Lin J W, Rudy B, Llinás R
Department of Physiology and Biophysics, New York University Medical Center, NY 10016.
Proc Natl Acad Sci U S A. 1990 Jun;87(12):4538-42. doi: 10.1073/pnas.87.12.4538.
Injection of rat brain mRNA into Xenopus oocytes has been shown to induce a calcium current (ICa) that is insensitive to dihydropyridine and omega-conotoxin. We examined the effect of funnel-web spider venom on two aspects of this expressed ICa: (i) the calcium-activated chloride current [ICl(Ca)] and (ii) the currents carried by barium ions through calcium channels (IBa). In the presence of 1.8 mM extracellular calcium, ICl(Ca) tail current became detectable between -30 and -40 mV from a holding potential of -80 mV and reached a maximal amplitude between 0 and +10 mV. Total spider venom partially (83%) and reversibly blocked the calcium-activated chloride current without changing its voltage sensitivity. A chromatographic toxin fraction from the venom also blocked this current (64%). The venom had a minimal effect on INa and IK. Direct investigation of inward current mediated by calcium channels was carried out in high-barium solution. IBa had a higher threshold of activation (-30 to -20 mV) and reached its maximal amplitude at about +20 mV. Total venom or a partly purified chromatographic toxic fraction blocked IBa partially and reversibly without changing its current-voltage characteristics. Furthermore, the extent of the total venom block depended on the concentration of extracellular barium. Only 35% of the IBa was blocked in 60 mM Ba2+, whereas the block increased to 65% and 71%, respectively, for 40 and 20 mM Ba2+. On the basis of these results, we propose that the calcium channels expressed from rat brain mRNA in Xenopus oocytes is similar to the recently discovered P-type channels.
已证明将大鼠脑信使核糖核酸注射到非洲爪蟾卵母细胞中可诱导出一种对二氢吡啶和ω-芋螺毒素不敏感的钙电流（ICa）。我们研究了漏斗网蜘蛛毒液对这种表达的ICa的两个方面的影响：（i）钙激活氯电流[ICl（Ca）]和（ii）钡离子通过钙通道携带的电流（IBa）。在存在1.8 mM细胞外钙的情况下，从 -80 mV的钳制电位开始，在 -30至 -40 mV之间可检测到ICl（Ca）尾电流，并在0至 +10 mV之间达到最大幅度。总蜘蛛毒液部分（83%）且可逆地阻断了钙激活氯电流，而不改变其电压敏感性。毒液的一种色谱毒素组分也阻断了这种电流（64%）。毒液对INa和IK的影响最小。在高钡溶液中对由钙通道介导的内向电流进行了直接研究。IBa具有较高的激活阈值（-30至 -20 mV），并在约 +20 mV时达到其最大幅度。总毒液或部分纯化的色谱毒性组分部分且可逆地阻断了IBa，但不改变其电流 - 电压特性。此外，总毒液阻断的程度取决于细胞外钡的浓度。在60 mM Ba2+中，只有35%的IBa被阻断，而对于40 mM和20 mM Ba2+，阻断分别增加到65%和71%。基于这些结果，我们提出在非洲爪蟾卵母细胞中由大鼠脑信使核糖核酸表达的钙通道类似于最近发现的P型通道。
