Khaziev Eduard, Samigullin Dmitry, Zhilyakov Nikita, Fatikhov Nijaz, Bukharaeva Ellya, Verkhratsky Alexei, Nikolsky Evgeny
Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center of the Russian Academy of SciencesKazan, Russia; Open Laboratory of Neuropharmacology, Kazan (Volga Region) Federal UniversityKazan, Russia; Institute of Applied Electrodynamics, Photonics and Living Systems, A.N. Tupolev Kazan National Research Technical UniversityKazan, Russia.
Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center of the Russian Academy of SciencesKazan, Russia; Open Laboratory of Neuropharmacology, Kazan (Volga Region) Federal UniversityKazan, Russia.
Front Physiol. 2016 Dec 12;7:621. doi: 10.3389/fphys.2016.00621. eCollection 2016.
Acetylcholine (ACh), released from axonal terminals of motor neurons in neuromuscular junctions regulates the efficacy of neurotransmission through activation of presynaptic nicotinic and muscarinic autoreceptors. Receptor-mediated presynaptic regulation could reflect either direct action on exocytotic machinery or modulation of Ca entry and resulting intra-terminal Ca dynamics. We have measured free intra-terminal cytosolic Ca ([Ca]) using Oregon-Green 488 microfluorimetry, in parallel with voltage-clamp recordings of spontaneous (mEPC) and evoked (EPC) postsynaptic currents in post-junctional skeletal muscle fiber. Activation of presynaptic muscarinic and nicotinic receptors with exogenous acetylcholine and its non-hydrolized analog carbachol reduced amplitude of the intra-terminal [Ca] transients and decreased quantal content (calculated by dividing the area under EPC curve by the area under mEPC curve). Pharmacological analysis revealed the role of muscarinic receptors of M subtype as well as d-tubocurarine-sensitive nicotinic receptor in presynaptic modulation of [Ca] transients. Modulation of synaptic transmission efficacy by ACh receptors was completely eliminated by pharmacological inhibition of N-type Ca channels. We conclude that ACh receptor-mediated reduction of Ca entry into the nerve terminal through N-type Ca channels represents one of possible mechanism of presynaptic modulation in frog neuromuscular junction.
乙酰胆碱（ACh）从神经肌肉接头处运动神经元的轴突末端释放，通过激活突触前烟碱型和毒蕈碱型自身受体来调节神经传递的效能。受体介导的突触前调节可能反映对胞吐机制的直接作用，或对钙离子内流及由此产生的终末内钙离子动态变化的调节。我们使用俄勒冈绿488微量荧光测定法测量了终末内游离的胞质钙离子浓度（[Ca]），同时对突触后骨骼肌纤维中自发的（微小终板电流，mEPC）和诱发的（终板电流，EPC）突触后电流进行了电压钳记录。用外源性乙酰胆碱及其非水解类似物卡巴胆碱激活突触前毒蕈碱型和烟碱型受体，可降低终末内[Ca]瞬变的幅度，并减少量子含量（通过将EPC曲线下的面积除以mEPC曲线下的面积来计算）。药理学分析揭示了M亚型毒蕈碱型受体以及对筒箭毒碱敏感的烟碱型受体在突触前[Ca]瞬变调节中的作用。通过药理学抑制N型钙离子通道，可完全消除乙酰胆碱受体对突触传递效能的调节作用。我们得出结论，乙酰胆碱受体介导的通过N型钙离子通道减少钙离子进入神经末梢，是青蛙神经肌肉接头突触前调节的一种可能机制。
