Cavarra M Soledad, Assef Yanina A, Kotsias Basilio A
Instituto de Investigaciones Médicas Alfredo Lanari, Facultad de Medicina, UBA, Buenos Aires and Universidad Maimónides, Buenos Aires, Argentina.
J Exp Zool A Comp Exp Biol. 2003 Jun 1;297(2):130-7. doi: 10.1002/jez.a.10237.
In this study, two electrode voltage clamp technique was used to assess the ionic current of oocytes of the South American toad Bufo arenarum and to study the dependence of these currents on the extracellular and intracellular Ca2+ concentrations. Ca2+ chelators, ionomycin -a calcium ionophore- and thapsigargin, a blocker of the Ca2+ pump of the sarcoplasmic reticulum, were used. The main results were the following: Most oocytes showed a voltage activated rectifying conductance. Ionomycin (1 microM) increased inward and outward currents in control solution. The effect of ionomycin was blocked partially at negative potentials and was blocked completely at positive potentials in absence of extracellular Ca2+. When the oocytes were treated with thapsigargin (2 microM) or BAPTA-am, a membrane-permeant intracellular chelator in control solution (10 microM), ionomycin did not increased either inward nor outward currents. The conclusion of our experiments is that there are two sources of Ca2+ for activation of the current induced by ionomycin, the cytoplasmic stores and the extracellular space. We believe ionomycin directly translocates Ca2+ from the SER into the cytoplasm but not from the extracellular medium. Ca2+ entry probably occurs through store-operated-Ca-channels.
在本研究中，采用双电极电压钳技术评估南美蟾蜍（Bufo arenarum）卵母细胞的离子电流，并研究这些电流对细胞外和细胞内Ca2+浓度的依赖性。使用了Ca2+螯合剂、离子霉素（一种钙离子载体）和毒胡萝卜素（肌浆网Ca2+泵的阻滞剂）。主要结果如下：大多数卵母细胞表现出电压激活的整流电导。离子霉素（1微摩尔）在对照溶液中增加内向和外向电流。在无细胞外Ca2+时，离子霉素的作用在负电位时部分被阻断，在正电位时完全被阻断。当用毒胡萝卜素（2微摩尔）或BAPTA-am（对照溶液中一种可透过膜的细胞内螯合剂，10微摩尔）处理卵母细胞时，离子霉素既不增加内向电流也不增加外向电流。我们实验的结论是，离子霉素诱导的电流激活有两个Ca2+来源，即细胞质储存库和细胞外空间。我们认为离子霉素直接将Ca2+从肌浆网转运到细胞质中，而不是从细胞外介质转运。Ca2+进入可能通过储存操纵性Ca通道发生。
