Vautrin J, Kriebel M E
Department of Physiology, State University of New York Health Sciences Center, Syracuse 13210.
Can J Physiol Pharmacol. 1993 Feb;71(2):165-74. doi: 10.1139/y93-023.
Muscle fibers from diaphragms of old (14 to 24 months) and young adult (1 to 2 months) inbred (strain C57BL/6) mice were voltage clamped at -140 mV with two microelectrodes near the neuromuscular junction. Miniature endplate currents (MEPCs) were digitized so that peak amplitudes and rise times could be determined. MEPC amplitude distributions from old mice varied greatly between fibers from the same diaphragm, and the mean MEPC amplitude (2.1 +/- 0.83 nA, mean +/- SD) was smaller than in young mice (5.2 +/- 0.59 nA). In old mice, some (50%) amplitude distributions were bell shaped, composed of mainly bell-MEPCs with a 2- to 5-nA mode, whereas others (30%) were skewed with a 0.5- to 2-nA mode, and some (20%) showed two peaks, representing both skew- and bell-MEPC classes. MEPC rise-time distributions from old mice varied between fibers, although they all had similar modes. Some (30%) were bell shaped (similar to those in young mice) with a mode between 0.5 and 1 ms (coefficient of variation, 40%), but most distributions were skewed. Endplates with smaller mean MEPC amplitudes showed a longer mean rise time, and for a given junction, MEPC amplitudes were correlated positively to the corresponding rise times. This observation, together with analyses of the rising phases, indicates that MEPCs with long rise times were not generated at remote sites. We discuss our results with regard to the hypothesis of a dynamic formation of transmitter packets, and we attribute long rise time, skew-MEPCs to a prolonged release process. During aging, the state of release that generates the skew-MEPC class appears more dominant than the state generating the bell-MEPC class.
使用两个微电极在近神经肌肉接头处将14至24月龄的老年（近交系C57BL/6）小鼠和1至2月龄的年轻成年小鼠膈肌的肌纤维钳制在-140 mV电压下。对微小终板电流（MEPCs）进行数字化处理，以便确定其峰值幅度和上升时间。来自老年小鼠的MEPC幅度分布在同一膈肌的不同纤维之间差异很大，并且平均MEPC幅度（2.1±0.83 nA，平均值±标准差）小于年轻小鼠（5.2±0.59 nA）。在老年小鼠中，一些（50%）幅度分布呈钟形，主要由模式为2至5 nA的钟形MEPCs组成，而其他一些（30%）呈偏态，模式为0.5至2 nA，还有一些（20%）显示出两个峰值，代表偏态和钟形MEPCs类别。来自老年小鼠的MEPC上升时间分布在不同纤维之间有所不同，尽管它们都有相似的模式。一些（30%）呈钟形（类似于年轻小鼠），模式在0.5至1毫秒之间（变异系数为40%），但大多数分布是偏态的。平均MEPC幅度较小的终板显示出较长的平均上升时间，并且对于给定的接头，MEPC幅度与相应的上升时间呈正相关。这一观察结果，连同对上升阶段的分析，表明上升时间长的MEPCs不是在远处部位产生的。我们根据递质小泡动态形成的假说来讨论我们的结果，并且我们将长上升时间、偏态MEPCs归因于延长的释放过程。在衰老过程中，产生偏态MEPC类别的释放状态似乎比产生钟形MEPC类别的状态更占主导。
