Weber W M, Liebold K M, Reifarth F W, Clauss W
Institut für Tierphysiologie, Jusois-Liebig-Universităt, Giessen, FRG.
J Membr Biol. 1995 Dec;148(3):263-75. doi: 10.1007/BF00235044.
Defolliculated oocytes of Xenopus laevis responded to removal of external divalent cations with large depolarizations and, when voltage clamped, with huge currents. Single channel analysis revealed a Cl- channel with a slope conductance of about 90 pS at positive membrane potentials with at least four substates. Single channel amplitudes and mean channel currents had a reversal potential of approximately -15 mV as predicted by the Nernst equation for a channel perfectly selective for Cl-. Readdition of Ca2+ immediately inactivated the channel and restored the former membrane potential or clamp current. The inward currents were mediated by a Ca2+ inactivated Cl- channel (CaIC). The inhibitory potency of Ca2+ was a function of the external Ca2+ concentration with a half maximal blocker concentration of about 20 microM. These channels were inhibited by the Cl- channel blockers flufenamic acid, niflumic acid and diphenylamine-2-carboxylate (DPC). In contrast, 4,4'-acetamido-4'-isothiocyanatostilbene-2, 2'-disulfonicacid (SITS), another Cl- channel blocker, led to activation of this Cl- channel. Like other Cl- channels, the CaIC was activated by cytosolic cAMP. Extracellular ATP inhibited the channel while ADP was without any effect. Injection of phorbol 12-myristate 13-acetate (PMA), a protein kinase C activating phorbol ester, stimulated the Cl- current. Cytochalasin D, an actin filament disrupting compound, reversibly decreased the clamp current demonstrating an influence of the cytoskeleton. The results indicate that removal of divalent cations activates Cl- channels in Xenopus oocytes which share several features with Cl- channels of the CLC family. The former so-called leak current of oocytes under divalent cation-free conditions is nothing else than an activation of Cl- channels.
非洲爪蟾去滤泡卵母细胞在去除细胞外二价阳离子时会出现大幅度去极化，在进行电压钳制时会产生巨大电流。单通道分析显示，在正膜电位下有一个斜率电导约为90 pS的氯离子通道，至少有四个亚状态。单通道幅度和平均通道电流的反转电位约为 -15 mV，这与能斯特方程预测的对氯离子具有完美选择性的通道一致。重新加入Ca2+会立即使通道失活，并恢复先前的膜电位或钳制电流。内向电流由Ca2+失活的氯离子通道（CaIC）介导。Ca2+的抑制效力是细胞外Ca2+浓度的函数，半数最大阻断浓度约为20 microM。这些通道被氯离子通道阻滞剂氟芬那酸、尼氟酸和二苯胺 -2-羧酸盐（DPC）抑制。相比之下，另一种氯离子通道阻滞剂4,4'-乙酰氨基-4'-异硫氰酸根合芪-2,2'-二磺酸（SITS）会导致该氯离子通道激活。与其他氯离子通道一样，CaIC被胞质cAMP激活。细胞外ATP抑制该通道，而ADP则无任何作用。注射佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA），一种激活蛋白激酶C的佛波醇酯，会刺激氯离子电流。细胞松弛素D是一种破坏肌动蛋白丝的化合物，可使钳制电流可逆性降低，表明细胞骨架有影响。结果表明，去除二价阳离子会激活非洲爪蟾卵母细胞中的氯离子通道，这些通道与CLC家族的氯离子通道有几个共同特征。在无二价阳离子条件下，卵母细胞先前所谓的漏电流只不过是氯离子通道的激活。
