Kasimov M R, Fatkhrakhmanova M R, Mukhutdinova K A, Petrov A M
Department of Normal Physiology, Kazan State Medical University, Butlerova st. 49, Kazan, 420012, Russia.
Department of Normal Physiology, Kazan State Medical University, Butlerova st. 49, Kazan, 420012, Russia.
Neuropharmacology. 2017 May 1;117:61-73. doi: 10.1016/j.neuropharm.2017.01.030. Epub 2017 Jan 31.
24S-hydroxycholesterol (24S-HC) is a brain-derived product of lipid metabolism present in the systemic circulation, where its level can change significantly in response to physiological and pathophysiological conditions. Here, using electrophysiological and optical approaches, we have found a high sensitivity to 24S-HC of the synaptic vesicle cycle at the mouse neuromuscular junctions. Treatment with 24S-HC increased the end plate potential amplitude (EPP) in response to a single stimulus and attenuated the EPP amplitude rundown during high frequency (HF) activity but had no influence on miniature EPP amplitude or frequency. The effects on evoked responses were associated with enhanced FM1-43 dye loading and unloading by endo- and exocytosis. Comparison of electrophysiological and optical data revealed an increase in the rate of vesicular cycling. The impact of 24S-HC was abolished or potentiated by stimulation or inhibition of NMDA-receptors respectively. Moreover, 24S-HC, acting in the same manner as the endothelial NO synthase (eNOS) inhibitor cavtratin, suppressed an increase in NO-sensitive dye fluorescence during HF stimulation, while l-glutamate had the opposite effect. Inhibitors of NOS (l-NAME and cavtratin, but not the neuronal NOS inhibitor TRIM), a scavenger of extracellular NO and a protein kinase G blocker all had stimulatory effects, similar to those of 24S-HC, on exocytosis induced by HF activity and completely masked the effect of 24S-HC. The data suggest that 24S-HC enhances synaptic vesicle cycling due to an attenuation of retrograde NO signaling that depends on eNOS. In this regard, 24S-HC counteracts the effects of NMDA-receptor stimulation at mouse neuromuscular junctions.
24S-羟基胆固醇（24S-HC）是脂质代谢产生的一种源自大脑的产物，存在于体循环中，其水平会因生理和病理生理状况而发生显著变化。在此，我们运用电生理和光学方法，发现在小鼠神经肌肉接头处，突触小泡循环对24S-HC具有高度敏感性。用24S-HC处理可使单次刺激引发的终板电位幅度（EPP）增加，并减弱高频（HF）活动期间EPP幅度的衰减，但对微小EPP幅度或频率没有影响。对诱发反应的影响与内吞和外排作用增强FM1-43染料的加载和卸载有关。电生理数据与光学数据的比较显示，小泡循环速率增加。分别刺激或抑制NMDA受体可消除或增强24S-HC的作用。此外，24S-HC的作用方式与内皮型一氧化氮合酶（eNOS）抑制剂cavtratin相同，可抑制HF刺激期间对NO敏感的染料荧光增加，而L-谷氨酸则具有相反的作用。NOS抑制剂（L-NAME和cavtratin，但不包括神经元型NOS抑制剂TRIM）、细胞外NO清除剂和蛋白激酶G阻滞剂，均对HF活动诱导的外排具有与24S-HC相似的刺激作用，并完全掩盖了24S-HC的作用。这些数据表明，24S-HC通过减弱依赖于eNOS的逆行NO信号传导来增强突触小泡循环。在这方面，24S-HC可抵消小鼠神经肌肉接头处NMDA受体刺激的作用。
