Abercrombie R F, Sjodin R A
J Gen Physiol. 1977 Jun;69(6):765-78. doi: 10.1085/jgp.69.6.765.
Several properties of the Na pump in giant axons from the marine annelid Myxicola infundibulum have been determined in an attempt to characterize this preparation for membrane transport studies. Both NaO and KO activated the Na pump of normal microinjected Myxicola axons. In this preparation, the KO activation was less and the NaO activation much greater than that found in the squid giant axon. However, when the intracellular ATP:ADP ratio of the Myxicola axon was elevated by injection of an extraneous phosphagen system, the K sensitivity of Na efflux increased to the magnitude characteristic of squid axons and the activating effect of NaO disappeared. Several axons were injected with Na2SO4 in order to determine the effect of elevated Nai on the Na efflux. Increasing Nai enhanced a component of Na efflux which was insensitive to ouabain and dependent on [Ca] in Na-free (Li) seawater. After subtracting the CaO-dependent fraction, Na efflux was related linearly to [Na]i in all solutions except in K-free (Li) seawater, where it appeared to reach saturation at high [Na]i.
为了对这种用于膜转运研究的标本进行特性描述，已经测定了来自海洋环节动物Myxicola infundibulum的巨轴突中钠泵的几种特性。NaO和KO都能激活正常微量注射的Myxicola轴突的钠泵。在这个标本中，KO的激活作用较小，而NaO的激活作用比在乌贼巨轴突中发现的要强得多。然而，当通过注射外源磷酸肌酸系统提高Myxicola轴突的细胞内ATP:ADP比值时，钠外流的钾敏感性增加到乌贼轴突特有的程度，并且NaO的激活作用消失。为了确定细胞内钠离子升高对钠外流的影响，向几根轴突中注射了Na2SO4。细胞内钠离子的增加增强了钠外流的一个成分，该成分对哇巴因不敏感，并且在无钠（锂）海水中依赖于[Ca]。减去依赖于CaO的部分后，除了在无钾（锂）海水中，在所有溶液中钠外流都与[Na]i呈线性关系，在无钾（锂）海水中，钠外流在高[Na]i时似乎达到饱和。
