Photo-released intracellular Ca2+ rapidly blocks Ba2+ current in Lymnaea neurons.
Photo-released intracellular Ca2+ rapidly blocks Ba2+ current in Lymnaea neurons.
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光释放的细胞内 Ca2 快速阻断 Lymnaea 神经元中的 Ba2 电流。
DOI：
10.1113/jphysiol.1993.sp019558
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Byerly,L
中科院分区：
文献类型：
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作者：
Johnson,BD;Byerly,L
1. 使用全细胞膜片钳技术对来自停滞蜗牛的分离神经元研究了细胞内 Ca2+ 对流经电压依赖性 Ca2+ 通道的 Ba2+ 电流的影响。通过笼状 Ca2+ 化合物 DM-硝基酚的闪光光解增加细胞内 Ca2+，并用光学指示剂 Fluo-3 进行测量。 2. 最高强度闪光后，峰值 Ba2+ 电流被阻断 42%，时间常数为 5 ms。无论通道是激活还是关闭，阻塞的发生都遵循相似的时间过程。闪光后残留的 Ba2+ 电流与闪光前的总 Ba2+ 电流具有相同的激活电压依赖性和失活速率。 3. Ba2+ 电流从块中恢复几乎完全，并且恢复时间常数为 16 s。当闪光之间间隔 7-10 分钟时，可以在同一细胞中研究光解诱导阻断的多次发作。在一些细胞中，从阻断恢复伴随着电流短暂增强至高于阻断前的幅度。 4. 神经元通过在施加闪光之前卸载 DM-硝基酚以及快速缓冲光解释放的 Ca2+，大大降低了光解增加 Ca2+ 的能力。 DM-Ca2+ 溶液细胞外液滴的最大闪光使 Ca2+ 从 110 nM 跃升至 40 µM。相比之下，负载 DM-Ca(2+) 的神经元上的相同闪光导致 Ca2+ 瞬态从 36 nM 的基线开始到 130 nM 的峰值。这种细胞内 Ca2+ 瞬变以三个时间常数（120 ms、2 s 和 13 s）衰减。 5. 内源缓冲液快速结合 Ca2+。当在闪光 2 ms 内监测细胞内 Ca2+ 时，无法检测到由于光释放 Ca2+ 结合而导致的快速 Ca2+ 峰值。在细胞内溶液中添加二溴-BAPTA 可使阻滞减少三分之一，这与测量的细胞内 Ca2+ 减少一致。这表明内源缓冲液可以与二溴-BAPTA 一样快地结合 Ca2+，并且与光解释放 Ca2+ 一样快。 6. 通过改变闪光强度获得的块的 Ca2+ 依赖性表明 130 nM 存在一定程度的饱和。与阻断和恢复的时间过程以及浓度依赖性一致的简单双态阻断模型给出了大约 50 nM 的解离常数和 7 x 10(8) M-1 s-1 的正向速率常数。（摘要截断为 400 字）
1. The effect of intracellular Ca2+ on Ba2+ current flowing through voltage‐dependent Ca2+ channels was studied using the whole‐cell patch‐clamp technique on isolated neurons from the snail Lymnaea stagnalis. Intracellular Ca2+ was increased by flash photolysis of the caged Ca2+ compound DM‐nitrophen and measured with the optical indicator fluo‐3. 2. After the highest intensity flashes, peak Ba2+ current was blocked by 42% with a time constant of 5 ms. The onset of the block followed a similar time course whether channels were activated or closed. The Ba2+ current surviving after the flash had the same voltage dependence of activation and rate of inactivation as did the total Ba2+ current before the flash. 3. Recovery of the Ba2+ current from block was nearly complete and occurred with a time constant of 16 s. Multiple episodes of photolysis‐induced block could be studied in the same cell when 7‐10 min were allowed between flashes. In some cells, recovery from block was accompanied by a transient enhancement of the current above the pre‐block magnitude. 4. Neurons greatly reduced the ability of photolysis to increase Ca2+, both by unloading the DM‐nitrophen before flashes were applied and by rapidly buffering the photolytically released Ca2+. Maximal flashes on extracellular droplets of the DM‐Ca2+ solution created a Ca2+ jump from 110 nM to 40 microM. In contrast, the same flashes on DM‐Ca(2+)‐loaded neurons resulted in a Ca2+ transient starting from a baseline of 36 nM to a peak of 130 nM. This intracellular Ca2+ transient decayed with three time constants (120 ms, 2 s and 13 s). 5. Endogenous buffer(s) binds Ca2+ rapidly. When intracellular Ca2+ was monitored within 2 ms of the flash, no rapid Ca2+ spike due to binding of photo‐released Ca2+ could be detected. Addition of dibromo‐BAPTA to the intracellular solution reduced the block by one third, which is consistent with the measured reduction of intracellular Ca2+. This indicates that the endogenous buffer can bind Ca2+ as rapidly as dibromo‐BAPTA and as fast as Ca2+ is released by photolysis. 6. The Ca2+ dependence of the block, obtained by varying flash intensity, indicates some saturation by 130 nM. A simple two‐state model of the block consistent with both the time course of block and recovery and the concentration dependence gave a dissociation constant of approximately 50 nM and forward rate constant of 7 x 10(8) M‐1 s‐1.(ABSTRACT TRUNCATED AT 400 WORDS)