Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095-1760, USA.
Adv Exp Med Biol. 2013;961:49-54. doi: 10.1007/978-1-4614-4756-6_5.
The plasma membrane Na(+)/Ca(2+) exchanger (NCX) plays a critical role in the maintenance of Ca(2+) homeostasis in a variety of tissues. NCX accomplishes this task by either lowering or increasing the intracellular Ca(2+) concentration, a process which depends on electrochemical gradients. During each cycle, three Na(+) are transported in the opposite direction to one Ca(2+), resulting in an electrogenic transport that can be measured as an ionic current.The residues involved in ion translocation are unknown. A residue thought to be important for Na(+) and/or Ca(2+) transport, Ser(110), was replaced with a cysteine, and the properties of the resulting exchanger mutant were analyzed using the giant patch technique. Data indicate that this residue, located in transmembrane segment 2 (part of the α-1 repeat), is important for both Na(+) and Ca(2+) translocations. Using cysteine susceptibility analysis, we demonstrated that Ser(110) is exposed to the cytoplasm when the exchanger is in the inward state configuration.
质膜 Na(+)/Ca(2+)交换器 (NCX) 在维持多种组织中的 Ca(2+) 稳态中发挥着关键作用。NCX 通过降低或增加细胞内 Ca(2+)浓度来完成此任务，这一过程取决于电化学梯度。在每个循环中，三个 Na(+)被反向转运一个 Ca(2+)，从而产生可以作为离子电流测量的电致运动。参与离子易位的残基尚不清楚。一个被认为对 Na(+)和/或 Ca(2+)转运很重要的残基，丝氨酸 (110)，被替换为半胱氨酸，并用巨斑技术分析所得交换器突变体的性质。数据表明，该残基位于跨膜片段 2（α-1 重复的一部分）中，对 Na(+)和 Ca(2+)的转运都很重要。使用半胱氨酸敏感性分析，我们证明了当交换器处于内向状态配置时，Ser(110)暴露于细胞质中。
