Hermoni M, Barzilai A, Rahamimoff H
Isr J Med Sci. 1987 Jan-Feb;23(1-2):44-8.
The Na+-Ca2+ exchanger is a major Ca2+ transporting molecule in excitable cells. It is localized in the plasma membrane and participates in the regulation of intracellular Ca2+ concentration. Li+ starting at a concentration of 5 mM inhibits Na+-Ca2+ exchange in synaptic plasma membrane (SPM) vesicles. Both the initial rate and steady state levels of Na+-gradient-dependent Ca2+ transport are inhibited. Experiments studying the mechanism of Li+ inhibition revealed the following: no competition was observed between Li+ and Na+ on the binding site to the exchanger; the depolarization of the SPM obtained by K+ was considerably diminished in the presence of Li+; and 3) the affinity of Ca2+ to the Na+-Ca2+ exchanger decreased in the presence of Li+. Since the Na+-Ca2+ exchanger operates in an electrogenic fashion, the combined effects of reduced membrane polarization with the reduction in Ca2+ affinity can explain the inhibitory effect of Li+.
钠钙交换体是可兴奋细胞中主要的钙转运分子。它定位于质膜，参与细胞内钙浓度的调节。浓度为5 mM的锂离子可抑制突触质膜（SPM）囊泡中的钠钙交换。钠梯度依赖性钙转运的初始速率和稳态水平均受到抑制。研究锂抑制机制的实验揭示了以下几点：1）未观察到锂离子与钠离子在交换体结合位点上的竞争；2）在存在锂的情况下，由钾离子引起的SPM去极化显著减弱；3）在存在锂的情况下，钙离子与钠钙交换体的亲和力降低。由于钠钙交换体以电生方式运作，膜极化降低与钙亲和力降低的综合作用可以解释锂的抑制作用。
