目前的工作,使用牛肾上腺髓质的嗜铬细胞(BCC),旨在描述铅(Pb2)诱导的哪种类型的离子电流变化是其对突触传递的影响的基础。我们观察到,当用K或乙酰胆碱刺激细胞时,Pb2的急性应用导致神经递质释放以浓度依赖性方式急剧抑制。IC50为119,57μM和5,19μM,分别。这种效果在冲洗后完全恢复。Pb2还以时间和浓度依赖性方式阻断BCC的钙通道,IC50为6,87μM。这种封锁在冲刷后被部分逆转。该化合物在所有测试电位下抑制钙电流,并显示I-V曲线向约8mV的更大负值的偏移。急性应用高浓度Pb2不会阻断钠电流。电压依赖性钾电流也很快受到高Pb2的影响。然而,钙和电压依赖性钾电流以剂量依赖性方式大幅下降,IC50为24,49μM。这种阻断与通过与Ca2激活的K通道(BK)偶联的电压依赖性钙通道防止Ca2流入有关,而不是直接连接到这些通道。在电流钳位条件下,BCC表现出-52.7mV的静息电位,激发由Na+和Ca2+通道打开产生的自发AP(1-2个尖峰/秒),并通过激活K+通道而终止。尽管Pb2+对离子通道有影响,我们发现Pb2+不会改变细胞的兴奋性,不改变膜电位,对动作电位发射没有影响。一起来看,这些结果表明Pb2+引起的神经毒性作用与通过阻断负责钙内流的离子电流而引起的神经递质释放的变化有关。
The present work, using chromaffin cells of bovine adrenal medullae (BCCs), aims to describe what type of ionic current alterations induced by lead (Pb2+) underlies its effects reported on synaptic transmission. We observed that the acute application of Pb2+ lead to a drastic depression of neurotransmitters release in a concentration-dependent manner when the cells were stimulated with both K+ or acetylcholine, with an IC50 of 119,57 μM and of 5,19 μM, respectively. This effect was fully recovered after washout. Pb2+ also blocked calcium channels of BCCs in a time- and concentration-dependent manner with an IC50 of 6,87 μM. This blockade was partially reversed upon washout. This compound inhibited the calcium current at all test potentials and shows a shift of the I-V curve to more negative values of about 8 mV. The sodium current was not blocked by acute application of high Pb2+ concentrations. Voltage-dependent potassium current was also shortly affected by high Pb2+. Nevertheless, the calcium- and voltage-dependent potassium current was drastically depressed in a dose-dependent manner, with an IC50 of 24,49 μM. This blockade was related to the prevention of Ca2+ influx through voltage-dependent calcium channels coupled to Ca2+-activated K+-channels (BK) instead a direct linking to these channels. Under current-clamp conditions, BCCs exhibit a resting potential of -52.7 mV, firing spontaneous APs (1-2 spikes/s) generated by the opening of Na+ and Ca2+-channels, and terminated by the activation of K+ channels. In spite of the effect on ionic channels exerted by Pb2+, we found that Pb2+ didn\'t alter cellular excitability, no modification of the membrane potential, and no effect on action potential firing. Taken together, these results point to a neurotoxic action evoked by Pb2+ that is associated with changes in neurotransmitter release by blocking the ionic currents responsible for the calcium influx.