Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, FRC Kazan Scientific Center of RAS, 2/31 Lobachevsky St, Kazan, 420111, RT, Russia.
Kazan State Medical University, 49 Butlerova St, Kazan, 420012, RT, Russia.
Neurochem Res. 2024 Feb;49(2):453-465. doi: 10.1007/s11064-023-04052-1. Epub 2023 Oct 28.
α2-Adrenoreceptors (ARs) are main G-protein coupled autoreceptors in sympathetic nerve terminals and targets for dexmedetomidine (DEX), a widely used sedative. We hypothesize that α2-ARs are also potent regulators of neuromuscular transmission via G protein-gated inwardly rectifying potassium (GIRK) channels. Using extracellular microelectrode recording of postsynaptic potentials, we found DEX-induced inhibition of spontaneous and evoked neurotransmitter release as well as desynchronization of evoked exocytotic events in the mouse diaphragm neuromuscular junction. These effects were suppressed by SKF-86,466, a selective α2-AR antagonist. An activator of GIRK channels ML297 had the same effects on neurotransmitter release as DEX. By contrast, inhibition of GIRK channels with tertiapin-Q prevented the action of DEX on evoked neurotransmitter release, but not on spontaneous exocytosis. The synaptic vesicle exocytosis is strongly dependent on Ca influx through voltage-gated Ca channels (VGCCs), which can be negatively regulated via α2-AR - GIRK channel axis. Indeed, inhibition of P/Q-, L-, N- or R-type VGCCs prevented the inhibitory action of DEX on evoked neurotransmitter release; antagonists of P/Q- and N-type channels also suppressed the DEX-mediated desynchronization of evoked exocytotic events. Furthermore, inhibition of P/Q-, L- or N-type VGCCs precluded the frequency decrease of spontaneous exocytosis upon DEX application. Thus, α2-ARs acting via GIRK channels and VGCCs (mainly, P/Q- and N-types) exert inhibitory effect on the neuromuscular communication by attenuating and desynchronizing evoked exocytosis. In addition, α2-ARs can suppress spontaneous exocytosis through GIRK channel-independent, but VGCC-dependent pathway.
α2-肾上腺素能受体（ARs）是交感神经末梢中的主要 G 蛋白偶联自身受体，也是广泛使用的镇静剂右美托咪定（DEX）的作用靶点。我们假设 α2-ARs 也是通过 G 蛋白门控内向整流钾（GIRK）通道调节神经肌肉传递的有力调节剂。通过使用细胞外微电极记录突触后电位，我们发现 DEX 诱导自发性和诱发神经递质释放的抑制以及小鼠膈肌神经肌肉接头中诱发胞吐事件的去同步化。这些作用被选择性的 α2-AR 拮抗剂 SKF-86466 所抑制。GIRK 通道激活剂 ML297 对神经递质释放具有与 DEX 相同的作用。相比之下，用 tertiapin-Q 抑制 GIRK 通道可防止 DEX 对诱发神经递质释放的作用，但不能防止自发性胞吐作用。突触囊泡胞吐作用强烈依赖于通过电压门控钙通道（VGCCs）的 Ca 内流，而该过程可通过 α2-AR-GIRK 通道轴负调控。事实上，抑制 P/Q-、L-、N-或 R-型 VGCCs 可阻止 DEX 对诱发神经递质释放的抑制作用；P/Q-和 N-型通道的拮抗剂也抑制了 DEX 介导的诱发胞吐事件的去同步化。此外，抑制 P/Q-、L-或 N-型 VGCCs 可防止 DEX 应用时自发性胞吐作用频率的降低。因此，通过 GIRK 通道和 VGCCs（主要是 P/Q-和 N-型）作用的 α2-ARs 通过减弱和去同步诱发的胞吐作用对神经肌肉通讯产生抑制作用。此外，α2-ARs 可以通过 GIRK 通道非依赖性但 VGCC 依赖性途径抑制自发性胞吐作用。
