Targeted Nanoparticles for Selective Marking of Neuromuscular Junctions and ex Vivo Monitoring of Endogenous Acetylcholine Hydrolysis

The present work for the first time introduces nanosensors for luminescent monitoring of acetylcholinesterase (AChE)-catalyzed hydrolysis of endogenous acetylcholine (ACh) released in neuromuscular junctions of isolated muscles. The sensing function results from the quenching of Tb(III)-centered luminescence due to proton-induced degradation of luminescent Tb(III) complexes doped into silica nanoparticles (SNs, 23 nm), when acetic acid is produced from the enzymatic hydrolysis of ACh. The targeting of the silica nanoparticles by α-bungarotoxin was used for selective staining of the synaptic space in the isolated muscles by the nanosensors. The targeting procedure was optimized for the high sensing sensitivity. The measuring of the Tb(III)-centered luminescence intensity of the targeted SNs by fluorescent microscopy enables us to sense a release of endogenous ACh in neuromuscular junctions of the isolated muscles under their stimulation by a high-frequency train (20 Hz, for 3 min). The ability of the targeted SNs to sense an inhibiting effect of paraoxon on enzymatic activity of AChE in ex vivo conditions provides a way of mimicking external stimuli effects on enzymatic processes in the isolated muscles.

Luminescent nanoparticles for rapid monitoring of endogenous acetylcholine release in mice atria

The present work introduces for the first time a nanoparticulate approach for ex vivo monitoring of acetylcholinesterase-catalyzed hydrolysis of endogenous acetylcholine released from nerve varicosities in mice atria. Amino-modified 20-nm size silica nanoparticles (SNs) doped by luminescent Tb(III) complexes were applied as the nanosensors. Their sensing capacity results from the decreased intensity of Tb(III)-centred luminescence due to the quenching effect of acetic acid derived from acetylcholinesterase-catalyzed hydrolysis of acetylcholine. Sensitivity of the SNs in monitoring acetylcholine hydrolysis was confirmed by in vitro experiments. Isolated atria were exposed to the nanosensors for 10 min to stain cell membranes. Acetylcholine hydrolysis was monitored optically in the atria samples by measuring quenching of Tb(III)-centred luminescence by acetic acid derived from endogenous acetylcholine due to its acetylcholinesterase-catalyzed hydrolysis. The reliability of the sensing was demonstrated by the quenching effect of exogenous acetylcholine added to the bath solution. Additionally, no luminescence quenching occurred when the atria were pre-treated with the acetylcholinesterase inhibitor paraoxon.

Functional role of muscarinic M(2) receptors in alpha,beta-methylene ATP induced, neurogenic contractions in guinea-pig ileum

1. The muscarinic acetylcholine receptors mediating the contractile response elicited to endogenous acetylcholine released by the selective P2X receptor agonist alpha,beta-methylene ATP (mATP) were investigated in guinea-pig ileum. 2. mATP (0.1 - 30 microM) elicited a concentration-dependent neurogenic contractile response inhibited by tetrodotoxin (TTX) and antagonized by the non-selective muscarinic receptor antagonist N-methylscopolamine (NMS). 3. The contractile response to mATP was pertussis toxin-insensitive, irreversibly antagonized by N-(2-chloroethyl)-4-piperidinyl diphenylacetate (4-DAMP mustard), and unaffected by the muscarinic M(2)/M(4) receptor selective antagonist AF-DX 116 (1 microM). 4. When measured in the presence of histamine and isoproterenol after treatment with 4-DAMP mustard, mATP elicited a pertussis toxin-sensitive contractile response potently antagonized by AF-DX 116. 5. Collectively, our data suggest that endogenous acetylcholine released by mATP can elicit a direct contractile response through the muscarinic M(3) receptor and an indirect contractile response through the muscarinic M(2) receptor by antagonizing the relaxant effects of isoproterenol on histamine induced contraction.