CALCIUM CURRENTS IN EMBRYONIC AND NEONATAL MAMMALIAN SKELETAL-MUSCLE
CALCIUM CURRENTS IN EMBRYONIC AND NEONATAL MAMMALIAN SKELETAL-MUSCLE
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DOI：
10.1085/jgp.91.6.781
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发表时间：
1988-06-01
影响因子：
3.8
通讯作者：
KNUDSON, CM
中科院分区：
文献类型：
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作者：
BEAM, KG;KNUDSON, CM
全细胞膜片钳技术用于研究在大鼠和小鼠骨骼肌管的原代培养物以及大鼠指短屈肌的新鲜分离纤维中发现的内向离子电流的特性。在每种细胞类型中，从保持电位（-80 或 -90 mV）进行去极化测试会引发三种不同的内向电流：钠电流 (INa) 和两种钙电流。 INa 是主要的内向电流：在生理条件下，估计最大内向 INa 至少比任一钙电流大 30 倍。两种钙电流被称为 Ifast 和 Islow，对应于它们的相对激活速率。 Ifast 通过测试去极化至约 -40 mV 及以上而被激活，在 10-20 ms 内达到峰值，并在 50-100 ms 内衰减至基线。 Islow 通过去极化至 .apprx 被激活。 0 mV 及以上，在 50-150 ms 内达到峰值，在 200 ms 测试脉冲期间衰减很小。 Ifast 因短暂、中等的去极化而失活；对于保持电位 1 秒的变化，在 -55 至 -45 mV 时发生半失活，在 -40 至 -30 mV 时发生完全失活。持有潜力的类似变化对伊斯洛没有影响。然而，Islow 会被短暂的强去极化（例如 0 mV 持续 2 秒）或维持的中度去极化（例如 40 mV 持续 60 秒）灭活。用钡替代钙对 Ifast 或 Islow 的幅度或时间进程几乎没有影响。相同的替换改变了 Islow .apprx 的激活曲线。超极化方向 10 mV，不影响 Ifast 的激活。在低浓度（50μM）下，与Ifast相比，镉优先阻断Islow，而在高浓度（1mM）下，它完全阻断Ifast和Islow。二氢吡啶钙通道拮抗剂(+)-PN 200-110(1μM)几乎完全阻断Islow而不影响Ifast。在-80mV的保持电位下，(+)-PN 200-110对Islow的阻断的半最大阻断浓度(K0.5)是182nM。在去极化保持电位下，Islow 失活 35-65%，K0.5 降至 5.5 nM。
The whole-cell patch-clamp technique was used to study the properties of inward ionic currents found in primary cultures of rat and mouse skeletal myotubes and in freshly dissociated fibers of the flexor digitorum brevis muscle of rats. In each of these cell types, test depolarizations from the holding potential (-80 or -90 mV) elicited three distinct inward currents: a sodium current (INa) and two calcium currents. INa was the dominant inward current: under physiological conditions, the maximum inward INa was estimated to be at least 30-fold larger than either of the calcium currents. The two calcium currents have been termed Ifast and Islow, corresponding to their relative rates of activation. Ifast was activated by test depolarizations to around -40 mV and above, peaked in 10-20 ms, and decayed to baseline in 50-100 ms. Islow was activated by depolarizations to .apprx. 0 mV and above, peaked in 50-150 ms, and decayed little during a 200-ms test pulse. Ifast was inactivated by brief, moderate depolarizations; for a 1-s change in holding potential, half-inactivation occurred at -55 to -45 mV and complete inactivation occurred at -40 to -30 mV. Similar changes in holding potential had no effect on Islow. Islow was, however, inactivated by brief, strong depolarizations (e.g., 0 mV for 2 s) or maintained, moderate depolarizations (e.g.,- 40 mV for 60 s). Substitution of barium for calcium had little effect on the magnitude or time course of either Ifast or Islow. The same substitution shifted the activation curve for Islow .apprx. 10 mV in the hyperpolarizing direction without affecting the activation of Ifast. At low concentrations (50 .mu.M), cadmium preferentially blocked Islow compared with Ifast, while at high concentrations (1 mM), it blocked both Ifast and Islow completely. The dihydropyridine calcium channel antagonist (+)-PN 200-110 (1 .mu.M) caused a nearly complete block of Islow without affecting Ifast. At a holding potential of -80mV, the half maximal blocking concentration (K0.5) for the block of Islow by (+)-PN 200-110 was 182 nM. At depolarized holding potentials that inactivated Islow by 35-65% K0.5 decreased to 5.5 nM.