Abashidze S, Jariashvili T, Kometiani Z
Laboratory of Membranology, IBeriatshvili Institute of Physiology, Georgian Academy of Sciences, Tbilisi, Georgia, USA.
BMC Biochem. 2001;2:8. doi: 10.1186/1471-2091-2-8. Epub 2001 Sep 3.
The Na/K-ATPase activity of the brain synaptic plasma membranes (SPM) is regulated by noradrenaline (NA) and the synaptosomal factor SF (soluble protein obtained from the synaptosome cytosol). In the absence of SF, NA inhibits Na/K-ATPase, while, on addition of SF to the reaction medium, there is a NA-dependent activation of Na/K-ATPase. On the other hand, EGTA augments the Na/K-ATPase activity and attenuates the ability of NA to inhibit Na/K-ATPase.
Considering that Ca2+ ion is a Na/K-ATPase modifier, it can be assumed that the effect of NA and SF is a Ca2+-dependent process. However, in the presence of 0.3 mM EGTA and 0.1 mM NA, the apparent inhibition constant for Ca2+ (at [Ca2+] > 0.3 mM) is not SF dependent, while the apparent activation constant for SF does not change at increasing Ca2+ concentration ([Ca2+] < 0.3 mM). At various Ca2+ concentrations (0.06, 0.35 and 0.6 mM), no significant changes occur in the mode of action of NA on the Na/K-ATPase activity in the presence of 5 microg/ml SF. EGTA also has no effect on the NA-independent activation of Na/K-ATPase evoked by high SF concentrations.
Taking into account that in the absence of EGTA similar results have been obtained, it can be concluded that the effect of NA and SF on brain Na/K-ATPase is a Ca2+-independent process.
脑突触质膜（SPM）的钠钾ATP酶活性受去甲肾上腺素（NA）和突触体因子SF（从突触体胞质溶胶中获得的可溶性蛋白质）调节。在没有SF的情况下，NA抑制钠钾ATP酶，而向反应介质中添加SF后，会出现依赖于NA的钠钾ATP酶激活。另一方面，乙二醇双四乙酸（EGTA）增强钠钾ATP酶活性并减弱NA抑制钠钾ATP酶的能力。
考虑到钙离子是钠钾ATP酶的修饰剂，可以假设NA和SF的作用是一个依赖于钙离子的过程。然而，在存在0.3 mM EGTA和0.1 mM NA的情况下，钙离子的表观抑制常数（在[钙离子] > 0.3 mM时）不依赖于SF，而SF的表观激活常数在钙离子浓度增加时（[钙离子] < 0.3 mM）不变。在各种钙离子浓度（0.06、0.35和0.6 mM）下，在存在5微克/毫升SF的情况下，NA对钠钾ATP酶活性的作用模式没有显著变化。EGTA对高浓度SF引起的钠钾ATP酶的非依赖于NA的激活也没有影响。
考虑到在没有EGTA的情况下也获得了类似的结果，可以得出结论，NA和SF对脑钠钾ATP酶的作用是一个不依赖于钙离子的过程。
