Spontaneous Acetylcholine Release Potentiation Induced by 2-Arachidonoylglycerol and Anandamide in Mouse Motor Synapses

Moscow University Biological Sciences Bulletin. 2021. Vol. 76. No. 1. P. 1–6.

Tarasova E., Khotkina N., Gaydukov A., Balezina O.

Changes in the parameters of miniature endplate potential (MEPP) of mouse diaphragm caused by exogenous application of two classical endocannabinoids, 2-arachidonoylglycerol (2-AG) (1 μM) and anandamide (AEA) (30 μM), were compared. A slowly developing stable increase in the MEPP amplitude by 50%, without affecting the frequency of MEPPs, was caused by 2-AG. This effect was prevented by AM-251, an inverse agonist of CB1-receptors, as well as by vesamicol, a blocker of the vesicular acetylcholine (ACh) transporter. On the contrary, AEA did not cause significant changes in the MEPP amplitude but induced a slowly developing (within 2 h) increase in MEPP frequency by 75% on average. The effect of AEA was prevented by AM-251 (1 μM) as well as by blocking of L-type Ca2+-channels with nitrendipine (1 μM) and inhibition of PKA activity by H89 (1 μM). It was concluded that both 2-AG and AEA are able to exert a noncanonical facilitating presynaptic effect on spontaneous ACh release. Even though these endocannabinoids activate the same type of CB-receptors, their facilitating effects do not overlap and are strictly aimed either at potentiating the size of ACh quanta (in case of 2-AG) or increasing the frequency of MEPP (in case of AEA). We assume that different intracellular targets and signaling pathways may be involved in the differentiated facilitating effects of 2-AG and AEA in mouse neuromuscular junctions.

Keywords: neuromuscular junction, anandamide, 2-arachidonoylglycerol, miniature endplate potentials (MEPPs), L-type Ca2+-channels, quantal size