Lester H A, Koblin D D, Sheridan R E
Biophys J. 1978 Mar;21(3):181-94. doi: 10.1016/S0006-3495(78)85518-0.
This paper compares the conductance induced by bath-applied acetyl-choline (ACh) and by the same transmitter released from nerve terminals at Electrophorus electroplaques. For the former case, dose-response relations are characterized by the maximal agonist-induced conductance, rgamma (130 mmho/cm2), and by the concentration which induces half this conductance; this concentration is termed Kapp and equals 50 micron at -85 mV. For the latter case, neurally evoked postsynaptic currents (PSCs) are characterized by the peak conductance during strongly facilitated release, gPSC, and by the rate constant for decay, alpha. Since gPSC roughly equals rgamma, it is concluded that the PSC activates nearly all available receptor channels. These and other data agree with recent estimates that during the growth phase of the quantal response, (a) the ACh concentration is at least several hundred micromolar; and (b) most nearby channels are activated. However both alpha and Kapp increase during depolarization, at a rate of about e-fold per 86 mV. These observations on voltage sensitivity suggest that a suprathreshold synaptic event is rapidly terminated because the action potential abruptly releases ACh molecules from receptors.
本文比较了在电鳗电板上，由浴槽施加乙酰胆碱（ACh）以及由神经末梢释放相同递质所诱导的电导。对于前一种情况，剂量 - 反应关系的特征在于最大激动剂诱导的电导rgamma（130 毫西门子/平方厘米）以及诱导该电导一半时的浓度；此浓度称为Kapp，在 -85 mV时等于50 微摩尔。对于后一种情况，神经诱发的突触后电流（PSC）的特征在于强易化释放期间的峰值电导gPSC以及衰减速率常数alpha。由于gPSC大致等于rgamma，因此得出结论，PSC激活了几乎所有可用的受体通道。这些以及其他数据与最近的估计一致，即在量子反应的增长阶段，（a）ACh浓度至少为几百微摩尔；并且（b）大多数附近的通道被激活。然而，alpha和Kapp在去极化期间都会增加，速率约为每86 mV增加一倍。这些关于电压敏感性的观察结果表明，阈上突触事件会迅速终止，因为动作电位会突然将ACh分子从受体上释放下来。
