Dudel J
Physiologisches Institut, Technischen Universität München, Munich, F.R.G.
Neurosci Lett. 1990 Aug 14;116(1-2):94-100. doi: 10.1016/0304-3940(90)90392-m.
Quantal synaptic currents were recorded by means of a macro-patch-clamp electrode, through which the terminal could be also depolarized by current pulses. The tip of the electrode was perfused rapidly, applying either Ringer's solution or an EGTA-buffered less than 0.1 microM Ca Ringer's. Muscle and nerve outside the electrode were superfused with normal or 10 mM Ca Ringer which served to keep the resting intracellular Ca concentration, Cair, in the terminal below the electrode relatively high. When Ca inflow was prevented by decreasing the Ca concentration to less than 0.1 microM, release was depressed, but still measurable, for low depolarizations, and much less or not at all depressed for large depolarizations to positive membrane potentials. The time course of the depressed release without Ca-inflow was the same as that in the controls with Ca inflow. It appears that the voltage dependent activator proposed in the Ca-voltage theory of release can elicit maximal release in the absence of Ca inflow, provided Cair is sufficiently high. The voltage dependencies of this activator as well as that of Ca inflow can be estimated from the results.
通过宏膜片钳电极记录量子突触电流，通过该电极，终末也可通过电流脉冲去极化。电极尖端快速灌注，应用任氏液或EGTA缓冲的低于0.1微摩尔/升钙离子的任氏液。电极外的肌肉和神经用正常的或10毫摩尔/升钙离子的任氏液进行灌流，以使终末内低于电极的静息细胞内钙离子浓度（Cair）相对较高。当通过将钙离子浓度降低至低于0.1微摩尔/升来阻止钙离子内流时，释放受到抑制，但对于低去极化仍可测量，而对于向正膜电位的大去极化，释放受到的抑制则小得多或根本没有受到抑制。无钙离子内流时释放受抑制的时间进程与有钙离子内流的对照相同。似乎在钙离子-电压释放理论中提出的电压依赖性激活剂在无钙离子内流的情况下，只要Cair足够高，就可引发最大释放。该激活剂以及钙离子内流的电压依赖性可从结果中估计出来。
