The non-competitive acetylcholinesterase inhibitor APS12-2 is a potent antagonist of skeletal muscle nicotinic acetylcholine receptors

APS12-2, a non-competitive acetylcholinesterase inhibitor, is one of the synthetic analogs of polymeric alkylpyridinium salts (poly-APS) isolated from the marine sponge Reniera sarai. In the present work the effects of APS12-2 were studied on isolated mouse phrenic nerve-hemidiaphragm muscle preparations, using twitch tension measurements and electrophysiological recordings. APS12-2 in a concentration-dependent manner blocked nerve-evoked isometric muscle contraction (IC50 = 0.74 mu M), without affecting directly-elicited twitch tension up to 2.72 mu M. The compound (0.007-3.40 mu M) decreased the amplitude of miniature endplate potentials until a complete block by concentrations higher than 0.68 mu M, without affecting their frequency. Full size endplate potentials, recorded after blocking voltage-gated muscle sodium channels, were inhibited by APS12-2 in a concentration-dependent manner (IC50 = 0.36 mu M) without significant change in the resting membrane potential of the muscle fibers up to 3.40 mu M. The compound also blocked acetylcholine-evoked inward currents in Xenopus oocytes in which Torpedo (alpha 1(2)beta 1 gamma delta) muscle-type nicotinic acetylcholine receptors (nAChRs) have been incorporated (IC50 = 0.0005 mu M), indicating a higher affinity of the compound for Torpedo (alpha 1(2)beta 1 gamma delta) than for the mouse (alpha 1(2)beta 1 gamma epsilon) nAChR. Our data show for the first time that APS12-2 blocks neuromuscular transmission by a non-depolarizing mechanism through an action on postsynaptic nAChRs of the skeletal neuromuscular junction. (c) 2012 Elsevier Inc. All rights reserved.