CA2+ TRANSPORT-PROPERTIES OF IONOPHORES A23187, IONOMYCIN, AND 4-BRA23187 IN A WELL-DEFINED MODEL SYSTEM
CA2+ TRANSPORT-PROPERTIES OF IONOPHORES A23187, IONOMYCIN, AND 4-BRA23187 IN A WELL-DEFINED MODEL SYSTEM
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DOI：
10.1016/s0006-3495(94)80959-2
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发表时间：
1994-05-01
影响因子：
3.4
通讯作者：
PFEIFFER, DR
中科院分区：
文献类型：
--
作者：
ERDAHL, WL;CHAPMAN, CJ;PFEIFFER, DR
离子载体 A23187、离子霉素和 4-BrA23187 的 Ca2+ 电中性转运模型已在由冻融挤出制备的 1-棕榈酰-2-油酰-sn-甘油磷脂酰胆碱囊泡组成的确定系统中进行了测试。使用装载 Quin-2 和装载 CaCl2 的囊泡来研究双向运输。 H+ 转运和膜电位的同时或并行测量分别表明，对于任何这些离子载体，当没有预先存在的跨膜电位时，生电转运事件不超过万分之一。当跨膜施加大约 150 mV 的电势时，A23187 催化的传输保持电中性；然而，对于离子霉素和 4-BrA23187，大约 10% 的转运事件可能是生电的。定义的囊泡系统也被用来确定 Ca2+ 转运速率如何随离子载体和 Ca2+ 浓度以及转运方向的变化而变化。结果的某些方面是出乎意料的，在生物系统中使用离子载体的研究人员应该考虑这一点。这些包括当这些物质被膜分离时，这些化合物明显无法与高亲和力 Ca2+ 指示剂完全平衡 Ca2+，运输速率随运输方向显着变化，以及运输程度是离子载体浓度的函数。至少其中一些意想不到的行为可以通过 Delta pH 对正向和反向传输动力学的强烈影响来解释。就 A23187 而言，数据还初步了解了运输物质的形成与该物质进入膜疏水区域之间的关系。
Models for the electroneutral transport of Ca2+ by ionophores A23187, ionomycin, and 4-BrA23187 have been tested in a defined system comprised of 1-palmitoyl-2-oleoyl-sn-glycerophosphatidylcholine vesicles prepared by freeze-thaw extrusion. Quin-2-loaded and CaCl2-loaded vesicles were employed to allow the investigation of transport in both directions. Simultaneous or parallel measurements of H+ transport and membrane potential, respectively, indicate that for any of these ionophores, electrogenic transport events do not exceed 1 in 10,000 when there is no preexisting transmembrane potential. When a potential of similar to 150 mV is imposed across the membrane, transport catalyzed by A23187 remains electroneutral; however, for ionomycin and 4-BrA23187, approximately 10% of transport events may be electrogenic. The defined vesicle system has also been utilized to determine how the rate of Ca2+ transport varies as a function of ionophore and Ca2+ concentration and with the direction of transport. Some aspects of the results are unexpected and should be considered by investigators using ionophores in biological systems. These include the apparent failure of these compounds to fully equilibrate Ca2+ with a high affinity Ca2+ indicator when these species are separated by a membrane, rates of transport that vary markedly with the direction of transport, and extents of transport that are a function of ionophore concentration. At least some of these unexpected behaviors can be explained by a strong influence of Delta pH on forward and reverse transport kinetics. In the case of A23187, the data also give some initial insights into the relationship between formation of the transporting species and the entry of this species into the membrane hydrophobic region.