Anales RANF

P.30 NICOTINIC α 7 RECEPTOR-INDUCED ADENOSINE RELEASE FROM PERISYNAPTIC SCHWANN CELLS CONTROLS ACETYLCHOLINE SPILLOVER FROM THE RAT MOTOR ENDPLATE J.B. Noronha-Matos 1 , L. Oliveira 1 , A.R. Peixoto 1 , L. Almeida 1 , L. Castellão-Santana 2 , C.R. Ambiel 3 , W. Alves-do Prado 2 & Paulo Correia-de-Sá 1,2, 1 Laboratório de Farmacologia e Neurobiologia, Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Portugal and 2 Dept. Farmacologia e Terapêutica, and 3 Dept. Ciências Fisiológicas, Universidade Estadual de Maringá, Paraná, Brazil. Acetylcholine (ACh) spillover from the motor endplate region may occur after long nerve firing bursts. It may also appear in the presence of cholinesterase inhibitors that are commonly used to improve the neuromuscular transmission in patients with Myasthenia gravis or to reverse the residual neuromuscular blockade in the context of general anesthesia. Despite nicotinic α 7 receptors ( α 7 nAChR) localized on perisynaptic Schwann cells (PSCs) can sense and control ACh spillover from the neuromuscular synapse, the mechanisms underlying communication between PSCs and the nerve terminal are not entirely understood. Here, we investigated whether adenosine could be the gliotransmitter mediating inhibition of transmitter release following α 7 nAChR activation. Rat phrenic hemidiaphragms were used to measure nerve-evoked (i) myographic recordings, (ii) [ 3 H]ACh release, and (ii) transmitter exocytosis using the FM4-64 fluorescent dye. The selective α 7 nAChR agonist, PNU282987, decreased tetanic (50 Hz-bursts)-induced muscle contractions. This effect, which was mimicked by the cholinesterase inhibitor neostigmine, derives from inhibition of transmitter exocytosis detected as decreases in [ 3 H]ACh release and FM4-64 dye unloading. The α 7 nAChR antagonist, methyllycaconitine, and the gliotoxin, fluoroacetate, prevented the inhibitory effects of neostigmine and PNU282987. Removal of endogenous adenosine with adenosine deaminase (ADA, 2.5 U/ml), inhibition of adenosine release via ENT1 with S-(4-nitrobenzyl)-6-thioinosine (NBTI, 10 µM), and blockade of A 1 receptors with 1,3-dipropyl-8-cyclopentylxanthine, all prevented inhibition of ACh exocytosis by PNU282987. Data suggest that α 7 nAChR controls tetanic-induced ACh spillover from the neuromuscular synapse by favoring adenosine outflow from PSCs via NBTI- sensitive ENT1 transporters and activation of presynaptic A 1 inhibitory receptors. Work supported by FCT (FEDER funding, project UID/BIM/4308/2016) and to Foundation of Support to the Scientific Development of the State University of Maringa (FSSD-SUM).