Dudel J, Parnas H, Parnas I
Physiologisches Institut, Technischen Universität München, Federal Republic of Germany.
Pflugers Arch. 1991 Sep;419(2):197-204. doi: 10.1007/BF00373007.
Cutaneous pectoris muscles of frogs were isolated, mounted in a chamber and superfused with Ringer's solution. With a macro-patch-clamp electrode placed on a section of a motor nerve terminal, quantal synaptic currents were elicited by depolarizing pulses and recorded. The electrode tip and the section of the terminal recorded from were perfused rapidly by Ringer's solution alone or containing 20-500 microM Cd2+ to block Ca2+ inflow. Separate superfusion of the muscle and the rest of the terminal with normal or elevated Ca2+ Ringer's solution provided a sufficiently high resting Ca2+ concentration in the terminal even when Ca2+ was blocked by Cd2+. The depolarization level of maximal Ca2+ inflow into the terminal was found by measuring maximal test pulse facilitation, Fc. In control solution as well as in the case of Cd2+ block, the rate of phasic release after depolarizing pulses rose further when depolarization was increased past the level of Fc, and reached a saturation level which was maintained at estimated depolarizations up to +200 mV. Block of Ca2+ inflow by Cd2+ decreased release substantially, but did not suppress it. The depression of release was greater in the range of large Ca2+ inflow (around Fc) than for very large depolarizations. The time course of phasic release was unaltered by blockage of Ca2+ inflow. It is concluded that Ca2+ inflow contributes to the promotion of evoked release only in the depolarization range in which Ca2+ inward current is large.(ABSTRACT TRUNCATED AT 250 WORDS)
分离青蛙的胸皮肌，置于腔室中并用任氏液灌流。将一个宏膜片钳电极置于运动神经末梢的一段上，通过去极化脉冲诱发量子突触电流并进行记录。电极尖端和记录的末梢部分单独用任氏液或含有20 - 500微摩尔/升Cd²⁺的任氏液快速灌流，以阻断Ca²⁺内流。用正常或升高Ca²⁺浓度的任氏液分别灌流肌肉和末梢的其余部分，即使Ca²⁺被Cd²⁺阻断，也能在末梢中提供足够高的静息Ca²⁺浓度。通过测量最大测试脉冲易化作用Fc来确定最大Ca²⁺流入末梢时的去极化水平。在对照溶液以及Cd²⁺阻断的情况下，当去极化超过Fc水平时，去极化脉冲后的相位释放速率进一步上升，并达到一个饱和水平，在估计的高达+200毫伏的去极化时保持不变。Cd²⁺阻断Ca²⁺内流使释放大幅减少，但并未完全抑制。在大Ca²⁺内流范围（约Fc）内释放的抑制比在非常大的去极化时更大。Ca²⁺内流的阻断未改变相位释放的时间进程。结论是，Ca²⁺内流仅在Ca²⁺内向电流较大的去极化范围内促进诱发释放。（摘要截短为250字）
