被细胞内ıCa！调节血液流动和压力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.