A fast‐activated inward calcium current in twitch muscle fibres of the frog (Rana montezume).
A fast‐activated inward calcium current in twitch muscle fibres of the frog (Rana montezume).
复制标题
青蛙（Rana montezume）抽搐肌纤维中快速激活的内向钙电流。
DOI：
--
复制
发表时间：
1986
期刊：
影响因子：
--
通讯作者：
E. STEFANIt
中科院分区：
文献类型：
--
作者：
Byg . Cota;E. STEFANIt
使用三微电极技术在 18 摄氏度下对青蛙完整的抽搐肌纤维进行电压钳实验。在 120 mM-四乙基甲磺酸铵和 10 mM-Ca2+ 存在下记录膜电流。通过添加 350 mM 蔗糖使记录溶液处于高渗状态以避免收缩。观察到在没有外部 Na+ 的情况下内向电流的两个分量。除了众所周知的缓慢、瞬态 Ca2+ 电流 (ICa,s) 之外，去极化还会引起快速激活的小幅度内向电流。内向电流的两种成分在河豚毒素存在的情况下持续存在。当用 Mg2+ 替代外部 Ca2+ 时，它们实际上消失了，并且通过向镀液中添加毫摩尔 Cd2+ 来阻止它们。因此，内向电流的快速激活成分也由 Ca2+ (ICa,f) 携带。 5 microM-地尔硫卓均不会降低 ICa,f 和 ICa,s。在 400 ms 去极化期间，检测到 ICa,f 约为 ‐60 mV，比 ICa,s 出现时的膜电位负 30 mV。在约 0 mV 时，ICa 的激活时间常数为 5 ms，ICa,s 的激活时间常数为 150 ms。在膜电位介于 ‐60 和 ‐30 mV 之间的去极化持续时间长达 2 秒期间，ICa,f 没有显着下降。 ICa,f 随着暴露于高渗记录溶液的时间而趋于消失。其最大振幅从前 5 分钟内的约 ‐25 microA/cm2 降至 25 分钟后的约 ‐5 microA/cm2，而 ICa.s 实际上保持不变（最大峰值振幅约为 ‐60 microA/cm2）。这些结果表明完整肌纤维中存在两种类型的电压依赖性 CA2+ 通道。快速激活的 Ca2+ 通道的动力学特性表明它们在单次抽搐期间显着激活。
Voltage‐clamp experiments were performed at 18 degrees C in intact twitch muscle fibres of the frog using the three micro‐electrode technique. Membrane currents were recorded in the presence of 120 mM‐tetraethylammonium‐methanesulphonate and 10 mM‐Ca2+. The recording solution was made hypertonic by adding 350 mM‐sucrose to avoid contraction. Two components of inward current in the absence of external Na+ were observed. Depolarization induced a fast‐activated inward current of small amplitude in addition to the well‐known slow, transient Ca2+ current (ICa,s). Both components of inward current persisted in the presence of tetrodotoxin. They practically disappeared on replacing external Ca2+ with Mg2+ and were blocked by millimolar additions of Cd2+ to the bath. Thus, the fast‐activated component of inward current was also carried by Ca2+ (ICa,f). Neither ICa,f nor ICa,s were reduced by 5 microM‐diltiazem. During 400 ms depolarizations ICa,f was detected at approximately ‐60 mV, 30 mV more negative than the membrane potentials at which ICa,s appeared. At about 0 mV the time constant for activation was 5 ms for ICa and 150 ms for ICa,s. ICa,f did not significantly decline during depolarizations up to 2s in duration at membrane potentials between ‐60 and ‐30 mV. ICa,f tended to disappear as a function of time on exposure to the hypertonic recording solution. Its maximum amplitude decreased from about ‐25 microA/cm2 during the first 5 min to about ‐5 microA/cm2 after 25 min while ICa.s remained practically unchanged (maximum peak amplitude of about ‐60 microA/cm2). These results indicate the existence of two types of voltage‐dependent CA2+ channels in intact muscle fibres. The kinetic properties of fast‐activated Ca2+ channels suggest that they significantly activate during a single twitch.
DOI：
10.1126/science.7053577
发表时间：
1982
期刊：
Science (New York, N.Y.)
影响因子：
--
作者：
Bianchi,CP;Narayan,S
通讯作者：
Narayan,S