Friedrich-Schedel-Institut für Neurowissenschaften, Biedersteinerstrasse 29, Munich, Germany.
Eur J Neurosci. 2009 Oct;30(7):1219-26. doi: 10.1111/j.1460-9568.2009.06915.x. Epub 2009 Sep 21.
In order to test whether the time courses of quantal releases after a depolarization pulse are affected by the depolarization amplitude, time courses were measured for small depolarization pulses that elicited close to threshold releases and for large depolarizations that elicited releases approaching saturation level. Diaphragms of young mice were excised and superfused with Bretag's solution at 18 degrees C. Synaptic currents were elicited and recorded through a perfused macropatch pipette. Releases elicited by threshold depolarizations rose earlier than releases elicited by saturation depolarizations. The short delays in the rising phases of release after large depolarizations may be due to the shift of Ca(2+) currents flowing during the pulse to tail currents. After its peak, release decayed with a time constant tau. For saturation depolarizations tau was about 0.3 ms, and for threshold depolarizations tau increased up to 0.8 ms. In order to differentiate between the effects of variations in Ca(2+) inflow and in depolarization, the amplitudes of large depolarization pulses were held constant while the amount of release was depressed by halving the Ca(2+) concentration at the terminal. The time course of the lowered releases was slightly delayed while tau remained at 0.3 ms as typical for saturation depolarizations. Double pulse facilitation unexpectedly revealed a short phase of depression of release after the pulse. This depression may contribute to the rapid decay (tau) of release after large depolarizations. The dependence of tau on depolarization amplitude indicates that the final phase of the time course of release is largely controlled by the amplitude of the preceding depolarization.
为了测试去极化脉冲后量子释放的时程是否受去极化幅度的影响，测量了引发接近阈释放的小去极化脉冲和引发接近饱和水平释放的大去极化脉冲的时程。年轻小鼠的膈膜在 18°C 下用 Bretag 溶液进行切除和超灌注。通过灌流大孔管电极刺激和记录突触电流。阈去极化引发的释放比饱和去极化引发的释放更早上升。大去极化后释放上升相的短延迟可能是由于脉冲期间流动的 Ca(2+)电流转移到尾电流。释放达到峰值后，以时间常数 tau 衰减。对于饱和去极化，tau 约为 0.3 ms，对于阈去极化，tau 增加到 0.8 ms。为了区分 Ca(2+)内流和去极化变化的影响，保持大去极化脉冲的幅度不变，同时通过将终末 Ca(2+)浓度减半来抑制释放量。降低释放的时程稍有延迟，而 tau 保持在 0.3 ms，与典型的饱和去极化一样。双脉冲易化出人意料地揭示了脉冲后释放的短暂抑制相。这种抑制可能有助于大去极化后释放的快速衰减（tau）。tau 对去极化幅度的依赖性表明，释放时程的最后阶段主要受前一个去极化幅度的控制。
