Zefirov A L, Mukhametzyanov R D, Zakharov A V, Mukhutdinova K A, Odnoshivkina U G, Petrov A M
Kazan State Medical University, Department of Normal Physiology, Kazan, 420012 Russia.
Institute of Neuroscience, Kazan State Medical University, Kazan, 420012 Russia.
Acta Naturae. 2020 Oct-Dec;12(4):105-113. doi: 10.32607/actanaturae.11054.
Intracellular protons play a special role in the regulation of presynaptic processes, since the functioning of synaptic vesicles and endosomes depends on their acidification by the H+-pump. Furthermore, transient acidification of the intraterminal space occurs during synaptic activity. Using microelectrode recording of postsynaptic responses (an indicator of neurotransmitter release) and exo-endocytic marker FM1-43, we studied the effects of intracellular acidification with propionate on the presynaptic events underlying neurotransmitter release. Cytoplasmic acidification led to a marked decrease in neurotransmitter release during the first minute of a 20-Hz stimulation in the neuromuscular junctions of mouse diaphragm and frog cutaneous pectoris muscle. This was accompanied by a reduction in the FM1-43 loss during synaptic vesicle exocytosis in response to the stimulation. Estimation of the endocytic uptake of FM1-43 showed no disruption in synaptic vesicle endocytosis. Acidification completely prevented the action of the cell-membrane permeable compound 24-hydroxycholesterol, which can enhance synaptic vesicle mobilization. Thus, the obtained results suggest that an increase in [H+]in negatively regulates neurotransmission due to the suppression of synaptic vesicle delivery to the sites of exocytosis at high activity. This mechanism can be a part of the negative feedback loop in regulating neurotransmitter release.
细胞内质子在突触前过程的调节中发挥着特殊作用，因为突触小泡和内体的功能依赖于H⁺泵对它们的酸化作用。此外，在突触活动期间，终末内空间会发生短暂酸化。我们使用微电极记录突触后反应（神经递质释放的指标）和外排-内吞标记物FM1-43，研究了丙酸盐介导的细胞内酸化对神经递质释放所涉及的突触前事件的影响。在小鼠膈肌和青蛙胸大肌的神经肌肉接头处以20赫兹频率刺激的第一分钟内，细胞质酸化导致神经递质释放显著减少。这伴随着刺激引起的突触小泡胞吐过程中FM1-43损失的减少。对FM1-43内吞摄取的评估表明突触小泡内吞作用未受干扰。酸化完全阻止了细胞膜可渗透化合物24-羟基胆固醇的作用，该化合物可增强突触小泡的动员。因此，所得结果表明，由于在高活动状态下抑制了突触小泡向胞吐部位的递送，[H⁺]增加对神经传递产生负调节作用。这种机制可能是调节神经递质释放的负反馈回路的一部分。
