Rodriguez-Tapia Eileen S, Naidoo Vinogran, DeVries Matthew, Perez-Medina Alberto, Galligan James J
The Neuroscience Program, Michigan State University, East Lansing, MI, 48824, USA.
Department of Pharmacology & Toxicology, Michigan State University, East Lansing, MI, 48824, USA.
Exp Physiol. 2017 Mar 1;102(3):299-313. doi: 10.1113/EP086027. Epub 2017 Jan 25.
What is the central question of this study? Subtypes of enteric neurons are coded by the neurotransmitters they synthesize, but it is not known whether enteric neuron subtypes might also be coded by other proteins, including calcium channel subtypes controlling neurotransmitter release. What is the main finding and its importance? Our data indicate that guinea-pig ileum myenteric neuron subtypes may be coded by calcium channel subtypes. We found that R-type calcium channels are expressed by inhibitory but not excitatory longitudinal muscle motoneurons. R-Type calcium channels are also not expressed by circular muscle inhibitory motoneurons. Calcium channel subtype-selective antagonists could be used to target subtypes of neurons to treat gastrointestinal motility disorders. There is evidence that R-type Ca channels contribute to synaptic transmission in the myenteric plexus. It is unknown whether R-type Ca channels contribute to neuromuscular transmission. We measured the effects of the nitric oxide synthase inhibitor nitro-l-arginine (NLA), Ca channel blockers and apamin (SK channel blocker) on neurogenic relaxations and contractions of the guinea-pig ileum longitudinal muscle-myenteric plexus (LMMP) in vitro. We used intracellular recordings to measure inhibitory junction potentials. Immunohistochemical techniques localized R-type Ca channel protein in the LMMP and circular muscle. Cadmium chloride (pan-Ca channel blocker) blocked and NLA and NiCl (R-type Ca channel blocker) reduced neurogenic relaxations in a non-additive manner. Nickel chloride did not alter neurogenic cholinergic contractions, but it potentiated neurogenic non-cholinergic contractions. Relaxations were inhibited by apamin, NiCl and NLA and were blocked by combined application of these drugs. Relaxations were reduced by NiCl or ω-conotoxin (N-type Ca channel blocker) and were blocked by combined application of these drugs. Longitudinal muscle inhibitory junction potentials were inhibited by NiCl but not MRS 2179 (P2Y receptor antagonist). Circular muscle inhibitory junction potentials were blocked by apamin, MRS 2179, ω-conotoxin and CdCl but not NiCl . We conclude that neuronal R-type Ca channels contribute to inhibitory neurotransmission to longitudinal muscle but less so or not all in the circular muscle of the guinea-pig ileum.
本研究的核心问题是什么？肠神经元的亚型由它们合成的神经递质编码，但尚不清楚肠神经元亚型是否也可能由其他蛋白质编码，包括控制神经递质释放的钙通道亚型。主要发现及其重要性是什么？我们的数据表明，豚鼠回肠肌间神经丛神经元亚型可能由钙通道亚型编码。我们发现R型钙通道由抑制性而非兴奋性的纵行肌运动神经元表达。R型钙通道在环行肌抑制性运动神经元中也不表达。钙通道亚型选择性拮抗剂可用于靶向神经元亚型以治疗胃肠动力障碍。有证据表明R型钙通道参与肌间神经丛的突触传递。尚不清楚R型钙通道是否参与神经肌肉传递。我们在体外测量了一氧化氮合酶抑制剂硝基-L-精氨酸（NLA）、钙通道阻滞剂和蜂毒明肽（SK通道阻滞剂）对豚鼠回肠纵行肌-肌间神经丛（LMMP）神经源性舒张和收缩的影响。我们使用细胞内记录来测量抑制性接头电位。免疫组织化学技术将R型钙通道蛋白定位在LMMP和环行肌中。氯化镉（泛钙通道阻滞剂）阻断，NLA和氯化镍（R型钙通道阻滞剂）以非累加方式减少神经源性舒张。氯化镍不改变神经源性胆碱能收缩，但增强神经源性非胆碱能收缩。舒张被蜂毒明肽、氯化镍和NLA抑制，并被这些药物联合应用阻断。舒张被氯化镍或ω-芋螺毒素（N型钙通道阻滞剂）降低，并被这些药物联合应用阻断。纵行肌抑制性接头电位被氯化镍抑制，但不被MRS 2179（P2Y受体拮抗剂）抑制。环行肌抑制性接头电位被蜂毒明肽、MRS 2179、ω-芋螺毒素和氯化镉阻断，但不被氯化镍阻断。我们得出结论，神经元R型钙通道参与对豚鼠回肠纵行肌的抑制性神经传递，但在环行肌中作用较小或并非全部起作用。
