Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile.
PLoS One. 2012;7(8):e44182. doi: 10.1371/journal.pone.0044182. Epub 2012 Aug 31.
In Drosophila photoreceptors Ca(2+)-permeable channels TRP and TRPL are the targets of phototransduction, occurring in photosensitive microvilli and mediated by a phospholipase C (PLC) pathway. Using a novel Drosophila brain slice preparation, we studied the distribution and physiological properties of TRP and TRPL in the lamina of the visual system. Immunohistochemical images revealed considerable expression in photoreceptors axons at the lamina. Other phototransduction proteins are also present, mainly PLC and protein kinase C, while rhodopsin is absent. The voltage-dependent Ca(2+) channel cacophony is also present there. Measurements in the lamina with the Ca(2+) fluorescent protein G-CaMP ectopically expressed in photoreceptors, revealed depolarization-induced Ca(2+) increments mediated by cacophony. Additional Ca(2+) influx depends on TRP and TRPL, apparently functioning as store-operated channels. Single synaptic boutons resolved in the lamina by FM4-64 fluorescence revealed that vesicle exocytosis depends on cacophony, TRP and TRPL. In the PLC mutant norpA bouton labeling was also impaired, implicating an additional modulation by this enzyme. Internal Ca(2+) also contributes to exocytosis, since this process was reduced after Ca(2+)-store depletion. Therefore, several Ca(2+) pathways participate in photoreceptor neurotransmitter release: one is activated by depolarization and involves cacophony; this is complemented by internal Ca(2+) release and the activation of TRP and TRPL coupled to Ca(2+) depletion of internal reservoirs. PLC may regulate the last two processes. TRP and TRPL would participate in two different functions in distant cellular regions, where they are opened by different mechanisms. This work sheds new light on the mechanism of neurotransmitter release in tonic synapses of non-spiking neurons.
在果蝇光感受器中，Ca(2+) 通透性通道 TRP 和 TRPL 是光转导的靶点，存在于感光微绒毛中，并由磷脂酶 C (PLC) 途径介导。使用一种新的果蝇脑切片制备方法，我们研究了 TRP 和 TRPL 在视觉系统的光层中的分布和生理特性。免疫组织化学图像显示，在光感受器轴突在光层中有相当大的表达。其他光转导蛋白也存在，主要是 PLC 和蛋白激酶 C，而视蛋白不存在。电压依赖性 Ca(2+) 通道 cacophony 也存在于那里。在光层中用 Ca(2+) 荧光蛋白 G-CaMP 异位表达在光感受器中进行的测量显示，cacophony 介导的去极化诱导的 Ca(2+) 增加。额外的 Ca(2+) 内流依赖于 TRP 和 TRPL，显然作为储存操作通道起作用。在光层中通过 FM4-64 荧光分辨的单个突触末梢显示，囊泡胞吐作用依赖于 cacophony、TRP 和 TRPL。在 PLC 突变体 norpA 末梢标记也受到损害，暗示这种酶的额外调节。细胞内 Ca(2+) 也有助于胞吐作用，因为这个过程在 Ca(2+) 储存耗尽后减少。因此，几种 Ca(2+) 途径参与光感受器神经递质释放：一种途径由去极化激活，涉及 cacophony；这由内部 Ca(2+) 释放和 TRP 和 TRPL 的激活补充，与内部储存库的 Ca(2+) 耗竭有关。PLC 可能调节后两个过程。TRP 和 TRPL 将参与两个不同的功能，在远离细胞区域，它们通过不同的机制打开。这项工作为非放电神经元的紧张型突触神经递质释放的机制提供了新的见解。
