Santafé M M, Garcia N, Lanuza M A, Uchitel O D, Tomás J
Unitat d'Histologia i Neurobiologia (UHN), Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, carrer St. Llorenç num 21, 43201, Reus, Spain.
Neuroscience. 2001;102(3):697-708. doi: 10.1016/s0306-4522(00)00507-8.
We studied the effect of several calcium channel blockers (omega-Conotoxin-GVIA, 1 and 3microM; omega-Agatoxin-IVA, 100nM; Nitrendipine, 1 and 10microM) on evoked transmitter release at singly and dually innervated endplates of the levator auris longus muscle from three- to six-day-old rats. In dually innervated fibers, a second endplate potential may appear after the first one when we increase the stimulation intensity. The lowest and highest endplate potential amplitudes are designated "small endplate potential" and "large endplate potential", respectively. The percentage of doubly innervated junctions remains almost constant throughout the age range examined. Nevertheless, the percentage of junctions innervated by three or more terminal axons drops, whereas the singly innervated junctions increase. Therefore, between postnatal days 3 and 6, roughly half the neuromuscular junctions may experience the final process of axonal elimination. The synaptic efficacy of the large endplate potential in dual junctions, measured as the mean amplitude of the synaptic potential and mean quantal content, was the same as in the junctions that had become recently mono-innervated in the same postnatal period. In singly innervated fibers, the endplate potential size was strongly reduced by both the P/Q-type voltage-dependent calcium channel blocker omega-Agatoxin-IVA (79.17+/-4.02%; P < 0.05) and the N-type voltage-dependent calcium channel blocker omega-Conotoxin-GVIA (56.31+/-7.80%; P < 0.05), whereas endplate potential amplitude was not significantly changed by the L-type voltage-dependent calcium channel blocker Nitrendipine. In dually innervated fibers, the P/Q-type voltage-dependent calcium channel blocker omega-Agatoxin-IVA and L-type voltage-dependent calcium channel blocker Nitrendipine increased the size of the small endplate potential (161.29+/-47.87% and 109.32+/-11.03%, respectively; P < 0.05 in both cases) and reduced the large endplate potential (74.42+/-15.32% and 70.91+/-10.04%, respectively; P < 0.05 in both cases). The N-type voltage-dependent calcium channel blocker omega-Conotoxin-GVIA significantly increased the small endplate potential in the first few minutes after toxin application (at 10min: 90.23+/-17.38%; P < 0.05). This increase was not maintained, while the large endplate potential was strongly inhibited (69.25+/-7.5%; P < 0.05). In conclusion, in the dually innervated endplates of the newborn rat, presynaptic calcium channel types can have different roles in transmitter release from each of the two inputs, which suggests that nerve terminal voltage-dependent calcium channels are involved in neonatal synaptic maturation.
我们研究了几种钙通道阻滞剂（ω-芋螺毒素-GVIA，1和3微摩尔；ω-阿加毒素-IVA，100纳摩尔；尼群地平，1和10微摩尔）对3至6日龄大鼠镫骨长肌单重和双重支配终板诱发性递质释放的影响。在双重支配的纤维中，当我们增加刺激强度时，第一个终板电位之后可能会出现第二个终板电位。最低和最高终板电位幅度分别被称为“小终板电位”和“大终板电位”。在整个检查的年龄范围内，双重支配连接的百分比几乎保持不变。然而，由三个或更多终末轴突支配的连接百分比下降，而单重支配的连接增加。因此，在出生后第3天至第6天之间，大约一半的神经肌肉接头可能经历轴突消除的最终过程。双重连接中，以突触电位的平均幅度和平均量子含量衡量的大终板电位的突触效能，与在同一出生后时期最近变为单重支配的连接中的相同。在单重支配的纤维中，P/Q型电压依赖性钙通道阻滞剂ω-阿加毒素-IVA（79.17±4.02%；P<0.05）和N型电压依赖性钙通道阻滞剂ω-芋螺毒素-GVIA（56.31±7.80%；P<0.05）均显著降低终板电位大小，而L型电压依赖性钙通道阻滞剂尼群地平对终板电位幅度无显著影响。在双重支配的纤维中，P/Q型电压依赖性钙通道阻滞剂ω-阿加毒素-IVA和L型电压依赖性钙通道阻滞剂尼群地平增加了小终板电位的大小（分别为161.29±47.87%和109.32±11.03%；两种情况均P<0.05），并降低了大终板电位（分别为74.42±15.32%和70.91±10.04%；两种情况均P<0.05）。N型电压依赖性钙通道阻滞剂ω-芋螺毒素-GVIA在毒素应用后的最初几分钟内显著增加了小终板电位（10分钟时：90.23±17.38%；P<0.05）。这种增加没有持续，而大终板电位受到强烈抑制（69.25±7.5%；P<0.05）。总之，在新生大鼠的双重支配终板中，突触前钙通道类型在来自两个输入中每个输入的递质释放中可能具有不同作用，这表明神经末梢电压依赖性钙通道参与新生儿突触成熟。
