The cardiac Na-Ca exchanger in giant membrane patches
The cardiac Na-Ca exchanger in giant membrane patches
复制标题
DOI：
10.1111/j.1749-6632.1996.tb44783.x
复制
发表时间：
1996-01-01
期刊：
影响因子：
--
通讯作者：
Hilgemann, DW
中科院分区：
文献类型：
--
作者：
Hilgemann, DW
许多技术对Na-Ca交换研究的进展做出了贡献。它们包括同位素通量法、1-3电压光学法、6和分子生物学。大膜贴片技术*被开发用于研究心脏Na-Ca交换电流，该技术改进了对膜两侧离子浓度的控制，可以自由进入细胞质膜侧，并且可以更快地控制膜电位。在1991年第二届钠钙交换国际会议上，这些方法上的优势已经导致了一些新的发现。首先，发现交换剂活性是由复杂的自抑制反应调节的，这种反应可以使交换剂脱离主动运输循环。这些反应可以分析为“失活”过程，或多或少类似于通道失活反应。其次，与其他人一致，“*.”交换剂的表观离子亲和取决于相反膜侧的离子浓度，正如预期的“连续”交换循环（即，首先向一个方向移动3na，然后向另一个方向移动1ca）。14,15第三，电流瞬变（或“电荷运动”）被确定为钠在缺乏钙的情况下的易位，而不是钙在缺乏~ 0 - diurn的情况下的易位。这些结果，连同对交换电流的电压和离子依赖性的改进数据，表明离子结合位点可能具有接近2的净电荷。因此，在三个钠离子的易位过程中，大约有一个净正电荷会在膜电场中移动，而钙离子的易位在很大程度上是电中性的。
Many techniques have contributed to progress in Na-Ca exchange research. They include isotope flux methods, 1-3 voltage optical methods, 6 and molecular bi~ logy.~ The giant membrane patch technique* was developed to study cardiac Na-Ca exchange currents with improved control of ion concentrations on both membrane sides, free access to the cytoplasmic membrane side, and faster control of membrane potential. At the time of the Second International Meeting on Sodium-Calcium Exchange in 1991, these methodological advantages had already led to several new in~ ights.~First, it was discovered that exchanger activity is modulated by complex autoinhibitory reactions which can move the exchanger out of an active transport cycle. I0, I1 These reactions can be analyzed as ‘inactivation’processes, analogous to a greater or lesser extent to channel inactivation reactions. Second, in agreement with others,‘*.” the apparent ion affinities of the exchanger depend on ion concentrations on the opposite membrane side as expected for a ‘consecutive’exchange cycle (ie, moving first 3 Na in one direction and then 1 Ca in the other direction across the membrane). 14, 15 Third, current transients (or ‘charge movements’) were identified for sodium translocation in the absence of calcium, but not for calcium translocation in the absence of~ 0diurn. I~ These results, together with improved data on the voltage-and ion-dependencies of exchanger currents, suggested that ion binding sites may have a net charge of close to-2. Thus, approximately one net positive charge would be moved across the membrane electrical field during the translocation of three sodium ions, while calcium translocation can be largely electroneutral.