Linck B, Qiu Z, He Z, Tong Q, Hilgemann D W, Philipson K D
Department of Physiology, University of California, School of Medicine, Los Angeles 90095-1760, USA.
Am J Physiol. 1998 Feb;274(2):C415-23. doi: 10.1152/ajpcell.1998.274.2.C415.
Three distinct mammalian Na+/Ca2+ exchangers have been cloned: NCX1, NCX2, and NCX3. We have undertaken a detailed functional comparison of these three exchangers. Each exchanger was stably expressed at high levels in the plasma membranes of BHK cells. Na+/Ca2+ exchange activity was assessed using three different complementary techniques: Na+ gradient-dependent 45Ca2+ uptake into intact cells, Na+ gradient-dependent 45Ca2+ uptake into membrane vesicles isolated from the transfected cells, and exchange currents measured using giant patches of excised cell membrane. Apparent affinities for the transported ions Na+ and Ca2+ were markedly similar for the three exchangers at both membrane surfaces. Likewise, generally similar responses to changes in pH, chymotrypsin treatment, and application of various inhibitors were obtained. Depletion of cellular ATP inhibited NCX1 and NCX2 but did not affect the activity of NCX3. Exchange activities of NCX1 and NCX3 were modestly increased by agents that activate protein kinases A and C. All exchangers were regulated by intracellular Ca2+. NCX1-induced exchange currents were especially large in excised patches and, like the native myocardial exchanger, were stimulated by ATP. Results may be influenced by our choice of expression system and specific splice variants, but, overall, the three exchangers appear to have very similar properties.
NCX1、NCX2和NCX3。我们对这三种交换体进行了详细的功能比较。每种交换体都在BHK细胞的质膜中高水平稳定表达。使用三种不同的互补技术评估钠钙交换活性：依赖钠梯度的45Ca2+摄取进入完整细胞、依赖钠梯度的45Ca2+摄取进入从转染细胞中分离的膜囊泡，以及使用切除细胞膜的巨膜片测量交换电流。在两个膜表面，三种交换体对转运离子Na+和Ca2+的表观亲和力明显相似。同样，对pH变化、胰凝乳蛋白酶处理以及各种抑制剂应用的反应通常也相似。细胞ATP耗竭抑制NCX1和NCX2，但不影响NCX3的活性。激活蛋白激酶A和C的试剂适度增加了NCX1和NCX3的交换活性。所有交换体都受细胞内Ca2+调节。NCX1诱导的交换电流在切除的膜片中特别大，并且与天然心肌交换体一样，受到ATP的刺激。结果可能受我们对表达系统和特定剪接变体的选择影响，但总体而言，这三种交换体似乎具有非常相似的特性。
