Bossu J L, Feltz A
J Physiol. 1986 Jul;376:341-57. doi: 10.1113/jphysiol.1986.sp016157.
In rat cranial sensory neurones a transient Ca current (iCa,t) is elicited by depolarizing the membrane potential from -80 mV to beyond -50 mV. In this paper the characteristics of the slow and fast inactivation processes of this current are described. Recordings were obtained in whole-cell clamp conditions from Cs-loaded cells. For most experiments, cells were dialysed at an internal pCa of 8, and Na and K currents were eliminated using a choline chloride- and K-free external medium containing 5 mM-Ca and 2 mM-Mg. The decay of iCa,t could be approximately fitted by a single exponential with a voltage-dependent time constant which decreased from about 150 ms at -50 mV to about 25 ms at -20 mV. This suggests a single process of inactivation but a detailed kinetic analysis of the onset and the offset of the inactivation revealed biphasic processes. The onset of inactivation displays two exponential phases. The fast phase lasts for 100-500 ms, and the slow phase lasts for a few seconds. The relative amplitude and the time constants of each phase vary with the inactivating potential. The recovery from inactivation is also biphasic, with either a fast or a slow component predominating, depending on whether a short- (some hundreds of milli-seconds) or a long- (in the order of tens of seconds) inactivating pulse has been used. At -80 mV, after a 300 ms inactivating pulse, responses recover to at least 40% of maximum within 200 ms and recovery is complete within 1 s; after a long predepolarization (10-20 s), recovery takes 4-5 s. Fast recovery was observed best after large but brief depolarizations and slow recovery was observed best following long inactivating pre-pulses of small amplitude. The voltage-dependence of slow and fast inactivation was determined by realizing inactivation curves. Fast inactivation developed between -60 and -20 mV while the slow process occurred at more hyperpolarized potentials, e.g. at -75 to -50 mV. Fast inactivation was not altered by the entry of Ca during the previous activation of the channel. Further, decay of iCa,t was not modified when Ba was substituted for Ca or the internal pCa was decreased. These are indications of a uniquely voltage-dependent process. A possible role of Ca entry in slow inactivation is discussed.(ABSTRACT TRUNCATED AT 400 WORDS)
在大鼠颅感觉神经元中，通过将膜电位从 -80 mV 去极化至 -50 mV 以上可诱发瞬时钙电流（iCa,t）。本文描述了该电流的慢失活和快失活过程的特征。记录是在全细胞钳制条件下从铯负载细胞中获得的。在大多数实验中，细胞在内部 pCa 为 8 的情况下进行透析，并且使用含有 5 mM 钙和 2 mM 镁的氯化胆碱和无钾的外部培养基消除钠电流和钾电流。iCa,t 的衰减大约可以用一个具有电压依赖性时间常数的单指数函数拟合，该时间常数从 -50 mV 时的约 150 ms 降至 -20 mV 时的约 25 ms。这表明存在单一的失活过程，但对失活起始和终止的详细动力学分析揭示了双相过程。失活的起始呈现两个指数阶段。快速阶段持续 100 - 500 ms，慢速阶段持续几秒。每个阶段的相对幅度和时间常数随失活电位而变化。从失活状态恢复也是双相的，快速或慢速成分占主导，这取决于使用的是短的（几百毫秒）还是长的（几十秒量级）失活脉冲。在 -80 mV 时，经过 300 ms 的失活脉冲后，响应在 200 ms 内恢复到至少最大值的 40%，并且在 1 s 内恢复完成；经过长时间预去极化（10 - 20 s）后，恢复需要 4 - 5 s。在大的但短暂的去极化后最容易观察到快速恢复，而在小幅度的长时间失活预脉冲后最容易观察到慢速恢复。通过绘制失活曲线确定了慢失活和快失活的电压依赖性。快失活在 -60 至 -20 mV 之间发展，而慢过程发生在更超极化的电位，例如在 -75 至 -50 mV。在通道先前激活期间钙的进入不会改变快失活。此外，当用钡替代钙或降低内部 pCa 时，iCa,t 的衰减没有改变。这些表明这是一个独特的电压依赖性过程。本文还讨论了钙进入在慢失活中的可能作用。（摘要截短至400字）
