Grandic_2012_Toxicol.Appl.Pharmacol_265_221

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 (IC(50)=0.74muM), without affecting directly-elicited twitch tension up to 2.72muM. The compound (0.007-3.40muM) decreased the amplitude of miniature endplate potentials until a complete block by concentrations higher than 0.68muM, 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 (IC(50)=0.36muM) without significant change in the resting membrane potential of the muscle fibers up to 3.40muM. The compound also blocked acetylcholine-evoked inward currents in Xenopus oocytes in which Torpedo (alpha1(2)beta1gammadelta) muscle-type nicotinic acetylcholine receptors (nAChRs) have been incorporated (IC(50)=0.0005muM), indicating a higher affinity of the compound for Torpedo (alpha1(2)beta1gammadelta) than for the mouse (alpha1(2)beta1gammaepsilon) 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.