Reis H J, Massensini A R, Prado M A, Gomez R S, Gomez M V, Romano-Silva M A
Laboratório de Neurofarmacologia, Divisão de Biologia Celular, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Belo Horizonte 31270-901, MG, Brazil.
Neuroscience. 2000;101(1):237-42. doi: 10.1016/s0306-4522(00)00354-7.
Glutamate is the major excitatory neurotransmitter in the CNS. The recent characterization of glutamate as a neurotransmitter in the enteric nervous system opened a new line of investigation concerning the role of glutamate in that system. The present study aimed to further characterize the enteric glutamate release and the calcium channels coupled to it. For this study the myenteric plexus-longitudinal muscle of guinea-pig ileum was stimulated with potassium chloride or with electrical pulses. The released glutamate was detected by spectrofluorimetry. Laser scanning confocal microscopy was used for analysis of immunolabeled enteric tissue for co-localization studies of calcium channels (N- and P/Q-type) and glutamate transporters (EAAC1). Here we report the effects of known Ca(2+)-channel blockers on glutamate release evoked by KCl-depolarization or electrical stimulation in the myenteric plexus. We find that N-type Ca(2+) channels control a major portion of evoked glutamate release from this system, with a very small contribution from L-type Ca(2+) channels. Moreover, alpha(1A)-like (P-type Ca(2+) channel) and alpha(1B)-like (N-type Ca(2+ )channel) immunoreactivity co-localized with glutamate transporters in the myenteric plexus. In addition, KCl-evoked or electrically stimulated glutamate release was sensitive to omega-agatoxin IVA, in a frequency-dependent manner, suggesting that P-type channels are also coupled to the release of glutamate. We, thus, conclude that both N-type and P-type Ca(2+) channels control most of the evoked glutamate release from the enteric nervous system, as also occurs in some parts of the CNS.
谷氨酸是中枢神经系统中主要的兴奋性神经递质。最近将谷氨酸鉴定为肠神经系统中的神经递质，开启了关于谷氨酸在该系统中作用的新研究方向。本研究旨在进一步表征肠谷氨酸释放及其相关的钙通道。在本研究中，用氯化钾或电脉冲刺激豚鼠回肠的肌间神经丛-纵行肌。通过荧光分光光度法检测释放的谷氨酸。激光扫描共聚焦显微镜用于分析免疫标记的肠组织，以进行钙通道（N型和P/Q型）和谷氨酸转运体（EAAC1）的共定位研究。在此我们报告已知的Ca(2+)通道阻滞剂对肌间神经丛中KCl去极化或电刺激诱发的谷氨酸释放的影响。我们发现N型Ca(2+)通道控制该系统中大部分诱发的谷氨酸释放，L型Ca(2+)通道的贡献非常小。此外，α(1A)样（P型Ca(2+)通道）和α(1B)样（N型Ca(2+)通道）免疫反应性与肌间神经丛中的谷氨酸转运体重叠。另外，KCl诱发或电刺激的谷氨酸释放对ω-芋螺毒素IVA敏感，呈频率依赖性，表明P型通道也与谷氨酸释放相关。因此，我们得出结论，N型和P型Ca(2+)通道控制肠神经系统中大部分诱发的谷氨酸释放，中枢神经系统的某些部分也是如此。
